Abstract Number: PB1072
Meeting: ISTH 2021 Congress
Background: Studies suggest that Asians may require lower doses of antithrombotics as compared to Caucasians. It is worthwhile to explore if serum rivaroxaban levels differ between SG and UK.
Aims: To compare steady-state trough rivaroxaban levels between SG and UK patients and identify factors affecting rivaroxaban plasma levels.
Methods: A total of 104 SG and 173 UK subjects were included in the study. Comparison of the median Cmin,ss between both cohorts was performed among appropriately dosed patients using the Mann-Whitney U test (non-normal). Measured Cmin,ss were classified as “higher than range” or “lower than range” with respect to the published reference range to determine factors affecting rivaroxaban levels. Covariates with a p value < 0.1 from the univariate analysis were included in the multivariate regression to determine factors driving out-of-range Cmin,ss.
Results: Median trough levels for 20mg dose-group (n = 189) did not differ between SG and UK groups which were predominantly Asian and Caucasian respectively. In the 15mg dose-group (14 SG vs 29 UK), trough rivaroxaban levels were significantly lower for the SG cohort (46.04ng/mL vs 70.08ng/mL, p = 0.041). After controlling for body mass index, appropriate dose and time from last dose to blood sampling, “UK cohort” (OR = 6.022, 95% CI = 1.293 – 28.043, p = 0.022) and “poorer renal function” (OR = 0.972, 95% CI = 0.948 – 0.996, p = 0.022) remained significant factors driving “higher than range” trough levels. A SG subgroup analysis revealed a 3% and 14.1% thrombo-embolic (TE) and bleeding risk respectively.
Conclusions: Caucasians are more likely to experience “higher than range” trough rivaroxaban levels as compared to Asians. TE rates in the SG cohort, suggest that the dose requirement could be higher for Asians without causing too many adverse drug reactions. Larger studies should be commissioned to determine all factors affecting TE and bleeding outcomes.
To cite this abstract in AMA style:Yong EX, Lin YY, Tan D, Chan E, Speed V, Patel J, Yap ES, Chang G, Gallagher P. A Comparative Cohort Study of Serum Rivaroxaban Levels in Singaporean (SG) and British (UK) Non-valvular Atrial Fibrillation (NVAF) Patients [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/a-comparative-cohort-study-of-serum-rivaroxaban-levels-in-singaporean-sg-and-british-uk-non-valvular-atrial-fibrillation-nvaf-patients/. Accessed December 7, 2021.
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