Intended for healthcare professionals


Impact of adverse events on prescribing warfarin in patients with atrial fibrillation: matched pair analysis

BMJ 2006; 332 doi: (Published 19 January 2006) Cite this as: BMJ 2006;332:141
  1. Niteesh K Choudhry (nchoudhry{at}, instructor in medicine,
  2. Geoffrey M Anderson, chair in health management strategies,
  3. Andreas Laupacis, chief executive officer,
  4. Dennis Ross-Degnan, associate professor,
  5. Sharon-Lise T Normand, professor of biostatistics,
  6. Stephen B Soumerai, professor
  1. Harvard Medical School and Brigham and Women's Hospital, Boston, USA 02120
  2. Department of Health Policy, Management and Evaluation, Faculty of Medicine, University of Toronto, Toronto, Canada
  3. Institute of Clinical Evaluative Sciences, Toronto, Canada
  4. Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, Boston, USA
  5. Department of Health Care Policy, Harvard Medical School, Boston, USA
  1. Correspondence to: N K Choudhry
  • Accepted 8 November 2005


Objectives To quantify the influence of physicians' experiences of adverse events in patients with atrial fibrillation who were taking warfarin.

Design Population based, matched pair before and after analysis.

Setting Database study in Ontario, Canada.

Participants The physicians of patients with atrial fibrillation admitted to hospital for adverse events (major haemorrhage while taking warfarin and thromboembolic strokes while not taking warfarin). Pairs of other patients with atrial fibrillation treated by the same physicians were selected.

Main outcome measures Odds of receiving warfarin by matched pairs of a given physician's patients (one treated after and one treated before the event) were compared, with adjustment for stroke and bleeding risk factors that might also influence warfarin use. The odds of prescriptions for angiotensin converting enzyme (ACE) inhibitor before and after the event was assessed as a neutral control.

Results For the 530 physicians who had a patient with an adverse bleeding event (exposure) and who treated other patients with atrial fibrillation during the 90 days before and the 90 days after the exposure, the odds of prescribing warfarin was 21% lower for patients after the exposure (adjusted odds ratio 0.79, 95% confidence interval 0.62 to 1.00). Greater reductions in warfarin prescribing were found in analyses with patients for whom more time had elapsed between the physician's exposure and the patient's treatment. There were no significant changes in warfarin prescribing after a physician had a patient who had a stroke while not on warfarin or in the prescribing of ACE inhibitors by physicians who had patients with either bleeding events or strokes.

Conclusions A physician's experience with bleeding events associated with warfarin can influence prescribing warfarin. Adverse events that are possibly associated with underuse of warfarin may not affect subsequent prescribing.


  • Contributors All authors were responsible for concept and design and critical revision of the manuscript. NKC acquired, analysed, and interpreted data, drafted the manuscript, provided statistical expertise, and is guarantor. GMA was responsible for administrative, technical, or material support and supervised the study. AL was responsible for administrative, technical, or material support. DR-D and SBS supervised the study. S-LTN provided statistical expertise and supervised the study.

  • Funding Funding: Harvard Pilgrim Health Care Foundation and a Canadian Institute for Health Research Chronic Disease New Emerging Theme (NET) programme grant (NET 54010). NKC was also supported by the Harvard Medical School fellowship in pharmaceutical policy research, a Frank Knox scholarship from Harvard University, and a Canadian Institutes of Health Research postdoctoral fellowship. SBS and DR-D are investigators in the HMO Research Network Center for Education and Research in Therapeutics, funded by the US Agency for Healthcare Research and Quality, and were also supported by grant No R01 AG022362-01 from the National Institute on Aging. AL is a senior scientist of the Canadian Institutes of Health Research.

  • Competing interests None declared.

  • Ethical approval The ethics review board of Sunnybrook and Women's College Health Sciences Centre, Toronto, approved this study.

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