While the confusion over the combined use of the two classes of drugs is not new, the recent trials conducted by Plavix’s manufacturer Sanofi-Aventis and Bristol-Myers Squibb clearly unearth the dangerous drug interactions.
"We think there is a significant interaction," FDA’s safety evaluator Mary Ross Southworth said. "In general, patients should avoid the combination of these two medications."
The cause and effect relationship
Plavix is the most commonly prescribed drug for heart patients. As Plavix prevents the blood from getting too sticky and forming clots, it reduces the risk of a recurrent cardiac attack.
However, Plavix is known to upset the stomach, resulting in gastric troubles, heartburn or even bleeding in severe cases. To alleviate such symptoms Plavix is often supported by acid-reducing drugs.
Conferring its side of side-effects, the acid-reducing drugs in-turn blocks an enzyme (CYP 2C19) in the body that turns Plavix into its active form, thus making the anti-clotting drug dangerously less effective.
Explaining the interference, Dr. Christopher Cannon, a cardiologist at Brigham and Women’s Hospital in Boston said, "The PPI drug blocks the conversion of clopidogrel to its active state, so it can't have the anti-clotting activity it is supposed to. You're taking Plavix, but it's not having the anti-clotting activity it should."
Other drugs that also inhibit CYP 2C19 enzyme resulting in significant drug interactions include:
Tagamet (cimetidine)
Prozac, Serafem, and Symbyax (fluoxetine)
Luvox (fluvoxamine)
Ticlid (ticlopidine)
Diflucan (fluconazole)
Nizoral (ketoconazole)
VFEND (voriconazole)
Intelence (etravirine)
Felbatol (felbamate)
While physicians feel taking the two drugs at an interval of 12 hours from each other may help avoid the harmful drug interaction, Southworth emphasized that the interference is such grave that the combination should be ‘avoided even if the two drugs are taken hours apart’.
Instead patients taking Plavix who require taking acid-lowering drugs can take alternatives to Prilosec, such as Mylanta, Maalox, or Zantac, as there's no evidence that these drugs interfere with Plavix’s anti-blood action, FDA said.
The results were presented Monday at the American Heart Association's annual meeting in Orlando, Florida.
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