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Mr. Erickson is director of professional affairs at Gallipot Inc.
A Closer Look at Thyroid USP
Thyroid USP (often 0.23%) and Armour Thyroid have been used interchangeably—Armour was the manufacturer of Thyroid Tablets; the powder, Thyroid USP, is another matter. When standards for potency were applied to the material formerly known as Desiccated Thyroid Glands USP (USP VIII), in the 1930s, the potency was measured in terms of combined iodine and the USP specified “…not less than 0.17% and not more than 0.23% of iodine in thyroid combination, …[t]he active constituent, [which] seems to be an organic combination of iodine, sometimes called thyroglobulin, for the iodine content of which the USP has fixed a standard and assay.” (Remington: The Science and Practice of Pharmacy. 7th ed.)
Thyroid (0.23%) USP recently has been in short supply— for current information about availability, please visit the manufacturer’s Web site www.armourthyroid.com.
Thyroid USP 32 (2009) provides levothyroxine sodium (T4) and l-triiodothyronine sodium (liothyronine, or T3), each not <90.0% and not >110.0% of the labeled amounts, calculated on the dried basis, and “...may contain a suitable diluent such as Lactose, Sodium Chloride, Starch, Sucrose, or Dextrose.” Thyroid Tablets USP contain not <90.0% and not >110.0% of the labeled amounts of levothyroxine and liothyronine, the labeled amounts being 38 mcg of levothyroxine and 9 mcg of liothyronine. This is a 4.22:1 ratio (4.22 parts of T4 to 1 part of T3).