WASHINGTON (AP) -- The Food and Drug Administration on Wednesday laid out new guidelines for the testing of drug-coated stents, more than two years after safety concerns curtailed use of the devices.

The proposed guidelines posted to FDA's Web site recommend device makers conduct large, analytic studies of their stents both before and after they are submitted to FDA.

In its most rigorous recommendation, FDA said companies should be prepared to track patients for up to five years after their stents are approved to monitor blood clots, heart attack and other potentially fatal events. Such long-term studies can cost companies millions of dollars.

Stents are tiny, mesh-wire tubes that prop open arteries after they have been surgically cleared of fatty plaque. They quickly became a highly lucrative business, after companies began adding drug coatings to the devices in 2003 to prevent scar tissue from growing over the mesh-wire.

But after data suggested that the drug coatings may put patients at higher risk of blood clots, sales have plummeted to about $2 billion from a peak of $3.1 billion in 2005.

A series of studies in 2006 showed that months after they are implanted, stent coatings can increase the risk of life-threatening blood clots unless patients continue to take anti-clotting drugs. Medical societies urge patients to continue taking the drugs for at least a year after implantation.

FDA guidelines are not legally binding, but companies typically follow them to ensure approval of their devices. The agency will take comments on the proposed guidelines for four months before redrafting them and issuing final guidelines.

FDA has cleared three drug-coated stents: Boston Scientific Corp.'s Taxus, Medtronic Inc.'s Endeavor and Johnson & Johnson's Cypher.

About 650,000 patients in the U.S. have drug-coated stents.

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