Key result
Azithromycin co-administration with warfarin does not significantly alter INR compared to active control.
Why the study?
The study was conducted to investigate a potential interaction between azithromycin and warfarin in patients stabilized on anticoagulation therapy.
Does adding azithromycin alter the international normalized ratio (INR) compared with terazosin in patients stabilized on warfarin therapy?
Case-Control (n=52)
No
Does adding azithromycin alter the international normalized ratio (INR) compared with terazosin in patients stabilized on warfarin therapy?
In patients with a stable therapeutic INR on warfarin, initiating azithromycin was not associated with a statistically significant change in INR within 14 or 30 days compared with terazosin.
Answers are grounded in this paper and cite their sources.
Azithromycin may not require INR adjustment in stable warfarin patients; case-control data leave open need for randomized confirmation.
Study Objective. To investigate a potential interaction between azithromycin and warfarin. Design. Retrospective case‐control study. Setting. Veterans Affairs medical center Patients. Fifty‐two patients stable on anticoagulation therapy. Intervention. Patients who received a prescription for azithromycin and warfarin at any time since the hospital was opened, June 1, 1995, to July 22, 1999, were identified through a computerized report generated from the pharmacy prescription package. Measurements and Main Results. Patients having a stable international normalized ratio (INR; defined as a therapeutic INR ± 0.2) for at least two consecutive visits before receiving an azithromycin prescription were reviewed. Changes in INR from before and after addition of azithromycin were compared with changes in a control group. Controls were identified from a computer‐generated report of patients who received a prescription for terazosin and warfarin at any time since the hospital was opened to July 22, 1999 (terazosin was chosen as it has no known interaction with warfarin). These patients also had a stable INR for at least two consecutive visits before receiving the terazosin prescription. In patients with INRs on record within 14 days after starting azithromycin or terazosin (9 patients/group), the average change in INR was 0.18 ± 0.48 in the azithromycin group and 0.07 ± 0.49 in the terazosin group (p=0.60). For patients with an INR on record within 30 days after starting azithromycin or terazosin (26 patients/group), the average change in INR was 0.25 ± 0.67 in the azithromycin group and 0.05 ± 0.55 in the terazosin group (p=0.18). Conclusion. An interaction between azithromycin and warfarin was not observed in this retrospective review of patients with a stable INR receiving the combination.
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Beckey et al. (2000) conducted a case-control in Patients stable on warfarin anticoagulation therapy (n=52). Azithromycin added to warfarin vs. Terazosin added to warfarin was evaluated on Average change in INR within 30 days after starting azithromycin or terazosin (p=0.18). Azithromycin co-administration with stable warfarin did not significantly alter INR compared with terazosin at 14 days (+0.18 vs +0.07; p=0.60) or 30 days (+0.25 vs +0.05; p=0.18).
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