Potential interaction between azithromycin and warfarin

Azithromycin is considered unlikely to interact with warfarin. Unlike other macrolide antibiotics, it is not hepatically metabolized and did not produ ce an interaction with warfarin in a single-dose study. A 71-year-old woman with a prosthetic heart valve, stabilized with warfarin, had international normalized ratios (INRs) maintained between 2.5 and 3.5. Six days after sh e received a prescription for a 5-day course of azithromycin, her INR was 1 5.16. Phytonadione 10 mg was administered subcutaneously and warfarin was h eld for 3 days until her INR fell to 2.10. She then was restabilized with w arfarin. Until more information is known about the safety of warfarin and a zithromycin, caution is advised when the agents are given together. Close m onitoring of INR is recommended, and warfarin dosage adjustment may be nece ssary.