The U.S. Pharmacopeia (USP) is urging manufacturers outside the U.S. to adopt a new monograph for levothyroxine sodium, which tightens potency specifications.

    USP released the new monograph in January after the FDA announced the new specification. The requirement, which takes effect October 2009, specifies that the product’s potency be 95 percent to 105 percent throughout its shelf life. The potency range was tightened from a specification of 90 percent to 110 percent.

    The FDA revised the specification last year after evaluating stability data from all levothyroxine sodium products. It found variable stability profiles and shelf lives for different versions of the drug, a concern for patients who use the thyroid replacement therapy and may get prescription refills made by different manufacturers with different potencies.

    Although the new specification is well known by firms marketing in the U.S., firms producing levothyroxine sodium products to USP specifications in other countries may not be prepared for the new standard, Karen Russo, director of small molecules and monograph acquisition at USP, said.