Original Report

The nature and frequency of potential warfarin drug interactions that increase the risk of bleeding in patients with atrial fibrillation†

  1. Patricia A. Howard PharmD, BCPS1,*,
  2. Edward F. Ellerbeck MD, MPH2,
  3. Kimberly K. Engelman PhD2,
  4. Kelly L. Patterson BSN3

Article first published online: 26 SEP 2002

DOI: 10.1002/pds.748

Issue

Pharmacoepidemiology and Drug Safety

Pharmacoepidemiology and Drug Safety

Volume 11, Issue 7, pages 569–576, December 2002

Additional Information

How to Cite

Howard, P. A., Ellerbeck, E. F., Engelman, K. K. and Patterson, K. L. (2002), The nature and frequency of potential warfarin drug interactions that increase the risk of bleeding in patients with atrial fibrillation. Pharmacoepidemiology and Drug Safety, 11: 569–576. doi: 10.1002/pds.748

Author Information

  1. 1

    Departments of Pharmacy Practice and Cardiovascular Medicine, University of Kansas Medical Center, Kansas City, KS, USA

  2. 2

    Department of Preventive Medicine, University of Kansas Medical Center, Kansas City, KS, USA

  3. 3

    Kansas Foundation for Medical Care, Topeka, KS, USA

*Professor of Pharmacy Practice, University of Kansas Medical Center, Department of Pharmacy, 3901 Rainbow Blvd., Kansas City, KS 66160-7231, USA.

  1. †

    Presented in part at the American College of Cardiology Annual Meeting, 21 March 2001, Orlando FL.

Publication History

  1. Issue published online: 25 OCT 2002
  2. Article first published online: 26 SEP 2002
  3. Manuscript Accepted: 24 MAY 2002
  4. Manuscript Revised: 20 MAY 2002
  5. Manuscript Received: 12 MAY 2002

Funded by

  • Health Care Financing Administration, Department of Health and Human Services. Grant Number: 500-99-KS01

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Keywords:

  • warfarin;
  • drug interactions;
  • bleeding;
  • atrial fibrillation

Abstract

Purpose

To determine the frequency with which atrial fibrillation (AF) patients receiving warfarin are prescribed interacting drugs that could increase bleeding risks.

Methods

We retrospectively examined medical records for 704 Medicare beneficiaries ≥65 years of age discharged from Kansas hospitals with AF. We identified all patients receiving warfarin and examined discharge prescriptions for drugs that could increase bleeding risk either by increasing the international normalized ratio (INR) or directly inhibiting hemostasis.

Results

Of 256 patients discharged on warfarin, 138 (54%) were prescribed another medication that could increase bleeding risk. Among these patients, 106 (41%) were discharged with a total of 150 prescriptions for drugs that could interact with warfarin to increase the INR. Antibiotics accounted for 67% of these prescriptions. Fifty-three patients (21%) received 56 prescriptions for drugs which could inhibit hemostasis. These were primarily antiplatelet drugs with 61% of the prescriptions for aspirin. Patients with coronary artery disease were more likely than others to be prescribed warfarin plus antiplatelet agents (OR=2.80; p=0.04). More than one interacting drug was prescribed for 20% of the patients.

Conclusions

AF patients discharged on warfarin were frequently prescribed concomitant medications that increase bleeding risks. These patients should be closely monitored and counseled to watch for signs of bleeding. Copyright © 2002 John Wiley & Sons, Ltd.

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