A popular heartburn medication can interfere with the blood thinner Plavix, a drug taken by thousands of Canada to reduce risks of heart attack and stroke, U.S. health authorities are warning.
The Food and Drug Administration in the U.S. said the stomach acid-blocking drugs drugs omeprazole and esomprazole cut in half the effectiveness of Plavix, known generically as clopidogrel.
The FDA says the key ingredient in the heartburn medications blocks an enzyme the body needs to break down Plavix, muting the drug's full effect.
"Patients at risk for heart attacks or strokes who use clopidogrel to prevent blood clots will not get the full effect of this medicine," the agency said in a statement.
Health Canada released similar safety information in August.
The brand name for esomprazole is Nexium. In Canada, omeprazol is called Losec and is available only by prescription; in the U.S. it's called Prilosec and is available in an over-the-counter dosage as well.
Plavix, the world's second-best selling drug behind the cholesterol drug Lipitor, can upset the stomach, which is why it is often prescribed with stomach acid-blocking drugs.
The FDA says patients who need to reduce their stomach acid should take drugs from the H-2 blocker family, which includes Mylanta and Zantac. FDA scientists say there is no evidence those drugs interfere with Plavix's anti-blood clotting action.
Nexium and Prilosec are both proton pump inhibitors; FDA regulators said they don't have enough information yet to say whether other drugs in that class shouldn't be used with Plavix.
Alarms have been raised before about the drug interaction between Plavix and other medications.
Earlier this year, a large study published in the Journal of the American Medical Association, found heart patients who took Plavix had a greater risk of suffering a heart attack if they were also taking a proton-pump inhibitor, such as Nexium, Prevacid and Prilosec.
And a study in the Canadian Medical Association Journal found heart attack patients taking clopidogrel had a 40 per cent greater risk of suffering another heart attack if they were also taking a PPI.
In August, the Canadian prescribing information for Plavis was revised to include information about the potential interaction. And in May, the Plavix label was changed in the U.S. to advise against using it in combination with certain heartburn drugs.
