The drugs may make the anti-clotting drug Plavix dangerously less effective, the FDA says. They block an enzyme in the body that turns the drug into its active form. Plavix is the second most-prescribed drug in the world.
It's not the first time questions have been raised about the potent stomach-acid-reducing drug Prilosec blunting the benefit of Plavix. But data from more recent studies suggested that Prilosec -- and a similar drug called Nexium -- might actually help patients on Plavix.
This led the FDA to ask Plavix maker Sanofi-Aventis to specifically study interactions between Plavix and Prilosec and between Plavix and Nexium, FDA safety evaluator Mary Ross Southworth, PharmD, said at a news conference.
"We think there is a significant interaction," Southworth said. "In general, patients should avoid the combination of these two medications."
But the FDA recommendation goes far beyond the two drugs studied. Nexium and Prilosec interfere with Plavix not because they are members of a particularly powerful class of acid-reducing drugs called proton pump inhibitors or PPIs, but because they inhibit an enzyme, CYP 2C19, that activates Plavix.
Several other drugs also inhibit CYP 2C19, and the FDA says patients on Plavix should avoid them as well. These drugs are:
- Tagamet (generic name: cimetidine)
- Prozac, Sarafem, and Symbyax (generic name: fluoxetine)
- Luvox (generic name: fluvoxamine)
- Ticlid (generic name: ticlopidine)
- Diflucan (generic name: fluconazole)
- Nizoral (generic name: ketoconazole)
- VFEND (generic name: voriconazole)
- Intelence (generic name: etravirine)
- Felbatol (generic name: felbamate)
Patients taking Plavix should not stop taking any of these drugs -- including Nexium and Prilosec -- until speaking with a doctor. It's dangerous to stop taking any medication without medical advice.
Patients taking Plavix should call their doctor as soon as possible to discuss all the other drugs and supplements they are taking, including over-the-counter medications.
The FDA warning does not cover other acid-reducing drugs except for Tagamet, which inhibits CYP 2C19. The FDA is actively looking at data on other PPIs, but at this time the FDA is not warning patients to avoid taking Plavix along with other PPIs.
While some doctors have tried to avoid drug interactions by having patients take Nexium or Prilosec 12 hours before or after taking other drugs, the FDA says this strategy will not avoid interactions between Nexium or Prilosec and Plavix.