Moxifloxacin—Warfarin Interaction: A Series of Five Case Reports

Abstract

OBJECTIVE: To report 5 cases of a moxifloxacin—warfarin drug interaction, all resulting in elevated international normalized ratios (INRs) and clinically significant hemorrhage in one case. CASE SUMMARIES: Between January 2002 and January 2004, 4 men and 1 woman (age range 63–92 y) were retrospectively identified as having significantly elevated INR results shortly after being prescribed moxifloxacin with concomitant warfarin therapy. DISCUSSION: This is the second series of case reports describing an interaction between warfarin and moxifloxacin. The current moxifloxacin product monograph indicates this drug has no significant effect on the pharmacokinetics of R- or S-warfarin or the prothrombin time (INR). A moxifloxacin—warfarin interaction probably led to prolonged hospitalization in 2 cases and significant gastrointestinal hemorrhage in one case. In 3 of the 5 cases, a moxifloxacin—warfarin interaction was assessed as probable, and in the remaining 2 cases, a moxifloxacin—warfarin interaction was assessed as possible by use of the Naranjo probability scale. CONCLUSIONS: Healthcare professionals should consider moxifloxacin for the potential to interact with warfarin. Routine, frequent INR monitoring for patients previously stabilized on warfarin during initiation and discontinuation of moxifloxacin may help detect this potential interaction.