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Journal of Pharmacy Practice

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Background: The cephalosporin class has been associated with an increased risk of bleeding among elderly patients receiving warfarin. Urinary tract infections (UTI) are the most prevalent infection in elderly patients.

Objective: To determine the extent of interaction between antibiotics used in the treatment of UTI, particularly specific cephalosporins and warfarin.

Methods: A retrospective chart review was conducted on chronic warfarin patients with a diagnosis of UTI treated with ceftriaxone, a first-generation cephalosporin, penicillin, or ciprofloxacin. The primary outcome was the comparison of the extent of international normalized ratio (INR) change from baseline between each antibiotic group.

Results: The ceftriaxone group was found to have a statistically significant higher peak INR value compared to all other studied antibiotics (ceftriaxone: 3.56, first-generation cephalosporins: 2.66, penicillins: 2.98, ciprofloxacin: 2.3; P = .004), a statistically significant greater extent of change in INR value (+1.19, +0.66, +0.8, +0.275; P = .006), and a statistically significant greater percentage change in INR value when compared to ciprofloxacin (54.4% vs 12.7%; P = .037).

Conclusion: Ceftriaxone interacts with warfarin to increase a patient’s INR value more than other commonly administered antibiotics for UTI treatment. Other antibiotics should be preferred for UTI treatment in patients on warfarin.


This is a post-print version of an article originally published in Journal of Pharmacy Practice, 2014, Volume 29, Issue 2.


The version of record is available at Journal of Pharmacy Practice. Archived with permission from Sage, all rights reserved.