Apixaban (BMS-562247-01) is an orally active anticoagulant that inhibits coagulation factor Xa, directly preventing the conversion of prothrombin to thrombin and the formation of cross-linked fibrin clots.

FXa (rabbit):0.17 nM(Ki), FXa (human):0.08 nM(Ki)

Apixaban demonstrates excellent pharmacokinetic properties in dogs, characterized by very low clearance (Cl: 0.02 L/kg/h), low volume of distribution (Vdss: 0.2 L/kg), a half-life (T1/2: 5.8 h), and oral bioavailability (F: 58%). Its antithrombotic efficacy is evident in models of venous thrombosis, arteriovenous shunt thrombosis, and electrically induced carotid artery thrombosis in rabbits, with EC50 values of 110 nM, 270 nM, and 70 nM, respectively.

When applied to normal human plasma in vitro, Apixaban extends coagulation time, doubling the prothrombin time (3.6 μM), modified prothrombin time (0.37 μM), activated partial thromboplastin time (7.4 μM), and HepTest (0.4 μM). Apixaban exhibits high selectivity in inhibiting human and rabbit Factor Xa, with Ki values of 0.08 and 0.17 nM, respectively. Additionally, Apixaban demonstrates maximum effectiveness in human and rabbit plasma in PT (Prothrombin Time) and APTT (Activated Partial Thromboplastin Time) assays, with comparatively lesser effects observed in rat and dog plasma.

Purified FXa is obtained after activation with Russell's viper venom followed by affinity chromatography. The resulting FXa is > 95% pure as judged by sodium dodecylsulfate polyacrylamide gel electrophoresis. The substrate affinity values for FXa, expressed as the Michaelis-Menten-Henri constant (Km), for human, rabbit, rat and dog FXa are determined using the chromogenic substrate S-2765, and are 36, 60, 240 and 70 μM, respectively. The substrate hydrolysis is monitored by measuring absorbance at 405 nm at 25°C for up to 30 min using a SpectraMax 384 Plus plate reader and SoftMax. FXa activity for each substrate and inhibitor concentration pair is determined in duplicate. The Ki values are calculated by non-linear least-squares fitting of the steady-state substrate hydrolysis rates to the equation for competitive inhibition (Equation 1) using GRAFIT, where v equals reactions velocity in OD min?1, Vmax equals maxiumum reaction velocity, S equals substrate concentration, and I equals inhibitor concentration.