Gene Ups Risk for Those on Blood-Thinner Plavix

So, what can be done to minimize the risk? "Checking people's genetic make-up after a heart attack is probably not necessary, since it may be better to do a different blood test to see if they have had a good anti-clotting response to clopidogrel," Storey said. He added that "new treatments that work more reliably than clopidogrel should hopefully be available within the next year or so."

Dr. Gregg C. Fonarow, a professor of cardiology at the University of California, Los Angeles, noted that treatment with Plavix in combination with aspirin does greatly reduce the risk of cardiovascular events in patients after an acute coronary event, or in patients undergoing coronary stent placement.

"However, it is well recognized there is variable response to clopidogrel, and some patients have thrombotic events, despite treatment with aspirin and clopidogrel," Fonarow said. "If these findings can be confirmed in additional studies, genetic testing may be useful in personalizing the choice and dosing of anti-platelet therapy in cardiovascular patients," he said.

Two other recent studies also found problems with Plavix in some patients.

In one study of 259 people treated with Plavix, published in the Aug. 12 issue of the Journal of the American College of Cardiology, researchers found that patients who smoked had significantly less clot formation than nonsmokers.

In a second study, published in the Oct. 28 online edition of the Journal of the American College of Cardiology, Austrian researchers found that calcium channel blockers drugs, widely prescribed to lower blood pressure, might reduce the Plavix' anti-clotting effects.

More information

For more on Plavix, visit the U.S. National Library of Medicine.

SOURCES: Robert F. Storey, M.D., Cardiovascular Research Unit, University of Sheffield School of Medicine, England; Gregg C. Fonarow, M.D., professor, cardiology, University of California, Los Angeles; Jan. 22, 2009, New England Journal of Medicine, Dec. 23, 2008, The Lancet, online