, Volume 23, Issue 10, pp 1589-1594
Date: 10 Jul 2008

Patient Reported Receipt of Medication Instructions for Warfarin is Associated with Reduced Risk of Serious Bleeding Events

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Adverse drug events are an important cause of preventable hospitalizations.


To identify whether patient report of receipt of medication instructions and markers of complex care (multiple physicians, recent hospitalization) predict the risk of serious bleeding for older adults on warfarin.


Prospective cohort study of older adults.


Subjects filled new or refill prescriptions for warfarin at the time of enrollment.


Hospitalizations were identified through a state-wide registry. Discharge summaries of hospitalizations for possible warfarin related bleeding events were reviewed by trained abstractors and clinical experts. Incidence rate ratios (IRR) were estimated based on person-months of exposure using Poisson regression models.


From March 2002 through May 2003, we enrolled a total of 2346 adults on warfarin. Over a two-year follow-up period, there were 126 hospitalizations due to warfarin-related bleeding (4.6 hospitalizations per 100 person-years of exposure). Patients who reported receiving medication instructions from either a physician or nurse plus a pharmacist had a 60% reduced rate of subsequently experiencing a serious bleeding event over the next 2 years (adjusted IRR 0.40, 95% CI 0.24–0.68). Having ≥4 physicians providing medication prescriptions over the last 3 months and filling prescriptions at >1 pharmacy over the last 3 months were independently associated with increased bleeding rates (adjusted IRRs 2.37, 95% CI 1.22–4.57 and 1.61, 95% CI 0.97–2.67, respectively).


The rate of warfarin-related hospitalization for bleeding is substantially lower for patients who report receiving medication instructions from a physician or nurse and a pharmacist.

This study was supported by grant P01-HS11530 from the Agency for Healthcare Research and Quality. Dr. Metlay was supported by an Advanced Research Career Development Award from the Health Services Research and Development Service of the Department of Veterans Affairs. Dr. Hennessy is supported by NIH grants R01HL076697 and R01AG025152. Dr. Haynes is supported by a National Institutes of Health National Research Service Award (5-F32-AG-026180). Dr. Kimmel is supported by a National Institutes of Health Mid-Career Investigator Award in Patient Oriented Research (K24HL070936) and by NIH grant R01HL066176. Dr. Feldman is supported by a National Institutes of Health Mid-Career Investigator Award in Patient Oriented Research (K24-DK-002651). The funding agencies had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript.
Portions of this research were presented, in abstract form, at the 22nd International Conference on Pharmacoepidemiology & Therapeutic Risk Management, Lisbon, Portugal (August, 2006), and the Annual Meeting of the Society of General Internal Medicine, Toronto, CA (April, 2007).