Serum thyroid hormones and blood folic acid during monotherapy with carbamazepine or valproate

Studies investigating the influence of antiepileptic drugs on thyroid hormones usually have compared patients chronically treated with antiepileptic drugs to controls. To date, this type of designs has produced divergent results both with regard to individual drugs and individual thyroid hormones. The present study comprised 31 patients with newly diagnosed epilepsy, commencing treatment with either carbamazepine or valproate. T3, T4, FT4, FT3, rT3, TSH, T3 resin uptake and blood folic acid, were determined before and during antiepileptic monotherapy, thus making the patient his own control. During treatment with carbamazepine, a significant decrease in T4, FT4, FT3, rT3 and TBG was observed. Valproate caused a decrease in T4, FT4 and T3. Neither of the drugs caused any changes in blood folic acid concentrations or persistent increases in the TSH values. None of the patients developed overt symptoms of hypothyreoidism. Conceivable mechanisms underlying these hormonal changes are reviewed.