THE ANTITHYROID ACTION OF 5-IODOTHIOURAGIL, 6-METHYL-5-IODOTHIOURACIL, THIOCYTOSINE AND (Ca) 4-n-PROPYL-6-OXYPYRIMIDYL-2-MERCAPTOACETIC ACID*

Abstract

Forty courses of therapy with 5-iodo-2-thiouracil were admd. to 29 patients with thyrotoxicosis. The responses simulated qualitatively those following iodide therapy more than those which thiouracil produces. In 15 patients the maximal response occurred within 10 days and in 21, within 15 days. The individuals who had not become euthyroid within 15 days did not attain this state with further continuation of such therapy. Five patients who received iodothiouracil in prepn. for subtotal thyroidectomy experienced a smooth operative and post-operative course. The thyroid gland revealed a relatively good degree of involution. Iodothiouracil inhibited the uptake of radioiodine by the thyroid of rats slightly more than did an equimolar dose of thiouracil, but less than an equivalent amt. of iodine given as KI. 5-iodo-6-methyl-2-thiouracil, used in the treatment of 6 thyrotoxic patients, was much less effective than was its non-methylated analogue. (Ca)-4-n-propyl-6-oxypyrimidyl-2-mercaptoacetic acid was used in the treatment of 5 patients with thyrotoxicosis and thiocytosine was employed in 1 subject. No patient received significant benefit from either drug. Each compound was distinctly less active than was thiouracil in antagonizing the uptake of radioiodine in the thyroid by normal subjects who had received tracer doses of the isotope several hrs. previously. Thiocytosine exhibited essentially the same amt. of goitrogenesis in rats as did thiouracil. None of the patients experienced a toxic reaction to any of the compounds studied. The results with 5-iodothiouracil are sufficiently encouraging to warrant further testing of this compound and other similar iodinated ones in the prepn. of thyrotoxic patients for thyroidectomy. Comparisons of the effects of equimolar quantities of iodide and thiouracil should also be made.