Retrospective Evaluation of a Potential Interaction Between Azithromycin and Warfarin in Patients Stabilized on Warfarin

Abstract

An interaction between azithromycin and warfarin was not observed in this retrospective review of patients with a stable INR receiving the combination.

Brief report: The risk of overanticoagulation with antibiotic use in outpatients on stable warfarin regimens

“…We conducted a retrospective cohort study of patients with stable warfarin doses and INRs who received a prescription for terazosin, azithromycin, levofloxacin, or TMP/SMX for clinical indications between January 1998 and December 2002 at a university‐affiliated Veteran's Affairs Medical Center. Terazosin was chosen as our control because of its lack of interaction with warfarin 9 . Participants were included if 2 inclusion INRs (the last occurring within 30 days prior to the introduction of the antibiotic/terazosin) were within±0.2 of the therapeutic range and within 0.5 of each other, and a repeat INR was drawn within 3 to 15 days after commencement of any of the antibiotic medications.…”

Prescribing azithromycin

“…[23][24][25][26][27][28][29] Due to its long half-life, interactions may continue for several days after it has been stopped. 10 Box Clinically significant interactions of azithromycin • Azithromycin should be used with great caution if co-administered with other drugs that prolong the QT interval.…”

“…Some retrospective series have failed to find interactions 24,25 or found an interaction but no adverse events. 26 Given the current uncertainty about interactions, it is prudent to monitor INR carefully in patients on warfarin who require azithromycin.…”

Concurrent Use of Warfarin and Antibiotics and the Risk of Bleeding in Older Adults

“…2, 15-17 Interactions between warfarin and specific antibiotic agents have been widely assessed, primarily through case reports, case series studies, 18-20 pharmacokinetic studies, 142122, 23 and three population-based studies. 2, 3, 5 Based on these investigations, quinolones, sulfonamides, macrolides, and azole antifungals are thought to carry the highest risk of warfarin toxicity, whereas amoxicillin and cephalexin are believed to have a more modest risk.…”