Warfarin Institute of America
DEDICATED TO YOUR HEALTH SINCE 2000
CLARITHROMYCIN INTERACTION WITH WARFARIN (Coumadin, Jantoven)
Clarithromycin can raise the INR by interfering with one of the enzymes that metabolizes warfarin (Coumadin, Jantoven). The effect of this is that the warfarin (Coumadin, Jantoven) stays in the body longer than usual. Then it exerts its effect on the clotting factors longer. This is similar to increasing the warfarin (Coumadin, Jantoven) dose.
The most common reaction is when clarithromycin is added to warfarin (Coumadin, Jantoven). After three to five days, the INR may be elevated. If the clarithromycin is for a trivial infection, why take the risk?
Clarithromycin is also one of the ingredients in Prevpak. This is used to eradicate bacteria in the intestinal tract which can cause ulcers. This is particularly troubling in someone who is taking warfarin (Coumadin, Jantoven) because some of the bacteria in the intestinal tract produce vitamin K. Eliminating these bacteria can cause the INR to increase.
Gooderham et al reported on a 72-year-old woman who was on warfarin (Coumadin, Jantoven) and digoxin. She had clarithromycin prescribed to treat an Helicobacter pylori infection. Twelve days later she complained of gastrointestinal symptoms, weakness, dizziness, and visual changes. She had a toxic level of digoxin and her INR was 7.3. All three medications were held and she recovered. References: Gooderham MJ et al. Concomitant Digoxin Toxicity and warfarin (Coumadin, Jantoven) Interaction in a Patient Receiving Clarithromycin. Ann Pharmacother 1999;33:769-9.
My conclusions:
- warfarin (Coumadin, Jantoven) increases your chances of having a gastrointestinal bleed.
- An ulcer increases your chance of having a gastrointestinal bleed.
- Raising the INR increases your chances of having a gastrointestinal bleed.
- There are safer medications than clarithromycin to take to treat an ulcer.
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Last modified May 7, 2006