THE INFLUENCE OF CARBAMAZEPINE ON THYROID HORMONES AND THYROXINE BINDING GLOBULIN IN HYPOTHYROID PATIENTS SUBSTITUTED WITH THYROXINE

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Abstract
Carbamazepine (CBZ) decreases the serum concentration of thyroid hormones. CBZ may increase the extra-thyroidal metabolism of thyroid hormones. To test this hypothesis CBZ was given to 9 hypothyroid patients substituted with thyroxine (T4). A significant decrease in serum concentrations of T4, calculated free T4 (FT4), triiodothyronine (T3) and calculated free T3 (FT3) was found after 3 wk of CBZ medication. The serum concentrations of TSH and the T4:T3 ratios were unaltered, while the serum concentrations of T4-binding globulin increased markedly in 8 of the 9 patients. These findings support the hypothesis of a CBZ induced increase in the extra-thyroidal metabolism of thyroid hormones.