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Clinical Pharmacist and Adjunct Clinical Instructor, Department of Pharmacy Services, University of Michigan Hospitals and Health Centers, Ann Arbor, MI
Medical Student, School of Medicine, University of North Carolina, Chapel Hill, NC
Medical Student, School of Medicine, University of North Carolina
Clinical Pharmacy Specialist, Division of Cardiovascular Medicine, The Gill Heart Institute, Lexington, KY
Assistant Professor, Division of Pharmacotherapy and Experimental Therapeutics, School of Pharmacy, University of North Carolina
Research Assistant Professor, Department of Biostatistics, School of Public Health, University of North Carolina
Graduate Student, Department of Biostatistics, School of Public Health, University of North Carolina
Associate Professor, School of Pharmacy, University of North Carolina
Associate Professor, Division of Cardiovascular Medicine, The Gill Heart Institute
Reprints: Dr. Smyth, Division of Cardiovascular Medicine, The Gill Heart Institute, 900 S. Limestone, Lexington, KY 40536, fax 859/281-4892, SusanSmyth{at}uky.edu
BACKGROUND: Aspirin therapy is a cornerstone in the prevention of atherothrombotic events, but recurrent vascular events are estimated to occur in 818% of patients taking aspirin for secondary prevention after 2 years. Estimates of biologic aspirin resistance vary from 5% to 60%, depending on the assay used. However, the relationship between biologic measurements of aspirin resistance and adverse clinical events remains unclear.
OBJECTIVE: To determine whether patients with documented myocardial infarction (MI) while on aspirin therapy (cases) were more likely to be aspirin resistant than were patients with coronary artery disease (CAD) who had no history of MI (controls) and to assess clinical predictors of aspirin resistance in patients with stable CAD.
METHODS: This casecontrol study examined aspirin responses using the VerifyNow Aspirin Assay system in 50 cases and 50 controls who had taken a dose of aspirin within 48 hours of presentation to the clinic visit. Odds ratios were estimated to determine the association between aspirin resistance and MI. Independent predictors of aspirin resistance were determined using univariate and multivariate analyses.
RESULTS: An increase in the prevalence of aspirin resistance among cases (16% vs 12% in controls) was not observed (OR 1.40; 95% CI 0.45 to 4.37; p = 0.566). In the overall CAD population, female sex was independently associated with aspirin resistance (OR 4.01; 95% CI 1.15 to 13.92; p = 0.029).
CONCLUSIONS: Additional large studies are required to understand whether biologically defined aspirin resistance is associated with increased risk for cardiovascular events, with special attention paid to sex differences.
Key Words: aspirin resistance, coronary artery disease, myocardial infarction
Published Online, April 24, 2007. www.theannals.com, DOI 10.1345/aph.1H621
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