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Levothyroxine Q&A

Information for Patients about Synthroid, Levoxyl, Unithroid and Levothroid


Updated December 13, 2003

June, 2001 -- You may be hearing news reports regarding the thyroid medication Synthroid® and other brands of levothyroxine sodium, and so we've prepared this information for help you better understand the issue, and better prepare you to discuss the topic with your physician or healthcare provider.

Is Synthroid an FDA-approved Levothyroxine Product? Are Any Levothyroxine Products Currently Approved?

Synthroid is not FDA-approved as of June 13, 2001. Two products -- [link url=http://thyroid.about.com/library/weekly/aa052501a.htm]Levoxyl and [link url=http://thyroid.about.com/library/weekly/aa082400a.htm]Unithroid -- have gone through the FDA approval process, and received approval. Unithroid, a ten-year old product produced by Jerome Stevens and distributed by Watson Pharmaceuticals was approved in August of 2000, before the original FDA approval deadline. Levoxyl, manufactured by King, was approved in late May of 2001. Forest Pharmaceutical's product Levothroid has submitted a new drug application, which is still pending at the FDA.

Why Did the FDA Ask for "New Drug Approval" for Levothyroxine?

In 1997, the FDA called for all levothyroxine drugs to be classified as new drugs, and therefore that would require them to go through new drug application. This ruling was made because, according to the FDA, "no currently marketed orally administered levothyroxine sodium product has been shown to demonstrate consistent potency and stability and, thus, no currently marketed orally administered levothyroxine sodium product is generally recognized as safe and effective."

If These Drugs Weren't Safe and Effective, Why Were They on the Market?

Levothyroxine, a synthetic form of the thyroid drug thyroxine (or T4) had been "grandfathered" in as being of the same category of drugs as natural dessicated thyroid hormone derived from the glands of pigs. The natural product - Armour Thyroid -- had been on the market since the early 1900s, prior to the formation of the FDA. Armour Thyroid is still available for sale, and was not included in the FDA's call for new drug application and approval, and therefore does not need to apply. Another drug, liotrix, brand name Thyrolar, a synthetic combination of thyroid hormones thyroxine and triiodothyronine (T4 and T3), has received FDA approval.

Why Did the FDA Leave These Levothyroxine Drugs on the Market Instead of Pulling Them?

The FDA decided to issue to the call for new drug approval but not pull the drugs off the market because they determined that the risk of taking away levothyroxine from the millions of patients who depended on thyroid hormone was far greater than the risk of the problems with potency, stability, safety and effectiveness. Therefore, the products were allowed to remain legally on the market -- although not FDA-approved -- until the deadline for applications and approvals.

What Were the FDA Deadlines for Approval?

The original deadline was August 14, 2000 for submission and approval of new drug applications. According to the Federal Register, "After August 14, 2000, any orally administered drug product containing levothyroxine sodium, marketed on or before the date of this notice, that is introduced or delivered for introduction into interstate commerce without an approved application, unless found by FDA to be not subject to the new drug requirements of the act under a citizen petition submitted for that product, will be subject to regulatory action."

Synthroid chose to file a citizen petition requesting that FDA acknowledge that Synthroid is not subject to the requirements of an new drug application and could be given a legal designation, "generally recognized as safe and effective" (GRAS/E). Prior to this request, however, extensive "Freedom of Information Act" requests by Synthroid's manufacturer, along with other administrative issues, resulted in the FDA extending the deadline for submission one year, until August 14, 2001.

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