DETERMINATION OF THE RELATIVE ACTIVITIES OF ANTITHYROID COMPOUNDS IN MAN USING RADIOACTIVE IODINE1

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Abstract
Because of the difficulty in evaluating the potency of antithyroid compounds according to the response to treatment of patients with thyrotoxicosis, a new method for assay of these drugs in normal human subjects is presented. This method depends upon modification of a predictable pattern of accumulation of radioactive iodine by the thyroid gland as detected by a Geiger-Muller counter. Results of assay of 32 compounds in 90 subjects are given. The assay values are in most instances considerably different from those obtained by previous methods which depended upon the goitrogenic effects in animals such as the rat and the chick. There is much closer agreement between the results by this method and those obtained from clinical trials, though some discrepancy, real or apparent, still exists. By this method some of the more active compounds tested were found to have the following potencies. Thiouracil was used as the reference standard and assigned an activity of 1; 2-mer-captoimidazole (10); thiocarbamylthioglycollic acid (2.5); 2-thiohydantoin (2.5); 2-mercaptothiazoline (2.5); 2-aminothiazole (2.5); 6-methylthiouracil (2); thiobarbital (2); 2-mercapto-benzimidazole (2.5); 3-mercapto-l,2,4-triazole (2); 2-mercapto[long dash]5-amino-l,3,4-thiadiazole (2); 2-mercapto-4-methylthiazole (1); thiouracil (1); thiourea (1); 6-n-propyl-thiouracil (0.75).