The influence of ethnicity on warfarin dosage requirement.
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 > or = 18 years, target international normalized ratio (INR) 2-3, and warfarin management within the clinic for > or = 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.
Dang
Mai-Trang N
MT
Department of Clinical Pharmacy, University of California at San Francisco, San Francisco, CA 94143-0622, USA.
Hambleton
Julie
J
Kayser
Steven R
SR
D001741:Black or African American / Q000706:statistics & numerical data; D000368:Aged; D044466:Asian People / Q000706:statistics & numerical data; D001281:Atrial Fibrillation / Q000188:drug therapy / Q000208:ethnology; D015331:Cohort Studies; D003920:Diabetes Mellitus / Q000188:drug therapy / Q000208:ethnology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006630:Hispanic or Latino / Q000706:statistics & numerical data; D006801:Humans; D007037:Hypothyroidism / Q000188:drug therapy / Q000208:ethnology; D019934:International Normalized Ratio; D002546:Ischemic Attack, Transient / Q000188:drug therapy / Q000208:ethnology; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013318:Stroke Volume / Q000187:drug effects; D020246:Venous Thrombosis / Q000188:drug therapy / Q000208:ethnology; D016277:Ventricular Function, Left / Q000187:drug effects; D014859:Warfarin / Q000494:pharmacology / Q000627:therapeutic use*; D044465:White People / Q000706:statistics & numerical data
D014859:Warfarin