Increased risk of bleeding during warfarin therapy with cotrimoxazole

January 01, 0001

Increased risk of bleeding during warfarin therapy with cotrimoxazole

These Canadian authors examined the risk of upper gastrointestinal (UGI) tract hemorrhage in older patients receiving warfarin in combination with antibiotics commonly used to treat urinary tract infection, with a focus on cotrimoxazole. This population-based, nested case-control study used health care databases in Ontario, Canada, between April 1997 and March 2007. The authors identified residents 66 years or older who were continuously treated with warfarin. Cases were hospitalized with UGI tract hemorrhage. For each case they selected up to 10 age- and sex-matched control subjects.

They found: "We identified 134,637 patients receiving warfarin, of whom 2151 cases were hospitalized for UGI tract hemorrhage. Cases were almost 4 times more likely than controls to have recently received cotrimoxazole (aOR 3.84). Treatment with ciprofloxacin was also associated with increased risk (aOR 1.94), but no significant association was observed with amoxicillin or ampicillin (1.37), nitrofurantoin (1.40), or norfloxacin (0.38). Compared with amoxicillin or ampicillin, cotrimoxazole prescription was associated with an almost 3-fold risk (ratio of ORs 2.80)."

The authors concluded: "Among older patients receiving warfarin, cotrimoxazole is associated with a significantly higher risk of UGI tract hemorrhage than other commonly used antibiotics. Whenever possible, clinicians should prescribe alternative antibiotics in patients receiving warfarin."

This evidence is enough to urge caution in prescribing cotrimoxazole for patients taking warfarin.

For the full abstract, click here.

Arch Intern Med 170(7):617-621,12 April 2010
© 2010 to the American Medical Association
Hemorrhage During Warfarin Therapy Associated With Cotrimoxazole and Other Urinary Tract Anti-infective Agents-A Population-Based Study. Hadas D. Fischer, David N. Juurlink, Muhammad M. Mamdani, Alexander Kopp, Andreas Laupacis. Correspondence to Dr. Fischer: [email protected]

Category: B. Blood/Blood Forming Organs/Immune Mechanisms, U. Urinary System. Keywords: warfarin, upper gastrointestinal bleeding, urinary tract infection, antibiotics, cotrimoxazole, nested case-control study, journal watch.
Synopsis edited by Dr Linda French, Toledo, Ohio. Posted on Global Family Doctor 27 April 2010

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