THE MODE OF ACTION OF ANTITHYROID DRUGS: RESULTS WITH TWO IN VITRO TESTS

Abstract

1. Two in vitro tests are described for measuring the inhibitory potency of antithyroid drugs on enzymic and non-enzymic oxidative iodination of protein; one, a milk enzymic iodination test, and the other an enzyme-free peroxide iodination test. 2. Five recognized antithyroid drugs have been tested: 2-thiouracil, 2-carbethoxythio-methyl-glyoxaline, potassium thiocyanate, resorcinol and sulphathiazole. By means of the milk enzymic test they could be ranged in order of potency, as indicated by the molar concentrations required for 50 % inhibition. They could also be separated into different types by the speed with which they pass from minimal to maximal inhibition with rising molar concentration. 3. With the enzyme-free peroxide test, thiouracil, but not resorcinol, was found to be inert; with the enzymic test, both were nearly equivalent in potency.