FDA seeks more data on bloodthinner Plavix

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regulators are reviewing the effectiveness in some patients of the widely used blood thinner Plavix, made by Sanofi-Aventis SA and Bristol-Myers Squibb Co.

The move comes after several studies found the blockbuster drug did not work as well in certain people possibly because patients metabolized it differently depending on their genetic makeup or their other medications, the U.S. Food and Drug Administration said on Monday.
Sanofi and Bristol will conduct studies on genetic factors and drug interactions with Plavix, also known as clopidogrel bisulfate, the FDA said in a statement on its website. "This information should lead to a better understanding about how to optimize the use of clopidogrel," it said.
Laura Hortas, a spokeswoman for Bristol, said she had no details on how many studies the companies would need or how long they would take. The finding "will allow us to understand and characterize the factors that may influence this complex issue," she said on behalf of both companies.
While some reports have suggested a possible interaction that makes Plavix less effective, others have not found such an issue, the FDA said.
One type of medicine that is often prescribed for patients also taking Plavix are heartburn drugs such as AstraZeneca PLC's Nexium and Prilosec and other proton pump inhibitors, the agency said.
The FDA said doctors and patients should continue to use Plavix as directed until further information is available. Doctors should reevaluate the use of some heartburn drugs, including over-the-counter versions, in patients taking Plavix, the FDA added.
It is not clear what the FDA's so-called "early communication" will have on sales of Plavix, a top-earner for the two drugmakers that has seen its sales rise this year. In the first nine months of 2008 it brought in $4.1 billion compared to $3.4 billion in the same period of 2007.
Several companies, including Apotex Inc and Dr. Reddy's Laboratories, are seeking to make generic versions of Plavix, which loses its patent protections starting in 2011.
Shares of Sanofi closed down nearly 2 percent in Paris while shares of Bristol were up nearly one percent to $22.60 on the New York Stock Exchange.
Plavix is an antiplatelet drug that aims to reduce the risk of dangerous blood clots that may cause heart attacks and strokes. In order to work, it must first be metabolized by the body, according to the FDA.
Figuring possible differences in how the drug breaks down "is important because decreases in the effectiveness of clopidogrel might be avoided, in part, by using other drugs with clopidogrel that do not interfere with its metabolism," the FDA said.
The studies cited by the FDA looked at various patients, including those with implanted stents that prop open blocked arteries, and were published last year in the American Journal of Cardiology and the Journal of the American College of Cardiology.
The FDA said the drugmakers had agreed to a timetable for doing the studies but did not give details. It could take months for the agency to review the findings after the studies are completed, it added.