The drug had global sales of $7.3 billion in 2007. The data caused researchers to wonder if the heartburn drugs might be interfering with a liver enzyme required to metabolize Plavix. Food and Drug Administration (FDA) are looking in to whether Plavix, a popular blood thinner used by millions, may be less effective in patients who also take certain heartburn medications.

The agency is also investigating whether the drug, which prevents deadly blood clots and reduces the risk of stroke and heart attack, may be less effective in those with certain genetic backgrounds. However, some heart experts are skeptical, saying that patients taking heartburn medications may have other underlying health problems that affect their risk for heart attack and other problems.

FDA Reviewing Plavix Concerns Officials with the U.S. Plavix, marketed by New York-based Bristol-Myers Squibb Co. In November, researchers discovered that Plavix users who also took popular prescription heartburn medications, such as Nexium, significantly increased their chances of being hospitalized for stroke, heart attack or chest pain. The agency said both subgroups may have trouble metabolizing the world €™s second-best-selling drug. And Paris-based Sanofi-Aventis SA, has been prescribed to more than 90 million people worldwide.

Doctors often prescribe drugs known as proton pump inhibitors (PPIs) to treat heartburn, a condition in.