Potency of United States Pharmacopeia Desiccated Thyroid Tablets as Determined by the Antigoitrogenic Assay in Rats

Abstract

Ten samples of USP desiccated thyroid, 2 from an investigator and 8 purchased on the open market across the nation, were tested for metabolic potency by the antigoitrogenic bioassay technique and for total iodine by the USP assay technique. Four of the 10 samples were found to be markedly off potency. Although all the tablets were found to conform to the specifications of the Pharmacopeia of the United States of America for the total iodine content, 4 were found to be so variable in potency that they were essentially useless or even potentially dangerous, if used according to their labeled potency. A small sampling such as reported, demonstrating a relatively high percentage of USP desiccated thyroid tablets to be of questionably standardized biological activity, suggests that thyroid substitution medication of variable potency may represent a common and widespread pharmaceutical problem in the United States.