FDA adds boxed warning to Plavix

ROCKVILLE, Md. A popular drug for preventing blood clots may be less effective when taken by a small percentage of patients, the Food and Drug Administration warned healthcare professionals and patients Friday.

The Food and Drug Administration is adding a boxed warning, the strongest possible warning label that a drug can have, to the safety labeling for Bristol-Myers Squibb’s and Sanofi-Aventis’ Plavix (clopidogrel). The action follows recent data showing that patients with reduced functioning of a liver enzyme may not be able to fully metabolize the drug, leaving them at continued risk for heart attack, stroke and cardiovascular death. The FDA added a warning for these so-called “poor metabolizers” in May 2009, but the boxed warning upgrades it.

Plavix requires the enzyme, called CYP2C19, in order to break down the drug in the body, but between 2% and 14% of the U.S. population has reduced CYP2C19 functioning.

“We want to highlight this warning to make sure healthcare professionals use the best information possible to treat their patients,” FDA Center for Drug Evaluation and Research analyst Mary Southworth said in a statement.

Plavix was the third top-selling drug in the United States in 2008, according to IMS Health, with $4.9 billion in sales.