FDA review may be limiting thyroxine supplies. (New Drug Applications Under Study).

WASHINGTON -- A Food and Drug Administration ruling may be limiting supplies of thyroxine preparations, according to a fact sheet released by the American Thyroid Association at its annual meeting.

In 1997, the FDA decided that a new review was needed to ensure the safety and efficacy of these products and required every manufacturer to file a New Drug Application for each agent.

Abbott Laboratories petitioned the FDA to "grandfather" its thyroxine preparation, Synthroid, and spare it from the New Drug Approval process. Two-thirds of the 13 million Americans who take thyroxine are prescribed Synthroid, the first such preparation to be branded more than 40 years ago. Synthroid is the third most commonly prescribed drug in the United States.

But the FDA rejected Abbott's petition in April and ruled in July that any manufacturer failing to submit a New Drug Application by August would have to remove its product from the market immediately.

The FDA also ruled that any manufacturer that filed its application by August but had not yet received approval would have to start phasing the product off the market.

The phase-out procedure called for reducing distribution by a set percentage every 3 months, so distribution would fall to 60% at 1 year and production would halt by 2 years.

King Pharmaceuticals, maker of Levoxyl, and Watson Pharmaceuticals, maker of Unithroid, secured FDA approval last year.