Impact of a Guideline for the Management of Antimicrobial/Warfarin Interactions in the Inpatient Setting and Across Transition of Care

Ann Pharmacother. 2016 Sep;50(9):734-40. doi: 10.1177/1060028016653765. Epub 2016 Jun 16.


Background: Drug-drug interactions (DDIs) with warfarin and antimicrobial agents are a common cause of international normalized ratio (INR) instability, which can affect the risk for bleeding and thrombotic events.

Objective: The purpose of this study was to assess the impact of a comprehensive guideline for the management of warfarin-antimicrobial DDIs across transitions of care. The guideline emphasizes improving identification of significant antimicrobial-warfarin DDIs during hospitalization, empirical warfarin dose modification based on DDI and baseline INR, patient education, documentation of the DDI, communication with outpatient providers regarding the DDI and anticipated antimicrobial stop date, and warfarin dose adjustment on discontinuation of antimicrobial.

Methods: This retrospective, single-center, quasiexperimental, pre-post study compared end points 3 months before and after guideline implementation. The primary outcome was time within therapeutic range (TTR).

Results: The study included 78 preguideline and 31 postguideline patients; baseline characteristics were similar between groups. Implementation of the guideline resulted in greater in-hospital TTR (72% vs 50%, P = 0.04) and improved TTR across transition of care (70% vs 46%, P = 0.01). Documentation of DDI in the pharmacy anticoagulation discharge summary significantly improved in the postguideline group (40% vs 14%, P = 0.02) and numerically improved within the daily pharmacy progress notes (94% vs 82%, P = 0.13). The implementation of the guideline was associated with a nonsignificant, numerical reduction in bleeding events compared with the preguideline group (0 vs 4 events, P = 0.11).

Conclusion: This single-center approach to optimize the comprehensive management of significant antimicrobial-warfarin DDIs resulted in improved communication with outpatient providers and improved INR TTR.

Keywords: antibiotics; anticoagulation; clinical practice; drug interactions; warfarin.

MeSH terms

  • Aged
  • Anti-Infective Agents / administration & dosage
  • Anti-Infective Agents / adverse effects*
  • Anti-Infective Agents / therapeutic use
  • Anticoagulants / administration & dosage
  • Anticoagulants / adverse effects*
  • Anticoagulants / therapeutic use
  • Blood Coagulation / drug effects
  • Drug Interactions
  • Female
  • Hemorrhage / chemically induced
  • Hemorrhage / drug therapy
  • Hospitalization
  • Humans
  • Inpatients
  • International Normalized Ratio / methods*
  • International Normalized Ratio / standards
  • Male
  • Middle Aged
  • Patient Transfer
  • Pharmaceutical Services / standards
  • Practice Guidelines as Topic / standards*
  • Retrospective Studies
  • Transitional Care / organization & administration
  • Transitional Care / standards*
  • Warfarin / administration & dosage
  • Warfarin / adverse effects*
  • Warfarin / therapeutic use


  • Anti-Infective Agents
  • Anticoagulants
  • Warfarin