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

D. S. Cooper, V. C. Saxe, M. Meskell, F. Maloof, E. C. Ridgway

Research output: Contribution to journalArticle

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 μg/ml in the normal subjects and 1.04 ± 0.1, 4.5 ± 0.7, and 7.1 ± 0.4 μg/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 < 0.001) and hyperthyroid patients (r = 0.83, P < 0.001). T3 and rT3 were measured serially over 24 h after single oral doses of 50, 200, and 300 mg PTU. In normal volunteers, serum T3 declined slightly but significantly after the 200- and 300-mg doses; an increase in rT3 was also noted, but the changes did not attain statistical significance. In the hyperthyroid patients, serum T3 fell from 501 ± 29 to 379 ± 27 ng/dl after 50 mg PTU (P < 0.001), from 433 ± 40 to 264 ± 18 ng/dl after 200 mg PTU (P < 0.001), and from 463 ± 40 to 335 ± 18 ng/dl after 300 mg PTU (P < 0.05). Serum rT3 rose after each dose: from 119 ± 12 to 131 ± 11 ng/dl (P = NS) after 50 mg PTU, from 113 ± 11 to 146 ± 12 ng/dl (P < 0.02) after 200 mg PTU, and from 111 ± 14 to 154 ± 20 ng/dl (P < 0.02) after 300 mg PTU. These data suggest that PTU dosage correlates with measurable effects of the drug on both intrathyroidal iodide organification and peripheral iodothyronine deiodination. The determination of serum PTU levels by RIA may be useful in optimizing antithyroid drug therapy in selected cases.

Original languageEnglish (US)
Pages (from-to)101-107
Number of pages7
JournalUnknown Journal
Volume54
Issue number1
DOIs
StatePublished - Jan 1 1982
Externally publishedYes

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Biochemistry
  • Endocrinology
  • Clinical Biochemistry
  • Biochemistry, medical

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