Influence of long-term carbamazepine treatment on thyroid function.

We have studied the effects of carbamazepine on thyroid function in sixteen recently diagnosed epileptic children and thirteen epileptic children receiving long-term carbamazepine therapy and compared these findings with the thyroid function of thirteen healthy control subjects. Thyrotropin (TSH), triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3) and free thyroxine (FT4) serum levels were determined in both recently diagnosed but as yet untreated epileptic children and normal controls. These hormone levels were determined again after 2 months of treatment and 12 months of treatment in epileptic children. No statistically significant difference was found in the endocrine parameters of untreated epileptic children and the normal control group. After both 2 months and 12 months of carbamazepine therapy, serum levels of T4, FT4 and FT3 were found to be low, but the serum T3 concentration was unaffected. Baseline TSH levels were not changed during carbamazepine therapy either. Serum TSH levels increased rapidly after thyrotropin-releasing hormone stimulation in both the before and 12 months after carbamazepine treatment groups, but the response was higher in the 12 months treatment group. The findings of the present study suggest that accelerated hormone metabolism is responsible for hormonal changes found in patients treated with carbamazepine. Carbamazepine also had effects on the function of the hypothalamo-pituitary axis.