Influence of anticonvulsant drugs on thyroid hormones in epileptic children.

Thyroid function tests were studied in epileptic children undergoing long-term anticonvulsive therapy with phenytoin, primidone or mephenytoin. Serum T4 was decreased in all three treated groups, serum T3 was diminished only in those treated with phenytoin or primidone. FT4 was also significantly decreased while serum TSH and TBG were not affected in the treated patients. The effect of anticonvulsant drugs on thyroid hormone catabolism and peripheral conversion of T4 seems to be important in these alterations.