The Food and Drug Administration is investigating whether blood thinner Plavix is less effective in some patients.

 

Plavix, known generically as clopidogrel, is the second-best-selling drug worldwide. The drug is marketed by Bristol-Myers Squibb Co. and Sanofi-Aventis. Studies have shown that Plavix can irritate the stomach so is frequently given with proton pump inhibitors such as Prilosec, Zegerid, Prevacid, Protonix, Aciphex and Nexium, which may make it less effective.

 

Genetic factors may also stand in the way the body metabolizes Plavix. Two studies released last month showed strong associations between a CYP2C19 variant and recurrent thrombotic coronary events in patients treated with Plavix. It seems that about 30 percent of people of European ancestry, 40 percent of people of African ancestry and 50 percent of people of Asian ancestry have this variant, suggesting that a large number of patients are at increased risk of heart attack although they follow treatment with Plavix.

 

The FDA said it is working with both Sanofi and Bristol-Myers to determine whether genetic factors, interactions with PPIs or both are responsible for the Plavix resistance phenomenon. The agency also said it may take “several months” before a conclusion is reached.

 

“The FDA will review the new information expeditiously upon receipt from the drug manufacturers and will communicate its conclusions and any recommendations to the public at that time,” the agency said.

 

Meanwhile, the agency recommended patients on Plavix continue to take it and physicians continue to prescribe it as before. However, a review on the drug may lead to lower sales than in previous years. Since 1988, when Plavix was made available, more than 90 million patients have taken it to reduce the risk of blood clots that can further lead to heart attacks or strokes.