Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, Not Requiring Professional Management
	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, Not Requiring Professional Management
	Prevention or Reduction of Drug Adverse Effect
	Beneficial or Supportive Interaction, Not Requiring Professional Management

Preliminary

Effect and Mechanism of Action

Aspirin and salicylic acid, its metabolite, can inhibit folate-dependent enzymes and interfere with folate metabolism. Increased urinary excretion of folate has been associated with chronic ASA use in patients with rheumatoid arthritis (RA). ³⁶ Administration of exogenous folic acid may compensate for and reverse these adverse effects on endogenous folate metabolism.

Research

In 1971, Alter et al. ³⁷ initiated the discussion of reduced blood levels of folate among individuals with rheumatoid arthritis taking aspirin chronically. ³⁷ Lawrence et al. ³⁸ conducted in vivo and in vitro studies of serum binding and urinary excretion of endogenous folate caused by aspirin ingestion. They analyzed serum and blood samples during two series of experiments involving one healthy woman following a fixed diet for 11 days and taking 650 mg aspirin orally every 4 hours during the middle 3 days. They found that “aspirin induced a brisk, significant but reversible fall in total and bound serum folate and a small but insignificant rise in urinary folate excretion.” Furthermore, aspirin in vitro also displaced significant amounts of bound serum folate. The authors concluded that “aspirin in therapeutic doses can contribute to subnormal serum folate values, and if it increases urinary folate excretion even slightly, may impair folate balance.” ³⁸

Baggott et al. ³⁹ found that salicylic acid was a competitive inhibitor (with respect to folate) of avian liver phosphoribosylaminoimidazolecarboxamide formyltransferase (AICAR transformylase, EC 2.1.2.3) and bovine liver dihydrofolate reductase (EC 1.5.1.3), whereas aspirin (as well as the antipyretic-analgesic drugs acetaminophen and antipyrine) were weak inhibitors of these enzymes. Their research suggests that, based on a structure-activity correlation, an aromatic ring with a side chain containing a carboxylic acid is a requirement for competitive inhibition of the transformylase. Thus, “aspirin exerts its anti-inflammatory effects after its conversion into salicylic acid, which possesses greater antifolate activity than its parent compound.” ³⁹ They also noted that sulindac, sulphasalazine, naproxen, and ibuprofen are the NSAIDs possessing more potent antifolate activity.

The evidence demonstrating interference with folate metabolism by aspirin is direct and incontrovertible, but the clinical significance of such interference and subsequent folate depletion appears to depend on dosage, duration of intake, and individual variability and susceptibility. High aspirin dosage levels over extended periods can produce adverse effects that are potentially significant and can increase the metabolic needs for folic acid. Further research is warranted given the broad use of ASA, especially over long periods.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians and other health care providers are advised to ask patients regarding their patterns of aspirin use, prescribed and self-administered, and to counsel folate supplementation as a prudent protective measure against potential adverse effects from long-term intake. The body of evidence indicates that although interference with folate metabolism is probable and cumulative depletion of folate possible, the effects of such processes will vary among individuals depending on other factors, such as age, gender, nutritional intake, supplement use, genomic variability, and drug depletion. Supplementation with a minimum of 400 µg folate daily represents a judicious intervention, given the multiple stressors affecting folate status and the low cost and strong safety profile of folic acid. The necessary amount of daily folic acid support can usually be obtained in a multivitamin formula. However, 800 µg/day is probably appropriate in some individuals, such as pregnant women and those with other risk factors. Low-dosage, chronic ASA intake, as in stroke prevention, is unlikely to contribute to significant compromise of folate status and function, barring other major influences. However, given its potential beneficial impact on homocysteine, supplementation with folic acid and allied nutrients is generally warranted in such patients to reduce risk of atherosclerosis and stroke.

• Evidence:

  Aluminum hydroxide (Alternagel, Amphojel).

Extrapolated, based on similar properties: Aluminum carbonate gel (Basajel), aluminum hydroxide combination drugs: aluminum hydroxide, magnesium carbonate, alginic acid, and sodium bicarbonate (Gaviscon Extra Strength Tablets, Gaviscon Regular Strength Liquid, Gaviscon Extra Strength Liquid); aluminum hydroxide and magnesium hydroxide (Advanced Formula Di-Gel Tablets, Co-Magaldrox, Di-Gel, Gelusil, Maalox, Maalox Plus, Mylanta, Wingel); aluminum hydroxide, magnesium trisilicate, alginic acid, and sodium bicarbonate (Alenic Alka, Gaviscon Regular Strength Tablets), calcium carbonate (Titralac, Tums); magnesium hydroxide (Phillips’ Milk of Magnesia MOM); combination drugs: magnesium hydroxide and calcium carbonate (Calcium Rich Rolaids); magnesium hydroxide, aluminum hydroxide, calcium carbonate, and simethicone (Tempo Tablets); magnesium trisilicate and aluminum hydroxide (Adcomag trisil, Foamicon); magnesium trisilicate, alginic acid, and sodium bicarbonate (Alenic Alka, Gaviscon Regular Strength Tablets); combination drug: sodium bicarbonate, aspirin, and citric acid (Alka-Seltzer).

• Evidence:

  Cimetidine (Tagamet; Tagamet HB).

• Extrapolated:

  Famotidine (Pepcid RPD, Pepcid, Pepcid AC), nizatidine (Axid, Axid AR), ranitidine (Zantac), combination drug: ranitidine, bismuth, and citrate (Tritec).

	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, Not Requiring Professional Management
	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, Not Requiring Professional Management
	Prevention or Reduction of Drug Adverse Effect
	Adverse Drug Effect on Nutritional Therapeutics, Strategic Concern

Emerging

Effect and Mechanism of Action

The influence of gastric acid sets the stage for folate absorption, which is maximal in the jejunum. Thus, medications that interfere with the normal pH of the gastrointestinal (GI) environment, particularly alkalinization of the proximal small intestine, can impair folic acid absorption and may cause low or deficient plasma and erythrocyte folate. ⁴⁰ However, some evidence indicates the degree to which a medication alters pH does not always parallel the degree to which it adversely affects folic acid absorption. ^40,41 Additionally, antacids containing aluminum hydroxide, magnesium hydroxide, or other minerals may bind to folate and reduce its absorption. ^41,42 These pharmacokinetic interactions may produce secondary metabolic effects because folic acid is required for proper metabolic function of vitamin B ¹² .

Research

A review of the available literature indicates medications that suppress gastric acidity can reduce folate bioavailability and absorption to a degree that might not affect most individuals but are of increased clinical significance in populations who use such medications frequently for extended periods and who also have compromised folate nutriture or increased metabolic demands, both of which are relatively common situations.

Cimetidine and ranitidine are H ² antagonists known to reduce folate absorption because of their effect on pH in the GI tract, although this is generally minor and unlikely to be of clinical significance in most individuals. Russell et al. ⁴¹ conducted two experiments investigating these issues. First, in vitro studies showed that neither cimetidine nor ranitidine physically bound folate or interfered with its metabolism (as indicated by a lack of inhibition of dihydrofolate reductase at concentrations of 5 and 50 µmol/L). Subsequently, 30 participants followed a standard regimen of either cimetidine or ranitidine and then were fed a specially formulated liquid meal containing 200 µg of folate. Monitoring of pH values at the ligament of Treitz showed that the slight acidity existing before consumption of the liquid meal was generally maintained during the 2-hour period after food intake. Folate absorption was 50% with the formula meal alone versus 45.8% with the formula meal plus cimetidine. The decrease in folate absorption with ranitidine did not attain statistical significance. Although drug-induced effect on intestinal pH was the focus, the observation that cimetidine reduced folate absorption more than ranitidine suggests a more complex interaction because ranitidine increased intestinal pH to a greater degree.

Russell et al. ⁴¹ also observed that aluminum with magnesium hydroxide reduces folate absorption to a small extent, apparently by adsorbing the nutrient, rather than through its effect on gastric acid. These researchers tested dietary folate absorption in 30 subjects by administering the antacid 1 hour and 3 hours after a specially formulated liquid meal containing 200 µg of folate. Folate absorption was 50.6% with the formula meal alone versus 43.1% when the antacid was administered after the formula meal. Acidity actually increased slightly during the 2-hour period after the liquid meal, as indicated by monitoring of pH values at the ligament of Treitz, despite the activity of the antacid.

Further research indicates that the aluminum hydroxide component of the antacid adsorbs folate onto its surface, as gel particles agglomerate and hydroxide begins to precipitate from the gel state (characteristic at pH range of ∼3.7-10), and removes it from contact with the aqueous phase. ⁴²

Evidence regarding the effects of proton pump inhibitors (PPIs) on folate and folic acid is lacking, but these agents might be expected to have a similar effect. This possible interaction poses significant risk because such medications are often prescribed for patients in populations most susceptible to folate deficiency, such as the elderly. The PPIs have clearly been shown to interfere with vitamin B ¹² absorption.

Reports

Ruscin et al. ^42a reported on a 78-year-old, nonvegetarian Caucasian woman with symptomatic gastroesophageal reflux who had vitamin B ¹² deficiency associated with long-term use (∼4 years) of cimetidine and a PPI; serum folate was within the normal range at 4.9 ng/mL. The patient responded to oral B ¹² replacement, thus demonstrating that she could adequately absorb non–protein-bound vitamin B ¹² from the GI tract and suggesting her deficiency was a result of food-cobalamin malabsorption. This case report suggests that long-term H ² /PPI antagonist therapy (≥4 years) may adversely impact vitamin B ¹² status but is unlikely to influence folate.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Most medications that suppress gastric acid appear to impact folate (and vitamin B ¹² ) absorption to some degree by at least one mechanism. The severity of such effect may vary based on individual physiological characteristics, diet, pathophysiology, and specific factors relating to particular drug agents or classes. Although the effects on folate absorption and nutriture are often dismissed as “marginal,” they may produce significant adverse effects, especially in undernourished populations and individuals with increased metabolic needs (e.g., pregnancy). Prudence suggests that physicians prescribing such medications advise patients to supplement with a folic acid/B ¹² combination. Increasing folate intake without accompanying B ¹² can stimulate systems that also use B ¹² and can result in lower B ¹² levels. Such preventive measures should also be communicated to patients who may be self-administering antacids on a chronic basis, especially if they are at risk of folate deficiency from dietary factors or depletion from medications.

	Prevention or Reduction of Drug Adverse Effect
	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management
	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, with Professional Management
	Drug-Induced Effect on Nutrient Function, Supplementation Contraindicated, Professional Management Appropriate
	Drug-Induced Nutrient Depletion, Supplementation Contraindicated, Professional Management Appropriate
	Bimodal or Variable Interaction, with Professional Management
	Minimal to Mild Adverse Interaction—Vigilance Necessary
	Potentially Harmful or Serious Adverse Interaction—Avoid

Consensus

Effect and Mechanism of Action

Antiepileptic drugs (AEDs) and related medications interact with supplemental folic acid and dietary folate through several mechanisms to produce varied, complex, reinforcing, and sometimes countervailing effects. Most drugs in this broad class interfere with folate function and cause folate depletion by inhibiting nutrient absorption, inducing microsomal oxidase enzymes (cytochrome P450) to increase hepatic folate metabolism, and adversely impacting the microbiota of symbiotic flora in the gut. ^43-45 Furthermore, the recycling of folate cofactors depends on vitamin B ⁶ and riboflavin, and riboflavin is necessary for activating vitamin B ⁶ to pyridoxal 5′-phosphate (PLP). ⁴⁶ Thus, induction of enzymes by anticonvulsants may strain available folate resources and limit synthesis of the cytochromic enzymes responsible for AED metabolism.

Numerous factors can adversely influence folate metabolism in individuals being treated with anticonvulsant medications. Decreased MTHFR activity in some individuals reduces conversion of folate to active forms. Primidone and phenobarbital, its metabolite, may both decrease folate absorption and increase its hepatic metabolism while also inhibiting the growth of folate-dependent symbiotic microflora. ⁴⁷ Valproic acid may interfere with folate absorption but may not induce enzymes; decreased folate levels are found after long-term valproate therapy. Carbamazepine can reduce folate absorption, but evidence is conflicting as to whether this enzyme inducer (CYP450) actually produces any significant effect on hepatic metabolism of folate. ^48,49 Many AEDs are metabolized through arene oxides, which are highly reactive intermediates and generally considered to be teratogenic. ⁵⁰ By impairing the action of epoxide hydrolase (the enzyme system responsible for detoxifying arene oxides), inadequate folate levels could result in incomplete metabolism of anticonvulsants and the accumulation of highly reactive epoxides and thus could contribute to fetal abnormalities. ^43,51 For example, the teratogenicity of carbamazepine appears to derive, at least in part, from the formation of the 10,11-epoxide metabolite, which may act as a free radical, binding to proteins and nucleic acids and disrupting DNA, RNA, and protein synthesis. ⁵² In contrast to carbamazepine, oxcarbazepine undergoes reduction of the carbonyl group to form MHD, which subsequently undergoes glucuronidation, and thus does not form the epoxide. ⁵³ However, such effects constitute only one of several factors in the significant rate of major malformations in offspring exposed to these medications during pregnancy. ^54-58 Anticonvulsant-induced low serum folate levels can also elevate homocysteine (Hcy) levels and thereby increase risk of cardiovascular disease, particularly atherosclerosis. ^59-61 Elevated Hcy levels are associated with pregnancy complications, neural tube defects (NTDs), and other birth defects. Notably, Hcy has been used as an experimental convulsant.

Conversely, folate may decrease serum levels of some medications (e.g., phenytoin), possibly by acting as a cofactor for the enzyme epoxide hydrolase, or otherwise increasing metabolism of the anticonvulsants and reducing serum drug levels, possibly to subtherapeutic levels. Thus, increased intake of supplemental folic acid, and/or theoretically of dietary folate, could impair the therapeutic activity of AEDs and could increase the incidence of seizure activity. In particular, folate in doses greater than 1 mg daily can compromise phenytoin seizure control by creating a “pseudo–steady state” in which phenytoin appears to be at steady state but actually is not; this effect may be due to competition for brain-cell surface receptors. ⁴³

Research

Although the issues of folate deficiency and depletion may have significant effects on the health and disease susceptibility of broad sections of the general population, their impact is perhaps most dramatic among individuals being treated with AEDs for seizure disorders and related conditions. Decades of research have demonstrated low folate levels (and increased Hcy levels) in patients treated with AEDs, particularly as polypharmacy. ^45,59-67 Nevertheless, although the interaction between AEDs and folates is well documented and potentially clinically important, its clinically significant incidence is uncertain and subject to many variables.

In their landmark 1966 study, Reynolds et al. ⁶⁸ examined folate status in 62 patients with epilepsy, 54 of whom were taking phenobarbital, primidone, or phenytoin singly or in various combinations, with eight serving as untreated controls. Serum folate concentrations in 76% of treated patients were below the range found in control subjects, and average folate concentration for the treated patients was 3.7 ng/mL, versus 6.4 ng/mL for the controls. Of 45 with bone marrow examination, 17 exhibited megaloblastic hematopoiesis, even though none of the treated patients was anemic, and only 7 of the 54 treated patients showed macrocytosis.

In a survey of the red blood cell (RBC) folate status of 200 patients with epilepsy and 72 controls, Goggin et al. ⁶⁹ found that median RBC folate levels were reduced significantly in patients treated with phenytoin or carbamazepine alone. Also, patients administered AED polypharmacy had reduced levels, with 22% in the group taking more than one drug showing reduced levels of RBC folate compared with 17% of those receiving carbamazepine monotherapy, 13% taking phenytoin only, and 9% taking sodium valproate only. Notably, patients treated with sodium valproate alone exhibited no significant decrease in RBC folate levels (compared to controls). Dietary folate intake was significantly reduced in all the patient groups compared with controls, but there was no significant correlation between RBC folate levels and dietary folate. The investigators concluded that “all anticonvulsant drugs interfere with folate metabolism.” ⁶⁹

Kishi et al. ⁴⁵ measured serum folate concentrations in epileptic outpatients treated with a single anticonvulsant drug, including carbamazepine, phenobarbital, and valproate, and in age-matched controls without anemia. They used a protein-binding radioassay to demonstrate that reduced serum folate was associated with hepatic CYP450 enzyme induction by carbamazepine and phenobarbital, but not valproate, compared with controls.

The influences of AEDs and the MTHFR genotype further complicate the research exploring the powerful relationship between folate status and homocysteine and its profound implications for health and disease. The methylenetetrahydrofolate reductase (MTHFR) genotype appears to modulate depletion of active folate and contribute directly to an increased incidence of hyperhomocysteinemia. Elevated Hcy levels have been documented after anticonvulsant treatment with phenytoin, carbamazepine, phenobarbital, and primidone, agents that induce CYP450. ^{59-61,66,67,70-72} Likewise, in addition to impairing folate status, long-term treatment with valproate also increases Hcy levels. ^67,72 Yoo and Hong ⁷³ demonstrated that the TT allele of the MTHFR C677T polymorphism, a common mutation in the MTHFR gene, is a significant determinant of hyperhomocysteinemia in epileptic patients receiving anticonvulsants.

The concerns raised by high Hcy levels extend beyond cardiovascular risk. In their study of 130 epileptic patients taking anticonvulsant monotherapy or multidrug polytherapy (including carbamazepine and/or phenytoin), Ono et al. ⁵⁹ noted that individuals diagnosed with megaloblastic anemia as a result of folate deficiency exhibit a high incidence of neuropsychiatric illness and elevated plasma total homocysteine (tHcy) levels. The four folate-deficient patients had received long-term treatment (>7 years) with multiple anticonvulsants. Their tHcy levels were higher than the 90th percentile of those in control subjects. Folate therapy normalized their Hcy and folate levels. Notably, disturbances of the remethylation pathway of Hcy can significantly impact numerous physiological activities, thereby influencing fetal development and contributing to malformations such as NTDs, spontaneous abortions, and other pregnancy complications. Dean et al. ⁷⁴ found that the MTHFR C677T polymorphism is associated with fetal anticonvulsant syndrome in the offspring of mothers administered AEDs during pregnancy.

The impact of anticonvulsant medications on folate status has been a concern since the introduction of AEDs, and thus research has focused most on the consequences of drug-induced folate deficiency, especially during pregnancy, and the clinical implications of compensatory folic acid coadministration. The strong association between increased risk of birth defects and treatment with AEDs is well established by a consistent body of epidemiological evidence. ^75-79 Hydantoins such as phenytoin are most frequently associated with teratogenesis. ^55,80 Valproic acid (VPA), divalproex, and valproate sodium have all been reported to cause birth defects when administered during the first 3 months of pregnancy. Specifically, VPA use during early pregnancy can result in a 1% to 2% incidence of spina bifida aperta in humans, a closure defect of the posterior neural tube.

Hendel et al. ⁴⁸ conducted research on the effect of carbamazepine and valproate treatment on folate metabolism in 11 epileptic patients and interpreted their findings as an inhibition of intestinal folic acid absorption caused by the antiepileptic therapy. However, Kishi et al. ⁴⁵ examined the role of induction of liver enzymes by AEDs in folate depletion and determined that patients treated with valproate, a non–enzyme inducer, exhibited serum folate levels that did not differ significantly from values in controls. Furthermore, NTDs in humans and rodents associated with VPA do not seem to be related to folate deficiency, and NTD incidence has not changed with administration of folic acid or its activated form, folinic acid. ⁸⁰ Several other studies have indicated that VPA has the least antifolate action of the major AEDs, and that folate is probably not involved in the mechanism of VPA-induced embryotoxicity. One study found that the consumption of ethanol potentiated VPA-induced NTDs in mice resulting from toxicokinetic interactions. ⁸¹ Subsequently, however, findings from a Finnish population-based study by Artama et al. ⁸² confirmed the teratogenicity of valproate. “The offspring of women with epilepsy on valproate [at doses >1500 mg/day] during the first trimester of pregnancy have a substantially increased risk for congenital malformations.” They also reported that the risk for teratogenic malformations is not elevated in offspring of mothers using carbamazepine, oxcarbazepine, or phenytoin (as monotherapy or polytherapy without valproate). This study is notable in being one of the few large studies on the teratogenic effects of AEDs to include a reference group of untreated women with epilepsy.

The incidence of NTDs, such as spina bifida and anencephaly, may dominate broad awareness of adverse effects, but cardiovascular defects, oral clefts, and urinary tract defects are also reported. Likewise, a Danish study by Fonager et al. ⁷⁷ found that the risks of low birth weight and preterm delivery were increased by 50% and 60%, respectively, in women exposed to anticonvulsant drugs. In another Danish study, Hvas et al. ⁷⁸ observed that the infants of women with drug-treated epilepsy exhibited a lower birth weight, shorter length, and a smaller head circumference than infants of untreated subjects.

For years clinicians and investigators were unsure as to whether the incidence of fetal abnormalities in mothers with seizure disorders was a result of the condition itself or of their medications. Kaneko et al. ⁸³ prospectively analyzed 983 offspring born in Japan, Italy, and Canada to identify the major risk factors for the increased incidence of congenital malformations in offspring of mothers being treated for epilepsy with AEDs during pregnancy and to determine the relative teratogenic risk of AEDs. The incidence of congenital malformations in offspring with drug exposure was 9.0%, versus an incidence without drug exposure of 3.1%. The highest incidence among offspring exposed to a single AED occurred with primidone (14.3%), followed by valproate (11.1%), phenytoin (9.1%), carbamazepine (5.7%), and phenobarbital (5.1%). The incidence of malformations was positively associated with the total daily dose and number of drugs, with specific combinations of AEDs (e.g., valproate and carbamazepine; phenytoin, primidone, and phenobarbital) producing a higher incidence of congenital malformations. Moreover, the presence of malformations in siblings was the only background factor associated with the incidence of malformations. These authors concluded that “the increased incidence of congenital malformations was caused primarily by AEDs, suggesting that malformations can be prevented by improvements in drug regimen, and by avoiding polypharmacy and high levels of VPA (more than 70 µg/mL) in the treatment of epileptic women of childbearing age.” ⁸³

In a multicenter study, Holmes et al. ⁵⁶ screened 128,049 pregnant women at delivery to investigate the frequency of anticonvulsant embryopathy (i.e., major malformations, growth retardation, hypoplasia of midface and fingers) and determine whether the abnormalities are caused by the maternal epilepsy itself or by exposure to anticonvulsant drugs in utero. They reported that the combined frequency of anticonvulsant embryopathy was higher in 223 infants exposed to one anticonvulsant drug than in 508 control infants (20.6% vs. 8.5%) and that the frequency was higher in 93 infants exposed to two or more anticonvulsant drugs than in the controls (28.0% vs. 8.5%). Moreover, the 98 infants born to the mothers with a history of epilepsy but no use of anticonvulsants during pregnancy did not exhibit a higher frequency of abnormalities than control infants. ⁵⁶

In 2003, Kaaja et al. ⁸⁴ prospectively followed up 970 pregnancies in women with epilepsy at a single maternity clinic from 1980 through 1998. Of the 979 total offspring, 740 were exposed to maternal AEDs during the first trimester, and 239 were not exposed. Serum folate concentrations were measured at the end of the first trimester, as were maternal AED levels (to minimize exposure). Major malformations were detected in 28 fetuses (3.8%) exposed to maternal AED and in two (0.8%) not exposed. Eight of the 28 cases had NTDs, which is fourteenfold the national rate. Seven had oral clefts, six had cardiovascular malformations, four had visceral malformations, and three exhibited miscellaneous malformations. Logistical regression analysis revealed that the occurrence of major malformations was independently associated with use of carbamazepine (odds ratio [OR] 2.5), valproate (OR 4.1), and oxcarbazepine (OR 10.8); low serum folate concentration; and low maternal level of education. Also, the authors found no association between major malformations and seizures during the first trimester. None of these women reported preconception use of folate, but all were advised to take multivitamins containing 0.1 to 0.8 mg of folate at the first antenatal visit, usually between the eighth and twelfth week of gestation. ⁸⁴

The risks of AED-induced folate deficiency on fetal development also involve the effect of AEDs on the efficacy of birth control. The most common AEDs induce the CYP450 enzymes that metabolize estrogens (e.g., ethinyl estradiol, mestranol), causing up to a 40% reduction in serum levels. ^85-88 Oral contraceptives (OCs) can also interfere with folate cofactor interactions, causing impaired DNA synthesis. Thus the use of OCs or Norplant does not reduce the need for folic acid coadministration in women of childbearing age and may actually increase such need because increased clearance of the contraceptive agents may impair their efficacy.

Compared with older anticonvulsants, particularly hydantoin derivatives, newer AEDs may exert less adverse effect on fetal development because of lesser adverse influence on vitamin status, among other reasons. ⁸⁹ Such probabilities, their implications, and clinical responses have yet to be adequately researched and supported by conclusive evidence.

The coadministration of folic acid to counterbalance the adverse effects of AEDs on folate nutriture has been investigated and refined to a point where broad parameters of efficacy and guidelines for clinical implementation now have general consensus. In a long-term study, Reynolds ⁹⁰ investigated the effects of 1 to 3 years of folate coadministration on the “mental state and fit-frequency” in 26 chronic epileptic patients with AED-induced folic-acid deficiency treated with one or more anticonvulsants. Mental state improved in 22 patients, but seizure frequency or severity was aggravated in 13 patients (50%). Reynolds concluded that “folic acid partially reverses both the therapeutic (antiepileptic) and retarding effects of phenobarbitone, phenytoin, and primidone.” ⁹⁰ Baylis et al. ⁹¹ assessed the effects of folic acid administration in 50 folate-deficient epileptic patients taking phenytoin, primidone, and phenobarbital in various combinations. Serum phenytoin levels fell from 20 to 10 µg/mL in a group of 10 patients after 1 month's treatment with folic acid, 5 mg/day. Likewise, serum phenytoin levels fell from 14 to 11 µg/mL in a second group of 40 patients administered 15 mg/day of folic acid. “In one patient the fall was to below the therapeutic range and was associated with deterioration in fit control.” ⁹¹ Phenobarbital levels were unchanged in the presence of folate supplementation.

In a randomized, double-blind trial, Gibberd et al. ⁹² tested the effects of folic acid coadministration on seizure frequency in a group of outpatients with epilepsy treated with phenytoin for at least 1 year. Although the group receiving folic acid in the treatment period showed a significant improvement in seizure frequency, the authors suggested that “subjective well-being of patients was not influenced by folic acid therapy” and concluded that “the improvement while on folic acid was not due to the folic acid treatment alone.” ⁹² Biale and Lewenthal ⁹³ conducted a study to determine the frequency of malformations among newborn infants of mothers receiving anticonvulsive therapy with and without folate supplementation. In the retrospective portion of the study involving 24 women not receiving folate, 10 children among the 66 newborns (15% frequency) exhibited congenital malformations, including congenital heart disease, cleft lip and palate, NTDs, and skeletal abnormalities; 3 of the 10 were stillborn or died immediately after delivery. In the prospective portion of the study, involving 22 women receiving folate, all 33 infants were born alive, and no congenital malformations occurred. The authors concluded that the “teratogenic activity of anticonvulsant drugs seems to be mediated by interference with folic acid metabolism, and such activity might be influenced by hereditary and environmental factors.” ⁹³ They recommended folic acid coadministration to epileptic women intending to become pregnant.

Berg et al. ⁴³ (1995) demonstrated the interdependence of the phenytoin-folate interaction by showing that the addition of folic acid to phenytoin therapy improved phenytoin pharmacokinetics and produced changes in blood levels of phenytoin. In a randomized crossover study involving six women of childbearing age, they compared outcomes of two groups of women, both receiving 300 mg phenytoin daily. Both groups had essentially equivalent dietary folate intake, but the subjects in the second treatment group also received 1 mg folic acid daily. The no–folic acid group exhibited a 38% reduction in serum folate level, with a serum phenytoin concentration in the low therapeutic range. The folic acid/phenytoin group showed a 26% increase in serum folate level, with a phenytoin level similar to that in phenytoin-only subjects. Notably, only one woman achieved phenytoin steady state during phenytoin-only treatment, but four women achieved steady state during treatment with both folic acid and phenytoin (PHT). The authors concluded that their findings suggest “an interdependence between PHT and folic acid and supports the observation that fertile women treated with PHT require folic acid supplementation to maintain a normal serum folate level.” ⁴³

Later in 1995, in their review of the literature on phenytoin-folate interactions, Lewis et al. ⁴⁴ proposed that folic acid should always be prescribed with phenytoin because of a synergistic effect. Folic acid supplementation in folate-deficient patients with epilepsy can change the pharmacokinetics of phenytoin and, without appropriate clinical management, may increase risk of possible seizure breakthrough by leading to lower serum phenytoin concentrations. Folate is hypothesized to be a cofactor in phenytoin metabolism and may be able to assist in obtaining a concentration where phenytoin appears to be at steady state but actually is not. Phenytoin and folic acid therapy initiated concomitantly with monitoring and titration can prevent decreased folate and obtain steady-state phenytoin concentrations sooner. The authors concluded that folic acid supplementation should be initiated concomitantly with phenytoin therapy because of the hypothesized cofactor mechanism, decreased adverse effects associated with folate deficiency, and better seizure control with no perturbation of phenytoin pharmacokinetics.

Subsequently, in a controlled trial, Eros et al. ⁹⁴ reported that both healthy and epileptic women taking less than 1 mg of folic acid daily had no increased risk of seizures. Of 60 epileptic women with periconception multivitamin supplementation with 800 µg of folic acid, none developed epilepsy-related side effects during the periconception period. One epileptic woman delivered a newborn with cleft lip and palate. However, a 22-year-old epileptic woman receiving carbamazepine, as well as taking a daily multivitamin supplement with 1.0 mg of folic acid from the twentieth week of gestation, exhibited a cluster of seizures after the periconception period. Furthermore, she developed status epilepticus and symptoms of systemic lupus erythematosus; this pregnancy ended with stillbirth. The authors concluded that an autoimmune disease (probably drug-induced lupus) had emerged in this epileptic patient and damaged the blood-brain barrier, so the 1-mg (or greater) therapeutic dose of folic acid may have triggered a cluster of seizures. Overall, they noted that administration of a physiological dose (<1 mg) of folic acid to women without autoimmune disease did not increase the risk of epileptic seizures.

Evidence is mixed as to what dosage level and form of folic acid coadministration is necessary to reverse adverse AED effects on folate metabolism yet avoid interfering with the therapeutic activity of the medications. A review of the evidence generally indicates that the levels of folic acid in typical multivitamin formulations (e.g., 400 µg/day) may be adequate for folate nutriture during pregnancy in healthy, nonmedicated women. Some sources, such as Hiilesmaa et al., ⁹⁵ suggest that “low-dose” folic acid (100-1000 µg/day) is sufficient to prevent deficiency during pregnancy in women treated with AEDs. In contrast, most authorities now report that 800 to 1000 µg/day is required for effective protection within the context of folate-depleting medications. Nulman et al. ⁸⁸ advise that “seizure control should be achieved at least six months prior to conception and, if clinically possible, by the lowest effective dose of a single anticonvulsant according to the type of epilepsy.” Moreover, they recommend that women undergoing AED polytherapy supplement with 5 mg of folic acid daily, for 3 months before conception and during the first trimester, to prevent malformations caused by drug-induced folic acid deficiency. ⁸⁸ Thus, based on individual variability and the medication involved, folate coadministration is simply not adequate for some women, and a change in AED regimen, such as eliminating valproate, may be necessary for a safe pregnancy. Furthermore, administration of 5-methyltetrahydrofolate (5-MTHF), such as folinic acid, may be required to counterbalance the adverse effects of folate-depleting medications as well as concurrent factors such as inadequate nutritional status, smoking, alcohol intake, and genetic variability.

Gingival hyperplasia is a common adverse effect associated with some AEDs, particularly phenytoin and valproic acid. The topical application of folate is generally helpful in the treatment of gingival overgrowth, especially in pregnant women, outside the context of anticonvulsants. ^96-98 Folate mouthwash appears to have an influence on gum health through local rather than systemic influence. Most research on phenytoin-induced changes in the gums indicates that daily rinses with a folate-based mouthwash may also inhibit gum disease caused by phenytoin. Notably, the level of dietary folate did not correlate with changes in hyperplasia in experimental subjects. ^99-101

The broad context of diet, lifestyle, economic status, and education frames the more narrow clinical issues of folic acid coadministration, Hcy status, and genomics. Lower economic status and educational levels are both associated with increased risk of birth defects in general and AED-induced malformations in particular. Likewise, children of women with epilepsy who smoked had lower gestational age and were at 3.4-fold increased risk of preterm delivery compared with infants of nonepileptic women who smoked. ⁷⁸ However, the findings of a 2002 British questionnaire-based survey of 795 women of childbearing age with epilepsy revealed significant shortcomings in education and awareness regarding pregnancy and childbearing. Of those women surveyed who considered the questions personally relevant, 38% to 48% recalled receiving information about contraception, pre-pregnancy planning, folic acid, and teratogenicity; overall, proportions were lower among adolescent women. ¹⁰²

Researchers and public health experts predict that the policies of dietary folate fortification and associated nutrition education programs adopted during the 1990s will have a significant, but not optimal, effect in preventing folate-related birth defects among healthy women, even those eating foods fortified with folic acid. ^{1,5,10,11,103} However, these folate intake recommendations, typically a 400 µg daily dose before and during pregnancy, as adopted by the U.S. FDA in 1998, and folate fortification of grains and other foods, estimated to increase actual daily intake of folic acid by approximately 78 µg, do not provide adequately for woman with compromised folate metabolism, particularly those taking folate-depleting medications. ¹⁰⁴

Botto et al. ¹⁰⁵ conducted an international retrospective cohort study of NTDs in relation to folic acid recommendations and found limited effect in Europe. After examining 13 birth defects registries, they reported that “the issuing of recommendations on folic acid was followed by no detectable improvement in the trends of incidence of neural tube defects” from 1988 to 1998. They concluded that dietary recommendations alone did not seem to influence trends in NTDs up to 6 years after clinical trials confirmed the effectiveness of folic acid, and that “cases of neural tube defects preventable by folic acid continue to accumulate.” ¹⁰⁵ Perhaps even more disturbing, evidence suggests that enrichment of foods with folic acid may not be circumventing widespread deficits in nutritional awareness and a related lack of proactive behavioral changes, to serve as an effective preventive measure. ¹¹ However, in reviewing results from the National Health and Nutrition Examination Survey (1999–2000), Pfeiffer et al. ¹ concluded: “Every segment of the US population appears to benefit from folic acid fortification.” Some commentators have also raised troubling yet essential questions about strong genetic selection pressure and potential adverse effects on the human genome from such public policy. ¹⁰⁶

More immediately, the policy of food fortification with folic acid expands the long-standing issue of folic acid supplementation with vitamin B ¹² supplementation from clinical management to unsupervised mass intervention into nutrient interrelationships. Thus, researchers might find it worthwhile to study the real potential of introducing a relative excess of folate into well-nourished populations who do not necessarily need it, while failing to enhance the nutrient intake of less well-fed populations and failing to consider B ¹² deficiencies, both relative and absolute.

Reports

A long-standing body of literature in case reports and scientific reviews documents the relatively high incidence of megaloblastic anemia and other hematological disorders among individuals undergoing long-term, and sometimes even short-term, therapy with AEDs. ^107-117

Guidolin et al. ¹¹⁸ reported on a 26-year-old woman being treated with carbamazepine for symptomatic partial epilepsy with simple and complex seizures. She experienced an increase in seizure frequency and severity after initiation of folic acid prophylaxis at 800 µg/day in anticipation of pregnancy.

Torres et al. ¹¹⁹ reported three cases of neonates with seizures who were unresponsive to one or more anticonvulsant medications but demonstrated immediate relief after administration of folinic acid.

When viewed within the context of relevant research literature, these reports reflect the broad trends and illustrate the need for further research into the individual variations in folate coadministration requirements, permutations of clinical response, and close supervision and regular monitoring during such coadministration, particularly on initiation or modification.

However, coadministration of preconception folic acid may not be protective for women with epilepsy. Craig et al. ¹²⁰ described a young woman whose seizures were controlled for 4 years by of valproic acid (2000 mg/day). Even though she supplemented with 4.0 mg of folic acid daily for 18 months before her pregnancy, she delivered a child with a lumbosacral NTD, a ventricular and atrial septal defect, cleft palate, and bilateral talipes. Likewise, two Canadian women delivered children with NTDs despite folate supplementation. One taking folic acid (3.5 mg/day) for 3 months before conception and valproic acid (1250 mg) aborted a child with lumbosacral spina bifida, Arnold Chiari malformation, and hydrocephalus. Another woman who supplemented with folic acid (5.0 mg/day) experienced one spontaneous abortion of a fetus with an encephalocele and two therapeutic abortions of fetuses with lumbosacral spina bifida. ¹²¹ It would be of interest to know if these women carried MTHFR genetic polymorphisms and might have been unable to properly metabolize and activate folic acid in its usual form.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing anticonvulsants and related medications are advised to educate their patients regarding implications of drug-induced depletion of folate and other nutrients and to assess their serum B ¹² and Hcy levels. The available evidence indicates that valproic acid, as monotherapy or a component of polytherapy, carries significantly greater risk of teratogenicity than other AEDs administered during pregnancy. Coadministration of folic acid and enhancement of dietary intake of folate-rich foods are almost always appropriate to prevent a drug-induced deficiency. Nevertheless, the data remain unclear and the benefits uncertain as to whether folate coadministration in women with epilepsy taking AEDs will reduce their risk. Further research using L-5-methyl folate is needed. Coadministration of folic acid (800 µg/day) and vitamin B ¹² (6 µg/day) may be sufficient in some cases, but levels typical of multivitamins have proved inadequate for many individuals. Dose titration enables reduction of adverse effects while minimizing the risk of interfering with the therapeutic activity of the AED(s). Special attention should be given to the possibility of decreased seizure control as folic acid supplementation is initiated, as well as to possible increased AED toxicity when administration of additional folic acid is halted.

The critical importance of ongoing supervision, nutritional assessment, and lifestyle education within the context of a frank and supportive therapeutic relationship cannot be overstated in the care of patients undergoing long-term therapy with AEDs. Close supervision and regular monitoring of serum levels of the medication(s) and clinical effects, as well as monitoring of folate and Hcy levels, are essential, especially with patients receiving long-term multidrug therapy. Although folate is generally considered nontoxic, large doses of folic acid may precipitate clinical B ¹² deficiency, especially if vitamin B ¹² status was already impaired. Spontaneously or iatrogenically hypochlorhydric patients may require much more than 6 µg of B ¹² for adequate function. Urinary and serum MMA levels may be the most reliable way of assessing functional B ¹² status. Beyond the concerns of folate deficiency and Hcy-associated risk in the general population, thrombosis from hyperhomocysteinemia in epileptic patients taking anticonvulsants represents a significant risk responsive to proactive clinical management. Genetic testing for folate polymorphisms may provide an especially valuable tool in risk assessment and clinical management of Hcy status in relation to folate nutriture during treatment with AEDs. Patients with a TT allele of the MTHFR C677T polymorphism, particularly in combination with the RFC1 80GG genotype, may have an even higher folate requirement than other patients treated with AEDs because of their significantly increased risk of elevated Hcy from compromised folate metabolism.

The dosage and number of folate-lowering drugs should be minimized and folic acid coadministration initiated in women with epilepsy who are contemplating pregnancy.

Seizure control should be achieved at least 6 months before conception and, if clinically possible, by the lowest effective dose of a single anticonvulsant individualized according to the type of epilepsy. Substitution of another agent is strongly indicated in women being treated with valproic acid, as monotherapy or a component of polytherapy. Folic acid at 5 mg/day (along with vitamins B ⁶ and B ¹² ) should be administered starting 3 months before conception and during the first trimester to prevent folic acid deficiency–induced malformations. Strong consideration should be given to using the activated form ( L-5-methyl or 5-formyl) of folate in this setting, unless genetic testing has ruled out MTHFR genetic polymorphisms. The addition of folic acid to a prenatal regimen becomes even more imperative for women using OCs while undergoing anticonvulsant therapy when they choose to become pregnant, because OCs also tend to adversely affect folate status. Some clinicians consider benzodiazepines or phenytoin to be effective for seizure cessation during labor and delivery. Administration of vitamin K immediately after birth is prudent. Furthermore, the neonate should be thoroughly assessed for epilepsy and anticonvulsant-associated dysmorphology.

	Potentially Harmful or Serious Adverse Interaction—Avoid
	Beneficial or Supportive Interaction, with Professional Management
	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management
	Prevention or Reduction of Drug Adverse Effect
	Bimodal or Variable Interaction, with Professional Management
	Drug-Induced Effect on Nutrient Function, Supplementation Contraindicated, Professional Management Appropriate

Consensus

Effect and Mechanism of Action

By definition, the agents in this drug class share the central mechanism of being “antifolate” as well as several key characteristics that influence folate metabolism and affect clinical implications of depletion. However, they differ in their pharmacological characteristics and mechanisms, therapeutic applications and effects, and characteristic patient populations, all of which influence their safety profile, adverse effects, and approaches to coadministration of folic acid.

Methotrexate is the prototype antifolate, used in oncology for decades before it was introduced to rheumatology, and still used in both specialties. The cancer chemotherapeutic agent lometrexol [(6R)-5,10-dideaza-5,6,7,8-tetrahydrofolate] is a representative later generation folate antimetabolite. Used mainly in treating solid tumors, lometrexol targets the de novo purine nucleotide biosynthesis pathway and limits DNA synthesis by inhibiting glycinamide ribonucleotide formyltransferase (GARFT), the first folate-dependent enzyme in de novo purine synthesis; it is avidly polyglutamated and retained in tissues expressing folylpolyglutamate synthetase. ^122-125 Lometrexol pharmacokinetics are often described by a three-compartment model and are considered independent of either lometrexol or folic acid dose. The cumulative hematological toxicity of lometrexol is related to cellular pharmacokinetics and tissue concentration and not plasma pharmacokinetics. ¹²⁶

Methotrexate is a folic acid antagonist used in the treatment of several types of cancer, rheumatoid arthritis (RA), psoriasis, and other conditions. Many of the adverse effects associated with methotrexate are similar to those of severe folate deficiency. Methotrexate produces its immunosuppressant and antineoplastic effects by binding to and reversibly inhibiting the activity of dihydrofolate reductase, which reduces folate to active tetrahydrofolate. ¹²⁷ By thus restricting levels of tetrahydrofolate, methotrexate decreases the availability of single-carbon fragments required for biosynthesis of purines, DNA, and cellular proteins. Perhaps the most widely used folate antagonist, methotrexate has varying patterns of use for different conditions, and the relationship of folic acid to the drug mechanism changes accordingly. This difference is especially important in individuals using methotrexate as a chemotherapeutic agent and those taking it for RA.

As with other antifolates, pemetrexed exerts its antineoplastic activity by inhibiting multiple tetrahydrofolate cofactor-requiring enzymes involved in the de novo biosynthesis of purine, thymidine, and pyrimidine nucleotides, thus interfering with folate-dependent metabolic processes critical to cell replication. Pemetrexed also inhibits dihydrofolate reductase. Its greater potency, compared with other antifolates, is related to its transport into cells by both the reduced–folate carrier system and the membrane folate-binding protein transport system. The enzyme folylpolyglutamate synthetase then intracellularly converts pemetrexed to polyglutamate forms, which are retained in cells and act as inhibitors of thymidylate synthase (TS) and GARFT. Thus, functionally, pemetrexed acts as a prodrug for its polyglutamate forms. Polyglutamation occurs more rapidly and extensively in tumor cells than in healthy tissues, and polyglutamated metabolites exhibit a prolonged intracellular retention in malignant cells and a 60-fold increase in inhibition of TS compared with the monoglutamated form. Pemetrexed has demonstrated significant antineoplastic activity against a variety of tumor types, including lung, breast, colon, mesothelioma, pancreatic, gastric, bladder, head and neck, and cervix. Tumors with codeletion of the methylthioadenosine phosphorylase gene, as a consequence of p16 deletions, may be particularly sensitive to pemetrexed. Attention has also focused on its ability to enhance the cytotoxicity and tolerability of doxorubicin, paclitaxel, cisplatin, gemcitabine, and other important chemotherapeutic agents. ^128-132

Raltitrexed is a quinazoline folate analog that selectively inhibits TS and thereby causes DNA fragmentation and cell death. Raltitrexed is transported into cells through a reduced folate carrier, where it is extensively polyglutamated. As with pemetrexed, polyglutamation enhances potency and extends half-life to increase the duration of TS inhibition and raltitrexed's antitumor activity.

In summary, the finding that folate intake does not seem to interfere with efficacy of these drugs, both in autoimmune disease and cancer applications, is both intriguing and clinically significant, suggesting these agents may have other mechanisms besides folate antagonism or being “antifolate.”

Research

Researchers and clinicians generally agree that impaired folate status plays a major role in the activity and toxicity of methotrexate and other antifolates. ¹²⁷ The degree of folate depletion during methotrexate therapy for autoimmune disease depends primarily on the weekly administered dose. The risk of adverse effects from interference with folic acid utilization is particularly significant with high dose and prolonged use. Folic acid (or 5-MTHF) coadministration can usually mitigate adverse effects of antifolates, but their ability to do so without impairing drug efficacy may vary significantly in low-dose treatment (e.g., methotrexate for RA or psoriasis) versus high-dose administration (e.g., cancer therapy). Furthermore, emerging trends suggest research may be warranted to explore the clinical potential of antifolates whose pharmacodynamic effects are less affected by variations in folate status among different patients.

The coadministration of folinic acid (Leucovorin) is well established in conventional practice as an adjunctive therapy to mitigate toxic effects of methotrexate, lometrexol, and related agents, particularly in the context of high-dose antineoplastic chemotherapy. Folinic acid (5-FTHF) is the most well-known reduced form of folic acid, available as a calcium salt for parenteral or oral administration, which competes with methotrexate for entry into cells and repletes intracellular pools of tetrahydrofolate. Overall, findings from studies conducted in the late 1980s and early 1990s were mixed as to both the effects of folinic acid coadministration in reducing methotrexate toxicity and drug-induced adverse effects and the possible impairment of methotrexate efficacy and therapy outcomes. ^133-140 Nevertheless, folinic acid has been used as a rescue agent throughout the history of clinical trials and has become part of conventional practice in the clinical application of antifolates, such as after high-dose methotrexate in the treatment of osteosarcoma. ¹⁴¹ For many years, folinic acid has been coadministered as part of a standard therapy using 5-fluorouracil for metastatic colorectal cancer (5-FU/leukovorin), at least in part because of its ability to increase the affinity of fluorouracil for TS. More recently, with raltitrexed, intravenous folinic acid, 25 mg/m ² every 6 hours, can reduce intestinal damage and improve recovery of neutrophil and platelet levels. ¹⁴² As a form of 5-formyltetrahydrofolate (5-FTHF), folinic acid's ability to bypass dihydrofolate reductase contributes both to its rapid action and therapeutic efficacy and its potential to reduce drug activity.

In certain circumstances, folic acid may be capable of reducing the symptoms of antifolate toxicity without interfering with clinical effectiveness. Evidence consistently demonstrates the safety and efficacy of folate coadministration with methotrexate in the treatment of RA, psoriasis, and similar autoimmune conditions. In contrast to folinic acid or 5-MTHF, folic acid still requires reduction by dihydrofolate reductase, a factor that may reduce its potency and the probability of it interfering with antifolate drug efficacy.

As the use of methotrexate for the treatment of RA has evolved, so has the understanding of the use of folic acid by individuals undergoing therapy. Although use of methotrexate for RA treatment has grown in recent years, more than 30% of patients abandon treatment because of drug-related adverse effects. Initially, researchers assumed that methotrexate's effects on folic acid were the source of its presumed benefits in cases of rheumatoid arthritis, as in chemotherapeutic uses. However, with time and further research, practice has shifted to support the coadministration of folic acid to counter the adverse effects of methotrexate in these cases for several reasons: (1) its well-proven ability to reduce toxic effects of methotrexate; (2) methotrexate causes folate deficiency, and the folate status of patients taking even low-dose methotrexate declines precipitously without adjunctive folic acid; and (3) plasma Hcy levels can increase significantly in those taking methotrexate but not folate, thereby significantly increasing risk of cardiovascular disease. These and other benefits are gained with no apparent loss of antirheumatic effect. Most researchers have found that folic acid levels were not related to parameters of disease activity and concluded that methotrexate does not exert its action in RA primarily by inhibiting dihydrofolate reductase. ^143-148

In 1993, Duhra ¹⁴⁹ studied 78 patients with psoriasis to determine the frequency, severity, and dose relationship of GI symptoms induced by low-dose, once-weekly oral methotrexate (MTX) therapy and the response to concomitant folic acid administration. After initiation of MTX, 32% of subjects reported GI symptoms, with nausea accounting for 80%. The author reported that the “onset and severity of symptoms were related to the weekly dose of methotrexate but not to the cumulative dose or to the duration of methotrexate therapy.” Folic acid, 5 mg daily, eliminated these adverse effects without impairing the therapeutic effect of the medication. Likewise, Morgan et al. ¹³⁸ found that “5 mg or 50 mg/week dose of folic acid supplementation does not alter the efficacy of methotrexate treated rheumatoid arthritis patients.” In a double-blind, placebo-controlled trial of 79 patients over 1 year, Morgan et al. ¹⁴⁸ demonstrated that folic acid coadministration (5 or 27.5 mg/week) prevents deficient blood folate levels and hyperhomocysteinemia, thus providing cardiovascular disease prevention, during long-term, low-dose MTX therapy for RA. Folate nutriture declined in patients administered low-dose MTX without adjunctive folic acid. The authors observed that “low blood folate levels and increased mean corpuscular volumes were associated with substantial methotrexate toxicity, whereas daily dietary intakes of more than 900 nmol (400 micrograms) of folic acid were associated with little methotrexate toxicity.” Plasma Hcy levels increased significantly and hyperhomocysteinemia occurred more often in the placebo group than in the folic acid–supplemented groups. The authors concluded that for long-term, low-dose MTX therapy, “there are now at least three reasons to consider supplementation with folic acid (a low cost prescription): (1) to prevent MTX toxicity, (2) to prevent or treat folate deficiency, and (3) to prevent hyperhomocysteinemia.” ¹⁴⁸

Suzuki et al. ¹⁵⁰ retrospectively analyzed 66 RA patients to assess the incidence and risk factors for elevation of serum hepatic alanine (ALT) and aspartate (AST) aminotransferases during MTX therapy. The frequency of elevation of serum AST or ALT was four to five times greater than in patients taking other disease-modifying antirheumatic drugs (DMARDs). Subsequently, the authors prospectively evaluated the effect of adjunctive folic acid on serum ALT and RA activity in 14 patients who exhibited sustained, high serum ALT levels. The ALT levels decreased with folic acid coadministration in all patients within 3 months. Eleven patients treated with folic acid showed no change in RA symptomatology, but three exited the study because of exacerbation of their RA symptoms. These researchers advised that “careful monitoring of serum hepatic aminotransferases is necessary in patients with predisposing factors, especially those receiving more than 0.15 mg/kg of MTX weekly.” ¹⁵⁰ They cautioned that although folic acid coadministration can reverse the sustained elevation of ALT, it might also exacerbate RA in some patients.

In a prospective, randomized, double-blind, placebo-controlled study, Griffith et al. ¹⁵¹ (2000) tested the benefits of folate support in RA patients receiving ongoing MTX treatment (<20 mg weekly) by withdrawing folic acid (5 mg/day) from one group and substituting a placebo. The authors monitored all toxicity (including absolute changes in hematological and liver enzyme indices), recorded patient reports of changes in drug efficacy, and tracked discontinuation of MTX over 1 year. Among the 25 subjects who concluded the study early, a significantly larger proportion (17; 46%) of those receiving MTX alone discontinued the drug, versus eight (21%) in the group remaining on folic acid. The placebo/MTX group reported an increased incidence of nausea (45% vs. 7%) at 9 months, and two patients in that group discontinued because of neutropenia. Although subjects in the placebo group exhibited significantly lower disease activity on several of the variables measured, the researchers adjudged that “these were probably not of clinical significance.” Overall, these findings indicate that folic acid coadministration reduced adverse effects and enabled patient tolerance and compliance without significantly interfering with MTX's therapeutic activity. ¹⁵¹

Also in 2000, van den Berg et al. ¹⁵² showed that 83.5% of patients (61 of 85) treated with concomitant folic acid during low-dose MTX therapy for RA continued treatment for more than 1 year, compared with 53.1% of patients (23 of 49) not receiving folic acid support. The authors attributed this pattern of decreased patient discontinuation of MTX to folic acid's effects in reducing adverse effects from the medication.

In a 48-week, randomized, double-blind, placebo-controlled clinical trial involving 434 RA patients, van Ede et al. ¹⁵³ compared the effects of MTX plus placebo, folic acid (1 mg/day), or folinic acid (2.5 mg/week) with regard to discontinuation of MTX because of adverse effects and MTX dosage, efficacy, and toxicity. The initial MTX dosage was 7.5 mg/week; dosage increases were allowed up to a maximum of 25 mg/week for insufficient responses. Folate dosages were doubled once the dosage of MTX reached 15 mg/week. These researchers reported that parameters of disease activity improved equally in all groups, although subjects in both folate groups required slightly higher dosages of MTX to obtain similar symptomatic improvement. However, only 17% of the folic acid group and 12% of the folinic acid group discontinued MTX therapy because of toxicity-related adverse effects, in contrast to 38% of the placebo group. The authors attributed these between-group differences to a decreased incidence of elevated liver enzyme levels in the folate groups. No other between-group differences were found in the incidence, severity, or duration of other adverse events, including GI and mucosal effects.

Hoekstraet al. ¹⁵⁴ analyzed data from a 48-week, multicenter, randomized clinical trial involving 411 patients with RA treated with MTX, comparing folates and placebo to assess factors associated with toxicity, final dose, and drug efficacy. Coadministration of folates and MTX was strongly related to the lack of hepatotoxicity, as well as reduced levels of drug discontinuation and efficacy of MTX therapy. Reaching a final dose of MTX of 15 mg/week or more was related to folate supplementation and the absence of prior GI events. Other baseline characteristics predictive of MTX treatment outcome included body mass index, gender, use of nonsteroidal anti-inflammatory drugs (NSAIDs), and creatinine clearance.

Khanna et al. ¹⁵⁵ examined the effect of folic acid on the efficacy of MTX treatment in RA patients at 12 months in two Phase III, randomized controlled trials of leflunomide in which MTX was used as a comparator. A U.S. study involved 482 patients with active RA; of these, 179 received at least one dose of MTX, and all were mandated to receive 1 mg of oral folic acid once or twice daily. A multinational European study involved 999 patients with active RA; of these, 489 received at least one dose of MTX, and oral folic acid was not required, although 50 received folate after developing an adverse event. After using propensity scores to adjust for differences in the baseline characteristics of folic acid users and non–folic acid users, the authors concluded that 9% to 21% fewer MTX-treated RA patients taking folic acid had 20%, 50%, or 70% improvement, according to American College of Rheumatology (ACR) standards, at 52 weeks compared with those who did not receive folic acid. Thus, 17% more patients in the group who did not receive folic acid met ACR improvement criteria, whereas ACR 50% responses were 14% higher in the non–folic acid group and ACR 70% responses 12% higher; such findings suggest that adjunctive folic acid may impair the efficacy of MTX in such patients. Furthermore, they reported relatively similar rates of adverse events among U.S. and European subjects, 93% and 94%, respectively, but a significantly higher occurrence of elevated liver transaminase levels among European subjects (62%), most of whom were not taking folic acid, in contrast to 29% of U.S. study patients, most of whom were taking folic acid. The authors also emphasized that physicians should consider a possible exacerbation when their RA patients taking MTX are started on folic acid, suggesting these patients may require a higher MTX dose. ¹⁵⁵

Kirby et al. ¹⁵⁶ investigated folic acid–prescribing patterns among dermatologists in the United Kingdom treating psoriasis patients with MTX. Of the 153 physicians who responded to the survey, 75% reported that they coadministered folic acid, 46% considered folic acid effective in reducing drug-induced nausea, and 60% reported that such nutrient support did not impair MTX efficacy in the treatment of psoriasis.

The efficacy of and tolerance for MTX therapy varies from patient to patient. Pharmacogenomic variability represents one important factor influencing clinical response and patient compliance. For example, the ability of leukemia cells to accumulate methotrexate polyglutamate (MTXPG) is an important determinant of the antileukemic effects of MTX. Kager et al. ¹⁵⁷ measured in vivo MTXPG accumulation in leukemia cells from 101 children with acute lymphoblastic leukemia (ALL) to determine distinct mechanisms of subtype-specific differences in MTXPG. They determined that “B-lineage ALL with either TEL-AML1 or E2A-PBX1 gene fusion, or T-lineage ALL, accumulate significantly lower MTXPG compared with B-lineage ALL without these genetic abnormalities or compared with hyperdiploid (fewer than 50 chromosomes) ALL.” They analyzed expression of 32 folate pathway genes in diagnostic leukemia cells from 197 children using oligonucleotide microarrays and found that ALL subtype-specific patterns of folate pathway gene expression were significantly related to MTXPG accumulation. Numerous studies have documented the incidence of increased intolerance to MTX and related antifolate therapies among individuals with genetic polymorphisms affecting folate metabolism. ^158-164 The utility of folic acid coadministration in such individuals, once identified, may appear self-evident, but well-designed clinical trials are warranted and surely will be forthcoming.

For example, ongoing research by Sanderson and colleagues at St. Thomas’ Hospital in London is focusing on new tools for predictive pharmacogenomics of antifolates, with a focus on treatment of inflammatory bowel disease. They have observed an association between genetic variation in levels of the enzyme thiopurine methyltransferase (TPMT) and inosine triphosphate pyrophosphatase (ITPase) and a significant risk of adverse responses (or lack of response) to these antifolate agents. (See later Mercaptopurine, Azathioprine, and Thioguanine [Thiopurines] section for further discussion.) Pretreatment assessment of these enzyme levels can provide a valuable tool in either avoidance of the drug or use at a lower dose to avoid adverse effects.

In a multicenter, cross-sectional study involving 226 adult patients treated with weekly MTX for more than 3 months, Dervieux et al. ¹⁶⁵ investigated the contribution of red blood cell (RBC) MTXPGs, RBC folate polyglutamates, and a pharmacogenetic index to the clinical status of RA patients. They calculated a composite pharmacogenetic index comprising low-penetrance genetic polymorphisms in reduced folate carrier (RFC-1 G80A), AICAR transformylase (ATIC C347G), and thymidylate synthase (TSER*2/*3). Using a multivariate analysis, they found that lower RBC MTXPG levels (median, 40 nmol/L) and a lower pharmacogenetic index were associated with a higher number of joint counts, higher disease activity, and Health Assessment Questionnaire (HAQ). An RBC MTX PG level below 60 nmol/L and a low pharmacogenetic index were associated with an increased likelihood of poor therapeutic response to MTX. These authors concluded that “therapeutic drug monitoring of methotrexate treatment combining pharmacogenetic and intracellular metabolite measurements may be useful to optimize methotrexate treatment” by enabling “more sophisticated” methods for optimizing dosing, personalizing care, and minimizing adverse effects. They also suggested that “prospective studies are warranted to investigate the predictive value of these markers for MTX efficacy.” ¹⁶⁵

Myelosuppression, neutropenia, and mucositis are among the most common and serious toxicities of pemetrexed, a newer antifolate drug developed for cancer treatment. Emerging evidence from research and clinical practice indicates that coadministration of oral folic acid or intramuscular vitamin B ¹² mitigates the toxicity profile of pemetrexed and clinical outcomes in difficult-to-treat cancers without impairing drug pharmacokinetics or compromising its antitumor effect, even over multiple treatment cycles. ^131,166-169 For example, in a Phase III study involving 456 chemotherapy-naive patients with malignant pleural mesothelioma, Vogelzang et al. ¹⁷⁰ found that the combination of pemetrexed and cisplatin improved survival time, time to progression, and response rates compared with controls treated with cisplatin alone. Notably, after 117 patients had enrolled, “folic acid and vitamin B ¹² were added to reduce toxicity, resulting in a significant reduction in toxicities in the pemetrexed/cisplatin arm … without adversely affecting survival time.” Furthermore, in a review of pemetrexed's pharmacology, Calvert ¹³² noted that multivariate analyses have “demonstrated that pretreatment total plasma homocysteine levels significantly predicted severe thrombocytopenia and neutropenia, with or without associated grade 3/4 diarrhea, mucositis, or infection.” She concludes: “Routine vitamin B ¹² and folic acid supplementation have resulted in decreased frequency/severity of toxicities associated with pemetrexed without affecting efficacy, making this novel antifolate a safe and efficacious anticancer agent.”

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Tolerance, safety, and compliance issues are significant in clinical management of patients treated with methotrexate and other antifolates. Physicians prescribing or administering these medications are strongly advised to inform patients regarding the high probability of drug-induced adverse effects on folate status and the clinical implications. Pharmacogenomic assessment (e.g., MTHFR, TPMT) can play a critical role in predicting drug efficacy and tolerance, especially with regard to folate metabolism and probable requirements, and in crafting an individualized treatment strategy. In most individuals, measured folic acid coadministration may enhance treatment efficacy and outcomes by reducing toxicity and adverse effects and increasing tolerance and compliance.

In treating patients with methotrexate for rheumatoid arthritis, psoriasis, and inflammatory bowel disease, large doses of folic acid can reduce adverse effects without compromising therapeutic activity. However, close supervision and regular monitoring of plasma drug levels and folate status, as well as plasma Hcy levels, are essential to safe and effective clinical management.

Concomitant use of folic acid during maintenance-phase antifolate treatment for leukemia and other forms of cancer is more controversial and requires a more careful, individualized, and closely managed approach to clinical care. Excessive repletion of folate may interfere with the intended therapeutic action of the medication in suppressing DNA synthesis and cellular proliferation of the malignant clone.

The administration of 5-FTHF (folinic acid) or 5-MTHF may be more efficacious in patients with high Hcy levels despite folic acid, B ¹² , pyridoxine, and methyl donor supplementation; in patients with low levels of dihydrofolate reductase enzyme activity; in those taking medications or supplements that suppress dihydrofolate reductase activity; and in patients with compromised liver or bone marrow function who might not reduce folate adequately.

	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, Not Requiring Professional Management
	Adverse Drug Effect on Nutritional Therapeutics, Strategic Concern
	Beneficial or Supportive Interaction, with Professional Management

Consensus

Effect and Mechanism of Action

Through their intended effect of limiting absorption and assimilation of dietary lipids, bile acid sequestrants may prevent absorption and reduce bioavailability of folic acid as well as other nutrients, such as the fat-soluble vitamins, A, D, E, and K. ^57,171-174

Through complementary mechanisms, folinic acid and cholestyramine can be used together to counter methotrexate toxicity.

Research

In 1979, Leonard et al. ¹⁷⁵ demonstrated that cholestyramine and colestipol bound, to a great extent, vitamin B ¹² –intrinsic factor complex, folic acid, and iron citrate in vitro. Likewise, in studying the mechanisms of intestinal folate transport, Strum ¹⁷⁶ found that cholestyramine (20 mg) adsorbs 95% of pteroylglutamate (folate) in vitro.

Using a rodent model, Hoppner and Lampi ¹⁷⁷ observed that cholestyramine significantly reduced the intestinal deconjugation, absorption, and bioavailability of folic acid compared with brewer's yeast folate.

Several human studies have specifically documented the effects of bile acid sequestrants on folate absorption and bioavailability. In a trial involving 20 children and young adults with familial hypercholesterolemia, Farah et al. ¹⁷⁸ investigated the effects of cholestyramine in the context of a diet low in cholesterol and high in polyunsaturated fats. Cholestyramine administration was associated with a significant decrease in mean serum folate levels in female patients. Tonstad et al. ¹⁷⁹ conducted a study involving 37 boys and 29 girls age 10 to 16 years with familial hypercholesterolemia, first in an 8-week, double blind, placebo-controlled protocol, then in open treatment for 44 to 52 weeks. Levels of serum folate, vitamin E, and carotenoids were reduced in the colestipol group. Only a minority of adolescents adhered to the new formulation of orange-flavored “colestipol granules” for the full year. Nevertheless, the authors concluded that “folate and possibly vitamin D supplementation is recommended.” Subsequently, in a randomized controlled trial involving children with familial hypercholesterolemia, Tonstad et al. ¹⁸⁰ and another Norwegian team of investigators found that heterozygosity and homozygosity for the C677T mutation in the MTHFR gene was associated with low serum folate and increased susceptibility to elevation of plasma tHcy during cholestyramine treatment. These authors recommended folic acid coadministration as “prudent in these children” because of the independent relationship between elevated plasma tHcy and cardiovascular disease.

The ability of hypocholesterolemic resins to adsorb and reduce bioavailability of both folic acid and methotrexate (MTX) may be relevant in countering the toxicity of this potent antimetabolite, well-known for a range of adverse effects influencing tolerance and compliance. Interestingly, cholestyramine may be used to enhance the biliary excretion of MTX, which acts as an antifolate through competitive inhibition. ¹⁸¹ Based on multiple experiments examining the relative adsorption of MTX and calcium leucovorin (folinic acid) onto cholestyramine in vitro, Merino-Sanjuan et al. ¹⁸² suggested that “cholestyramine may be a potentially useful adjunctive therapy in the treatment of an overdose of MTX.” Fernandez et al. ¹⁸³ described severe MTX-induced toxicity secondary to renal failure in a patient with non-Hodgkin's lymphoma. “Corrective measures included folinic acid rescue therapy, cholestyramine resin administration, hydration and urine alkalinization, urine pH monitoring, and extracorporeal clearance techniques.”

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing bile acid sequestrants are advised to coadminister folic acid, vitamins B ¹² and B ⁶ , mixed tocopherols and tocotrienols, vitamin D, coenzyme Q10, and other synergistic nutrients within a comprehensive and individualized strategy of integrative therapeutics for the prevention and treatment of cardiovascular disease. The relationship between folate status and homocysteine would be adequate by itself to justify increased intake of dietary folate and supplemental folic acid, of at least 800 µg/day, in such a patient population. The probable interference with absorption and bioavailability of folate and other relevant nutrients by these hypocholesteremic resins further heightens the imperative for enhanced nutriture. Daily administration of a high-potency multivitamin/mineral combination will replace the nutrients impeded by the drug. Folic acid (as well as other nutrients and medications) should be taken 1 hour before or 4 to 6 hours after bile acid sequestrants to reduce impairment of absorption and obtain optimal bioavailability.

	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management
	Prevention or Reduction of Drug Adverse Effect
	Beneficial or Supportive Interaction, Not Requiring Professional Management
	Adverse Drug Effect on Nutritional Therapeutics, Strategic Concern

Consensus but Preliminary

Effect and Mechanism of Action

Drug-induced anemia is well established as an adverse effect of chloramphenicol. ¹¹⁰ Aplastic anemia has resulted from chloramphenicol in a small percentage of patients. Folic acid administration may reduce adverse effects of chloramphenicol to some degree. In patients prescribed folic acid for preventive benefits or therapeutic effects, concurrent administration of chloramphenicol for an extended period (or sometimes only a short period) can interfere with the hematopoietic response to folic acid and reduce effectiveness of folic acid in the treatment of anemias.

Research

Specific research on the interaction between chloramphenicol and dietary folate or supplemental folic acid is lacking. However, consensus as to probable effects and outcomes is based on widely recognized functions and activities of the two substances.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians are advised to monitor closely all major hematological parameters in patients prescribed chloramphenicol. Known toxicity has generally led to its disuse, except when no suitable alternative is available or the mortality of the treated disease is high.

	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management
	Prevention or Reduction of Drug Adverse Effect
	Beneficial or Supportive Interaction, Not Requiring Professional Management
	Adverse Drug Effect on Nutritional Therapeutics, Strategic Concern

Preliminary

Effect and Mechanism of Action

Colchicine is reported to depress blood folate levels.

Research

Depression of whole-blood folate activity by colchicine was demonstrated in 1965 and has not since been the subject of direct research. ¹⁸⁴ No clinical trials have been published on the mitigation of adverse effects through folic acid coadministration. Further research through well-designed clinical trials may be warranted.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing colchicine should closely monitor both folate and Hcy levels in patients. Pending substantive research through well-designed clinical trials, coadministration of folic acid, 800 µg/day, can provide a safe and potentially effective means of compensating for drug-depletion effects and may support the clinical strategies toward reducing cardiovascular risk.

	Drug-Induced Adverse Effect on Nutrient Function, Supplementation Therapeutic, Not Requiring Professional Management
	Prevention or Reduction of Drug Adverse Effect
	Beneficial or Supportive Interaction, Not Requiring Professional Management

Emerging, Mixed

Effect and Mechanism of Action

A consistent body of evidence demonstrates that fibrates, particularly fenofibrate and bezafibrate, cause marked elevations in total plasma homocysteine (tHcy) levels. The molecular mechanisms involved have not been elucidated, but multiple mechanisms may contribute to this effect. Numerous studies show that coadministration of folic acid, especially with synergistic nutrients, can mitigate this particular adverse drug effect, but such intervention does not appear to alter clinical outcomes and thus may not constitute an “adverse clinical event.”

Nutrient depletion resulting from hypolipidemic drugs, as indicated by plasma levels, appears to be lacking, a secondary factor of lesser clinical significance, or simply one that has not been adequately demonstrated within the design and time frame of the available clinical trials. ¹⁸⁵ Impairment of renal function, alteration of creatine-creatinine metabolism, and changes in methyl transfer are regarded as more probable mechanisms. ^186,187 Many of the effects of fibrates are known to be mediated by the peroxisome proliferator-activated receptor alpha (PPAR-α), a transcription factor belonging to the nuclear receptor family, and fibrates appear to increase homocystinemia through a PPAR-α–mediated mechanism. ^188,189 For example, bezafibrate is a known activator of PPARs that can activate both PPAR-α and PPAR-β.

These and other findings suggest that the Hcy form elevated by fibrates may be protein-bound Hcy rather than atherogenic, reduced Hcy. Furthermore, although folic acid effectively reduces the fibrate-induced elevation of tHcy and creatinine, it does not affect the drug-induced elevation of total plasma cysteine (tCys). ¹⁹⁰

Research

An extensive body of scientific research has explored the effects of fibrates on Hcy levels, the role of folate in these effects, and the impact of such adverse effects and compensatory folate support within the overall strategy of cardiovascular risk reduction and outcomes. Fibrates are among the drugs of choice in conventional treatment of hypertriglyceridemia and low levels of high-density lipoprotein (HDL) cholesterol, both recognized as significant risk factors for cardiovascular disease. Increased blood levels of homocysteine, an amino acid derived from the methionine cycle, are generally associated with increased risk of endothelial damage, atherosclerosis, and coronary, cerebral, or peripheral vascular disease, although it is uncertain whether such elevations in Hcy represent a cause or a consequence of the pathological process. Some fibrates, particularly fenofibrate and bezafibrate, raise tHcy levels by 20% to 40%, but evidence from human research is still lacking to demonstrate that agents in this drug class induce depletion of folic acid or other nutrients known to modulate Hcy. Notably, multiple studies have found that gemfibrozil does not increase Hcy. Thus the overall trend in the literature shows that fibrate administration, particularly fenofibrate and bezafibrate, causes often-dramatic elevations in Hcy levels and that folic acid coadministration can neutralize this adverse effect, but suggests cardiovascular outcomes are unaffected by fibrate-induced hyperhomocysteinemia.

Significant evidence demonstrates that fenofibrate, bezafibrate, and potentially other frequently prescribed fibrates greatly increase plasma Hcy levels, and that coadministration of folate and synergistic nutrients can reduce this effect, even though fibric acid derivatives apparently do not reduce blood concentrations of these key nutrients. De Lorgeril et al. ¹⁹¹ reported a 46% increase in plasma Hcy in patients treated with fenofibrate for 12 weeks. Later in 1999, Dierkes et al. ¹⁹² reported that fenofibrate (200 mg) and bezafibrate (400 mg) significantly reduced triglycerides but also increased plasma Hcy by 44% and 17.5%, respectively, in 20 male patients (age 39-56) with hypertriglyceridemia but normal renal and thyroid function after 6 weeks of therapy. In discussing the underlying mechanisms, the authors noted that “the vitamin status does not appear to be involved in the first line, because folate, cobalamin, and vitamin B ⁶ (in the bezafibrate group) remained unaltered.” In contrast, they emphasized that “creatinine and cystatin C increased, suggesting an alteration of renal function.” The tHcy concentrations increase as renal function deteriorates, and fibrates increase serum creatinine moderately and reversibly.

In 2001, Dierkes et al. ¹⁹³ conducted a randomized, double-blind crossover study involving hyperlipidemic men for 6 weeks to investigate the ability of nutrient coadministration to mitigate the Hcy elevation induced by fenofibrate. Subjects administered fenofibrate plus folic acid (650 µg), vitamin B ⁶ (5 mg), and vitamin B ¹² (50 µg) demonstrated an increase in Hcy concentration of 13% ± 25%, whereas those given fenofibrate plus placebo exhibited an increase of 44% ± 47%. The authors advised that “fenofibrate may counteract the cardioprotective effect of lipid lowering” and that nutrient coadministration “may therefore be warranted for routine use.” Folic acid supplementation in patients treated with fenofibrate significantly reduced the increase in plasma Hcy levels.

In 2003, in a randomized, open-label study of 22 patients with mixed hyperlipidemia, Melenovsky et al. ¹⁹⁰ compared the effect of micronized fenofibrate (200 mg daily) alone versus fenofibrate plus folic acid (10 mg every other day) on plasma Hcy levels over a 9-week treatment period. Overall, plasma Hcy levels increased by 6.85 µmol/L in subjects treated with fenofibrate only, but increased by 2.01 µmol/L in the group treated with both fenofibrate and folic acid, a statistically significant difference.

Although they arrived at similar conclusions, none of these studies were designed to determine whether amelioration of this adverse effect increases the clinical benefit of fibrates. ^190-193

Bissonnette et al. ¹⁸⁵ investigated tHcy levels as a post hoc analysis after testing the effect of micronized fenofibrate on postprandial lipemia in the fasted and fed states. The randomized, placebo-controlled, double-blind study involved 20 men with established coronary artery disease (CAD), or at least two cardiovascular risk factors, who had elevated plasma triglyceride levels and reduced HDL cholesterol levels, and in whom a fibrate was clinically indicated. As expected, fenofibrate caused a marked reduction in all triglyceride-rich lipoprotein parameters, but administration was also associated with an increase in fasting tHcy and fed tHcy levels, 6 hours after the fat load. The fenofibrate-induced changes in tHcy level were not associated with changes in plasma levels of folate, vitamins B ⁶ or B ¹² , or creatinine, but methionine and cysteine were significantly increased.

Thus, several research teams have concluded that the effects of fibrates, particularly fenofibrate, in elevating plasma tHcy levels could compromise their putative cardioprotective properties, and that concomitant support with folate and related nutrients may contribute to the overall clinical strategy.

Among conventional hypolipidemic agents, statin drugs have exhibited a significant lack of adverse effects on folate relative to fibrates. In response to concern that elevated tHcy could compromise the cardiovascular benefit from lipid lowering by fibrates, Mayer et al. ^193a conducted an open, randomized, prospective crossover study to investigate the effects of fenofibrate. The 24 volunteers had total cholesterol of 6 mmol/L or higher and triglycerides less than 5 mmol/L, with normal blood pressure, normal blood glucose, and without any pharmacotherapy or clinical vascular or metabolic disease. In successive 6-month phases, the researchers measured lipids, tHcy, folate, vitamin B ¹² , and renal function markers after diet, after 200 mg of fenofibrate (3 months in monotherapy followed by 3 months in combination with 10 mg folate), and then after fluvastatin (3 months of 40 mg followed by 3 months of 80 mg). They found that fenofibrate monotherapy increased tHcy from 10.0 to 14.2 µmol/L while coadministration of folate decreased tHcy to 10.6 µmol/L. Fuvastatin, however, did not significantly influence the tHcy concentrations. In a trial involving 128 patients with primary hyperlipidemia, Milionis et al. ¹⁹⁴ compared the effects of atorvastatin, simvastatin, and fenofibrate on serum Hcy levels. Although neither statins nor fenofibrate had any effect on serum vitamin B ¹² and folic acid levels, Hcy levels were significantly increased only by fenofibrate and did not change from baseline after statin treatment.

Emerging research into the molecular mechanisms underlying the differential effects of fibrates on Hcy subfractions may help to understand their tendency to increase tHcy, establish the relative benefits of their hypolipidemic effects, and elucidate the strategic implications of such factors in preventing cardiovascular disease. Plasma tHcy comprises both reduced, free oxidized Hcy and protein-bound Hcy; the reduced Hcy is thought to be the atherogenic, but minor, subfraction. In a set of animal experiments, Luc et al. ¹⁸⁹ demonstrated that activation of PPAR-α mediates the effect of fenofibrate on gene expression and modulates the effect of fenofibrate on Hcy levels. In particular, the usual fenofibrate-induced increase in Hcy levels was completely abolished in PPAR-α–deficient mice. Likewise, Legendre et al. ¹⁸⁸ applied a rodent model in investigating the effects of fibrates known to be mediated by the nuclear receptor PPAR-α. Using PPAR-α–deficient mice, they found that fenofibrate increases serum tHcy by inducing a selective increase of the protein-bound fraction. Furthermore, in comparing the effects of fenofibrate versus fenofibrate plus folate in rats, they observed that fenofibrate increased serum tHcy by 69%, whereas the coadministration of folate with fenofibrate increased tHcy by only 7%. Nevertheless, as with the mice, only the protein-bound fraction of Hcy was increased in the rats administered fenofibrate; the atherogenic, reduced Hcy was unaffected.

Thus, both studies concluded that fenofibrate and other fibrates increase homocystinemia in a PPAR-α–dependent manner, and that such findings constitute a valid animal model for analyzing the molecular mechanisms of fibrate-induced elevations in dyslipidemic patients. ^188,189 Findings from animal studies can be taken only as provisional, but they suggest a more complete and clinically effective knowledge of cardiovascular risk factors requires that research fully account for the specific variables within each physiological parameter (e.g., forms of Hcy or cholesterol), the interplay among multiple risk factors, and the influences of individual genomic variability on susceptibility and therapeutic response.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing fibrates, particularly fenofibrate and bezafibrate, are advised to coadminister folic acid, vitamin B ¹² , vitamin B ⁶ , and riboflavin based on their synergistic role in the comprehensive strategy of preventing and treating cardiovascular disease. Even though evidence indicates that these hypolipidemic agents do not deplete these nutrients, coadministration is prudent based on their beneficial effect in lowering Hcy levels and otherwise countering the disease process. Such modulation of hyperhomocysteinemia is generally a clinically appropriate tactic, even if, as suggested by the animal research just discussed, fibrate-induced Hcy elevation is of the nonatherogenic form. Thus, regular monitoring of tHcy levels is essential in patients taking fibrates, with special attention to subfractions. Evidence indicates that such nutrient administration carries a high safety profile and does not interfere with the therapeutic activity of the medication.

Multiple interventions, coordinated and evolving within an integrative strategy, can often provide the most effective means of preventing and treating the pathophysiological processes of endothelial damage, atherosclerosis, and coronary, cerebral, or peripheral vascular disease. Within the standards of conventional practice, gemfibrozil or statins represent the other primary options for addressing hypertriglyceridemia or dyslipidemia, respectively. Concomitant use of L-carnitine, coenzyme Q10, magnesium, fish oils (omega-3 fatty acids), mixed tocopherols and tocotrienols, and vitamin D may also be appropriate, according to the characteristics and needs of the individual patient, any comorbid conditions, and medications. The research regarding fibrates and their effects on folate and Hcy illustrates the need for further studies and evolution of clinical practice in assessing cardiovascular risk. Refined laboratory evaluation of complex and interdependent biomarkers should not only include C-reactive protein and Hcy, but also further develop the implications of variations, such as free versus bound Hcy.

Beneficial or Supportive Interaction, with Professional Management

Preliminary to Emerging

Effect and Mechanism of Action

Affective disorders such as depression are caused, at least in part and in certain individuals, by a deficiency of serotonin (5-hydroxytryptamine, 5-HT), noradrenaline (norepinephrine), dopamine, or a combination of these key monoamines. Folate and vitamin B ¹² are major determinants of one-carbon metabolism, in which S-adenosylmethionine (SAMe), a key methyl donor in numerous methylation reactions, is synthesized from methionine. Folate plays a pivotal role in the synthesis of tetrahydrobiopterin, which is the cofactor for the hydroxylation of phenylalanine and tryptophan and is the rate-limiting step in the synthesis of these and related neurotransmitters. Thus, coadministration of folic acid (or enhancement of dietary intake of folates) in conjunction with fluoxetine or other conventional antidepressants may produce an additive or synergistic effect, particularly on serotonin.

Research

Folate deficiency, impaired methylation, and hyperhomocysteinemia have been associated with depression and related mood disorders in many studies. In individuals with certain genomic characteristics, folate deficiency may play an even greater role in impaired metabolism of serotonin, SAMe, dopamine, and noradrenaline. Poor therapeutic response to antidepressants may be related to depressed folate status. Both gender and certain polymorphisms (e.g., MTHFR C677T polymorphism) influence folate and homocysteine (Hcy) metabolism and their relationship to depression and response to antidepressants. ¹⁹⁵ In a systematic review and meta-analysis of randomized controlled trials involving treatment of depression with folic acid, Taylor et al. ¹⁹⁶ concluded that “limited available evidence suggests folate may have a potential role as a supplement to other treatment for depression,” but that it is “currently unclear if this is the case both for people with normal folate levels, and for those with folate deficiency.” Folic acid administration can be beneficial in many individuals, and coadministration has enhanced efficacy of antidepressants in certain cases. Enhanced folate nutriture may also help reduce the cardiovascular risk factors associated with the hyperhomocysteinemia prevalent in one third or more of individuals diagnosed with depression.

Decreased serum/RBC folate and serum vitamin B ¹² and an increase in plasma Hcy have been associated with greater susceptibility to depression and poorer response to antidepressant treatment. According to a review by Coppen and Bolander-Gouaille, ¹⁹⁷ Hong Kong and Taiwan populations with traditional Chinese diets (rich in folate), including patients with major depression, have high serum folate concentrations. However, these countries have very low lifetime rates of major depression. In a large population-based study, Norwegian researchers observed an association between depression and hyperhomocysteinemia and the 677CT polymorphism in the MTHFR gene. For the TT MTHFR genotype, the odds ratio for depression was 1.69 compared with the CC genotype. Folate and vitamin B ¹² were not associated with anxiety disorder or depression in general, but the risk of depression was tripled in middle-aged women with serum folate less than 5 nmol/L. ¹⁹⁸ Likewise, in geriatric populations, both depression and dementia have been associated with lower folate levels. ^199,200

In a study on the effects of folic acid fortification of flour in the United States since 1998, Ramos et al. ²⁰¹ report that plasma folate concentrations are associated with depressive symptoms in elderly Latina women despite dietary folic acid fortification. Notably, using radioassay to determine plasma folate concentrations, these researchers reported that the prevalence of folate deficiency (plasma folate ≤6.8 nmol/L) in the cohort of elderly Latinos (age 60 or older) in the Sacramento, California, area as less than 1%, significantly lower than almost every other estimate of folate deficiency in the general population, let alone the elderly. The possible inconsistencies in these findings indicate the need for continued research into both the adequacy of standard methods of testing for folate deficiency and the effectiveness of folic acid fortification of foods. Overall the assembled data and clinical prudence suggest the need for folic acid supplementation at a significantly higher dosage level than typically attainable through such policies and methods.

A series of clinical trials have consistently found that patients with low folate status are more susceptible to depression, slower to respond to antidepressant medications, and more refractory to fluoxetine treatment. In an experiment involving 213 depressed adults treated with fluoxetine, 20 mg/day, Mischoulon et al. ²⁰² found that “neither macrocytosis nor anemia predicted low serum folate/B ¹² , or antidepressant refractoriness.” Fava et al. ²⁰³ investigated folate, vitamin B ¹² , and homocysteine status in 213 outpatients with major depressive disorder taking 20 mg/day of fluoxetine for 8 weeks. Subjects with low serum folate levels were more likely to be diagnosed with melancholic depression and were significantly more likely not to respond to fluoxetine. Also, Hcy and B ¹² levels were not associated with depressive subtype or treatment response. Similarly, in a double-blind trial involving 55 patients with major depressive disorder, Papakostas et al. ¹⁹⁵ found that low serum folate levels, but not elevated Hcy or low vitamin B ¹² levels, were associated with poorer response to fluoxetine treatment. In a related study, these researchers measured serum folate, vitamin B ¹² , and Hcy at baseline and followed 71 outpatients with remitted major depressive disorder for 28 weeks of continued treatment with fluoxetine (40 mg/day) to monitor for depressive relapse. The presence of low serum folate levels, but not low B ¹² or elevated Hcy level, was associated with relapse during continued treatment with fluoxetine. ²⁰⁴ In a third study involving 110 outpatients with major depressive disorder (MDD) who responded to an 8-week trial of fluoxetine, Papakostas et al. ²⁰⁵ observed that subjects with low folate levels (≤2.5 ng/mL) were more likely to experience a later onset of clinical improvement by an average 1 weeks than eufolatemic patients. They noted a lack of association between B ¹² and Hcy levels and time to clinical improvement.

Coadministration of folic acid appears to enhance the antidepressant action of fluoxetine. In a randomized, placebo-controlled trial involving 127 patients diagnosed with major depression, Coppen and Bailey ²⁰⁶ demonstrated enhancement of the antidepressant action of fluoxetine (20 mg/day) by concomitant folic acid (500 µg/day). Subjects administered folic acid showed a significant increase in plasma folate. However, among the fluoxetine plus folate group, increases in plasma folate levels, decreases in Hcy levels, and improvements in depression scores were all significantly stronger in women than in men. Reports of adverse effects were significantly higher in the fluoxetine plus placebo group than in those given folic acid. These authors concluded: “Folic acid is a simple method of greatly improving the antidepressant action of fluoxetine and probably other antidepressants.” They recommend a folic acid dosage sufficient to decrease plasma Hcy and note the higher dose requirements for folic acid in men to obtain a therapeutic response; as to the exact dose, they suggest that further research is required “to ascertain the optimum dose of folic acid.” ²⁰⁶

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians treating individuals susceptible to or diagnosed with depressive disorders are advised to discuss the potential benefits of folic acid supplementation and enhancing dietary folate intake. In patients for whom prescribing an antidepressant such as fluoxetine is appropriate, concomitant folic aid (800 µg/day), preferably with vitamin B ¹² (1 mg daily), can often enhance the action of the medication with no attendant risk. Assessment of folate, B ¹² , and Hcy status is warranted and may be clinically useful, as might testing for MTHFR polymorphisms, because those with low activity of MTHFR may be more responsive to L-5-methyl folate than to folic acid.

	Prevention or Reduction of Drug Adverse Effect
	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management

Emerging , but generally presented as Consensus

Effect and Mechanism of Action

Isoniazid is generally considered the most potent antitubercular medication and is always used in conjunction with other drugs to prevent development of resistance. These drugs appear to adversely affect the action of folate and potentially induce depletion. However, the incomplete evidence thus far available suggests that such effects may be indirect, through the metabolic interrelationships among various vitamins, rather than direct effects on folate itself.

Isoniazid, the hydrazide derivative of isonicotinic acid, interferes with the synthesis of lipids, nucleic acids, and the mycolic acid of the cell walls of pathogenic mycobacteria such as Mycobacterium tuberculosis. Although its precise mode of action is not known, many of the adverse effects associated with isoniazid, such as peripheral neuropathy, result from its activity as a synthetic analog of pyridoxine and the subsequently induced relative pyridoxine deficiency. This interference of isoniazid with vitamin B ⁶ appears to be the primary mechanism for its well-known interference with the synthesis of vitamin B ¹² ; both effects will interfere with the synthesis and activity of folate. ¹⁷¹ In individuals being treated with phenytoin, isoniazid may also adversely affect folate by decreasing the excretion of the anticonvulsant or enhancing its activity. Notably, isoniazid can induce seizures in susceptible individuals.

Rifampin blocks RNA synthesis by binding to the beta subunit of the bacterial DNA-dependent RNA polymerase.

Research and Reports

Drug-drug interactions involving isoniazid and rifampin are widely known, but systematic research into interactions between these agents and nutrients, specifically folate, is lacking. Numerous studies and case reports, primarily from the 1960s and 1970s, suggest that isoniazid and rifampin can interfere with the synthesis or activity of folate and have the potential to induce depletion. ^207-216 Many secondary sources present such drug-induced adverse effects as though they were well documented. Such assertions are plausible, and the general consensus appears to approach the likelihood of a clinically significant interaction as “probable.” Low serum folate levels have been reported in patients undergoing isoniazid therapy. Nevertheless, evidence from large, well-designed clinical trials is lacking to support these attributions, and the reports available primarily describe the adverse effects of these agents in the context of multiple interdependent nutrients, particularly vitamins B ³ , B ⁶ , and B ¹² , rather than folate or folic acid per se. Furthermore, a renewal of research would be necessary to determine the frequency, severity, and circumstances of clinically significant adverse reactions due to drug-induced effects upon folate, and thus refine the general occurrence or peculiar conditions needed to substantiate a conclusive interactions assessment.

In a randomized, placebo-controlled trial involving children age 1 to 35 months living in Zanzibar, Sazawal et al. ¹⁸ found that “supplementation with iron and folic acid in preschool children in a population with high rates of malaria can result in an increased risk of severe illness and death.” Routine prophylactic folate supplementation in such situations should be avoided pending further research. However, within the context of an active program “to detect and treat malaria and other infections, iron-deficient and anaemic children can benefit from supplementation.”

The effect of isoniazid or rifampin, alone or in combination with other antituberculosis drugs, on the human fetus is not known. Safety for use during pregnancy has not been established. No isoniazid-related congenital anomalies have been found in reproduction studies in mammalian species (mice, rats, and rabbits). However, offspring of rodents given oral doses of 150 to 250 mg/kg/day of rifampin during pregnancy have exhibited an increase in congenital malformations, primarily spina bifida and cleft palate.

• Note:

  Therapeutic levels of rifampin interfere with standard laboratory assays for serum folate and vitamin B ¹² . ²¹⁷ Alternative testing methods, such as the neutrophilic hypersegmentation index (NHI), need to be considered when assessing folate and vitamin B ¹² concentrations in individuals being treated with rifampin, although if abnormal, the NHI cannot distinguish between a B ¹² deficiency and a folate deficiency. It can be used, however, as an indication to administer both nutrients, which regardless is sound practice.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing antitubercular drugs as monotherapy or in combination should be aware of potential adverse effects on folate status caused by these medications, directly or more likely indirectly. In particular, long-term administration of isoniazid may lead to pyridoxine deficiency and may prevent isoniazid-induced niacin deficiency. Some physicians may choose to monitor folate, B ³ , B ⁶ , and B ¹² status and coadminister a multivitamin only if deficiency is observed. Given the high safety profile, low cost, and minimal potential for significant adverse effects, prudence suggests that prophylactic supplementation may be judicious. Many experienced practitioners of nutritional therapeutics prescribe nutrients in higher dosage levels to patients undergoing isoniazid or rifampin therapy, for example, folic acid (800 µg/day) and vitamin B ⁶ (50-100 mg/day). Nevertheless, prophylactic folic acid (and iron) may be contraindicated for children in malarial environments.

These potent antitubercular agents should be prescribed during pregnancy only when therapeutically absolutely necessary. Likewise, given the high degree of uncertainty and the severity of teratogenic potential, their use in women capable of bearing children should be carefully weighed against the benefits of therapy. Coadministration of folic acid (800 µg/day) is appropriate in the event that administration of antitubercular drugs is required.

	Prevention or Reduction of Drug Adverse Effect
	Beneficial or Supportive Interaction, with Professional Management
	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management

Emerging to Consensus

Effect and Mechanism of Action

Homocysteine (Hcy) is often elevated in individuals with Parkinson's disease, and levodopa can aggravate this pathological tendency. Metabolism of levodopa requires vitamin B ⁶ and can induce B ⁶ depletion if available supplies are inadequate. Coadministration of dopa decarboxylase inhibitors such as carbidopa limits peripheral degradation of levodopa and prevents vitamin B ⁶ depletion, but also increases conversion of levodopa to 3- O-methyldopa (3-OMD) by catechol- O-methyltransferase (COMT), the key enzyme in the metabolism of Hcy. COMT requires magnesium (Mg ⁺⁺ ) and S-adenosylmethionine (SAMe), which is synthesized from adenosine triphosphate (ATP) and methionine, as a methyl donor and yields S-adenosylhomocysteine (SAH), which is converted to total homocysteine (tHcy). Plasma tHcy depends on folic acid and vitamins B ² , B ⁶ , and B ¹² , which work together to support remethylation from tHcy to methionine. ²¹⁸ However, methylation of levodopa (and dopamine) by COMT interferes with this process by consuming methyl groups in the transmethylation reaction, thereby causing significant increases of SAH concentrations in tissues, which is rapidly converted to Hcy, as well as significant decreases of SAMe.

Folate intake, in conjunction with vitamin B ⁶ , may contribute to the prevention or treatment of Parkinson's disease and other forms of dementia, or folate and B ⁶ may work with antiparkinsonian medications by enhancing their therapeutic effects or reducing their adverse effects.

Research

The high occurrence of elevated Hcy levels in parkinsonian patients has attracted the attention of clinicians and researchers since the 1990s. ^219,220 In addition to being a major risk factor for atherothrombotic disease, hyperhomocysteinemia is also strongly associated with an increased risk of dementia and cognitive impairment, both of which are common in the course of Parkinson's disease. Growing evidence indicates that Hcy may damage DNA in the substantia nigra, the area of the brain affected in Parkinson's disease. Kuhn et al. ²¹⁹ observed significantly elevated plasma Hcy levels in subjects with Parkinson's disease and speculated that Hcy may be an independent risk factor for vascular disease in Parkinson's disease. However, they cautioned that this pattern of “elevated levels of homocysteine may be either caused by an unknown endogenous metabolic disturbance or by antiparkinsonian treatment, because no association to severity or duration of disease was found.”

Emerging but mixed evidence indicates that the effect of L-dopa on plasma Hcy is accentuated under conditions of impaired Hcy metabolism and may be influenced by B-vitamin status, including folate deficiency. Animal studies have indicated that levodopa-induced hyperhomocysteinemia is a consequence of significant O-methylation and that the COMT inhibitors can prevent such elevation of Hcy concentrations by reducing the O-methylation of levodopa. ^221,222 Using a rat model, Daly et al. ²²³ demonstrated that plasma Hcy concentration was significantly higher in male rats 1 hour after intraperitoneal injection with 100 mg L-dopa/kg, and this increase was greater in the folate-deficient rats than in the replete controls. In a second experiment involving nondeficient female rats, such drug-induced elevations of Hcy persisted with daily L-dopa injections over 17 days, although less so than in animals treated with L-dopa for only 1 day. In a 1999 letter, Muller et al. ²²⁴ reported increased Hcy levels in parkinsonian patients undergoing long-term L-dopa therapy compared with previously untreated parkinsonian patients and controls. The authors expressed concern that L-dopa was promoting atherosclerosis and vascular disease. Other letters from clinicians, such as Yasui et al., ²²⁵ have also reported levodopa-induced hyperhomocysteinemia in patients with Parkinson's disease. Muller et al. ²²⁶ reported a decrease in methionine and SAMe levels and increased Hcy in a study involving 20 Parkinson's patients treated with levodopa and dopa decarboxylase inhibitors and corresponding controls. These same researchers investigated O-methylation in treated parkinsonian subjects and found that Hcy was significantly elevated in the group with higher 3-OMD concentrations and positively correlated to 3-OMD. ²²⁷

Rogers et al. ²²⁸ investigated the influence of L-dopa on elevated plasma Hcy levels and CAD in a study involving 235 patients with Parkinson's disease, 201 of whom had been treated with levodopa, with the remaining 34 levodopa naive. Mean plasma Hcy levels were significantly higher in patients treated with levodopa, and patients with Hcy levels in the higher quartile had increased prevalence of CAD compared with levodopa-naive patients. However, the authors observed no difference in the plasma concentration of folate, cobalamin, or MMA between the two groups and concluded that folate or vitamin B ¹² deficiency does not explain the elevated Hcy levels. In contrast, a study involving 40 subjects diagnosed with idiopathic Parkinson's disease, 20 of whom were taking levodopa and the other 20 levodopa naive, Miller et al. ²²⁹ observed that mean plasma Hcy concentration was higher in the treatment group than in the controls and correlated with plasma folate, vitamin B ¹² , and pyridoxal-5′-phosphate (B ⁶ ) concentrations in the treatment group, but not in the controls. They concluded that the extent to which L-dopa caused hyperhomocysteinemia in Parkinson's patients is influenced by B-vitamin status, and that increased B-vitamin intake is necessary to maintain normal plasma Hcy concentrations in patients treated with L-dopa. In a review, Lokk ^229a (2003) concluded that levodopa therapy can affect latent folic acid and vitamin B ¹² deficiency and further contribute to risk of elevated Hcy levels in patients with Parkinson's disease.

These findings indicate that levodopa-induced hyperhomocysteinemia, of varying degree, can be caused by competition at the site of methylation, rather than by a deficiency of folate or other B vitamins, but that coexisting risk factors for elevated Hcy (e.g., smoking) or compromised nutrient status can contribute to an additive effect.

Clinical outcomes with Parkinson's disease, hyperhomocysteinemia, and nutrient status vary among individuals, and the mixed research findings suggest the need for research into the influences of such underlying genetic variation. Yasui et al. ²³⁰ measured plasma Hcy and cysteine levels in 90 Parkinson's patients with the MTHFR C677T (TT) genotype. The authors not only found that Hcy levels were elevated by 60% in levodopa-treated Parkinson's patients, but also observed that TT-genotype patients exhibited the most marked Hcy elevation, and their Hcy and folate levels were inversely correlated. Subsequently, Woitalla et al. ²¹⁸ compared plasma folic acid, B ⁶ , B ¹² , and tHcys levels in 83 levodopa-treated Parkinson's patients and 44 controls. Patients with the CT (heterozygous) or TT (homozygous) genotype had significantly higher tHcy levels than controls or Parkinson's patients with the CC (wild-type) allele. Furthermore, although concentrations of B ⁶ or B ¹² did not differ, folic acid was significantly higher in parkinsonian patients with the CT mutation.

Levodopa-induced hyperhomocysteinemia can aggravate the neurodegenerative processes contributing to dementia, depression, vascular disease, and Parkinson's disease. O’Suilleabhain et al. ²³¹ conducted neuropsychometric tasks and tested plasma Hcy levels in 97 patients with a mean Parkinson's duration of 3.6 years to determine if hyperhomocysteinemia in Parkinson's patients is associated with depression or with cognitive or physical impairments. Subjects with elevated Hcy level were slightly older (68 vs. 62 years), were more depressed, had worse cognition, and performed worse on neuropsychometric tasks than normohomocysteinemic patients. Notably, those with hyperhomocysteinemia had similar plasma concentrations of vitamin B ¹² and folate. In a study involving 31 levodopa-treated patients with Parkinson's disease and 27 control subjects, Muller et al. ²³² investigated peripheral neuronal dysfunction, specifically sural nerve axonal neurodegeneration, in patients treated with antiparkinsonian drugs using electrophysiological sural nerve conduction assessment. Sensory nerve action potentials significantly differed between Parkinson's patients and controls, but sensory nerve conduction velocity results showed no significant differences. Daily levodopa/dopa decarboxylase inhibitor intake was significantly related to tHcy levels, with significant associations between tHcy levels and sensory nerve action potentials. The authors suggested that sensory nerve action potentials might serve as a surrogate marker for the levodopa metabolism–induced elevation of Hcy levels.

Use of other pharmacological therapies for Parkinson's disease, such as COMT inhibitors (COMT-I) or dopamine agonists, may provide an effective alternative to levodopa-induced Hcy elevation and attendant risks, including decreased folate levels. O’Suilleabhain et al. ²³³ prospectively measured the effects of levodopa initiation on plasma tHcy and B-vitamin status, as well as the effects of levodopa dose changes and treatment with dopamine agonists and entacapone. They compared vitamin B ¹² , folate, and tHcy concentrations, at baseline and after several months of treatment, in 30 patients initiating levodopa, 15 whose L-dopa dose was doubled, 14 whose L-dopa dose was halved or stopped, 15 starting or stopping entacapone, and 16 patients initiating or doubling dopamine agonist monotherapy. The tHcy concentration increased from 8.7 to 10.1 µmol/L, and average vitamin B ¹² concentration decreased from 380 to 291 pmol/L an average of 94 days after initiation of 604 (240-1050) mg/day of L-dopa. Furthermore, although subjects who doubled their daily L-dopa dose exhibited tHcy elevations from 9.5 to 11.1 µmol/L, no significant effects were observed with L-dopa reduction, agonist treatment, and entacapone treatment. Thus, these authors concluded that initiation of L-dopa “elevates tHcy and lowers vitamin B ¹² concentration to modest degrees,” ²³³ but that clinical implications, if any, were uncertain.

An Italian research team has been conducting ongoing research into the effects of various antiparkinsonian drugs on Hcy. In 2005, Lamberti et al. ²³⁴ compared plasma levels of Hcy, B ¹² , and folate in 26 Parkinson's patients treated with levodopa, 20 treated with levodopa plus a COMT-I, and 32 controls. Plasma Hcy was increased significantly in the two Parkinson's groups and significantly lower in the group treated with levodopa plus COMT-I. Folate concentrations were significantly lower in the levodopa-treated group, but statistical analysis indicated that the difference in mean Hcy levels observed among Parkinson's patients was associated with COMT-I coadministration rather than folate concentrations. No significant differences were observed in vitamin B ¹² levels. In a parallel study, Zoccolella et al. ²²⁰ compared Hcy, B ¹² , and folate levels in 45 Parkinson's patients (15 in each of three groups receiving dopamine agonists, L-dopa, or L-dopa plus a COMT-I) and in 15 controls. They determined that “ L-dopa administration significantly increases Hcy concentrations and that the addition of COMT-I effectively reduces the homocysteinemia.” Also in 2005, Valkovic et al. ²³⁵ found that mean plasma Hcy concentration was higher in 19 Parkinson's patients receiving levodopa monotherapy than in subjects receiving a combination of levodopa and the COMT-I entacapone or in a control group of 17 subjects receiving dopamine agonists.

Even though the relationship between folate (and vitamin B ¹² ) and Hcy and the effects of levodopa on Hcy are well established, evidence from human trials specifically investigating the potential benefits of nutrient coadministration are limited. Chen et al. ²³⁶ prospectively investigated intake of folate, vitamin B ⁶ , or vitamin B ¹² in 248 men and 167 women with documented Parkinson's disease diagnoses to determine whether higher nutrient intake was related to a lower risk of disease. Folate intake was not associated with the risk of Parkinson's disease, nor was intake of vitamins B ⁶ or B ¹² . The authors concluded that their data “does not support the hypothesis that higher intake of folate or related B vitamins lowers the risk of Parkinson's disease.” However, in an Italian study related to those previously cited, Lamberti et al. ²³⁷ compared plasma Hcy, folate, and cobalamin levels in 20 Parkinson's patients treated with L-dopa at baseline and after 5 weeks of treatment with cobalamin and folate with levels in 35 controls. Hcy levels were higher in Parkinson's patients treated with L-dopa compared with age and gender–matched controls, and coadministration of cobalamin and folate was effective in reducing Hcy concentrations.

Further research involving well-designed clinical trials, especially long-term prospective cohort studies, is warranted to establish further the efficacy of folate (and B ¹² ) administration in patients undergoing levodopa therapy, alone in or in combination with other antiparkinsonian drugs, as a countermeasure against drug-induced hyperhomocysteinemia, and to formulate therapeutic strategies for safe and effective coadministration.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians treating individuals with Parkinson's disease or related conditions are advised to prescribe concomitant folic acid, cobalamin (B ¹² ), and pyridoxal-5′-phosphate (B ⁶ ), especially in light of the high incidence of strokes among such patients. MTHFR genotyping and regular tHcy monitoring are also recommended in Parkinson's patients. Although conclusive evidence is lacking to support claims that increased folate intake might prevent the onset of Parkinson's disease, folic acid supplementation is safe and inexpensive and may support healthy neurological function, counter Hcy elevation, and reverse adverse effects of levodopa, especially in those with the MTHFR C677T (TT) genotype or other factors increasing susceptibility to folate deficiency and hyperhomocysteinemia.

No evidence yet indicates that coadministration of folic acid or vitamin B ¹² would impair the therapeutic activity of levodopa or related medications. However, supplemental B ⁶ at levels greater than 10 to 15 mg/day could override the ability of carbidopa or benserazide (in Sinemet and Madopar, respectively) to limit the effects of vitamin B ⁶ on levodopa. The levels of B ⁶ found in most multivitamins are unlikely to interfere with the medication's therapeutic activity. In general, nutrients administered concomitantly with antiparkinsonian medications are best ingested with meals at least 2 hours before or after levodopa or at bedtime with a small amount of food.

Beneficial or Supportive Interaction, with Professional Management

Emerging to Consensus

Effect and Mechanism of Action

Folate and vitamin B ¹² play major roles in one-carbon metabolism, in which SAMe is formed and methyl groups are made available for neurological function.

Research

Limited research suggests that low folate levels do not appear to characterize patients treated with lithium, but folate status may influence therapeutic response to lithium therapy. Stern et al. ²³⁸ measured serum and RBC folate levels in 17 outpatients receiving prophylactic lithium carbonate for recurrent major affective disorder. They observed “no evidence for low folate concentrations or for any significant correlation between folate levels and affective morbidity.” Subsequently, a team of Chinese researchers investigated whether folate concentrations were lower in patients undergoing long-term lithium therapy, and if the medication might play a role in decreasing such levels. Lee et al. ²³⁹ found that serum folate correlated negatively with lithium dose and serum level among 46 Chinese and mostly manic-depressive (85%) outpatients attending a lithium clinic in Hong Kong. However, mean folate levels in the lithium-treated patients did not differ from lithium-free outpatients, and “virtually no patients had low serum (0%) or erythrocyte (2%) folate.” Nevertheless, they noted that patients “with a good response to lithium in the previous one year had a higher mean serum folate level than those with unsatisfactory response.” They concluded that “folate at high concentrations enhances lithium prophylaxis,” even though “data suggest that folate deficiency is uncommon among Chinese psychiatric outpatients.” ²³⁹ Notably, neither of these studies specifically focused on whether increased folate intake (food or supplements) might enhance the efficacy of lithium therapy, decrease adverse effects, or allow reductions of therapeutic lithium dose.

The general finding in human trials indicates that concomitant folic acid administration can enhance the therapeutic efficacy of lithium. In a 1982 study involving 107 patients receiving long-term lithium, Coppen and Abou-Saleh ²⁴⁰ found that “those with lower plasma folate concentration had a higher affective morbidity than those with higher folate, both at the time and during the previous two years.” In 1986, Coppen et al. ²⁴¹ determined that folic acid enhances lithium prophylaxis in reducing affective morbidity. In a double-blind trial, they administered folic acid (200 µg/day) or placebo to 75 patients receiving lithium therapy. Patients with the highest plasma folate concentrations exhibited a significant reduction in their affective morbidity, with a 40% reduction in affective morbidity among subjects in whom plasma folate increased to 13 ng/mL or higher. Based on these findings, the authors suggested that a daily dose of 300 to 400 µg folic acid would be useful in long-term lithium prophylaxis.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing lithium therapy, especially on a long-term basis, are advised to discuss with patients the potential therapeutic benefit of concomitant folic acid administration, typically 200 to 400 µg/day or more. Higher folic acid dosage may be appropriate in some patients, based on diet, comorbid conditions, other medications, and genomic variability (e.g., MTHFR genotype). Evidence is lacking to suggest that lithium use depletes folate, or that folic acid reduces adverse effects associated with lithium. Given the probability of an additive or synergistic effect from coadministration, close supervision, regular monitoring, and dose titration are warranted, particularly with introduction of folate or change in dose of either agent.

	Potential or Theoretical Adverse Interaction of Uncertain Severity
	Bimodal or Variable Interaction, with Professional Management
	Potential or Theoretical Beneficial or Supportive Interaction, with Professional Management

Mixed and Preliminary

Effect and Mechanism of Action

Mercaptopurine, azathioprine, and thioguanine are cytotoxic antimetabolites used in the treatment of irritable bowel syndrome, leukemia, and some cancers. The mechanisms involved in their therapeutic activity have not been fully elucidated. Thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of all three drugs. Mercaptopurine requires intracellular anabolism by hypoxanthine guanine phosphoribosyltransferase (HGPTPT, or HGPRT) to become cytotoxic. Likewise, azathioprine is an immunosuppressive prodrug, the S-imidazole precursor of 6-mercaptopurine, converted to 6-MP in the liver by TPMT. Intracellular activation of thioguanine, a 6-thiopurine analog of the naturally occurring purine bases hypoxanthine and guanine, results in incorporation into DNA as a false purine base.

Mercaptopurines act through purine antagonists and consequently tend to induce macrocytic nonmegaloblastic anemia. Serum folate levels are typically low in patients treated with these medications. Folate coadministration may moderate the adverse effects of these agents, thereby enhancing tolerance and facilitating efficacy. However, determining whether folate also interferes with the anticancer efficacy of this class of drugs requires further clinical research.

Research

Many patients are intolerant or resistant to thiopurine drugs, and their clinical management remains a challenge. Myelosuppression is the major dose-limiting effect with these agents. Hematopoietic toxicity, rapid bone marrow suppression, and leukopenia present a particularly significant risk in individuals with an inherited deficiency of TPMT or HGPTPT, even at normal dose levels. ^242-249 Notably, relative leukopenia is typically not associated with clinical response. ²⁵⁰ Adverse drug reactions and intolerance to azathioprine, occurring in 15% to 28% of patients, may be attributable more often to polymorphism in the ITPA gene and inosine triphosphate pyrophosphatase (ITPase) deficiency, which results in the benign accumulation of the inosine nucleotide ITP; preliminary evidence, however, is mixed. ^251-253 All these enzymes are involved in folate handling.

Genetic variation in the way individuals handle folate can be predicted to influence activity of the TPMT enzyme, which may assist in predicting adverse drug reactions in some patients. For example, polymorphisms in the gene encoding MTHFR may have an indirect impact on thiopurine drug methylation by influencing levels of the methyl donor SAMe. ²⁵³ As a result of genetic variation, 1 in 300 of the Caucasian population have a total lack of TPMT and are at high risk of severe toxicity if given azathioprine; 1 in 10 individuals have half the level and are also at increased risk of side effects. With prior knowledge of such genetic polymorphisms and related enzyme levels, the drug can be avoided or used at a lower dose, or other strategies can be used to minimize adverse effects.

The available findings of drug-induced depletion of folate are limited but consistent with scientific knowledge of renal transplant patients in general and patients treated with azathioprine in particular. In assessing the impact of renal transplant and azathioprine on folate status, Zazgornik et al. ²⁵⁴ monitored serum folic acid levels in 26 chronic hemodialysis patients, 52 renal transplant recipients, and 20 healthy controls using radioimmunoassay. Diminished serum folic acid levels were found not only in patients shortly after surgery, but also in patients with excellent graft function up to 6 years after transplantation. The mean serum folic acid level was significantly lower in both the dialyzed patients and the renal transplant recipients than in the controls. The highest serum folic acid level was observed in a transplant patient who had not taken azathioprine for 2 years. Macrocytosis was found in 52% of the renal transplant patients and was observed only in patients with good graft function treated with azathioprine. Serum vitamin B ¹² levels were within the normal range in both dialyzed and renal transplant patients. No intervention trials of folic acid administration in renal transplant patients taking azathioprine have been done, so the question remains whether folate replacement might improve clinical outcomes or increase risk of graft rejection by interfering with azathioprine-induced immune suppression.

Concomitant folic acid may protect proliferative capacity of the bone marrow and moderate hematological parameters of drug toxicity in patients treated with these purine antagonists. In a retrospective longitudinal study, Lennard et al. ²⁵⁵ investigated myelosuppression and the effect of folate coadministration on 6-mercaptopurine (6-MP) remission maintenance therapy in 10 children with acute lymphoblastic leukemia (ALL). During the control period they observed significant correlations between 6-MP dose and 6-thioguanine (6-TG) nucleotide concentration, the active cytotoxic metabolite of 6-MP, and also between 6-TG nucleotide concentrations and the peripheral neutrophil count at 14 days. With the introduction of folic acid these relationships were no longer evident, and the children tolerated significantly higher doses of 6-MP longer before neutropenia developed. Although folate does not affect the conversion of 6-MP to 6-TG, white blood cell (WBC) counts were elevated for a longer period despite the same exposure to 6-TG, indicating possible interference with the cytotoxicity of 6-TG on neutrophils. Thus, although they reported “no significant difference in red cell 6-thioguanine nucleotide concentration in the absence and presence of folate supplements,” the authors expressed concern that “folate supplements may interfere with remission maintenance therapy in ALL.” ²⁵⁵ Similarly, in a trial involving 53 children with ALL in maintenance treatment with methotrexate (MTX) and 6-MP, Schroder et al. ^255a administered daily folic acid (75-200 µg) in vitamin tablets to 25 subjects for at least the preceding 3 months. Compared with children who received no folic acid, subjects receiving folic acid exhibited improved proliferative capacity of the bone marrow, as demonstrated by significantly higher erythrocyte folate (ery-folate) concentration, higher platelet counts, higher leukocyte counts, higher neutrophil counts, and lower erythrocyte mean cell volumes. Nevertheless, these authors recommended that “since none of the children was folate deficient as judged by the ery-folate [level],... vitamins given to children in maintenance treatment with MTX and 6-MP for ALL should not contain folic acid.”

The present data indicate that folic acid appears to protect normal neutrophils from 6-TG and antagonize the effects of MTX and 6-MP on normal hematopoiesis. However, folate may or may not antagonize these antimalignancy effects; that is, folate may or may not protect leukemia (ALL) cells, even though it appears to protect normal neutrophils from the cytotoxic effect of these drugs. Schroder et al. ^255a assumed that folic acid protects normal WBCs from the cytotoxic effect of 6-TG and therefore might protect leukemia cells as well. Such speculation may or may not be well founded. Folate coadministration also might actually improve clinical outcomes. There have been documented instances of natural products that kill cancer cells without affecting normal cells or, conversely, protect normal cells from cytotoxic agents without protecting malignant cells. Such determinations could only be made in this case by investigating relapse of ALL as the endpoint of the trial. This would require a fairly large study, giving half the children folic acid and the other half placebo (and control for dietary folate, not easy in adults, let alone children), and using relapse of leukemia as the endpoint. Institutional review boards (IRBs) might consider this an unethical experiment, even though risk of missing a clinical benefit must be balanced against risk of losing therapeutic efficacy. The question arises whether folic acid might have an opposite effect on 6-TG and ALL cells versus its effect on 6-TG and normal neutrophils. At least this issue should be further studied in vitro and in animal models. The possibility of increased tolerance of maintenance chemotherapy by folate supplementation leading to improved clinical outcomes in childhood ALL warrants further investigation.

Regular monitoring, with periodic blood counts every 2 weeks initially and then every 3 months thereafter, is required given the action of these drugs in interrupting production of RBCs, WBCs, and platelets. In a study of 57 patients with inflammatory bowel disease treated with low-dose 6-MP, Bernstein et al. ²⁵⁶ determined that “leukopenia was not uncommon in patients treated with low-dose 6-MP, but was not clinically significant.” Furthermore, macrocytosis may occur in the absence of vitamin B ¹² and folate deficiencies. The authors thus concluded that, despite the risk of myelosuppression, weekly blood count monitoring was not necessary when administering low-dose 6-MP therapy.

Evidence is lacking from large prospective or population-based studies on the use of these immunosuppressants during pregnancy. Effects on folate metabolism could play a potentially significant role in pregnant women.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing purine antagonists such as mercaptopurine, azathioprine, or thioguanine are advised to investigate the patient's folate status and coadminister folic acid as indicated. The evidence for benefit from such nutrient support is preliminary and inconclusive and suggests that concomitant folate administration might impair the therapeutic activity of these medications. Screening for polymorphisms and gene promoter activity, particularly the TPMT gene, before initiation of azathioprine therapy may be valuable in predicting pharmacogenomic responses and assisting drug tolerance. Close supervision, regular monitoring, and a coordinated strategy involving health care professionals experienced in both conventional pharmacology and nutritional therapeutics are essential to providing safe and effective individualized treatment within such an integrative approach.

	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, with Professional Management
	Prevention or Reduction of Drug Adverse Effect
	Beneficial or Supportive Interaction, with Professional Management
	Adverse Drug Effect on Nutritional Therapeutics, Strategic Concern

Emerging or Consensus

Effect and Mechanism of Action

Metformin can reduce the absorption and lead to lower serum levels of folate, total vitamin B ¹² , and transcobalamin II (TCII)–B ¹² complex levels. Metformin interferes with calcium-dependent membrane action and impairs B ¹² –intrinsic factor complex uptake by ileal cell surface receptors. ^257,258 Although this involves at least one mechanism, food-cobalamin malabsorption or drug-induced changes in intestinal bacterial flora have also been suggested. ^259,260 The available evidence is insufficient to determine whether the reported increase in total homocysteine (tHcy) levels is secondary to reduced folate levels, vitamin B ¹² levels, or a combination of both.

Decreased nutrient bioavailability plays a central role in the moderate elevations in plasma Hcy levels observed with long-term metformin therapy. Hyperhomocysteinemia is more prevalent in diabetic populations, women with polycystic ovary syndrome, and other patients likely to be prescribed biguanide therapy than among the general population. ^174,261,262 Drug-induced elevations would further increase the risk of diabetes-associated conditions, such as coronary artery disease (CAD), vascular disease, and hypertension resulting from adverse effects on platelets, clotting factors, and endothelium, although not necessarily retinopathy or albuminuria. ^263-266

• Note:

  The biguanide class was introduced when metformin and phenformin were developed in 1957. Metformin first became available in France in 1979 and has been widely used in Europe since that time. Phenformin and buformin, other biguanides, are well-established causes of lactic acidosis and have been removed from the U.S. market because of the high incidence of this adverse effect. Metformin was eventually found to be 20 times less likely to cause lactic acidosis and was cleared for use in the treatment of type 2 diabetes in the United States in 1994. Nevertheless, phenformin and buformin are still available internationally as oral agents for the treatment of diabetes and have reportedly been used in the United States.

This discussion focuses on metformin, and the evidence presented is based primarily on research involving metformin. Some studies mentioned also include phenformin and buformin or provide findings that may reasonably be extrapolated to these related biguanides.

Research

Long-term use of metformin has largely been associated with elevated Hcy levels in a wide range of human trials, although findings regarding the severity and clinical significance of this effect have varied.

The initial research into metformin-induced adverse effects on nutritional status focused on vitamin B ¹² . Carpentier et al. ²⁶⁷ compared the hematological effects in 30 diabetic patients treated with metformin versus those in 27 patients treated with insulin and 13 treated with sulfonylureas. Compared with the other groups, serum levels of vitamin B ¹² were significantly lower in patients receiving metformin, with five subjects exhibiting serum levels of vitamin B ¹² below 270 pg/mL and five others with borderline values. However, no differences were observed between the three groups in the mean serum folic acid levels, RBC counts, RBC volumes, or hemoglobin concentrations. These authors noted that the study period was not long enough to determine accurately whether vitamin B ¹² deficiency would develop. In a 1980 case report, Callaghan et al. ²⁶⁸ reported that megaloblastic anemia caused by vitamin B ¹² malabsorption was associated with long-term metformin treatment.

DeFronzo and Goodman ^268a observed effects on serum vitamin B ¹² and folic acid in two large, randomized, parallel-group, double-blind controlled studies comparing metformin, glibenclamide, and diet over 29 weeks in moderately obese patients with non–insulin-dependent diabetes mellitus (NIDDM) whose diabetes was inadequately controlled by diet alone. They reported that “serum folate concentrations did not change in either the metformin or placebo groups” but that “serum vitamin B ¹² concentration at week 29 was lower in the metformin group (by 22 percent) but did not change in the placebo group.” No changes were observed in hematocrit or hemoglobin in either group.

Drug-induced depletion of folate and vitamin B ¹² appears to play a key role in biguanide-induced hyperhomocysteinemia, but testing methodology and patient variables may influence the occurrence and severity of this adverse effect. In 1997, Hoogeveen et al. ²⁶⁹ investigated fasting serum tHcy level in a cross-sectional study involving 40 NIDDM patients who had received treatment with metformin (500-2550 mg/day) for at least 6 months and 71 matched NIDDM metformin-naive patients. Mean serum tHcy level was 11.5 µmol/L in the metformin-exposed patients, “slightly higher” than the 10.6 µmol/L in the nonexposed patients. Also in 1997, in an open, prospective, randomized study involving 60 nondiabetic male patients with coronary heart disease, Carlsen et al. ²⁷⁰ compared the effects of metformin on serum tHcy and related parameters with or without metformin (up to 2000 mg/day) in the context of diet and lifestyle advice and lovastatin (40 mg/day). After 12 and 40 weeks of metformin treatment, tHcy levels increased moderately but significantly in the metformin group relative to the control group while serum vitamin B ¹² levels decreased, with both trends greater over time. Serum folate levels did not change after 12 weeks, but decreased by 8.0% after 40 weeks compared to controls. However, serum levels of tHcy and methylmalonic acid (MMA) did not change. Based on this last variable, the authors concluded that “it remains an open question whether the increase in tHcy levels is secondary to reduced vitamin B ¹² levels, folate levels or a combination of both.” ²⁷⁰

Similarly, Hermann et al. ²⁷¹ reported that serum B ¹² remained unchanged in a 12-month, placebo-controlled, double blind trial investigating glycemic improvement from coadministration of metformin in 16 insulin-treated, obese type 2 diabetes patients. However, comparing the effects of metformin and sulfonylurea therapy, Bauman et al. ²⁵⁸ reported that metformin induced a 29% decline in serum levels of vitamin B ¹² but a 36.6% drop in serum holotranscobalamin II (holo-TCII). Similarly, in a subsequent cross-sectional cohort study, Hermann et al. ²⁷² found that by “considering the four variables reflecting vitamin B ¹² status, apart from MMA there were more patients in the metformin group with abnormalities indicating vitamin B ¹² deficiency.” Moreover, such effects were exhibited “most clearly for holotranscobalamin,” for which none of the control subjects had values less than the lower reference value, whereas eight (16%) of the metformin-treated subjects had reduced levels.

In an epidemiological study, Smulders et al. ²⁶⁴ applied multiple-regression analysis to 85 NIDDM subjects. In a subset of 31 subjects treated with metformin, levels of Hcy and vitamin B ¹² were similar to those without metformin. Also, low-normal values of folate (<20 nmol/L), vitamin B ¹² (<350 pmol/L), and creatinine clearance, as well as postmenopausal status in women, were significant predictors of fasting Hcy level, whereas B ⁶ levels (<80 nmol/L), creatinine clearance, and female gender were determinants of post–methionine load Hcy levels.

In a randomized, placebo-controlled trial, Wulffele et al. ²⁷³ investigated the effects of metformin therapy (vs. placebo) for 16 weeks on serum concentrations of Hcy, folate, and vitamin B ¹² in 353 patients treated with insulin for type 2 diabetes mellitus. Compared with placebo, metformin was associated with a “modest” increase in serum Hcy levels (4%; 0.2-8 µmol/L), and decreases in folate (−7%) and vitamin B ¹² (−14%). Furthermore, applying structural equation modeling, they demonstrated that the increase in Hcy was an indirect effect mediated by direct effects on folate and vitamin B ¹² , rather than a direct effect on Hcy by metformin. The authors concluded that a persistent increase in serum Hcy of 3 µmol/L was associated with an increased risk of coronary heart disease and stroke in nondiabetic individuals, and that available evidence indicates that this risk may be even greater in diabetic patients.

Wolever et al. ²⁵⁹ found that miglitol (Glyset), an alpha-glucosidase or alpha-amylase inhibitor, prevents the metformin-induced fall in serum folate and vitamin B ¹² in subjects with type 2 diabetes. Keeping dietary folate intake consistent, they observed that “serum folate and vitamin B ¹² , respectively, did not change on placebo, but fell by 14% and 15% on metformin and rose by 12% and 23% on miglitol.” Notably, with the combination of metformin and miglitol, “both folate and vitamin B ¹² tended to rise, but the difference from metformin was only significant for folate.” These authors concluded that “that increased carbohydrate delivery to the colon increases intestinal biosynthesis of folate.”

In a study involving nine women with polycystic ovary syndrome (PCOS) conducted at the Center for Perinatal Studies at Swedish Medical Center in Seattle, Vrbikova et al. ²⁶² found that a second-trimester Hcy elevation was associated with a 3.2-fold increased risk of preeclampsia. The authors noted that women with PCOS were already at increased risk for atherosclerosis, and that elevated Hcy could also contribute to pregnancy complications.

The adverse effects of metformin on folate and vitamin B ¹² status, Hcy levels, and related cardiovascular risk can often be mitigated by coadministration of folate, B ¹² , and calcium. In a 12-week, prospective, randomized, double-blind placebo-controlled study, Aarsand and Carlsen ²⁷⁴ studied whether administration of folate reduces serum tHcy levels in patients receiving long-term metformin treatment. All subjects who had been receiving metformin (minimum of 1000 mg/day) for at least 1 year were included, and all baseline serum tHcy levels were within the reference range. In addition to metformin, one group received concomitant folate (0.25 mg/day) in addition to iron (Fe ⁺⁺ ; 60 mg/day), whereas the placebo group received only 60 mg/day of Fe ⁺⁺ . Of the 28 subjects who finished the trial, 26 had been diagnosed with NIDDM, two with hyperlipidemia. Subjects in the folate group demonstrated reduced serum levels of tHcy (vs. placebo group) by 13.9% and 21.7% at weeks 4 and 12, respectively, as well as increased serum levels of vitamin B ¹² (9.9% and 9.6%) and folate (96.9 and 89.9%). In the trial cited earlier, Bauman et al. ²⁵⁸ investigated the effects of metformin antagonism on B ¹² –intrinsic factor complex uptake by ileal cell surface receptors, a calcium-dependent membrane action. After observing “diminished B ¹² absorption and low serum total vitamin B ¹² and TCII-B ¹² levels” in patients receiving metformin therapy, they found that calcium coadministration reverses metformin-induced B ¹² malabsorption.

In a related study with uncertain clinical implications, Child et al. ²⁷⁵ investigated the effect of oral folic acid on Hcy, glutathione, glycemia, and lipids in type 2 diabetic patients. After administering folic acid (10 mg daily) for 3 months to 27 diabetic patients (26 male, one female; age 48-68) with microalbuminuria, they observed an increase in RBC folate that correlated with a reduction in microalbuminuria. Notably, “plasma glutathione increased despite reduction in its precursor Hcy,” but correlated with levels of vitamin B ⁶ ; however, this change in glutathione correlated inversely with change in hemoglobin A ^1c (HbA ^1c ), total cholesterol, and triglycerides and positively with HDL cholesterol. Thus, oral folic acid supplementation reduced plasma Hcy level and increased glutathione level in subjects with type 2 diabetes, but levels of HbA ^1c , triglycerides, and HDL cholesterol deteriorated. In addition, the authors noted that “some aspects of the response to folate may be different in patients on metformin.” ²⁷⁵

Lifestyle interventions can be more effective than metformin for curbing the incidence of diabetes in individuals at high risk. Continued research emerging from the work of the Diabetes Prevention Program (DPP) Research Group emphasizes that although metformin can be effective, a broader strategic approach emphasizing diet and exercise can produce more fundamental benefits. Analyzing DPP trial data in the New England Journal of Medicine,Knowler et al. ²⁷⁶ showed that, overall, metformin reduced the risk of diabetes by about 31%, compared with a 58% reduction for those assigned to intensive nutrition and exercise counseling. The study's 3234 participants were significantly overweight and had “impaired glucose tolerance.” Approximately 1000 subjects were put on a low-fat diet (25% of overall calories), told to engage in moderate physical exercise, such as walking for 30 minutes, received training in goal setting and problem solving, and were invited to participate in group events. In addition to reducing diabetes risk, the lifestyle intervention group exhibited reduced body weight by 5% to 7%. In a subsequent analysis, Molitch et al. ²⁷⁷ concluded that, on the basis of these rates, the estimated number of persons who would need to be treated for 3 years to prevent one case of diabetes during this period is 6.9 for the lifestyle intervention versus 13.9 for metformin. Likewise, Orchard et al. ²⁷⁸ calculated that “diet and exercise delayed the onset of type 2 diabetes by about 11 years, while metformin delayed the onset by about three years.” Increased dietary intake of folate-rich foods, especially dark-green leafy vegetables, would fit well within such an approach.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians treating patients with dysglycemia, diabetes, PCOS, or related conditions using metformin are advised to integrate such biguanide therapy within a comprehensive therapeutic strategy. Regular exercise and a diet emphasizing low-glycemic-load carbohydrates and healthy sources of fats (such as olive oil or fish oils) can provide the most effective foundation for such an approach. Coadministration of folic acid (400 µg once or twice daily), vitamins B ¹² and B ⁶ , and calcium can help reduce associated risks and adverse effects attributable to the medication, particularly cardiovascular risks linked to elevated Hcy levels.

Close supervision, active support for lifestyle changes, and regular monitoring are all essential to successful intervention. Folate and Hcy levels, as well as liver function, should be checked regularly. Total serum cobalamin is not sufficiently specific and does not reflect intracellular B ¹² deficiency. Screening for genetic polymorphisms, especially MTHFR genotype, affecting folate status and Hcy susceptibility may be appropriate because interindividual variability may be significant for both therapeutic response to biguanides and folate metabolism. Serum holo-TCII is a sensitive marker of cobalamin balance, more accurately assessing B ¹² availability for the cells, but this analysis may not be feasible in routine clinical practice. MMA and tHcy can reflect intracellular B ¹² deficiency, but these metabolites may also increase in various clinical conditions, most notably with impaired renal function.

	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, Not Requiring Professional Management
	Prevention or Reduction of Drug Adverse Effect

Preliminary, but generally regarded as Consensus

Effect and Mechanism of Action

Oral neomycin can decrease absorption and/or increase elimination of folic acid and other nutrients, including beta-carotene, calcium, carbohydrates, fats, iron, magnesium, potassium, sodium, and vitamins A, B ¹² , D, and K. ^279,280 These effects increase with time in long-term neomycin therapy and can be most significant in elderly persons. ²⁸¹

Research

In 1966, Faloon et al. ²⁸² documented the adverse effects of neomycin on intestinal absorption of nutrients. ²⁸² In 1969, Hardison and Rosenberg ²⁸³ further elucidated the effect of neomycin on bile salt metabolism and fat digestion in humans. Subsequently, the adverse effects of neomycin on nutrient status were explored extensively in the pioneering work of D.A. Roe (1923–1993) of Cornell University, Division of Nutritional Sciences, through publications such as “Drug-Induced Nutritional Deficiencies” (1976). As such, this characterization has largely become the “consensus” of the literature documenting adverse drug effects and drug-induced nutrient depletions, without passing through the stages of published case reports, human trials, reviews, and so on, which constitute the emerging standard within the scientific literature of drug-nutrient interactions. Further research may be warranted.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing a course of oral neomycin longer than a few days are advised to coadminister a multivitamin-mineral supplement containing folic acid. Depletion is improbable with short-term use of oral neomycin associated with surgery or perioperative care. A course of probiotic flora is also appropriate following broad-spectrum antibiotics to restore normal gut ecology and prevent sequelae adversely affecting vitamin B ¹² synthesis and folate metabolism.

Beneficial or Supportive Interaction, with Professional Management

Emerging

Effect and Mechanism of Action

Nitroglycerin and other organic nitrates have been used clinically as nitric oxide (NO)–donating agents for more than 100 years in cardiovascular therapeutics and continue to be widely used in ischemic heart disease, even though knowledge of their intimate mechanism of action is incomplete. Progressive attenuation of their efficacy (tolerance) is a frequent problem in patients with acute coronary syndromes undergoing continuous, long-term therapy, as is cross-tolerance to endothelial NO; tolerance can also occur within 24 to 48 hours after administration of a nitrate medication.

Nitrate medications appear to cause tolerance by inducing nitric oxide synthase (NOS) dysfunction, probably as a result of reduced bioavailability of tetrahydrobiopterin. This metabolic syndrome is characterized by mitochondrial dysfunction and mediated significantly by inhibition of vascular aldehyde dehydrogenase (ALDH-2). ²⁸⁴ Also, Loscalzo ²⁸⁵ suggests that nitrate “depletes NADPH and an NADPH-dependent cofactor essential for the enzymatic activity of endothelial nitric oxide synthase.” Several mechanisms may explain this phenomenon, including nitrate-mediated depletion of intracellular thiols, enhanced mitochondrial reactive oxygen species (ROS) formation, and increased superoxide production. Endothelial nitric oxide synthase (eNOS) is an enzyme that predominantly produces NO under normal physiological conditions, controlled by the regulatory coenzyme calmodulin, the substrate L-arginine, and the cofactor tetrahydrobiopterin. However, in the context of dyslipidemia and other pathophysiological conditions, eNOS production shifts from NO to superoxide. Thus, increased intracellular oxidative stress appears to be a mechanism for nitrate tolerance.

Folic acid can prevent nitroglycerin-induced nitrate tolerance and cross-tolerance to endothelial NO by enhancing the regeneration and bioavailability of tetrahydrobiopterin in the context of the oxidative stress associated with long-term nitroglycerin administration. The mechanisms of this activity have not been fully elucidated. Dihydrofolate reductase reduces dietary folate to tetrahydrofolate using reduced nicotinamide-adenine dinucleotide phosphate (NADPH) as a cofactor. NADPH is also a required cofactor for NOS activity and for the synthesis of tetrahydrobiopterin from the direct and salvage pathways. However, NOS is unable to function either as an L-arginine oxidase or as an oxygen reductase when supplies of NADPH are compromised. “Thus, one plausible argument for the benefits of folate in nitrate tolerance is that it [nitrate] depletes NADPH and an NADPH-dependent cofactor essential for the enzymatic activity of endothelial nitric oxide synthase.” ²⁸⁵ However, evidence is lacking to confirm or refute this proposed mechanism.

Folic acid and its active form, 5-methyltetrahydrofolate (5-MTHF), have been shown in some studies to prevent uncoupling of the eNOS, reduce eNOS-mediated superoxide production, enhance NO synthesis by NOS, and restore impaired NO bioavailability, particularly in dyslipidemic conditions. ^286-292 Such inhibition of eNOS uncoupling could contribute to improved endothelial function. The tetrahydrobiopterin radical appears to be directly involved in the facilitated catalysis of eNOS by 5-MTHF and thus the formation of NO. ²⁹³ Related research showing the benefits of ascorbic acid in potentiating eNOS activity, by increasing intracellular tetrahydrobiopterin, complements the hypothesis that the tetrahydrobiopterin radical plays a role in NO synthesis by mediating reductive activation of the ferrous heme-O ² moiety of the eNOS enzyme. ²⁹⁴ Other research indicates that the pteridine-binding domain in NOS is similar to the folate-binding site of dihydrofolate reductase. ²⁹⁵

Continued research will determine the validity and significance of each of these hypotheses and clarify the relative role of each mechanism in folate's apparent ability to improve endothelial function and ameliorate nitrate tolerance.

Research

Clinical research investigating therapeutic synergies using folic acid in concert with nitrate preparations is only in the initial phases. Although a body of research exists on the mechanisms in the relationship between nitrates and nitric acid, including the potential roles of folates, a comprehensive model of folate and its activities has yet to be elucidated.

In an animal study, Gruhn et al. ²⁹⁶ found that administration of tetrahydrobiopterin improves endothelium-dependent vasodilation in nitroglycerin-tolerant rats and concluded that “altered bioavailability of tetrahydrobiopterin is involved in the pathophysiology of endothelial dysfunction seen in nitroglycerin tolerance.” Subsequently, Sydow et al. ²⁸⁴ observed decreases in vascular mitochondrial aldehyde dehydrogenase (ALDH-2) activity, nitroglycerin (GTN) biotransformation, and cyclic guanosine monophosphate (cGMP)–dependent kinase activity in rats treated for 3 days with GTN infusions. Multiple inhibitors and substrates of ALDH-2 had little effect on tolerant vessels, whereas these agents reduced both GTN stimulation of cGKI and GTN-induced vasodilation in control vessels. Furthermore, “GTN increased the production of reactive oxygen species (ROS) by mitochondria,” and “antioxidants/reductants decreased mitochondrial ROS production and restored ALDH-2 activity.” These findings indicate that mitochondrial ROS and inhibition of vascular ALDH-2 play a significant role in mediating nitrate tolerance.

In a small, randomized, double-blind trial, Gori et al. ²⁹⁷ tested the effects of concomitant folic acid (10 mg daily for 1 week, a relatively high dose) on development of tolerance to continuous transdermal GTN (0.6 mg/hour) in 18 healthy male volunteers (age 19-32). In measurements taken on the return visit, folic acid “prevented GTN-induced endothelial dysfunction, as assessed by responses to intraarterial acetylcholine and N-monomethyl- L-arginine.” The authors also noted that “responses to intraarterial GTN were significantly greater than those observed after transdermal GTN plus placebo” in the subjects treated with folic acid plus transdermal GTN. Thus, they concluded that “oxidative stress contributes to nitrate tolerance,” and that “supplemental folic acid prevents both nitric oxide synthase dysfunction induced by continuous GTN and nitrate tolerance in the arterial circulation of healthy volunteers.”

These data are consistent with the mechanisms previously discussed and provide a foundation for continued research into an expanded role for folic acid coadministration in preventing nitrate tolerance and enhancing the therapeutic effects of nitrate therapy. Confirmatory findings in high-powered, well-designed clinical trials would have major implications for the treatment of atherothrombotic vascular disease.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing nitroglycerin or related nitrate preparations are advised to coadminister folic acid to prevent tolerance to the medication over time and as part of the broader strategy for reduction of cardiovascular risk. Evidence from complementary research suggests that such patients might also benefit from concomitant L-arginine, vitamin C, coenzyme Q10, vitamin B ¹² , and magnesium. Implementation of such an integrative strategy requires close supervision and regular monitoring, most effectively by a multidisciplinary team incorporating health care professionals trained and experienced in both conventional pharmacology and nutritional therapeutics.

	Prevention or Reduction of Drug Adverse Effect
	Beneficial or Supportive Interaction, with Professional Management

Emerging to Consensus

Effect and Mechanism of Action

Exposure to nitrous oxide (N ² O) can produce megaloblastic anemia, neuropathy, and birth defects, all caused primarily by induced deficiency of vitamin B ¹² and secondarily by the effects of vitamin B ¹² deficiency on folate metabolism. Such adverse effects of N ² O were well established long before the mechanisms of its effects on folate and vitamin B ¹² were elucidated. Nitrous oxide can significantly interfere with activity of vitamin B ¹² , alter intracellular folate coenzyme levels, perturb the normal pathways of folic acid metabolism by oxidizing the enzyme-B ¹² (Co+) complex formed during catalysis, and thereby inactivate methionine synthase. ^298-300 Anesthesia with N ² O may also impair DNA synthesis in bone marrow cells. ³⁰¹ Notably, researchers have often employed N ² O as a probe for investigating the folate–vitamin B ¹² interrelationships because of these well-known effects. ³⁰²

Thus, N ² O exposure can cause an accumulation of cytosolic 5-methyltetrahydrofolate (5-MTHF; e.g., in liver and pancreas), at the expense of other reduced folates, specifically tetrahydrofolate (THF) and 5-formyltetrahydrofolate (5-FTHF), which in turn can lead to significantly lower total mitochondrial folates. ^303,304 This phenomenon is known as the methyl trap hypothesis,first presented in 1962, which states that, in the context of methionine synthase inactivation resulting from vitamin B ¹² deficiency, folates are trapped as 5-MTHF, the synthesis of which is not reversible in vivo. ^305,306

Research

Researchers have studied the adverse effects of N ² O on folate activity and the benefits of folic acid administration for more than 20 years. Using the deoxyuridine (dU) suppression test in 1985, Amos et al. ³⁰¹ investigated secondary development of folate deficiency and delayed recovery after N ² O anesthesia in 48 patients admitted to an intensive care unit (ICU). The pattern of correction of the abnormal dU suppression tests on admission to the ICU, after N ² O anesthesia, was “typical of that seen in vitamin B ¹² deficiency”; 3 days later “the pattern had changed to that usually seen in folate deficiency.” Likewise, “serum folate levels fell to subnormal values,” and although elevated after N ² O administration, urinary folate excretion was “insufficient by itself to explain the development of folate deficiency.” Moreover, administration of physiological amounts of folic acid accelerated the recovery of the bone marrow abnormalities present after N ² O anesthesia.

In a 1986 rat study, Keeling et al. ³⁰⁷ found that coadministration of folinic acid provided protection against N ² O teratogenicity. “The incidence of major skeletal abnormalities in the untreated nitrous oxide group was significantly increased to five times that of the control groups, whereas the incidence in the nitrous oxide group receiving folinic acid was not significantly different from control.”

Two teams of researchers conducted parallel experiments investigating the short-term effects of N ² O on folate and vitamin B ¹² metabolism in rats and human patients. Koblin et al. ³⁰⁸ found that exposure to nitrous oxide (60% N ² O, 40% O ² ) in rats of various ages greatly enhanced urinary excretion of formic acid and formiminoglutamic acid (FIGLU), compounds that are elevated in the urine of mammals with a deficiency in folate. Urinary formic acid excretion increased threefold to 25-fold the first day after 6 hours of N ² O exposure and returned to background levels by the second day after exposure in all age groups. Urinary FIGLU excretion increased 100-fold to 300-fold the first day after N ² O exposure, with the highest FIGLU excretion rates in the elderly rats and the lowest in the young rats. FIGLU excretion rates returned to baseline levels by the second day after N ² O exposure in all age groups. Increasing age was progressively associated with decreased plasma folate, but no age-dependent changes were observed in RBC folate, liver folate, or plasma vitamin B ¹² levels.

Subsequently, Koblin et al. ³⁰⁹ investigated folic acid metabolism in 49 surgical patients exposed to isoflurane alone or combined with N ² O. They found no increase in urinary formic acid and FIGLU in 23 patients exposed to N ² O for total hip replacement. However, patients undergoing resection of acoustic neuromas (with mean duration of anesthesia of 9.3 hours) exhibited a small, transient increase in the FIGLU/creatinine ratio, which peaked at the end of anesthetic exposure and returned toward control levels by the first day after anesthesia and surgery. The researchers noted a lack of predictive association between low preoperative levels of RBC folate and low-normal levels of serum vitamin B ¹² and an increase in formic acid or FIGLU in response to N ² O. They concluded: “Although an occasional patient may prove highly susceptible to and develop signs of severe vitamin B ¹² and folic acid deficiency after exposure to N ² O, our findings suggest that this is a rare event.” ³⁰⁹

In a study involving 40 patients under N ² O anesthesia for 70 to 720 minutes, Ermens et al. ³¹⁰ demonstrated that postoperative plasma levels of folate and homocysteine (Hcy) increased up to 220% and 310%, respectively, in a manner correlating significantly with exposure time. This response appeared rapidly, after 75 minutes of N ² O exposure, and required several days to return to normal levels. Plasma Hcy levels had not returned to preoperative levels within 1 week in eight patients receiving N ² O anesthesia. Based on these findings, the authors suggested that elevated plasma Hcy levels may be used for monitoring N ² O-induced cobalamin inactivation and the resultant disturbance of Hcy and folate metabolism.

In related 1991 in vitro research using blast cells from leukemia patients, Ermens et al. ³⁰³ found that 8 hours’ exposure to N ² O caused an equal decrease of 10-FTHF and 5-FTHF in both acute myeloid leukemia (30%) and acute lymphoid leukemia (45%), whereas 5-MTHF increased (130%). They concluded that N ² O treatment of leukemic cells causes an accumulation of 5-MTHF at the expense of other folate forms. In a similar 1997 experiment, Horne et al. ³⁰⁴ investigated the effects of N ² O inactivation of methionine synthase on the compartmentation of folate metabolism in rat pancreas. Rats exposed to N ² O exhibited cytosolic 5-MTHF concentrations that were significantly greater (59% of total folates) and THF concentrations significantly lower (32%) than those in controls. Exposure to N ² O was associated with significantly lower activity of methionine synthase and concentration of THF and 5-FTHF, but not 5-MTHF or 10-FTHF, thus leading to significantly lower total mitochondrial folates. These findings are consistent with emerging knowledge of the mechanisms involved.

Issues of adverse effects of N ² O may represent a significant risk to medical and dental personnel exposed daily to low levels of anesthetic. Salo et al. ³¹¹ gathered peripheral blood samples from eight anesthetists and seven internists in a survey of potential occupational health hazard to operating theater personnel chronically exposed to trace N ² O concentrations. They observed no definite signs of B ¹² -N ² O interaction in peripheral blood counts or films, serum vitamin B ¹² or plasma, or erythrocyte folate concentrations.

The issue of how this interaction might affect individuals abusing nitrous oxide has not been addressed in a systematic or direct manner and deserves consideration as a potential area of concern.

Reports

Nunn et al. ³¹² reported the case of a “seriously ill patient” who exhibited “megaloblastic changes in his bone marrow” following N ² O anesthesia for 105 minutes. After a 7-hour delay and administration of folinic acid (30 mg), a second round of N ² O was administered; 4 hours later his marrow was normal.

Flippo and Holder ²⁹⁹ reviewed five cases in which “patients unsuspected of having vitamin B ¹² deficiency developed subacute combined degeneration of the spinal cord following nitrous oxide anesthesia.” They attributed these adverse effects to N ² O-induced “irreversible oxidation to the Co++ and Co forms that renders vitamin B ¹² inactive” and that impairs DNA synthesis and the methylation of myelin basic protein involved in the maintenance of the myelin sheath. They cautioned that “patients with vitamin B ¹² deficiency are exceedingly sensitive to neurologic deterioration” after N ² O anesthesia, which, if unrecognized, could cause “irreversible” deterioration and “may result in death.”

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians are advised to consider assessment of vitamin B ¹² and folate status as part of preoperative care in patients who will be receiving major anesthesia that includes N ² O. Administration of folic acid (1000 µg/day) and vitamin B ¹² (100 µg/day), beginning 1 week before and extending through 1 week after prolonged exposure to N ² O, is prudent if the patient is susceptible to or has a history of nutrient deficiency and if N ² O exposure will be of extended duration. Such concerns are amplified and further monitoring and compensatory nutrient support warranted in pregnant women because of the significantly greater risk inherent in transient depletion of folate levels, particularly in early gestation. Patients with normal vitamin B ¹² and folate levels who undergo N ² O anesthesia for less than 2 hours generally do not require supplementation; however, such prophylaxis would be safe, compatible, and inexpensive.

Evidence is lacking to support a recommendation for routine supplementation by medical or dental staff regularly exposed to N ² O. However, consideration should be given to the need for B ¹² and folate administration to individuals who have a recent history of, or are known to be currently engaged in, the habitual use of N ² O as a recreational drug. Urinary MMA level and plasma tHcy determination might be sensitive markers for monitoring in both situations.

	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, Not Requiring Professional Management
	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, with Professional Management
	Impaired Drug Absorption and Bioavailability, Negligible Effect
	Prevention or Reduction of Drug Adverse Effect

Preliminary

Effect and Mechanism of Action

In vitro and animal research indicates that the “antifolate activity of NSAIDs, and hence cytostatic consequences, are important factors in producing anti-inflammatory activity.” ³⁹ Some NSAIDs, such as sulindac and sulfasalazine (SASP), are known antifolates. With chronic use and when taken in high doses, many NSAIDs may exert antifolate activity by impairing folate absorption and transport, which could decrease serum folate concentrations and cause deficiency. ^{38,39,313-315} Furthermore, many NSAIDs (including ibuprofen, indomethacin, mefenamic acid, naproxen, piroxicam, salicylic acid, sulindac, and sulphasalazine) and NSAID-like drugs act as competitive inhibitors of enzymes involved in folate metabolism and transport, including phosphoribosyl aminoimidazolecarboxamide formyltransferase transformylase (AICAR transformylase), dihydrofolate reductase, methylenetetrahydrofolate reductase, and serine transhydroxymethylase. Other in vitro experiments indicate that these NSAIDs can act as folate antagonists and inhibit the THF-dependent biosynthesis of serine from glycine and formate (i.e., C1 index) by human blood mononuclear cells (BMCs). In contrast, aspirin, acetaminophen, and antipyrine were weak inhibitors of these enzymes; acetaminophen exerted a weak inhibitory effect on the C1 index. Notably, both aspirin and salsalate exert anti-inflammatory effects after conversion to salicylic acid, which possesses greater antifolate activity than either parent compound. ^39,314

Other NSAIDs, such as p-aminosalicylic acid (an older antituberculosis agent), may decrease folic acid absorption in the GI tract and decrease serum folate concentrations. ³¹⁶ Furthermore, p-aminosalicylic acid is also a structural analog of p-aminobenzoic acid (PABA) and thus inhibits de novo folate synthesis.

Research

Most evidence regarding the effects of NSAIDs on folate comes from in vitro and animal research, as previously reviewed. Some of these studies derive from human studies, but not clinical trials. Thus, although a coherent body of data indicates that NSAIDs exert multiple actions that may be deleterious to folate levels and functions, only preliminary evidence is available from human trials to confirm these phenomena and delineate the associated factors or determine their clinical significance.

Baggott et al. ³⁹ observed in vitro that the C1 index of BMCs from rheumatoid arthritis (RA) patients receiving drugs with minimal antifolate activity (e.g., acetaminophen) is higher than the C1 index from RA patients receiving NSAIDs with more potent antifolate activity (e.g., sulindac, sulfasalazine, naproxen, ibuprofen). “The mean activity of the transformylase in BMCs taken from healthy humans was 1.98 nmol of product/h per 10 ⁶ cells and the activity was positively correlated with BMC folate levels.”

Analyzing serum and blood samples from a healthy female subject following a fixed diet for 11 days and taking 650 mg aspirin orally every 4 hours during the middle 3 days, Lawrence et al. ³⁸ observed a “brisk, significant but reversible fall in total and bound serum folate and a small but insignificant increase in urinary folate excretion.” Noting also that aspirin in vitro “displaced significant amounts of bound serum folate,” they concluded that “aspirin in therapeutic doses can contribute to subnormal serum folate values, and if it increases urinary folate excretion even slightly, may impair folate balance.” (See also Acetylsalicylic Acid.)

No direct evidence has confirmed that folate coadministration is beneficial for individuals taking most NSAIDs. Conversely, no evidence to date has suggested that concomitant folate administration might interfere with the therapeutic activity of such NSAIDs, although this may be possible given the role of antifolate activity in the mechanisms of action observed in many of these drugs. Nevertheless, the positive clinical outcomes regarding coadministration of folate with methotrexate in autoimmune arthritides indicates that folate does not necessarily interfere with the therapeutic action of antifolate drugs.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing NSAIDs should consider discussing with patients the potential benefits of concomitant folic acid (400 µg once or twice daily) and increased dietary folate intake with frequent, long-term, or high-dose NSAID therapy. Monitoring for folate deficiency using serum/RBC folate levels and plasma Hcy may be advisable.

Substantive evidence is lacking to confirm, or even suggest, that routine low-dose NSAID use is likely to affect folate status adversely in most individuals. The available evidence indicates that the adverse effect may be marginal in some cases and could be severe in a few patients, particularly with chronic use at higher dosage levels. Such concerns may be particularly relevant in pregnant women and in patients with compromised dietary folate status or susceptibility caused by individual genomic variability.

	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, Not Requiring Professional Management
	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, with Professional Management
	Prevention or Reduction of Drug Adverse Effect

Preliminary to Emerging

Effect and Mechanism of Action

Oral contraceptives (OCs) may lower serum and RBC folate, but such changes do not appear to induce folate deficiency or cause anemia or megaloblastic changes under most circumstances. OCs are also associated with lowered levels of cyanocobalamin, which in turn can adversely affect folate status and related hematological parameters. ^317,318 The mechanisms of such possible effects have not been elucidated. In 1968, Shojania et al. ³¹⁹ noted the high incidence of folate deficiency in pregnancy and proposed that “one would expect a similar effect in women on longterm oral contraceptives, which are known to produce a pseudopregnancy state.”

Folic acid may protect against precancerous cervical dysplasia in women, especially those taking OCs.

Research

It has been well established that birth control pills, especially those containing higher estrogen doses, impair folate metabolism and tend to deplete folic acid, with several possible adverse repercussions, especially increased risk of cervical dysplasia and vascular thrombosis. However, evidence is mixed regarding the probability of occurrence and clinical significance of such an adverse effect; the issue remains contentious. Differing estrogen doses in various OC formulations, as well as such confounding variables as dietary folate intake and genetic polymorphisms affecting folate, may account for some of the inconsistency in research findings. ³²⁰

Folic acid deficiency enhances OC-induced platelet hyperactivity and oxidative stress. In various studies in female rats and also in women, OCs were found to induce a platelet hyperactivity related to increased oxidative stress. Many researchers suspect that OCs deplete folate stores and point to cases of megaloblastic anemia reported to occur in women taking OCs.

Using a rat model, Durand et al. ³²¹ determined that dietary folic acid deficiency contributed to the thrombogenicity of OCs and “magnified OC-induced oxidative stress, which resulted in platelet hyperactivity by elevating the pro-oxidant homocysteine plasma concentration.” Animals were fed for 6 weeks with either a folic acid–deficient diet (250 µg/kg folic acid) or a control diet (750 µg/kg folic acid). Half the animals in each group received an OC (ethinyl estradiol plus lynestrenol). The authors observed that folic acid deficiency and OCs “individually potentiated platelet aggregation in response to thrombin and ADP [adenosine diphosphate] and the release and metabolism of arachidonic acid, in particular, the biosynthesis of thromboxane. These platelet activities were further enhanced in animals given both the folic acid–deficient diet and the OC treatment.” Furthermore, folic acid deficiency “enhanced the pro-oxidant state in OC-treated rats characterized by (1) a fall in platelet and plasma n-3 fatty acids, (2) an increase in plasma lipid peroxidation products such as conjugated dienes, lipid peroxides, and thiobarbituric reactive substances, [and] (3) a rise in ex vivoerythrocyte susceptibility to free radicals.” Also, OC administration “led to a reduction of plasma and erythrocyte folate concentrations associated with a moderate hyperhomocysteinemia.” Despite the limitations of this animal model, the authors concluded that their findings “suggest that in addition to cigarette smoking, inadequate folic acid intake might predispose those taking OC to vascular thrombosis.” ³²¹

Most human studies have found that OC use adversely affects folate status, but conclusions vary depending on estrogen dose levels, methods of assessing folate levels, and duration of trial period. In a preliminary 1968 study of 86 women (24 normal nonpregnant women of childbearing age and 62 women taking OCs), Shojania et al. ³¹⁹ determined that the OC group showed, on average, a significantly lower serum folate level than the control group, with 30% (19) of the OC women exhibiting a serum folate level lower than the lowest value in the control group. The authors recommended that the “serum folate level of women on long-term oral contraceptives be determined, especially when they stop the medication and plan for conception.”

Subsequently, in a 1975 review, Lindenbaum et al. ³²² reported that “in some series, but not in others, serum and/or red cell folate concentrations have been reduced in oral contraceptive users” but that “a disturbance in folate balance serious enough to cause symptoms (i.e., megaloblastic anemia) occurs very rarely.” In a 1991 study, Mooji et al. ³²³ compared folate concentration in serum and RBCs, as well as other nutrient levels, over four cycles in 29 women taking OCs (containing 30 µg of ethinyl estradiol) and 31 women serving as non-OC controls, with both groups administered a multivitamin and folic acid supplement. OCs did not lower serum and RBC folate levels or induce folate deficiency, at least within the limited time frame of the trial. The authors concluded that “supplementation during OC use or just after discontinuing treatment cannot be justified for healthy young women,” but added that, “in the case of women with a critical vitamin balance or higher folate needs, multivitamin supplementation may be considered.”

In 1993, Steegers-Theunissen et al. ³²⁴ compared serum folate levels after oral folate loading in a study of the kinetics of folic acid monoglutamate involving 29 users of OCs containing less than 50 µg of estrogen and in 13 women serving as controls. Median serum folate concentrations after oral folate loading were decreased in OC users, reaching statistically significant lower levels after 210 minutes (260 nmol/L) compared with controls (400 nmol/L). Apparently, OCs with less than 50 µg estrogen significantly affected folate kinetics and vitamin B ¹² levels. Even so, the authors concluded that “folate and vitamin B ¹² status does not seem to be at risk.”

In 1998, Green et al. ³²⁵ investigated the impact of “currently available” OCs, as well as smoking and alcohol, on serum and RBC folate and serum B ¹² and homocysteine in 229 adolescent females (age 14-20) in Canada. Use of OCs was associated with an estimated 33% lower serum B ¹² level than nonuse, but OC use (as well as alcohol use and smoking) was not significantly associated with lower serum or RBC folate levels, after controlling for folate intake.

The investigators in many of these studies concluded that the effect of OCs on folate is not clinically significant, but their findings are generally limited by the parameters employed to assess folate status and the short duration of the trials.

A “rigorous meta-analysis” of 14 studies by Baillargeon et al. ³²⁶ found that “current use” (i.e., use at the time of the event or within 3 months) of low-dose OCs “significantly increases the risk of both cardiac and vascular arterial events,” including vascular arterial complications with third-generation OCs. Overall, the use of low-dose OCs was associated with a doubling of the risk of cardiovascular outcomes (myocardial infarction or ischemic stroke), with both second-generation and third-generation OCs being associated with a significantly increased risk of ischemic stroke (relative risk, 2.12). The association between third-generation OC use and myocardial infarction proved nonsignificant.

Researchers often allude to but generally do not directly address the implications for women who might subsequently become pregnant. To address this critical issue, Martinez and Roe ³²⁷ investigated residual effects of OCs on the folate status of pregnant women who had discontinued intake of these drugs within 6 months of conception. They found that OC users demonstrated “lower plasma and red blood cell folate values than did the respective control subjects.” Factoring in seasonal variability in RBC folate values, which were lower in the winter months, RBC folate values were more affected by previous drug use in the winter group than in the summer group. Also, dietary folate exhibited a significant effect on plasma and RBC folate, and blood folate values were significantly lower in OC users for any given level of folate intake. Correlation of post–OC use folate levels versus non-OC users and risk of subsequent neural tube defect (NTD) pregnancies would be useful.

Researchers and clinicians have long debated the role of folate in the relationship between OC use and the occurrence of cervical dysplasia and cancer. In 1973, Whitehead et al. ³²⁸ reported megaloblastic changes in the cervical epithelium in association with OC therapy and reversal with folic acid. In 1982, Butterworth et al. ³²⁹ published promising initial research from a 3-month, double-blind placebo-controlled trial where megadoses of folic acid (10 mg daily) were associated with regression of cervical intraepithelial neoplasia (CIN) among OC users. In a 1975 review, Lindenbaum et al. ³²² concluded that “about 20 percent of women taking contraceptive hormones manifest mild megaloblastic changes on Papanicolaou smears of the cervicovaginal epithelium which disappear after folic acid therapy,” but that (then) “current evidence, however, would not indicate that any significant benefit would ensue from routine folate supplementation in women on oral contraceptives.”

In 1996, Zarcone et al. ³³⁰ found that folic acid supplements did not alter the course of established cervical dyplasia. Further, at this time, no substantial evidence has been published to support the view that folic acid supplementation alone can play a significant role in the treatment of cervical cancer. In related research concerning human papillomavirus (HPV), often associated with cervical dysplasia, Kwasniewska et al. ³³¹ determined that statistically lower levels of folic acid were found in the women with CIN-HPV (+) and cited other studies showing that lower levels of antioxidants coexisting with low levels of folic acid increase the risk of CIN development. In contrast, Sedjo et al. ³³² found “no significant associations … between HPV persistence and dietary intake of folate, vitamin B ¹² , vitamin B ⁶ , or methionine from food alone or from food and supplements combined or from circulating folate” in 201 women with a persistent or intermittent HPV infection. Moreover, among women not using OCs, folic acid has not been found to improve abnormal Pap smears. However, folate replacement in the range of 5 to 20 mg has been associated with reversal of dysplasia, particularly HPV-related dysplasia (which is the vast majority). The older literature was unaware of the relationship between HPV and cervical dysplasia, and some of the negative studies may have used too low a folic dose. There may also have been disproportionate numbers of MTHFR mutations in the negative studies. Studies should be repeated that control for these factors, with either genetic testing or use of activated folate.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing OCs are advised to discuss with their patients the potential adverse effects of these exogenous hormones on the status of folate and other nutrients, especially vitamin B ⁶ . Folate testing may be warranted, but coadministration of folic acid (400-800 µg/day) with vitamin B ⁶ (50-100 mg/day) can provide safe and inexpensive support against cardiovascular and other potential adverse effects without interfering with the intended contraceptive effect. Enhanced dietary folate intake and folic acid supplementation are especially important for women who stop using OCs with the intention (or simply the possibility) of becoming pregnant. Those who are diagnosed with cervical dysplasia or who are concerned with increased risks of stroke might particularly benefit from incorporating folic acid into a therapeutic program under the care of a nutritionally trained health care professional. Vitamin B ¹² status should also be checked by serum B ¹² levels or serum/urine MMA levels and corrected as necessary whenever high-dose folic acid therapy is implemented.

Drug-Induced Nutrient Depletion, Supplementation Therapeutic, Not Requiring Professional Management

Preliminary

Effect and Mechanism of Action

Proteolytic enzymes, including pancreatin, have been reported to form insoluble complexes with folate and interfere with absorption. Diminished absorption of dietary folate could lead to folate deficiency. ³³³

Research

In vitro and human studies have reported impairment of folic acid absorption in the presence of oral pancreatic extracts. Russell et al. ³³⁴ described higher serum folate levels “among newly diagnosed, untreated patients with pancreatic insufficiency than among treated patients despite greater fat malabsorption in the former group.” Further, in vivo experiments involving “folate absorption tests using tritium-labeled pteroylmonoglutamatic acid showed folate absorption to be enhanced in pancreatic insufficiency patients as compared to control subjects.” Also, “pancreatic extract significantly inhibited folate absorption” in both normal subjects and patients with pancreatic insufficiency. The authors recommended that “folate status should be monitored in patients being treated for pancreatic insufficiency,” especially when pancreatic extract and bicarbonate are coadministered. Further research is warranted.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Health care professionals prescribing pancreatin and other proteolytic enzymes are advised to suggest concomitant supplementation with folic acid (400 µg/day) to counteract any resultant decrease in folate absorption and prevent diminished folate status. Monitoring of folate levels may be appropriate in patients with susceptibility to or history of folate deficiency or comorbid conditions, in whom folate deficiency could cause enhanced risk. Administering folate supplements several hours before or after intake of pancreatic enzyme preparations would also appear prudent.

	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management
	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, with Professional Management
	Bimodal or Variable Interaction, with Professional Management
	Potential or Theoretical Adverse Interaction of Uncertain Severity

Emerging to Consensus

Effect and Mechanism of Action

Pyrimethamine is a competitive inhibitor of dihydrofolate reductase that acts as a folic acid antagonist and can reduce serum folic acid levels. Pyrimethamine is widely recognized as a cause of megaloblastic anemia resulting from a folate deficiency. In combination with sulfadiazine, it is often used in the treatment of toxoplasmosis. However, bone marrow suppression, resulting predominantly from depression of folate metabolism and causing neutropenia and thrombocytopenia, is a frequent toxic adverse effect. Coadministration of folic acid (or more often, 5-MTHF as folinic acid) can mitigate adverse effects on folate levels and function but could decrease pyrimethamine efficacy because of pharmacodynamic antagonism.

Fansidar, an antimalarial agent, is a combination of sulfadoxine and pyrimethamine that inhibits sequential steps involved in the biosynthesis of tetrahydrofolic acid. Thus, interference with protozoal nucleic acid and protein production is achieved by depleting folic acid, an essential cofactor in the biosynthesis of nucleic acids. Sulfadoxine competitively inhibits the enzyme dihydropteroate synthetase; it is a structural analog of PABA. The dual sequential action of these two agents creates a synergistic effect that enables reduction of the minimum effective dose of each medication but amplifies the antifolate effects.

Research

Although the mechanism of action of pyrimethamine and its adverse effects on folate status are widely acknowledged, the frequency and conditions of clinically significant interactions are not well known. At lower doses the need for folic acid coadministration has not been researched adequately to enable well-founded conclusions. The risk of bone marrow suppression can increase significantly with concurrent use of pyrimethamine and other antifolates, such as methotrexate or sulfa antibiotics. At higher doses, such as used in treatment of toxoplasmosis and Pneumocystis cariniipneumonia, folate support may be necessary. However, such concurrent administration may impair the therapeutic activity of pyrimethamine, although this has not been established with careful clinical research.

Of several dihydrofolate reductase inhibitors tested against P. cariniiin a rat model, Walzer et al. ³³⁵ noted that “all drugs were well tolerated except pyrimethamine, which caused bone marrow depression; folinic acid ameliorated this adverse reaction but did not interfere with P. cariniitreatment.” This suggests that the previous caution regarding potential interference with therapeutic activity of pyrimethamine by at least some forms of folic acid may not be a concern.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing pyrimethamine, alone or in combination with other agents, are advised to consider coadministration of folic acid or 5-MTHF as a preventive measure. Folinic acid is the form of 5-MTHF most often used in conventional practice, 5 to 15 mg/day (orally, intravenously, or intramuscularly) until normal hematopoiesis restored, although L-5-MTHF (Metafolin) may be preferable, because it is the chiral form used by the body. Folate and pyrimethamine levels should be monitored regularly. Pyrimethamine dose may also need to be reduced or the medication discontinued if folate deficiency develops, depending on patient response. Caution is also warranted in patients with hepatic or renal impairment. Pyrimethamine may precipitate hemolytic anemia in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency.

Although the safety of pyrimethamine in pregnancy has not been well researched, prudence suggests that increased folic acid supplementation may be warranted with female patients who are or might become pregnant.

	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, Not Requiring Professional Management
	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, Not Requiring Professional Management
	Adverse Drug Effect on Nutritional Therapeutics, Strategic Concern
	Prevention or Reduction of Drug Adverse Effect

Emerging to Consensus

Effect and Mechanism of Action

Sulfonamides, including sulfasalazine, interfere with the absorption, bioavailability, and activity of folic acid, as well as adversely affecting vitamin B ⁶ and vitamin K. Sulfasalazine can impair absorption and transport of folic acid and dietary folate, most likely acting as a competitive inhibitor. ^314,336-338 The target of sulfonamides, and the basis for their selectivity, is the enzyme dihydropteroate synthase (DHPS) in the folic acid pathway. ³³⁹ Sulfasalazine also inhibits other folate-dependent enzymes, particularly dihydrofolate reductase, methylenetetrahydrofolate reductase, and serine transhydroxymethylase, as discussed earlier with interactions involving NSAIDs as a class. Animal research indicates that “sulfasalazine interferes with a folate recognition site which is common to these enzymes and to the intestinal transport system.” ³¹³ Sulfasalazine-induced blood dyscrasias might involve folic acid depletion. “The mechanisms by which sulfasalazine antagonizes folate metabolism are dose-dependent and, consequently, higher doses might precipitate folate deficiency.” ³⁴⁰

Research

Sulfasalazine is well known for adversely affecting folate, but some controversy exists as to whether the drug by itself can cause clinically significant deficiencies of folic acid. Megaloblastic anemia caused by sulfasalazine has responded to drug withdrawal alone. ³⁴¹ However, a high proportion of the literature indicates a multifactorial causality for folate depletion in the affected populations, with the adverse effects of sulfasalazine being an important but not necessarily adequate stress. The conditions for which sulfasalazine is typically prescribed are often associated with malabsorption, poor diet, old age, and chronic inflammation. For example, a high proportion of individuals with inflammatory bowel disease and ulcerative colitis exhibit compromised folate status. ³⁴²

In addition to the increased risks associated with hyperhomocysteinemia resulting from drug-induced folate deficiency, the association between folate status and colorectal cancer risk may be especially relevant to individuals in such populations. Ulcerative colitis, folate-related polymorphisms, and folate deficiency have all been linked to an increased risk for colon cancer. ^343-348 A wide range of authors further suggest that increased folate intake may play a preventive (and/or therapeutic) role against some colorectal cancers. ^348-354 Significant research demonstrates the contributory role of sulfasalazine in the etiology of folate deficiency among patients treated for ulcerative colitis. However, other evidence suggests that although sulfasalazine impairs folate absorption among such patients, “this only becomes significant if other reasons for folate deficiency are also present.” ^336,355 Thus, optimal folate status represents an important factor in the therapeutic strategy for care of patients with ulcerative colitis and irritable bowel disease and increased risk for colorectal cancer.

The available evidence indicates that the risk of clinically significant folate deficiency may not be high among patients treated with sulfasalazine generally, but that high doses increase adverse effects, including deficiency, and that folate deficiency could play a significant role in both GI and overall disease risk. However, a review of the range of human studies in this area also suggests that the researchers’ choices for laboratory measures to assess absorption and metabolism folate and their implications may be influential in shaping the findings and conclusions.

In 1981, Halsted et al. ³³⁶ found that sulfasalazine inhibits the absorption of folates in patients with ulcerative colitis. In 1982, Longstreth and Green ³⁴² analyzed hematological data, including serum and RBC folate assays, from 45 outpatients with chronic colitis, 27 of whom were receiving maintenance doses of sulfasalazine. Mean hemoglobin, hematocrit, serum folate, and RBC folate levels were similar overall in sulfasalazine users and nonusers. However, among the sulfasalazine users, “RBC folate was inversely correlated with drug dose; serum folate was not,” and those “taking 2 g or more of sulfasalazine daily had lower mean RBC folate levels (221.2 ± 27.3 ng/mL) than patients either taking less (371.7 ± 35.0 ng/mL) or nonusers (330.3 ± 30.3 ng/mL).” Also, mean RBC corpuscular volume (MCV) was related to drug dose but not to RBC folate. The authors concluded: “Although maintenance sulfasalazine use rarely causes clinically significant folate deficiency, subclinical tissue depletion occurs as a dose-related effect.” ³⁴²

In a case-control study of patients with chronic ulcerative colitis, Lashner et al. ³⁵⁶ found a 62% lower risk of colon cancer with folate supplementation, compared to ulcerative colitis patients who did not supplement with folic acid. In a later study involving 98 patients with ulcerative colitis, Lashner and a different team ³⁵⁷ found that individuals who have ulcerative colitis and who supplement folic acid had a 55% lower risk of developing colon cancer. The dose of folate varied with the risk of neoplasia, and folate use also varied with the degree of dysplasia. Although these findings were not statistically significant, the authors concluded that daily folate supplementation may protect against the development of dysplasia or neoplasia in ulcerative colitis patients. Although diverse factors contribute to colon cancer, many researchers suggest that folic acid deficiency may increase susceptibility, and that folic acid supplementation and enhanced dietary folate intake may have a preventive effect.

The implications of sulfasalazine therapy on folate status in patients treated for rheumatoid arthritis (RA) parallel those of patients with bowel disorders. In a prospective study of 30 subjects, Grindulis and McConkey ³⁴⁰ investigated the effects of sulfasalazine on folate deficiency in RA patients, who often have low serum and RBC folate concentrations. Pretreatment serum and RBC folate concentrations were low-normal. They administered 2 g sulphasalazine over 24 weeks, using 500 mg penicillamine daily for controls, although knowledge of possible interactions between folate status and penicillamine is incomplete. No change was observed in serum and RBC folate concentrations in either group. However, MCV increased only in patients taking sulfasalazine, possibly reflecting reticulocytosis secondary to drug-induced hemolysis. Measurement of reticulocyte counts might clarify any future investigation in this area.

In 1996, Krogh Jensen et al. ³¹⁵ analyzed plasma total homocysteine (tHcy, as a sensitive marker of folate deficiency), serum folate, erythrocyte (RBC) folate, serum cobalamin, and routine indices of hemolysis in 25 arthritis outpatients treated with sulfasalazine, to assess the frequency of folate deficiency and hemolysis among such patients. Notably, none of the subjects had taken folate-containing vitamins for at least 8 weeks preceding the trial; it is unclear whether this was by exclusion design or simply reflective of the patient population. The control group consisted of 72 healthy hospital staff. The patient group exhibited median plasma tHcy that was significantly higher than controls, with five patients (20%) having plasma tHcy levels that exceeded the upper-normal limit. Median serum folate was significantly lower in the patient group, with 11 patients (40%) exhibiting depressed serum folate. Notably, there was no difference in the levels of RBC folate between the two groups, and only three patients (12%) had RBC folate values below the reference interval. Furthermore, no patient had cobalamin deficiency, as assessed by serum cobalamin and methylmalonate, but the treated group exhibited significantly lower S-cobalamin levels. These findings also indicate it is “unlikely that any patient had increased plasma tHcy due to cobalamin deficiency.” The authors also reported that 12 of the 24 treated subjects in whom HbA ^1c was measured had decreased levels indicating chronic hemolysis. They proposed that the chronic hemolysis caused by sulfasalazine “might explain the similar RBC folate values in the two groups because of a relatively higher folate content of young erythrocytes.” The authors concluded that observed patterns in plasma tHcy among those treated with sulfasalazine “suggest that a substantial number of patients may have folate deficiency at the tissue level.” ³¹⁵ Their findings also demonstrate the need for determination of and testing with sensitive indicators of folate status, which RBC folate does not appear to be.

Initial research indicates that drug-induced effects on folate are not likely to have teratogenic effects, but evidence is limited and inconclusive. In a population-based case-control study of the safety of sulfasalazine use during pregnancy, Norgard et al. ^357a found no significant increased prevalence of selected congenital abnormalities in the children of women treated with sulfasalazine during pregnancy. Further research is warranted.

Reports

In 1986, Logan et al. ³⁵⁸ reported that sulfasalazine-associated pancytopenia may be caused by acute folate deficiency. They described three patients who, after taking sulfasalazine for more than 2 years, “suddenly developed severe pancytopenia with gross megaloblastic changes in the marrow.” Administration of “high dose oral folic acid” achieved a “good response” in two patients, “but the third required folinic acid.” The authors proposed acute folate deficiency as the apparent mechanism involved, noting that “the requirement for folinic acid in one case suggests that the known inhibition of folate metabolism by sulphasalazine also contributes.” Furthermore, they observed that “the syndrome appears to be associated with high dosage and slow acetylator status.” Subsequently, therapy was well tolerated in two patients after the drug was “restarted at reduced dosage with folate supplements”; both patients were “slow acetylators.” The progression of disease in the third patient, however, led to colectomy, and her acetylator status was not determined.

In a 1999 review, Hoshino et al. ³⁵⁹ reported a case of ulcerative colitis with folate-deficient megaloblastic anemia induced by sulfasalazine.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing sulfasalazine for longer than 2 weeks should be alert to risk factors for compromised folate status, monitor blood and tissue folate levels using sensitive indicators, and coadminister folic acid, typically 500 to 600 µg twice daily, when appropriate. Folate has no known risks at the suggested levels and can potentially provide a number of benefits to those taking sulfasalazine. In particular, folate supplementation during sulfasalazine administration is recommended, especially to reduce the risk of dysplasia or cancer in patients with ulcerative colitis. Recommendations within conventional practice have favored high-folate foods rather than folic acid supplements, but increased intake through both forms seems reasonable and more likely to be effective. Clinically significant adverse effects are improbable with sulfasalazine therapy of 2 weeks or less. Even though evidence of heightened risks during pregnancy is lacking, prudence suggests that all women undergoing sulfasalazine therapy supplement with 1000 µg or more of folic acid for 6 months before becoming pregnant and continuing throughout pregnancy.

The available research consistently demonstrates that sulfasalazine exerts multiple adverse effects on folate and suggests that such antagonistic effects on folate metabolism are dose dependent. Consequently, higher doses (and longer duration of treatment) will tend to increase risk and degree of adverse effects and might precipitate folate deficiency. Such risks increase in patients with genetic predispositions to folate metabolism dysfunctions or other factors contributing to compromised folate status. Given the low cost and nontoxic nature of folic acid, enhanced intake (via supplements or foods) represents a simple, low-risk adjunctive therapy for every patient taking sulfasalazine, unless otherwise indicated.

	Beneficial or Supportive Interaction, with Professional Management
	Bimodal or Variable Interaction, with Professional Management
	Impaired Drug Absorption and Bioavailability, Precautions Appropriate
	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management

Emerging to Consensus

Effect and Mechanism of Action

The several mechanisms of interaction between the tetracycline class of antibiotics and folic acid are complex and conflicting, depending on dose, duration, timing, and patient characteristics. Folic acid may interfere with the absorption and effectiveness of tetracycline antibiotics if ingested simultaneously, and vice versa. ³⁶⁰ Tetracyclines inhibit bacterial protein synthesis by binding to the 30S ribosome, blocking access of the aminoacyl tRNAs at the “A” acceptor site on the mRNA-ribosome complex. These drugs may interfere with the activity and induce the depletion of folic acid and other nutrients, particularly other B vitamins. ³⁶¹ Additionally, extended or recurrent use of antibiotics can cause folate depletion by eliminating the healthy intestinal flora, a major source of endogenous biosynthesis of folate (and B ¹² ). ^362,363 Many patients with conditions for which tetracyclines are prescribed have depleted folate nutriture.

Research

Omray and Varma ³⁶⁰ demonstrated that oral administration of a vitamin C– and vitamin B–complex formulation could impair absorption and reduce bioavailability of tetracycline hydrochloride through pharmacokinetic interference. However, numerous clinicians and authors fail to mention such risks or advise appropriate corrective measures in discussions of coadministration of these agents.

Some patient populations receiving antibiotic therapy have pathophysiological conditions, medical history, and lifestyle/dietary factors characterized by malnutrition, malabsorption, or nutrient depletion. For example, evidence spanning four decades indicates that tetracyclines and folic acid may provide enhanced therapeutic efficacy in many situations (e.g., treatment of tropical sprue), but that separation of oral intake may be essential to efficacy. ³⁶⁴ Westergaard ³⁶⁵ summarizes the evolution and rationale of the primary treatment strategy as follows: Patients with tropical sprue typically present with macrocytic anemia due to malabsorption of folate and/or vitamin B ¹² . Treatment of tropical sprue with folic acid replacement was introduced more than 50 years ago and has become standard medical treatment. Vitamin B ¹² replacement is usually added if there is evidence of B ¹² deficiency or malabsorption. Treatment of tropical sprue with folate and B ¹² cures the macrocytic anemia and the accompanying glossitis, and often results in increased appetite and weight gain. However, even prolonged treatment with these vitamins fails to restore villus atrophy, and malabsorption usually persists. The benefit of antibiotic treatment of tropical sprue was first documented during World War II, when sulfonamides were used to treat epidemics of tropical sprue in British and Italian troops in India. Antibiotic treatment has since become the standard treatment, and tetracycline has replaced sulfonamides. The recommended length of treatment with tetracycline is 6 months and it is given in combination with folate.

Reports

Similarly, in a discussion of several cases of tropical sprue among indigenous patients in Australia, with a history of excessive alcohol intake and characterized by alteration in the intestinal microflora, overgrowth of coliform bacteria, mucosal damage and malabsorption, and protein loss, Hanson ³⁶⁶ recommended that concomitant tetracycline use, specifically doxycycline, and folic acid therapy “can be rapidly and dramatically effective, although the tetracycline course should continue for 3-6 months.”

• Note:

  Falsely low serum folate concentrations may occur with the Lactobacillus caseiassay method in patients receiving tetracycline therapy.

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing tetracycline antimicrobials, repeatedly or for more than 2 weeks, are advised to coadminister folic acid; a moderate supplemental dose of 400 to 800 µg/day typically is adequate. These levels may also be obtained through a diet rich in leafy green vegetables, beans, beets, citrus, meat, and wheat germ. The importance of such nutrient support is amplified in pregnant women and individuals with compromised nutritional status or a history of high alcohol intake.

No evidence demonstrates an increased risk for major birth defects in children exposed to tetracycline in the first trimester of pregnancy. Nevertheless, tetracyclines are generally contraindicated after the first trimester of pregnancy (and in children <8 years old) because they tend to cause staining of teeth, hypoplasia of dental enamel, and abnormal bone growth in children and in the fetuses of pregnant women.

Coadministration of probiotic flora along with vitamins B ¹² and K is usually appropriate. The aim of an integrative approach combining tetracycline, folate, and vitamin B ¹² is to restore intestinal mucosal structure, normalize absorptive function, correct folate and B ¹² deficiencies, and correct any macrocytic anemia.

In most patients, only the probiotic flora are appropriate when a shorter course of a tetracycline (7-10 days) is administered as a countermeasure to the antibiotic-induced disruption of healthy intestinal ecology. Regular supplementation with vigorous cultures of Lactobacillus acidophilus, Bifidobacterium bifidus,and other probiotic bacteria for 2 to 4 weeks can safely and effectively preclude or reverse subsequent antibiotic-induced folate depletion; up to 6 months of probiotic intake may be necessary to fully reestablish the symbiotic intestinal flora in patients receiving more than one course of antibiotics.

Tetracycline should be administered at least 2 hours before or 4 hours after oral intake of folic acid, alone or as part of a B-complex or multivitamin formulation, to avoid interference with gastric absorption. Evidence for such an adverse interaction is minimal, but prudence suggests that such simple precautions may be beneficial.

	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management
	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, Not Requiring Professional Management
	Adverse Drug Effect on Nutritional Therapeutics, Strategic Concern
	Beneficial or Supportive Interaction, with Professional Management

Emerging to Consensus

Effect and Mechanism of Action

Triamterene impairs folate absorption and bioavailability and may contribute to folate depletion, at least in part because of its structural similarity to folic acid. Animal research also found that triamterene acted as a competitive inhibitor of folate absorption in the rat intestine. ³⁶⁷ Triamterene also acts as a relatively weak folate antagonist by inhibiting dihydrofolate reductase, which is necessary to converting unreduced dietary folates into tetrahydrofolates, the biologically active folates. Triamterene has been known to contribute to the appearance of megaloblastosis in patients with decreased folic acid stores. ^114,368-370

Research

For more than four decades, researchers have investigated the mechanisms as well as the frequency and circumstances of clinically significant triamterene-induced adverse effects on folate, particularly teratogenesis and hyperhomocysteinemia. In 1967, Maass et al. ³⁷¹ first investigated the effect of triamterene on folic reductase activity and reproduction in the rat. In 1986, Zimmerman et al. ³⁶⁷ investigated the effect of triamterene on folic acid absorption in the rat jejunum. Applying an in vivo intestinal loop method, triamterene inhibited the intestinal absorption of folic acid in a dose-dependent fashion, with 50% inhibition of systemic absorption occurring at a luminal concentration of 0.01 mmol/L of triamterene. However, animal studies are not always predictive of human response.

Schalhorn et al. ³⁶⁸ documented the dose-related inhibitory effect of triamterene and its metabolites on human leukocyte dihydrofolate reductase. The authors concluded by emphasizing the potential significance of these findings in relation to “the possible toxic side effects of long-term triamterene treatment in patients suffering from alcoholic cirrhosis, who may have impaired metabolism of triamterene and a concomitant severe folate deficiency.”

Mason et al. ³⁷² studied 272 elderly individuals in two free-living populations receiving chronic diuretic therapy and found normal folic acid levels and no signs of folic acid deficiency among 32 patients who used triamterene at unknown dose levels on a long-term basis, but lacked additional risks for folic acid deficiency. The possibility of confounding variables limits the strength of findings from this observational study.

The administration of multivitamin supplements containing folic acid appears to diminish the occurrence of birth defects associated with periconception exposure to triamterene and other folic acid antagonists. ³⁷³ Hernández-Díaz et al. ⁷⁶ investigated possible adverse effects of a broad range of folic acid antagonists (including trimethoprim, triamterene, carbamazepine, phenobarbital, and primidone) during pregnancy in an ongoing case-control study of birth defects (1979–1998) in the United States and Canada. First, they studied the exposure to folic acid antagonists that act as dihydrofolate reductase inhibitors (including triamterene) and to certain antiepileptic drugs in 3870 infants with cardiovascular defects, 1962 infants with oral clefts, and 1100 infants with urinary tract defects; the control group consisted of 6249 infants with structural defects and 2138 infants with chromosomal or mendelian defects. The authors determined that the “relative risks of cardiovascular defects and oral clefts in infants whose mothers were exposed to dihydrofolate reductase inhibitors during the second or third month after the last menstrual period, as compared with infants whose mothers had no such exposure, were 3.4 and 2.6 respectively.” Furthermore, they observed that the “use of multivitamin supplements containing folic acid diminished the adverse effects of dihydrofolate reductase inhibitors, but not that of antiepileptic drugs.” ⁷⁶ Subsequently, these researchers examined related data to determine whether periconception exposure to folic acid antagonists (FAAs) might increase the risk of neural tube defects (NTDs), specifically spina bifida, anencephaly, and encephalocele. Their findings suggest that “a number of FAAs may increase NTD risk, and they provide estimates of risk for selected drugs.” ⁷⁹ However, these data concerned a number of folate antagonists and, as such, are limited in their applicability to triamterene.

A probable link between hypertension and folate deficiency, via homocysteine (Hcy), suggests that any adverse effects by diuretics on folate status could contribute to increased risk for cardiovascular disease. Comparing blood samples from 17 hypertensive patients receiving long-term diuretic therapy and 17 hypertensive patients not taking diuretics, Morrow and Grimsley ³⁷⁴ observed that, in general, long-term diuretic therapy (>6 months) is associated with a significant increase in serum Hcy concentration and a significant decrease in RBC folate concentration. In 2005, Forman et al. ²⁶⁶ found that higher total folate intake was associated with a decreased risk of incident hypertension, particularly in younger women.

Reports

Case reports in the literature describe patients, particularly with cirrhosis or otherwise-compromised liver function, who developed megaloblastic anemia while being treated with triamterene, most often at higher doses (150-600 mg/day). ^114,375

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Patients receiving antihypertensive therapy using triamterene or related diuretics may benefit from the Hcy-lowering effects of folic acid, particularly if they have a history of, or significant risk factors for, inadequate folate intake, nutrient depletion, or hyperhomocysteinemia. Such concomitant nutrient support may be prudent, even though evidence indicates that triamterene at typical doses is not likely to affect folate status to a clinically significant degree in most patients. Folate supplementation during (or before) pregnancy is essential, and an increased dose may be warranted in women treated with triamterene; other treatment options might also need to be considered.

Even though the research thus far indicates adverse effects from triamterene in patients with folate deficiency, it is important to note that the diet of a significant portion of the population in the United States, Canada, the United Kingdom, and similar settings does not provide the recommended levels of folate. Assessment of tissue folate and plasma tHcy levels, within the context of the individual patient's risk factors including (e.g., diet, family history, genomic polymorphisms), is essential to shaping a customized and evolving integrative strategy for prevention and treatment of cardiovascular disease.

A therapeutic strategy incorporating coadministration of folic acid might require using 5-MTHF, the vitamin's activated form, such as folinic acid, in some patients, because triamterene interferes with the vitamin's activation, thus rendering common folic acid supplements potentially ineffective. Research is lacking to confirm or disprove this possibility.

	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, with Professional Management
	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management
	Prevention or Reduction of Drug Adverse Effect
	Bimodal or Variable Interaction, with Professional Management
	Potential or Theoretical Adverse Interaction of Uncertain Severity

Emerging to Consensus

Effect and Mechanism of Action

Trimethoprim and sulfamethoxazole (cotrimoxazole) interfere with the bacterial biosynthesis of folic acid by inhibiting tetrahydrofolate synthesis. ³⁷⁶ Trimethoprim acts as folate antagonist by inhibiting dihydrofolate reductase, which is necessary to converting unreduced dietary folates into tetrahydrofolates, the biologically active form. ^377,378 It is generally considered that trimethoprim inhibits the bacterial enzyme more efficiently than the human enzyme (sensitivity of bacterial enzyme 10000-fold > mammalian), and therefore the drug theoretically has only a minimal risk of adverse effects on biosynthesis of folic acid in humans. However, the risk of folate depletion and inhibition of granulopoiesis can be significant with high-dose or prolonged use, presumably more so in the presence of folate deficiency; neutropenia may result. Sulfamethoxazole and other sulfonamides interfere with folate by competitively displacing PABA from its binding site on dihydropteroate synthase, the enzyme that catalyzes a key step in the biosynthesis of folic acid. ³⁷⁹ Teratogenicity and macrocytic anemia are known adverse effects associated with cotrimoxazoleinduced folate deficiency.

Concomitant intake of folic acid at high doses could theoretically decrease efficacy of trimethoprim and sulfamethoxazole because of antagonistic effects. Coadministration of 5-methyltetrahydrofolate (5-MTHF), such as folinic acid (leucovorin calcium), instead of folic acid, is usually appropriate given the inhibition of dihydrofolate reductase by the antibiotics.

Research

Sulfamethoxazole and trimethoprim are known inhibitors of tetrahydrofolate synthesis and may partially deplete reduced folate levels. ^376,377 Furthermore, folic acid deficiency increases risks of toxicity from these agents. This interaction is widely acknowledged. Trimethoprim-sulfamethoxazole (TMP-SMX) is associated with folic acid deficiency anemia, but the incidence of this adverse effect is generally believed to be rare. Overall, consensus has yet to emerge as to the frequency, severity, and circumstances of clinically significant events or management of potential interference between trimethoprim and folic acid.

Kahn et al. ³⁷⁷ found that administration of trimethoprim (1 g/day) for more than 14 days appears to impair folate utilization to some extent, which may lead to hematological changes reversible with folic acid (400 µg/day). Bjornson et al. ³⁸⁰ conducted two linked studies investigating the antifolate action contributing to the neutropenia occasionally observed in patients treated with TMP-SMX. First, they administered TMP-SMX to 12 healthy adults and observed that the “number of circulating granulocytes and granulocyte progenitors was not significantly altered by a 5-day course of therapy.” However, they conducted experiments that simulated the in vivo condition of folate deficiency to investigate the antifolate action of these drugs on circulating granulocyte precursors (CFU-C) from normal donors and the mechanism of inhibition on granulopoiesis. Trimethoprim (8 µg/mL) resulted in a 47% decrease in the total number of colonies, whereas the combination of 8 µg/mL trimethoprim and 40 µg/mL sulfamethoxazole resulted in a 52% decrease in the number of colonies. In both situations, adding folinic acid to the culture prevented this inhibitory effect. In contrast, sulfamethoxazole (40 µg/mL) alone exerted “no discernible effect on granulopoiesis.” ³⁸⁰

In a study of 12 AIDS/HIV patients with or suspected of Pneumocystis cariniipneumonia, Bygbjerg et al. ³⁸¹ found that neither folic acid nor folinic acid reversed cotrimoxazole-induced cytopenia. They concluded, however, that although “routine prescription of folinic acid is not recommended,” supplementation with folic acid is inexpensive and “may be beneficial and should be prescribed.” Subsequently, Safrin et al. ³⁸² reported that coadministration of folinic acid with TMP-SMX for P. cariniipneumonia in AIDS patients is associated with an increased risk of therapeutic failure and decreased survival rate.

No evidence has appeared to support the proposition that administration of folic acid or an activated 5-MTHF might significantly impair the therapeutic activity of trimethoprim or sulfamethoxazole. It is now generally accepted that concomitant folic acid, in typical doses, does not interfere with the antibacterial activity of trimethoprim or TMP-SMX. ^383,384

Reports

Numerous case reports have described “neutropenia developing during even brief periods of oral therapy, particularly in individuals with either folate deficiency or increased folate requirements.” ³⁸⁰

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing trimethoprim and sulfamethoxazole, alone or in combination, should be aware that these agents may impair folate metabolism to a clinically significant extent. Concomitant folate may prevent or reverse adverse effects on folate activity and hematopoietic processes but generally is not necessary unless the patient has a preexisting folate deficiency, increased folate requirements, or otherwise-compromised folate status. Trimethoprim and TMP-SMX should be prescribed with caution in patients with known or potential folic acid deficiency; close supervision and regular monitoring of folate status are warranted.

Although some researchers and clinicians suggest that administration of folinic acid (leucovorin calcium) may be necessary to achieve such effects, because of drug-induced inhibition of dihydrofolate reductase, others have found that folic acid can usually achieve a therapeutic response. Pharmacogenomic variants related to folate metabolic pathways may also influence which form is required. Other forms of 5-methyltetrahydrofolate, such as 6(S) 5-MTHF ( L-methyl folate or Metafolin), would be expected to be equally efficacious.

Many authorities caution against use of trimethoprim and sulfamethoxazole during pregnancy. Concomitant folic acid becomes imperative if such medications are necessary during pregnancy, with a dose of at least 800 µg/day being appropriate.

	Drug-Induced Adverse Effect on Nutrient Function, Coadministration Therapeutic, with Professional Management
	Drug-Induced Nutrient Depletion, Supplementation Therapeutic, with Professional Management
	Prevention or Reduction of Drug Adverse Effect

Consensus

Effect and Mechanism of Action

Hematological toxicity is the most common adverse effect related to long-term administration of zidovudine (AZT), with macrocytosis developing in a large majority of AZT-treated subjects, despite folate and vitamin B ¹² supplementation. The macrocytosis is caused by AZT interfering with DNA replication in bone marrow RBC precursors. As a nucleoside analog, AZT interferes with HIV DNA production by reverse transcriptase, but also with non-HIV DNA as well. Folate and B ¹² deficiency leads to RBC macrocytosis, also by interfering with DNA synthesis, but based on deficiency versus toxicity. Consequently, administration of folate/B ¹² may fail to ameliorate AZT's hematological toxicity.

Research

In a rodent model using CBA/Ca mice, Cronkite et al. ³⁸⁵ found that “higher doses of folate given daily” resulted in partial amelioration of AZT-induced macrocytic anemia. A B ¹² /folate regimen was ineffectual.

In several placebo-controlled studies, macrocytosis, anemia, and granulocytopenia were the most significant adverse effects associated with zidovudine use, especially among patients with advanced, symptomatic HIV disease. Significant anemia most often occurred after 4 to 6 weeks of therapy and in many cases required dose adjustment, discontinuation of zidovudine, or blood transfusions. ³⁸⁶ In 2002, Romanelli et al. ³⁸⁷ conducted a retrospective chart review in an outpatient HIV clinic and concluded that “macrocytosis may be useful in assessing adherence to zidovudine-containing antiretroviral regimens.”

Manfredi et al. ³⁸⁸ investigated the kinetics of modifications of some hematological parameters of erythroid series in 65 patients with HIV infection treated with AZT for a mean duration of 7.6 months and correlated the observed evolution of these laboratory changes with the onset of severe anemia. They reported “no correlation between an elevated mean corpuscular volume and the development of severe anaemia (Hb less than or equal to 9 g/dL) in an individual patient; a fall in the reticulocyte count appears to be the earliest peripheral blood sign of the development of bone marrow toxicity.”

In 1993, Snower and Weil ³⁸⁹ studied 100 consecutive inpatients in a large metropolitan urban hospital with mean corpuscular volumes greater than 110 fL. Of these, 44% were AIDS patients receiving zidovudine, 19% were alcoholic patients, and 12% had malignant neoplasms. Only 3% were folate deficient and 4% vitamin B ¹² deficient by conventional measures. The authors concluded that “zidovudine has become the most common cause of macrocytosis in the hospitalized urban patient population,” and “vitamin B ¹² and folate deficiencies have decreased in proportion.”

However, in a prospective, randomized study involving 60 HIV-infected patients receiving zidovudine, Falguera et al. ³⁹⁰ compared hematological toxicity of either ZDV (AZT, 500 mg daily) alone or in combination with folinic acid (15 mg daily) and intramascular vitamin B ¹² (1000 µg monthly). During the study, vitamin B ¹² and folate levels were significantly higher in vitamin-treated patients, but no differences in hemoglobin, hematocrit, mean corpuscular volume, or white cell, neutrophil, or platelet count were observed between groups at 3, 6, 9, and 12 months. Moreover, they observed “severe hematologic toxicity” in four zidovudine-only patients and seven assigned to the vitamin-treated group. They reported “no correlation between vitamin B ¹² or folate levels and development of myelosuppression.” The authors concluded that coadministration of vitamin B ¹² and folinic acid with AZT therapy “does not seem useful in preventing or reducing ZDV-induced myelotoxicity in the overall treated population, although a beneficial effect in certain subgroups of patients cannot be excluded.” ³⁹⁰

Nutritional Therapeutics, Clinical Concerns, and Adaptations

Physicians prescribing zidovudine/AZT are advised to monitor closely the folate and vitamin B ¹² status of patients, using sensitive indicators capable of accurately assessing hematological and tissue levels of these vitamins and their functional surrogates, such as homocysteine and methylmalonate. Concomitant administration of folic acid (or 5-MTHF) and B ¹² may be appropriate to prevent or reverse adverse effects, with prophylactic measures generally being prudent in patients with a history of folate deficiency, compromised nutritional status, or other risk factors for susceptibility. However, clinical experience and research indicate that such nutrient support is often inadequate in reducing macrocytosis and marrow suppression in many patients, and that modification of the drug regimen is often necessary.

Acyclovir (Zovirax)

Acyclovir is a synthetic purine nucleoside analog that achieves its antiviral activity by acting as a purine antagonist, and it is known to induce macrocytic nonmegaloblastic anemia. The mechanism of interaction with folic acid, when it occurs, appears to be direct bone marrow toxicity, rather than being mediated through a folate interaction. However, concomitant folate deficiency would very likely compound any drug toxicity and should therefore be avoided.

Close monitoring of folate status through sensitive indicators is prudent, especially in patients on long-term acyclovir therapy who have a history of folate deficiency, compromised nutritional status, or other risk factors for susceptibility.

Antibiotics

See also individual agents or classes.

Along with the serious issue of multidrug antibiotic resistance, the loss or impairment of endogenous production of B vitamins, including folate, is one of the most important adverse effects resulting from a substantial course of antibiotics, by significantly damaging or destroying the symbiotic bacterial flora of the intestinal microbiota. Acidophilus,bifidobacteria, and other enteral bacteria manufacture folic acid and other B vitamins, such as niacin, biotin, and vitamin B ⁶ . ^391-401

The effects of antibiotics as a broad grouping of agents and drug classes on folate status is more accurately described as “unresearched” rather than unproven. Although knowledge and appreciation of the manifold functions of healthy bacteria have grown exponentially in recent years, the full clinical significance is not yet understood. Continued research into the systemic long-term effects of broad-spectrum antimicrobials is warranted, with implications on the functions and activity of folic acid deserving special attention.

Concomitant or subsequent administration of folic acid, vitamin B ¹² , and large doses of vigorous variegated probiotic flora provides a safe and inexpensive means of supporting healthy gut ecology and nutrient metabolism to prevent or correct direct and indirect adverse effects from antibiotic therapy, particularly in high doses or with repeated or long-term courses.

Beta-1-adrenergic blocking agents (beta-1 antagonists):Acebutolol (Sectral), atenolol (Tenormin); combination drugs: atenolol and chlorthalidone (Co-Tendione, Tenoretic), atenolol and nifedipine (Beta-Adalat, Tenif); betaxolol (Kerlone), bisoprolol (Zebeta), carteolol (Cartrol), esmolol (Brevibloc), labetalol (Normodyne, Trandate), metoprolol (Lopressor, Toprol XL); combination drug: metoprolol and hydrochlorothiazide (Lopressor HCT); nadolol (Corgard), nebivolol (Nebilet), oxprenolol (Trasicor), penbutolol (Levatol), pindolol (Visken), propranolol (Betachron, Inderal LA, Innopran XL, Inderal); combination drug: propranolol and bendrofluazide (Inderex); sotalol (Betapace, Betapace AF, Sorine), timolol (Blocadren).

Similar properties but evidence indicating no or reduced interaction effects:

Beta-adrenergic blocking eyedrops (ophthalmic forms):Betaxolol (Betoptic), carteolol (Cartrol, Ocupress), levobunolol (Betagan), metipranolol (OptiPranolol), timolol (Timoptic).

Calcium channel blockers:Amlodipine (Norvasc); combination drug: amlodipine and benazepril (Lotrel); bepridil (Bapadin, Vascor), diltiazem (Cardizem, Cardizem CD, Cardizem SR, Cartia XT, Dilacor XR, Diltia XT, Tiamate, Tiazac), felodipine (Plendil); combination drugs: felodipine and enalapril (Lexxel), felodipine and ramipril (Triapin); gallopamil (D600), isradipine (DynaCirc, DynaCirc CR), lercanidipine (Zanidip), nicardipine (Cardene, Cardene I.V., Cardene SR), nifedipine (Adalat, Adalat CC, Nifedical XL, Procardia, Procardia XL); combination drug: nifedipine and atenolol (Beta-Adalat, Tenif); nimodipine (Nimotop), nisoldipine (Sular), nitrendipine (Cardif, Nitrepin), verapamil (Calan, Calan SR, Covera-HS, Isoptin, Isoptin SR, Verelan, Verelan PM); combination drug: verapamil and trandolapril (Tarka).

Folate is essential for the metabolism of the atherogenic amino acid homocysteine (Hcy). The reduction of plasma and erythrocyte folate concentrations is also associated with a moderate hyperhomocysteinemia. Moderate hyperhomocysteinemia is an independent risk factor for cardiovascular disease that may be causal. Numerous studies have confirmed a strong association between lower folate levels and elevated Hcy and the efficacy of enhanced folate intake in the reduction of Hcy levels. ^402-417

The coadministration of folic acid with a beta blocker or calcium channel blocker may provide a synergistic effect in an integrative approach to prevention and treatment of cardiovascular disease involving atherosclerosis, especially coronary artery disease. For example, Landgren et al. ⁴¹⁸ studied the effect on plasma Hcy of 6 weeks’ treatment with daily oral folic acid doses of 2.5 or 10 mg, compared with no treatment, in patients with a recent history of myocardial infarction (MI). Folic acid lowered plasma Hcy in all but 2 of 33 treated patients, with no difference between the effect of 2.5 and 10 mg of folic acid. In the untreated group, plasma Hcy increased in the post-MI period. Thus far, no clinical trials are available that specifically investigate the efficacy of an integrative approach combining beta blockers with nutrients such as folic acid. Such research is warranted.

Several calcium channel blockers are known to produce “clinically and histologically similar gingival enlargements in certain susceptible patients.” ⁴¹⁹ Disturbances in folate uptake are among the factors contributing to such drug-induced adverse effects. As with other drugs, the coadministration of folic acid, prophylactically or in response to symptoms, may play a role in preventing and correcting these events.

Supplementation with folic acid could lower Hcy levels and thereby reduce the risk of the cardiovascular conditions for which these medications are usually prescribed on a systemic basis. Although folic acid is essentially nontoxic, physician supervision is appropriate when introducing any new elements into the therapeutic regimen. A moderate supplemental dose of folic acid is usually about 400 µg/day, in the form of a folic acid supplement or as part of a multivitamin formula. These levels can also be obtained through a diet rich in beets, leafy green vegetables, beans, citrus, meat, and wheat germ. A higher intake level, in the range of 650 to 800 µg or greater, may be more efficacious in individuals with preexisting cardiovascular disease, a significant family history, less responsive hyperhomocysteinemia, or other risk factors. Furthermore, enhanced intake of vitamins B ⁶ and B ¹² , as well as betaine, is also essential because these nutrients work with folate to metabolize homocysteine.

Betamethasone (Celestone), cortisone (Cortone), dexamethasone (Decadron), fludrocortisone (Florinef), hydrocortisone (Cortef), methylprednisolone (Medrol) prednisolone (Delta-Cortef, Orapred, Pediapred, Prelone), prednisone (Deltasone, Liquid Pred, Meticorten, Orasone), triamcinolone (Aristocort).

Similar properties but evidence lacking for extrapolation: Inhaled or topical corticosteroids.

Oral corticosteroids, particularly when administered for extended periods or at high dosage levels, can both decrease the activity and effects of folic acid and cause depletion of folate. Such drug-induced adverse effects on folate status may contribute to the hyperhomocysteinemia observed in some patients with autoimmune diseases, such as Crohn's disease and systemic lupus erythematosus (SLE, lupus), undergoing long-term steroid therapy. ^420,421 Further research through well-designed clinical trials is warranted.

Physicians prescribing extended courses of oral corticosteroids are advised to monitor all major folate and Hcy levels in these patients. Pending substantive research through clinical trials, coadministration of folic acid, 800 µg/day, can provide a safe and potentially effective means of compensating for drug-related interference and depletion effects and can support clinical strategies toward reducing cardiovascular risk. The probability that inhaled or topical corticosteroids might cause such adverse effects is low or nonexistent, and reports or warnings are lacking in the scientific literature.

Cycloserine (Seromycin).

For decades researchers have reported that cycloserine may interfere with the absorption and activity of folic acid (as well as of vitamins B ⁶ and B ¹² ). ^171,422 Case reports of folate deficiency induced by antitubercular drugs, including cycloserine, were published in the 1960s. ²¹¹ Well-designed clinical trials are lacking to confirm these preliminary and anecdotal findings, assess their clinical implications, and determine whether folic acid coadministration would effectively counter such adverse effects without impairing the therapeutic activity of the medication. Such research may be warranted. Pending further studies, coadministration of folic acid and vitamin B ¹² may be prudent with close supervision and regular monitoring.

Fluorouracil (5-FU; Adrucil, Efudex, Efudix, Fluoroplex).

See also Antifolates and Related Antimetabolites.

Folinic acid (leucovorin or Leukovorin) is a form of 5-MTHF often administered in conventional oncology care, particularly to treat metastatic colorectal cancer, enhancing the binding affinity of 5-FU to its target enzyme, thymidylate synthase (TS). In breast and other cancers, for which 5-FU is used as part of combination chemotherapy (e.g., CMF, platinum/5-FU), leucovorin is generally not used because of its increased toxicity in this context. However, leucovorin has continued to be used with 5-FU in the emerging combination chemotherapies for gastrointestinal (GI) cancers (e.g., with oxaliplatin, irinotecan). Evidence is mixed as to whether polymorphisms in the TS and dihydropyrimidine dehydrogenase (DPD) genes contribute to interpatient variability in 5-FU pharmacokinetics, response, and toxicity, although significant DPD deficiency is a well-established cause of life-threatening 5-FU toxicity. ^423,424

In 1995, Mainwaring and Grygiel ⁴²⁵ published case reports describing severe fluorouracil toxicity in two patients coincident with taking multivitamins containing folic acid. One patient, a woman with carcinoma of the rectum, was treated with intravenous fluorouracil (500 mg/m ² ) daily for 5 days, commencing a month after surgery. She was admitted at the end of the chemotherapy exhibiting numerous signs interpreted as fluorouracil toxicity, including anorexia, severe mouth ulcerations, bloody diarrhea, and vaginal bleeding. An inventory of her oral intake revealed that she was taking 5 mg folic acid within a B-complex multivitamin, as well as loperamide, sulfasalazine, hormone replacement therapy (HRT), and vitamins K and B ¹² . A month later, when chemotherapy was resumed after discontinuation of folic acid, she tolerated the treatment well, and signs of toxicity were absent. Similarly, the second patient, a man, experienced severe mouth ulceration and bloody diarrhea 2 days after starting treatment with fluorouracil for colon cancer. Discontinuation of his daily multivitamin preparation, containing 500 µg folic acid, allowed resumption of 5-FU with no such adverse effects during subsequent courses at the same dosage level. Apparently, the elevated folate levels caused by supplementation had increased the inhibition of thymidine synthesis by fluorouracil and increased the toxicity of the chemotherapeutic agent. Thus the adverse reaction in these cases resulted more from shortcomings in physician-patient communication and lack of supervision than from an irresolvable incompatibility, especially because a 5-MTHF agent such as folinic acid is much more potent than folic acid.

Although these reports do not meet the full standards of qualification, the observed events are consistent with the effects of folinic acid. Patients undergoing chemotherapy with 5-FU should be advised to avoid folic acid intake, and supplements should be inspected for its presence; a trusting therapeutic relationship and frank communication are necessary to obtain full disclosure from many patients using nutritional supplements. Although use of folic acid in the form of leucovorin or other L-methyl folates may be plausible, research on coadministration in such cases is lacking and may be warranted. Close supervision and regular monitoring would be essential in any such application, as indicated by the risks of self-administration detailed in these case reports.

Bumetanide (Bumex), ethacrynic acid (Edecrin), furosemide (Lasix), torsemide (Demadex).

See also Triamterene and Related Potassium-Sparing Diuretics.

Decreased folic acid levels and increased Hcy levels are associated with long-term furosemide therapy for hypertension. ³⁷⁴ Higher total folate intake is associated with a decreased Hcy levels and decreased risk of incident hypertension, particularly in younger women. ^266,320,426 Conversely, elevated plasma Hcy levels are associated with increased risk of atherosclerosis and cardiovascular disease. ^402,427-430

In general, patients receiving antihypertensive therapy using furosemide or related loop diuretics are likely to benefit from the Hcy-lowering effects of folic acid and vitamin B ¹² , as well as concomitant magnesium, coenzyme Q10, and mixed tocopherols. Assessment of the individual patient's risk factors, including diet, family history, and genomic polymorphisms, is essential to crafting a customized and evolving integrative strategy for prevention and treatment of cardiovascular disease.

Coadministration of folic acid may be prudent, safe, and inexpensive but has not been specifically investigated. Well-designed and adequately powered clinical trials are warranted.

Conjugated equine estrogens and medroxyprogesterone (Premelle cycle 5, Prempro); medroxyprogesterone, oral (Cycrin, Provera); medroxyprogesterone, injection (depot medroxyprogesterone acetate, DMPA; Depo-Provera, Depo-subQ Provera 104); progestin and estrogen injectable: estradiol cypionate and medroxyprogesterone acetate (Cyclofem, Lunelle).

See also Oral Contraceptives.

In a 1-year study of predominantly malnourished women from two urban centres in India (Bombay/Mumbai and Hyderabad) and one rural center in Thailand (Chiang Mai), Joshi et al. ⁴³¹ found that 3-month injectable depot medroxyprogesterone acetate (DMPA) used for contraception was associated with increased blood folate and serum vitamin A. The clinical implications of these findings are unclear, and further research is warranted.

Raltitrexed (ZD-1694; Tomudex).

See also Antifolates and Related Antimetabolites.

Raltitrexed is a quinazoline folate analog indicated in the treatment of advanced colorectal cancer. It causes DNA fragmentation and cell death, selectively inhibiting TS and thereby interfering with the de novo synthesis of thymidine triphosphate (TTP) and DNA synthesis. The manufacturer and some researchers have cautioned that concomitant folic acid may interfere with the action and reduce the efficacy of raltitrexed and recommended that folic acid intake be avoided immediately before or during raltitrexed administration. ^432-434 Coadministration of leucovorin is similarly contraindicated. These interactions have been proposed on theoretical grounds and have not been confirmed by clinical trials or systematic review of qualified case reports. Raltitrexed is contraindicated during pregnancy and for at least 6 months after discontinuation of treatment if either partner is receiving raltitrexed. ⁴³⁴

Pemetrexed (Alimta), a similar drug, has shown no decrease in efficacy but a significant decrease in toxicity when coadministered with folate and vitamin B ¹² . Thus the earlier antifolates discussion may be relevant in extrapolating speculative approaches to the interactions involving folate and raltitrexed.

Bendroflumethiazide (bendrofluazide; Naturetin); combination drug: bendrofluazide and propranolol (Inderex); benzthiazide (Exna), chlorothiazide (Diuril), chlorthalidone (Hygroton), cyclopenthiazide (Navidrex); combination drug: cyclopenthiazide and oxprenolol hydrochloride (Trasidrex); hydrochlorothiazide (Aquazide, Esidrix, Ezide, Hydrocot, HydroDiuril, Microzide, Oretic); combination drugs: hydrochlorothiazide and amiloride (Moduretic); hydrochlorothiazide and captopril (Acezide, Capto-Co, Captozide, Co-Zidocapt); hydrochlorothiazide and enalapril (Vaseretic); hydrochlorothiazide and lisinopril (Prinzide, Zestoretic); hydrochlorothiazide and losartan (Hyzaar); hydrochlorothiazide and metoprolol (Lopressor HCT); hydrochlorothiazide and spironolactone (Aldactazide); hydrochlorothiazide and triamterene (Dyazide, Maxzide); hydroflumethiazide (Diucardin), methyclothiazide (Enduron), metolazone (Zaroxolyn, Mykrox), polythiazide (Renese), quinethazone (Hydromox), trichlormethiazide (Naqua).

See also Furosemide and Related Loop Diuretics and Triamterene and Related Potassium-Sparing Diuretics.

Some derivative sources have suggested that coadministration of folic acid with thiazide diuretics could reduce adverse drug effects and enhance the efficacy of the broader therapeutic aims. Specific evidence is lacking to substantiate such interactions. However, patients receiving thiazide therapy are likely to benefit from the homocysteine-lowering effects of folic acid and vitamin B ¹² , as well as concomitant magnesium, coenzyme Q10, and mixed tocopherols. Assessment of the individual patient's risk factors, including diet, family history, and genomic polymorphisms, is essential to shaping a customized and evolving integrative strategy for prevention and treatment of cardiovascular disease.

Vitamin B ² (riboflavin); vitamin B ⁶ (pyridoxine); vitamin B ¹² (cobalamin).

The B vitamins work synergistically, so adequate and proportionate amounts of all B vitamins need to be available for optimal functioning. Deficiency (or excess) of any single nutrient can lead to abnormalities in the metabolism, interrelationships, and activity of one or more of the other B vitamins. In particular, vitamins B ² , B ⁶ , and B ¹² work with folate in maintaining healthy homocysteine (Hcy) levels. ^417,435,436 Riboflavin (B ² ) is the precursor for FAD, the cofactor for methylenetetrahydrofolate reductase (MTHFR). ^437,438 For example, Schnyder et al. ⁴³⁹ found that a combination of folate (1 mg), vitamin B ¹² (400 µg), and B ⁶ (10 mg) significantly reduces Hcy levels and decreases the rate of restenosis after coronary angioplasty. A synergy between vitamin D and mecobalamin (B ¹² ) appears to play a preventive role in risk of hip fracture among stroke patients, with Hcy as a predictive factor. ^440,441 Combinations of these nutrients are used in health optimization, disease prevention, and therapeutic interventions related to a wide range of body systems and medical conditions, including bronchial dysplasia in smokers, chronic fatigue, and vitiligo.

The emergent trend in the scientific research and clinical practice among providers experienced in nutritional therapeutics suggests that it is important to match generous quantities of B ¹² with folate administration, especially in older people. Supplementing folic acid without B ¹² can stimulate systems that also use B ¹² and result in lower B ¹² levels. Assessment of B ¹² status and concomitant administration of B ¹² with folate are generally advisable to enhance physiological synergies and to prevent masking of B ¹² deficiency. Furthermore, recent research indicates that a fundamental reconfiguration of assessment standards and therapeutic strategy is necessary to achieve correction of serious or even mild deficiency states. Conventional guidelines have recommended folate doses in hundreds of micrograms and B ¹² in single-digit micrograms. However, a landmark study (2005) showed that once individuals become B ¹² -deficient (by MMA levels), they typically require 500 to 600 µg at least (i.e., >200 times the RDA) to correct mild vitamin B ¹² deficiency, particularly elderly patients. ²⁰ Thus, equivalent amounts of B ¹² are generally advisable with folate administration.

See Pancreatic Enzymes under Nutrient-Drug Interactions.

Vitamin C

Vitamin C plays a key role in the conversion of folic acid to its active form and helps to reduce folic acid excretion.

Zinc

An interaction between zinc and folic acid has often been suggested, at least partly because bioavailability of dietary folate is increased by the action of folate conjugase, a zinc-dependent enzyme. Therefore, low zinc intake or zinc deficiency could impair absorption of food pteroylpolyglutamates and decrease folate bioavailability. Conversely, some studies and many derivative sources have suggested that folic acid may reduce zinc absorption and impair zinc utilization in individuals, particularly with high folate doses in those with marginal zinc status. ^442-444 However, Butterworth and Tamura ⁴⁴⁵ reviewed the mixed findings in the research literature, as of 1989, and concluded that the “weight of current evidence favors the view that daily supplements of 5 to 15 mg folic acid do not have significant adverse effects on Zn nutriture in healthy nonpregnant subjects.” Subsequently, in a trial involving 12 men (age 20-34) fed low-zinc diets (3.5 mg/day), Kauwell et al. ⁴⁴⁶ found that administration of folic acid at 800 µg/day, a relatively high dose, for 25 days did not alter zinc status, nor did zinc intake impair folate utilization.

Coffee (Caffea arabica, Caffea canephora, Caffea robusta).

In a randomized, placebo-controlled study, Strandhagen et al. ⁴⁴⁷ found that administration of folic acid decreases the homocysteine-increasing effect normally associated with coffee prepared by the filter method.