Effect of the Direct Factor Xa Inhibitor Apixaban in Rat Models of Thrombosis and Hemostasis

Apixaban is an oral, direct, and highly selective factor Xa inhibitor in late-stage clinical development for the prevention and treatment of thromboembolic diseases. Apixaban was evaluated in rat thrombosis and hemostasis models. Thrombosis was produced in the carotid artery by FeCl2 application, in the vena cava by either FeCl2 application or tissue factor injection, and in an arterial-venous shunt. Hemostasis was assessed using cuticle, renal cortex, and mesenteric artery bleeding times. Intravenous apixaban infusions of 0.1, 0.3, 1, and 3 mg/kg per hour increased the ex vivo prothrombin time to 1.24, 1.93, 2.75, and 3.98 times control, respectively. The 0.3, 1, and 3-mg/kg per hour doses inhibited thrombosis in all models. Concentrations for 50% thrombus reduction ranged from 1.84 to 7.57 mM. The 3-mg/kg per hour dose increased cuticle, renal, and mesenteric bleeding times to 1.92, 2.13, and 2.98 times control, respectively. Lower doses had variable (1 mg/kg per hour) or no effect (0.1, 0.3 mg/kg per hour) on hemostasis. Heparin's prolongation of renal and cuticle bleeding time was twice that of apixaban when administered at a dose that approximated apixaban (3 mg/kg per hour) efficacy in arterial thrombosis. In summary, apixaban was effective in a broad range of thrombosis models at doses producing modest increases in multiple bleeding time models.