FDA acts to control thyroid drug potency

WASHINGTON, Oct. 3 (UPI) -- The U.S. Food and Drug Administration tightened its potency specifications for the thyroid drug levothyroxine sodium.

The new rules for the drug, which is used to treat underactive thyroid glands and other thyroid conditions, are designed to ensure it retains its potency during its entire shelf life.

Levothyroxine sodium products are used by more than 13 million patients. The drug is manufactured under the brand names Synthroid, Levoxyl, Levothroid and Unithroid.

The FDA is mandating levothyroxine sodium drug products meet a 95 percent to 105 percent potency specification until their expiration date. The shelf life is the length of time a drug can be stored before it degrades to unacceptable levels.

FDA officials said the 95 percent lower potency specification will ensure the drugs don't degrade by more than 5 percent of the labeled claim before their expiration date and the 105 percent upper specification addresses occasional analytical testing variability.

Currently, the products are allowed a potency range of 90 percent to 110 percent.