Carbamazepine does not interact with thyroid hormone receptors in human fibroblasts

Treatment with carbamazepine is associated with decreases in the serum levels of thyroxine, free thyroxine and triiodothyronine without alteration in the thyrotropin. Therefore, the mechanism of action of carbamazepine on the hypothalamo-pituitary thyroid axis may involve interference in the feedback regulation of secretion of thyroid hormone by interacting with the pituitary thyroid hormone receptors. The present authors investigated the ability of carbamazepine to compete with the nuclear uptake of [125I]triiodothyronine in dispersed intact cultured fibroblasts of human skin. Carbamazepine did not inhibit the specific binding of [125I]triiodothyronine into the nuclei of intact fibroblasts, suggesting that it does not interact with thyroid hormone receptors in this system and is unlikely to do so in vivo.