Rivaroxaban is an oral, direct inhibitor of Factor X, being developed for the prevention and treatment of arterial and venous thrombosis with a Ki of 0.4 nM. Rivaroxaban also inhibits prothrombinase activity (IC50 = 2.1 nM). Rivaroxaban also shows a similar affinity to purified human (IC50 = 0.7 nM) and rabbit Factor X (IC50 = 0.8 nM), but a lesser potency against purified rat Factor X (IC50 = 3.4 nM). Endogenous human and rabbit Factor X in plasma is inhibited to a similar extent by Rivaroxaban (IC50 = 21 nM and 21 nM, respectively), while 14-fold higher concentrations are required in rat plasma (IC50 = 290 nM). Rivaroxaban exhibits high permeability and polarized transport across Caco-2 cells as a substrate of the P-gp, but exhibits no inhibitory effect on P-gp-mediated drμg transport up to concentrations of 100 μM in vitro. Rivaroxaban is an oral, direct inhibitor of Factor X, being developed for the prevention and treatment of arterial and venous thrombosis with a Ki of 0.4 nM. Rivaroxaban also inhibits prothrombinase activity (IC50 = 2.1 nM). Rivaroxaban also shows a similar affinity to purified human (IC50 = 0.7 nM) and rabbit Factor X (IC50 = 0.8 nM), but a lesser potency against purified rat Factor X (IC50 = 3.4 nM). Endogenous human and rabbit Factor X in plasma is inhibited to a similar extent by Rivaroxaban (IC50 = 21 nM and 21 nM, respectively), while 14-fold higher concentrations are required in rat plasma (IC50 = 290 nM). Rivaroxaban exhibits high permeability and polarized transport across Caco-2 cells as a substrate of the P-gp, but exhibits no inhibitory effect on P-gp-mediated drug transport up to concentrations of 100 μM in vitro.