||Letaxaban, also known as TAK-442, is a potent, selective, and orally active factor Xa inhibitor, which is a tetrahydropyrimidin-2(1H)-one derivative. TAK-442inhibited endogenous FXa activity in platelet-poor human [half-maximal inhibitory concentration (IC(50)): 53 nM, TAK-442] and rat (IC(50): 32 nM, TAK-442) plasma. TAK-442 inhibited in vitro reconstituted human prothrombinase (system included FXa, calcium, and washed platelets) with an IC(50) value of 51 nM. In a rat model of balloon injury, thrombin activity on the surface of injured vessels increased to 3.2-, 22-, and 5.8-fold the activity on the surface of the intact aorta at 5 minutes, 1 hour, and 24 hours after the injury, respectively. At approximately 1 hour after the injury, TAK-442 blocked platelet-associated thrombin generation on the surface of injured aortas with an IC(50) value of 19 nM.