Anticonvulsant medications such as phenytoin, carbamazepine and valproate reduce serum folate status. Individual studies have estimated an incidence of 1 5% folate deficiency in this group, compared with 2% for control groups (Froscher et al 1995). However, the figure may be as high as 97% with long-term phenytoin therapy (Rivey et al 1984). This may be due to increased use of folate in drug metabolism and/or decreased mucosal absorption (Berg et al 1992, Pelton et al 2000). Sometimes, folic acid supplements are recommended to avoid deficiency, but this requires close supervision to ensure drug efficacy is not substantially reduced (Rivey et al 1984).
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