Acute effects of propylthiouracil (PTU) on thyroidal iodide organification and peripheral iodothyronine deiodination: correlation with serum PTU levels measured by radioimmunoassay.

Abstract

Propylthiouracil (PTU) levels in serum have been measured by RIA in five normal volunteers and four patients with untreated Graves' disease. Peak PTU levels after 50, 200, and 300 mg PTU were 0.91 ± 0.13, 2.9 ± 0.6, and 4.0 ± 0.6 jug/ml in the normal subjects and 1.04 ± 0.1, 4.5 ± 0.7, and 7.1 ± 0.4 jug/ml in the hyperthyroid patients, respectively. Peak PTU levels and PTU area under the curve were significantly greater at the 300-mg dose (P < 0.01) in the hyperthyroid patients compared to the normal subjects. The effect of PTU on iodide organification was assessed by perchlorate discharge testing. Both the normals and the hyperthyroid patients had normal basal perchlorate-dischargeable 123I. Four hours after an oral dose of PTU, the hyperthyroid patients had a greater percentage of perchlorate-dischargeable 123I than the euthyroid controls (+38 ± 5% vs. +13 ± 2% P < 0.02). There was a highly significant correlation between serum PTU levels and perchlorate-dischargeable iodide in both normals (r = 0.86; P...