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Abbott must prove Synthroid's safety and efficacy to FDA

Synthroid (levothyroxine sodium, Abbott), a 42-year-old treatment for hypothyroidism, must now be proven to be safe and effective in order to stay on pharmacy shelves.

The Food & Drug Administration recently rejected a citizen petition from Knoll Pharmaceutical filed in 1997. The petition sought continued marketing approval for Synthroid without submitting clinical studies. Abbott last March acquired Knoll, which had bought Synthroid from Boots in 1995.

The FDA had found potency and stability problems with levothyroxine products as a class and told manufacturers they had to submit New Drug Applications with trial results or citizen petitions with supporting literature proving safety and efficacy. King Pharmaceuticals, which makes Levoxyl, and Watson Pharmaceuticals, which makes Unithroid, won FDA clearance via the NDA route.

In rejecting the petition for Synthroid, the FDA said it was difficult to prove its safety and efficacy because the "formula has been changed numerous times throughout its marketing history." The agency also cited a "long history of manufacturing problems" that indicated the drug "has not been reliably potent and stable." Most of the problems were before Knoll acquired Synthroid.

Abbott said on June 1 that it wanted "to assure patients, physicians, and pharmacists" that Synthroid, the third-most-prescribed drug in the United States, was safe and effective for its eight million users. The Illinois-based company said it would submit an NDA shortly. The deadline for approval is Aug. 14, but it is considered unlikely the FDA would take Synthroid off the market before acting on the NDA.

Just how levothyroxine products got on the market without formal FDA approval is not clear. The agency said there was the belief that they were pre-1938 drugs and not subject to the clinical testing of safety and efficacy requirements of later products.

The Gray Panthers, the activist senior citizen group, said if Abbott "cannot meet the FDA's safety standards, then Synthroid should be removed from the marketplace." The American Association of Clinical Endocrinologists said in response "this proposed action is extremely misguided and unwarranted."

In the meantime, community pharmacists are fielding many calls from concerned patients. Some have already received calls from physicians requesting them to switch their Synthroid patients to an FDA-approved product. Nonetheless, the response among the pharmacists contacted by Drug Topics is similar: "Don't panic." James Vasquez, R.Ph., pharmacy manager at Walgreens, Hillsdale, N.J., is reassuring his patients. He tells them about Synthroid's long, safe history and advises them "not to worry," because he is confident Abbott will receive FDA approval for the drug, ensuring its continued availability.

Michael F. Conlan/ Tammy Chernin, R.Ph.

 

Mike Conlan. Abbott must prove Synthroid's safety and efficacy to FDA. Drug Topics 2001;11:14.