Responding to concerns of duration-related weakening efficacy of levothyroxine sodium, indicated for the treatment of underactive thyroid glands and other thyroid conditions, the FDA is tightening the potency specifications of this drug to ensure it retains its potency over the entire shelf life. The FDA is mandating that medications containing levothyroxine sodium meet a potency specification ranging from 95% to 105% until they reach their expiration date. (The 105% upper limit is used to address analytical testing variability.)

"These medicines are vital to people taking thyroid replacement or suppression therapies," said Janet Woodcock, MD, acting director of the FDA's Center for Drug Evaluation and Research. "Tightening the potency specifications will ensure that the most vulnerable patients taking thyroid medication will receive the appropriate level of drug therapy needed for their condition."