UPDATE 3-FDA warns heartburn drugs interfere with Plavix
* Prilosec, Nexium cut Plavix effectiveness by nearly half
* FDA: Plavix label to highlight interaction risk
* Warning follows data from new Sanofi-Aventis study (Recasts first sentence, adds details on new study, comment from FDA official)
WASHINGTON, Nov 17 (Reuters) - Common heartburn pills Prilosec and Nexium cut the blood-thinning effect of Sanofi-Aventis SA's (SASY.PA) and Bristol-Myers Squibb Co's (BMY.N) heart drug Plavix, U.S. officials warned on Tuesday.
The stomach drugs inhibit a key enzyme and reduce by almost half the anti-clotting effect of Plavix, which is taken by millions of people to reduce the risk of heart attacks and stroke, the Food and Drug Administration said.
Plavix is the world's second-biggest-selling medicine, with global sales of around $9 billion.
The U.S. label for Plavix, known also as clopidogrel, is now being updated with new warnings on the use of AstraZeneca Plc's (AZN.L) Prilosec and other similar drugs, including Nexium, the agency said.
Plavix is widely used with such so-called proton pump inhibitors, or PPIs, to reduce stomach acid and avoid gastric problems.
Prilosec is available generically as omeprazole and is also sold over-the-counter (OTC) by Procter & Gamble Co (PG.N).
The medicine used to be AstraZeneca's top-selling product but has now been overtaken by the company's newer product, Nexium, which sold $5.2 billion in 2008.
Mary Ross Southworth, deputy director for safety in the FDA's division of cardiovascular and renal products, said the problem of interaction between such drugs and Plavix had been highlighted in a new 150-patient study conducted by Sanofi.
Results of that study were presented to the FDA over the summer.
"We think that the mechanism of action is because of omeprazole's activity on the 2C19 enzyme," Southworth told reporters.
That enzyme is important because it is needed to break down Plavix into its active form in the body. If the action of the enzyme is restricted, less-active Plavix is available in the bloodstream.
The FDA said patients who needed a medicine for stomach acid should take antacid tablets or alternative older drugs like ranitidine and famotidine -- available on prescription or OTC -- but not cimetidine.
Worries about mixing Plavix and PPIs are not new, but experts have continued to debate the pros and cons of combining the medicines.
An analysis presented at the European Society of Cardiology annual meeting in Barcelona in August appeared to offer reassurance by finding that PPIs did not interfere with the clinical benefits of either Plavix or Eli Lilly (LLY.N) and Daiichi Sankyo's (4568.T) new drug Effient. [ID:nLV266191]
Southworth, however, said this sub-analysis from a larger clinical trial had significant limitations, since patients were not randomized in terms of PPI use. (Reporting by Ben Hirschler, editing by Gerald E. McCormick, Tim Dobbyn and Matthew Lewis)