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New Plavix Findings Fuel Debate on Platelet Testing

Doubling Plavix Dose Doesn't Help Certain High-Risk People
By
WebMD Health News
Reviewed by Laura J. Martin, MD

Nov. 17, 2010 (Chicago) -- Doubling the dose of the anticlotting drug Plavix does not reduce heart attacks or deaths in certain high-risk people, a study shows.

The study participants were determined to be at high risk of cardiovascular complications after undergoing a test showing that their blood was still prone to clotting despite taking the anticlotting medication. Clots can lodge in an artery, causing a heart attack or stroke.

Whether the test, called platelet reactivity testing, should be given to people taking Plavix has been the subject of much debate.  

"We're not set up to recommend it at this time," says Mariell Jessup, MD, medical director of the Penn Heart and Vascular Center at the University of Pennsylvania.

High-Dose Plavix Doesn't Cut Cardiovascular Events

Some people are genetically predisposed to be poor metabolizers of Plavix, and they have higher rates of heart attacks, strokes, and death.

To compensate for this poor response, doctors often increase the dose of Plavix in these patients. But the strategy of using the platelet reactivity test to guide treatment with Plavix had not been evaluated in a large clinical trial until now.

Matthew Price, MD, of the Scripps Clinic in La Jolla, Calif., presented the findings at the American Heart Association annual meeting.

Using the platelet reactivity test, Price and colleagues identified more than 2,200 patients who were poor metabolizers of Plavix after taking the standard Plavix dose 12 to 24 hours after angioplasty and stenting, procedures that open blocked heart arteries.

The patients were then given either a high or a standard dose of Plavix for six months.

After six months, the rate of death due to cardiovascular disease, heart attack, or developing a blood clot inside the stent was 2.3% in both groups.

The study was funded by Accumetrics Inc., which makes the platelet reactivity test used in the study.

Platelet Testing

But platelet reactivity testing is not dead, doctors tell WebMD.

Other strategies may prove helpful for people whose test shows high platelet activity, they say.

It could be an even higher dose of Plavix is needed, Jessup says.

More potent blood-thinning pills -- such as Effient or the experimental pill Brilinta -- may also prove to be effective for high-risk people, she says.

Also, platelet reactivity testing may prove useful for people with clogged arteries who have not yet had stents implanted and thus are at even higher risk of heart attacks and strokes, says Jessica Mega, MD, of Harvard Medical School.

There is also the possibility that the current study just didn't have enough participants to detect differences between the group that got the higher dose of Plavix and the group that got the standard dose, she says. A larger study is needed to address that issue.

This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.

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