FDA seeks more data on bloodthinner Plavix

By Susan Heavey

WASHINGTON (Reuters) - U.S. health 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.