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International Journal of Clinical Pharmacy

, Volume 39, Issue 4, pp 831–835 | Cite as

Evaluation of the effect of torsemide on warfarin dosage requirements

  • Sophia Lai
  • Jeremiah D. Momper
  • Felix K. YamEmail author
Research Article

Abstract

Background According to drug interaction databases, torsemide may potentiate the effects of warfarin. Evidence for this drug–drug interaction, however, is conflicting and the clinical significance is unknown. Objective The aim of this study is to evaluate the impact of torsemide initiation on warfarin dosage requirements. Setting This study was conducted at the Veterans Affairs Healthcare System in San Diego, California. Method A retrospective cohort study was conducted using Veterans Affairs data from patients who were converted from bumetanide to torsemide between March 2014 and July 2014. Patients were also prescribed and taking warfarin during the observation period. Warfarin dosage requirements were evaluated to determine if any changes occurred within the first 3 months of starting torsemide. Main outcome measure The primary outcome was the average weekly warfarin dose before and after torsemide initiation. Results Eighteen patients met study inclusion criteria. The weekly warfarin dose before and after initiation of torsemide was not significantly different (34 ± 15 and 34 ± 13 mg, p > 0.05). Of those eighteen patients, only two experienced elevations in INR that required a decrease in warfarin dosage after torsemide initiation. Between those two patients, dosage reductions ranged from 5.3 to 18%. Conclusion These results indicated that most patients did not require any warfarin dosage adjustments after torsemide was initiated. The potential for interaction, however, still exists. While empiric warfarin dosage adjustments are not recommended when initiating torsemide, increased monitoring is warranted to minimize the risk of adverse effects

Keywords

Anticoagulation INR Interaction Torsemide Warfarin 

Notes

Funding

The authors received no financial support for the research, authorship, or publication of this article.

Conflicts of interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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Copyright information

© Springer International Publishing 2017

Authors and Affiliations

  • Sophia Lai
    • 1
  • Jeremiah D. Momper
    • 2
  • Felix K. Yam
    • 1
    • 2
    Email author
  1. 1.VA San Diego Healthcare SystemSan DiegoUSA
  2. 2.Skaggs School of Pharmacy and Pharmaceutical SciencesUniversity of California, San DiegoLa JollaUSA

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