Factors determining the maintenance dose of warfarin in Chinese patients

Chinese patients are reportedly more sensitive than Caucasians to the anticoagulant effect of warfarin. We examined warfarin dose requirements and their determinants in 151 Chinese out-patients on stable maintenance dose of warfarin with international normalized ratio of 2 to 2.5. Mean daily warfarin requirement was 3.3 +/- 1.4 mg, much lower than reported doses in Caucasian patients. The most important determinant was age (r = -0.43, p < 0.001), with progressively lower warfarin requirement with increasing age (p = 0.0001). There was a weaker association with body weight (r = 0.20, p = 0.01). Patients with chronic rheumatic heart disease tended to require a smaller dose than those with heart valve replacements (2.94 +/- 1.24 vs. 3.69 +/- 1.42 mg, p < 0.01). We confirm that Chinese patients require a smaller dose of warfarin for the same degree of anticoagulation. Age is the most important factor affecting dose requirement, although body weight and underlying disease also play a role.