Effect of chronic primidone treatment on folate-dependent one-carbon metabolism in the rat

Drug and environmental factors associated with adverse pregnancy outcomes. Part I: Antiepileptic drugs, contraceptives, smoking, and folate

OBJECTIVE

Part I of this review examines the relationship between antiepileptic drugs (AEDs) and pregnancy outcomes. Drug-induced folate deficiency and the role of AED metabolism are emphasized. Part II will discuss periconceptional folate supplementation for prevention of birth defects. Part III will discuss the mechanism of folate's protective effect, therapeutic recommendations, compliance, and cost.

DATA SOURCES

A MEDLINE search was conducted for journal articles published through December 1997. Additional sources were obtained from Current Contents and citations from the references obtained. Search terms included phenytoin, carbamazepine, phenobarbital, primidone, valproic acid, oral contraceptives, clomiphene, drug-induced abnormalities, spina bifida, anencephaly, neural tube defect, folate, folic acid, and folic acid deficiency.

STUDY SELECTION

Relevant animal and human studies examining the effects of AEDs, smoking, and oral contraceptives on folate status and pregnancy outcome are reviewed.

DATA EXTRACTION

Studies and case reports were interpreted. Data extracted included dosing, serum and red blood cell folate concentrations, teratogenicity of anticonvulsant medications, metabolism of AEDs and folate, and genetic susceptibility to AED-induced teratogenicity.

DATA SYNTHESIS

Low serum and red blood cell folate concentrations are associated with adverse pregnancy outcomes. Decreases in serum folate are seen with AEDs, oral contraceptives, and smoking. Since similar birth defects are observed with multiple AEDs, metabolism of aromatic AEDs to epoxide metabolites and genetic factors may play a role in teratogenesis.

CONCLUSIONS

Adequate prepregnancy planning is essential for women who have epilepsy. Women receiving folate-lowering drugs may be at increased risk of adverse pregnancy outcomes. Therefore, epileptic women contemplating pregnancy should be treated with the minimum number of folate-lowering drugs possible and receive folic acid supplementation.

Changes in hepatic folylpolyglutamate pattern in phenobarbitone-treated rats

Folate deficiency is a common unpleasant secondary effect of anticonvulsant therapy. In order to contribute to the knowledge of biochemical mechanisms leading to this condition, the effects of two i.p. high doses of phenobarbitone administered to the rat (acute treatment) on the distribution of hepatic folate derivatives have been studied. A significant decrease of unsubstituted tetrahydro- and dihydropteroylpentaglutamates and 5,10-methylenetetrahydropentaglutamates was observed. The hypothesis that a lower availability of NADPH, which is utilized for hydroxylation reactions in phenobarbitone metabolism, may limit folate reduction is proposed.

Chronic carbamazepine treatment in the rat: efficacy, toxicity, and effect on plasma and tissue folate concentrations

Folate depletion has often been a problem in chronic antiepileptic drug (AED) therapy. Carbamazepine (CBZ), a commonly used AED, has been implicated in some clinical studies. A rat model was developed to examine the effects of chronic CBZ treatment on folate concentrations in the rat. In the course of developing this model, a common vehicle, propylene glycol, by itself in high doses, was found to exhibit protective properties against induced seizures and inhibited weight gain. Seizures induced by hexafluorodiethyl ether (HFDE) were also found to be a more sensitive measure of protection by CBZ than seizures induced by maximal electroshock (MES). Oral administration of CBZ as an aqueous suspension every 8 h at a dose of 250 mg/kg was continuously protective against HFDE-induced seizures and was minimally toxic as measured by weight gain over 8 weeks of treatment. The CBZ levels measured in plasma and brain of these animals, however, were below those normally considered protective. This treatment with CBZ had no apparent adverse effect on folate concentrations in the rat, and, indeed, the folate concentration increased in liver after 6 weeks of treatment and in plasma at 8 weeks of treatment.