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at time of writing, Pharmacy Practice Resident, Department of Clinical Pharmacy, University of California at San Francisco, San Francisco, CA; now, Clinical Pharmacist, Transplant Surgery, Clinical Instructor, Department of Pharmacy Services, University of Washington Medical Center, Seattle, WA
Associate Clinical Professor of Medicine, Division of Hematology Oncology, Department of Medicine, University of California at San Francisco
Professor of Clinical Pharmacy, Department of Clinical Pharmacy, University of California at San Francisco
Reprints: Dr. Kayser, Department of Clinical Pharmacy, University of California at San Francisco, 521 Parnassus Ave., Box 0622, San Francisco, CA 94143-0622, fax 415/476-6632, skayser{at}itsa.ucsf.edu
BACKGROUND: The optimal dose of warfarin varies among individuals, and the prediction of a maintenance dose is difficult. Ethnicity has been reported to influence warfarin dosing.
OBJECTIVE: To quantitate the influence of ethnicity on warfarin dose requirement.
METHODS: We conducted a retrospective cohort study at a university
anticoagulation clinic to evaluate the influence of ethnicity on warfarin
dose. Inclusion criteria included age 
18 years, target international
normalized ratio (INR) 2–3, and warfarin management within the clinic
for 3 months with a minimum of 5 clinic visits. We collected clinical and
demographic data including age, gender, weight, ethnicity, disease states,
concomitant medications, indication, weekly warfarin dosage, and INR. To
assess potential confounders, multivariate, repeated-measures regression
analysis was used to identify and adjust for variables that may influence the
maintenance dose of warfarin.
RESULTS: Of the 345 patients who met the inclusion criteria, 27% were Asian American, 6% Hispanic, 54% white, and 14% African American. The adjusted mean (95% CI) weekly warfarin doses for patients with an INR goal of 2 to 3 were Asian Americans 24 mg (21 to 27), Hispanics 31 mg (25 to 37), whites 36 mg (34 to 39), and African Americans 43 mg (39 to 47) (p < 0.001). Additional factors found to influence warfarin dose requirement included age, weight, concomitant use of amiodarone, and diagnosis of venous thromboembolism.
CONCLUSIONS: Warfarin dose requirements vary across ethnic groups even when adjusted for confounding factors, suggesting that genetic variation contributes to interpatient variability.
Key Words: ethnic influence, polymorphism, warfarin
Published Online, April 26, 2005. www.theannals.com, DOI 10.1345/aph.1E566
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