Two common medications may interact to cause internal bleeding, from the Harvard Heart Letter

Millions of people take warfarin (Coumadin, generic). Many of them don't know that common antibiotics and antifungal medications can boost its blood-thinning ability and raise the risk of internal bleeding, reports the June 2012 Harvard Heart Letter.

The interaction can occur not only with oral agents, but with antibiotic or antifungal ointments, creams, and suppositories as well. A recent study showed that so-called all classes of antibiotics and azole antifungals increased the risk of bleeding among people taking warfarin. the increases were:

  • 4.7-fold for azole antifungals
  • 2.7-fold for cotrimoxazole
  • 2.5-fold for cephalosporins
  • 1.9-fold for penicillin
  • 1.9-fold for macrolide antibiotics
  • 1.7-fold for quinolones

Among people taking warfarin and one of these medications, "the risk of gastrointestinal bleeding increases, and a bump on the head could become a bleed in the brain," says Dr. Tejal Gandhi, associate professor of medicine at Harvard Medical School and an expert on outpatient drug safety.

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