Comparison of rivaroxaban concentrations between Asians and Caucasians and their correlation with PT/INR

The objectives of this study are to compare steady-state trough (Cmin,ss) and peak (Cmax,ss) concentrations of rivaroxaban between Asians and Caucasians and to evaluate the relationship between rivaroxaban concentrations and prothrombin time/international normalized ratio (PT/INR). Recruited patients were advised on the time to take rivaroxaban. Cmin,ss and PT/INR were taken when patients arrived. Cmax,ss and PT/INR were drawn between 2 and 4h later after the patient took rivaroxaban with food. Thirty patients were included in the analyses: 57% (n=17) males and 43% (n=13) females, 77% (n=23) on 20mg and 23% (n=7) on 15mg. Median PTtrough and PTpeak are moderately correlated with Cmin,ss (r(2)=0.43) and Cmax,ss (r(2)=0.49), respectively. Patients on 15mg have lower Cmin,ss and Cmax,ss versus Caucasians [12ng/ml vs. 57ng/ml (Cmin,ss); 87ng/ml vs. 229ng/ml (Cmax,ss), p<0.01 for both]. Patients on 20mg also have lower Cmin,ss and Cmax,ss versus Caucasians [14ng/ml vs. 44ng/ml (Cmin,ss); 101ng/ml vs. 249ng/ml (Cmax,ss), p<0.01 for both]. Subgroup analysis shows patients with BMI30 have lower Cmax,ss than patients with BMI<30 [80.47ng/ml vs. 124 (p=0.014)]. Cmin,ss and Cmax,ss were lower in Singaporeans than Caucasians. This may have an impact on the effectiveness of rivaroxaban in Singaporeans. Patients with higher BMI may not benefit similarly as patients with lower BMI. Lastly, the Dade Innovin reagent's measure of PT/INR is not sensitive towards changes in rivaroxaban concentrations.