A comparison of the effects of propylthiouracil and methimazol on circulating thyroid hormones and various measures of peripheral thyroid hormone effects in thyrotoxic patients

Two groups of patients with newly diagnosed thyrotoxicosis were treated with propylthiouracil (PTU) 400 mg every 6 h for 4 days followed by methimazol (MMI) 40 mg every 6 h for 4 days or by MMI for 4 days followed by PTU for 4 days. The shift from MMI to PTU induced a considerable decrease in serum T3 while shift from PTU to MMI led to an increase in serum T3. Serum T4 decreased gradually during the whole treatment period. The opposite variations in serum T3 were accompanied by similar opposite variations in basal metabolic rate (BMR) (P less than 0.001). Hence the rapid variations in serum T3 which can be induced by PTU in thyrotoxic patients, are followed by rapid alterations in the thyrotoxic state as evaluated by BMR.