Purpose: Antiepileptic drugs (AEDs) may affect serum thyroid hormone concentrations. This study aimed to evaluate thyroid function in men taking carbamazepine (CBZ), oxcarbazepine (OCBZ), or valproate (VPA) for epilepsy.
Methods: Ninety men with epilepsy (40 taking CBZ, 29 taking OCBZ, and 21 taking VPA monotherapy) and 25 control subjects participated in the study. After clinical examination, a blood sample for hormone, gamma-glutamyl-transferase (GGT) and antibody (ab) assays was obtained.
Results: Serum thyroxine (T4) and free thyroxine (FT4) concentrations were low in men taking CBZ or OCBZ. Forty-five percent of men taking CBZ and 24% of men taking OCBZ had serum T4 and/or FT4 levels below the reference range. However, no correlations were found between T4 or FT4 and GGT concentrations in men taking CBZ or OCBZ. Thirteen percent of men taking CBZ, 17% of men taking OCBZ, and 6% of control men had increased levels of thyroid peroxidase (TPO)-ab and/or thyroglobulin (TG)-ab, but these were not associated with altered serum thyroid hormone concentrations. Serum triiodothyronine and thyrotropin levels in men taking CBZ or OCBZ were normal. In men taking VPA, the concentrations of thyroid hormones, thyrotropin, and antithyroid ab were normal.
Conclusions: Serum thyroid hormone concentrations are low in CBZ- or OCBZ-treated men. However, these low levels do not seem to be due to liver enzyme induction or activation of immunologic mechanisms. Therefore, interference with hypothalamic regulation of thyroid function by CBZ and OCBZ seems possible. VPA does not have any significant effects on thyroid function.