Thyroglobulin and thyroid hormones in patients on long-term treatment with phenytoin, carbamazepine, and valproic acid.

Serum concentrations of total triiodothyronine (T3) and thyroxine (T4) as well as serum thyroid-stimulating hormone (TSH) and thyroglobulin (Tg) were measured in 24 patients with epilepsy taking anticonvulsants (either phenytoin, carbamazepine, or valproic acid as single treatment) and in a control group of 28 patients with scoliosis but without thyroid disease. The T4 as well as the TSH concentrations were depressed in patients on phenytoin or carbamazepine treatment. The T3 concentration was increased in the patients on carbamazepine or valproic acid treatment, whereas the Tg levels were unaffected by all three drugs. Thus, a slight depression of the TSH concentration within the normal range does not influence the Tg release. The lack of change in the Tg concentration also speaks against a direct effect of the antiepileptic drugs on the thyroid gland.