After surviving a heart attack, patients are often given specific drugs to prevent another one. One of those drugs, clopidogrel, sold under the brand name Plavix, may not work as well in patients who also are taking proton-pump inhibitors or PPIs, a study of blood platelets shows.

“We very often prescribe both clopidogrel, which is a blood-thinning medication, sort of like a super-aspirin, along with drugs that protect the stomach,” said cardiologist Dr. John Rumsfeld of the Denver VA Medical Center.

PPIs are also often prescribed because doctors know there is a higher risk of bleeding with clopidogrel, said another Denver VA cardiologist, Dr. P. Michael Ho.

Researchers looked at the records of more than 8,000 heart-attack patients who were prescribed clopidogrel. They compared patients who only took the blood thinner with others who also took the acid-blocker medication.

Those on the drug combination showed a “25 percent increased risk of having another heart attack or dying following hospitalization,” Ho said.

The study – published in the Journal of the American Medical Association – showed nearly two-thirds of patients were taking the drug combination.

Prescribing clopidogrel is still strongly recommended for these patients, but doctors add that a PPI medication should only be given if doctors have “a very strong, compelling reason for it,” Rumsfeld said.

The authors of the study emphasize patients should talk with their physicians before they stop taking any medications.