Endocrine Insider
October 11, 2007

The U.S. Food and Drug Administration (FDA) announced on October 3 that it is tightening the potency specifications for levothyroxine sodium (L-T4). The decision results from an FDA study of potency throughout shelf life of L-T4 products, which the agency undertook after The Endocrine Society and other interested organizations raised concerns about adverse events related to switching L-T4 products in patients. The agency’s decision is in line with the recommendations of a joint advisory committee that met last October to hear the study results. Society Past-President Leonard Wartofsky, MD, testified at the meeting, and the proceedings were reported in the October 6, 2006 issue of Endocrine Insider.

The ruling means FDA will soon mandate that L-T4 products must fall within 95-105 percent of the expected potency throughout the entire shelf life. The current allowable range is 90-110 percent. Manufacturers will have up to two years to comply with the new restriction.

The FDA’s recent efforts are a reasonable step to ensuring the safety of patients taking L-T4. However, the Society urges the agency to do more. Since 2005, The Endocrine Society, the American Association of Clinical Endocrinologists (AACE), and the American Thyroid Association (ATA) have been requesting that FDA reconsider its current system for determining bioequivalence of L-T4 products. Tightening of potency specifications will alleviate some, but not all, of the measured variability among L-T4 products, and it does nothing to address the flawed method by which FDA determines bioequivalence of the drugs. (For more information, see the joint statement by the Society, AACE, and ATA.)

The Society is encouraged by FDA’s attention to L-T4 products and will continue to advocate with FDA for the safety of patients taking levothyroxine.

Click here for more information from the FDA on its recent ruling: http://www.fda.gov/cder/drug/infopage/levothyroxine/default.htm.