Despite higher absolute event rates for efficacy and safety outcomes in East Asians , the relative efficacy of rivaroxaban ( 20 mg once daily ; 15 mg once daily for creatinine clearance of 30-49 mL/min ) versus warfarin with respect to the primary efficacy end point ( stroke/systemic embolism ) was consistent among East Asians and non-East Asians ( interaction P = 0.666 ) .