Upper Gastrointestinal Tract Hemorrhage, Warfarin, and Urinary Tract Antibiotics

(cotrimoxacin=trimetroprim sulfa (Mijn opmerking)

Findings from a population-based investigation indicate that cotrimoxazole increased hemorrhage risk among patients on long-term warfarin therapy.

Hemorrhage is a well-known side effect of long-term warfarin use in older patients. Interactions between warfarin and certain other drugs can increase the risk for this complication. In a recent nested case-control study conducted using healthcare databases from Ontario, Canada, researchers examined the risk for upper gastrointestinal (GI) tract hemorrhage among patients receiving both warfarin and antibiotics commonly used to treat urinary tract infections.

The cohort consisted of 134,637 patients aged 66 who had been continuously treated with warfarin for 180 days. Of these patients, 45,972 had received a concomitant prescription for an antibiotic of interest. The 2151 patients (1.6%) who were hospitalized for upper GI tract hemorrhage during the study period were considered cases; up to 10 age- and sex-matched controls were selected for each case.

Cases were nearly four times as likely as controls to have received cotrimoxazole (adjusted odds ratio, 3.84; 95% confidence interval, 2.33–6.33). Ciprofloxacin use was also associated with increased bleeding risk (AOR, 1.94; 95% CI, 1.28–2.95). No significant association was seen between hemorrhage and use of amoxicillin, ampicillin, nitrofurantoin, or norfloxacin.