The effects of long-term antithyroid drug treatment on serum reverse T3 in patients with Graves' disease.

The effects of long-term treatment with antithyroid drugs, carbimazole (CMI) or propylthiouracil (PTU), on serum reverse triiodothyronine (rT3) levels were studied in 23 patients with Graves' disease. Nineteen patients were given CMI and four PTU for a minimum of six months. After one month of treatment the serum levels of thyroxine (T4), triiodothyronine (T3) and rT3 had normalized in both groups. When L-thyroxine was added to the regimens after two months of therapy, both serum T4 and rT3 levels increased, whereas serum T3 level continued to fall. The serum levels of rT3 seemed to be dependent on and followed the T4 levels so closely that determinations of rT3 in the medical management of patients with Graves' disease will be of little clinical use.