Thyroid function in epileptic patients treated with carbamazepine

The effects of carbamazepine monotherapy on thyroid function were evaluated in patients with epilepsy. A prospective follow-up of 40 patients with recently diagnosed epilepsy was carried out to evaluate the short-term effects. Thirty-three patients receiving long-term carbamazepine therapy (average duration, 4.2 years) and 34 healthy control subjects were studied. Levels of serum thyroxine, free thyroxine, and thyroxine binding globulin were decreased after both 2 and 12 months of therapy with carbamazepine. Low serum thyroxine and free thyroxine concentrations were also found after long-term monotherapy with carbamazepine. Baseline thyrotropin did not change during carbamazepine therapy, but thyrotropin responses to thyrotropin-releasing hormone rose slightly. No correlation was found between serum carbamazepine and hormone concentrations. The results not only support previous suggestions that carbamazepine induces the hepatic clearance of thyroid hormones but also suggest that carbamazepine may have an inhibitory effect at the hypothalamic level.