FDA Adds Black-Box Warning to Plavix

HEALTH -- March 12, 2010 at 2:36 PM EDT

The Food and Drug Administration has issued its strictest safety warning for the anti-clotting medication Plavix after determining the popular blood thinner may leave some patients at risk for heart attack or stroke.

The FDA ruled Plavix labels must begin carrying a so-called boxed warning because 2 to 14 percent of Americans have a genetic variation that prevents their bodies from properly metabolizing the drug.

The patients have low levels of a liver enzyme that's necessary for the body to process Plavix. Without that enzyme, the drug doesn't work as well and may leave patients at risk for the heart attacks and strokes it was meant to prevent.

There is a genetic test that can reveal whether a patient is one of those "poor metabolizers." However, it costs about $500 and it is not standard practice for most doctors to order the test before prescribing the medication.

In a statement, the FDA advised:

"Patients should not stop taking Plavix unless told to do so by their health care professional. They should talk with their health care professional if they have any concerns about Plavix, or to find out if they should be tested for being a poor metabolizer."

With global sales of $8.6 billion, Plavix was the world's second-best selling drug in 2008 behind Pfizer's cholesterol drug Lipitor. Plavix is marketed by New York-based Bristol-Myers Squibb Co. and Paris-based Sanofi Aventis SA.

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