Abstract
To investigate the variation in the thyroxine content of commercial thyroid preparations, thyroid tablets from 15 representative pharmaceutical firms were obtained in the open market and analyzed for total iodine, inorganic iodine and thyroxine. Harington and Randall 1 made a similar survey, and found in tablets “each equivalent to 5 grains of fresh thyroid gland”, a variation of about 600% in the thyroxine content, as estimated by the total iodine in the acid-insoluble fraction. However, recent work 2 , 3 , 4 suggests that absolute thyroxine values based on this method may be too high since after 4 hours' hydrolysis with N/1 NaOH the acid-insoluble fraction appears to consist of a heterogeneous mixture of free thyroxine and incompletely hydrolyzed polypeptides containing diiodotyrosine. It was therefore thought desirable to follow a procedure which we had found satisfactory for the iodine partition of pathological thyroid glands. 4 This is based on the Leland and Foster method for the estimation of thyroxine, 3 a modified Kendall method for the determination of total iodine 5 and aqueous extraction of the desiccated gland for estimation of inorganic iodine. All determinations were done in duplicate, the mean discrepancy between duplicates in the thyroxine determinations being 2.7%.
Fifteen different products were found to have the following thyroxine iodine contents, in terms of mg. per one grain table, .0099, .0124, .0187, .0226, .0257, .0260, .0270, .0280, .0291, .0305, .0312, .0323, .0325, .0329, .0355. The difference between the minimum and maximum values observed is .0256 mg., a variation of 259% with respect to the minimum figure.
The variations in the physiological activity of commercial thyroid preparations as indicated by biological assay 6 , 7 , 8 and in the thyroxine content as suggested by the data of Harington and Randall and ourselves, seem to be inconsistent with present therapeutic standards.
Get full access to this article
View all access options for this article.