The FDA has today issued a new public-health warning on the possible interaction between clopidogrel and the proton-pump inhibitor (PPI) omeprazole. The alert states: "New data show that when clopidogrel and omeprazole are taken together, the effectiveness of clopidogrel is reduced. Patients at risk for heart attacks or strokes who use clopidogrel to prevent blood clots will not get the full effect of this medicine if they are also taking omeprazole."
The FDA alert says the new information on which its warning is based comes from new studies that compared the amount of clopidogrel's active metabolite in the blood and its effect on platelets in people who took clopidogrel plus omeprazole vs those who took clopidogrel alone. A reduction in active metabolite levels of about 45% was found in people who received clopidogrel with omeprazole compared with those taking clopidogrel alone. The effect of clopidogrel on platelets was reduced by as much as 47% in people receiving clopidogrel and omeprazole together. These reductions were seen whether the drugs were given at the same time or 12 hours apart, the statement adds.
Based on the current scientific information, the clopidogrel label has been updated with new warnings on omeprazole and other drugs that inhibit the CYP2C19 enzyme that could interact with clopidogrel in the same way. In addition, the manufacturer of clopidogrel is conducting follow-up studies to explore this and other drug interactions.
It adds that patients who use clopidogrel and need a medication to reduce stomach acid can use antacids or H2 antagonists such as ranitidine, famotidine, or nizatidine, because the FDA does not believe that these medicines will interfere with the anti-clotting activity of clopidogrel. However,cimetidine should not be used, it says.
It also says that other drugs that are potent inhibitors of the CYP2C19 enzyme would be expected to have a similar effect and should be avoided in combination with clopidogrel. These include: cimetidine, fluconazole, ketoconazole, voriconazole, etravirine, felbamate, fluoxetine, fluvoxamine, and ticlopidine. "Since the level of inhibition among other PPIs varies, it is unknown to what amount other PPIs may interfere with clopidogrel. However, esomeprazole, a PPI that is a component of omeprazole, inhibits CYP2C19 and should also be avoided in combination with clopidogrel," it adds.
Ref: Food and Drug Adminstration. Public-health advisory: Updated safety information about a drug interaction between clopidogrel bisulfate (marketed as Plavix) and omeprazole (marketed as Prilosec and Prilosec OTC). November 17, 2009. [http://www.fda.gov/Drugs/DrugSafety/PublicHealthAdvisories/ucm190825.htm]