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Moxifloxacin-warfarin interaction: a series of five case reports

Dean H T Elbe1, Sandra W Chang

  • 1Department of Pharmacy, The Richmond Hospital, Richmond, British Columbia, Canada. dean.elbe@vch.ca

The Annals of Pharmacotherapy
|January 6, 2005
PubMed
Abstract

Insights

This study reports five cases where moxifloxacin and warfarin interacted, leading to increased international normalized ratios (INRs) and bleeding. Healthcare providers should monitor INR closely when these drugs are used together.

Area of Science:

  • Pharmacology
  • Drug Interactions
  • Clinical Medicine

Background:

  • Warfarin is a widely used anticoagulant.
  • Moxifloxacin is a broad-spectrum fluoroquinolone antibiotic.
  • The potential for drug interactions between warfarin and moxifloxacin requires investigation.

Observation:

  • Five cases of patients (age 63-92) experiencing elevated international normalized ratios (INRs) after starting moxifloxacin while on warfarin therapy were identified.
  • These elevated INRs were associated with significant clinical events, including prolonged hospitalization in two cases and gastrointestinal hemorrhage in one case.
  • The Naranjo probability scale assessed the likelihood of a drug interaction as probable in three cases and possible in two cases.

Findings:

  • A drug interaction between moxifloxacin and warfarin can lead to significantly elevated INRs.
  • This interaction may result in serious clinical consequences, such as hemorrhage.
  • The current product monograph for moxifloxacin does not adequately reflect its potential to interact with warfarin.

Implications:

  • Healthcare professionals must be aware of the potential for moxifloxacin to interact with warfarin.
  • Close monitoring of INR is crucial for patients stabilized on warfarin when initiating or discontinuing moxifloxacin.
  • This interaction highlights the need for updated drug information and cautious prescribing practices.

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