May 7, 2009 (United Press International) -- The anti-clotting action of the medication clopidogrel -- Plavix -- can be compromised by common drugs for the treatment of heartburn, U.S. researchers said.

Principal investigator Eric J. Stanek of Medco Health Solutions (NYSE:MHS) in Franklin Lakes, N.J., said the study specifically focused on the effects of proton pump inhibitors -- omeprazole or Prilosec; esomeprazole or Nexium; pantoprazole or Protonix; and lansoprazole or Prevacid. Together those drugs accounted for about 96 percent of proton pump inhibitors use in the study.

Patients who receive a drug-eluting stent benefit from taking anti-clotting medications, including thienopyradines -- such as clopidogrel or ticlopidine -- and aspirin, for at least one year following the procedure.

The researchers analyzed integrated data on pharmacy and medical claims from more than 10 million patients, including 16,690 patients taking clopidogrel for one year following coronary stenting. Of these, 41 percent also took a proton pump inhibitors, on average, for more than nine months of the year.

Over that 12-month period, the overall major adverse cardiovascular events risk was 51 percent higher among patients taking any proton pump inhibitors. The findings were equally concerning when the effects of individual proton pump inhibitors were analyzed. Omeprazole correlated with a 39 percent increased risk of major adverse cardiovascular events, esomeprazole to a 57 percent increased risk, pantoprazole to a 61 percent increased risk and lansoprazole to a 39 percent increased risk. All of the associations were highly statistically significant.

The findings were presented at the Society for Cardiovascular Angiography and Interventions' 32nd annual scientific sessions.