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Intracerebral hemorrhage secondary to a warfarin-metronidazole interaction

Amanda Howard-Thompson1, April C Hurdle, Lori B Arnold

  • 1Department of Pharmacy, Methodist University Hospital, Memphis, Tennessee 38104, USA.

The American Journal of Geriatric Pharmacotherapy
|April 9, 2008
PubMed
Abstract

Insights

Metronidazole and warfarin drug interaction can increase bleeding risk, leading to intracerebral hemorrhage. This case highlights the importance of medication reconciliation, especially when patients receive care from unfamiliar providers.

Area of Science:

  • Pharmacology
  • Clinical Medicine
  • Drug Interactions

Background:

  • The interaction between warfarin and metronidazole has not been widely reported in over 25 years.
  • This case report is the first to document this interaction in association with intracerebral hemorrhage.

Observation:

  • A 78-year-old woman on stable warfarin therapy developed an intracerebral hemorrhage after a 5-day course of metronidazole for an upper respiratory infection.
  • She was also prescribed levofloxacin, but the Naranjo scale indicated metronidazole as the probable cause of the adverse event.

Findings:

  • Metronidazole likely increased S-warfarin concentrations, leading to a significantly elevated International Normalized Ratio (INR) from 2.5 to 8.0.
  • The patient experienced a severe nosebleed and was diagnosed with an intraparenchymal hemorrhage.

Implications:

  • This case underscores the potential for serious drug interactions between metronidazole and warfarin, necessitating careful medication review.
  • Lack of provider awareness regarding concomitant warfarin use and fragmented pharmaceutical care likely contributed to this adverse event.

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