Preclinical pharmacokinetics and pharmacodynamics of apixaban, a potent and selective factor Xa inhibitor

Apixaban is a potent, highly selective, reversible, oral, direct factor Xa (fXa) inhibitor in development for thrombosis prevention and treatment. The preclinical pharmacokinetic (PK) attributes of apixaban feature small volume of distribution (Vd), low systemic clearance (CL), and good oral bioavailability. Apixaban is well absorbed in rat, dog, and chimpanzee, with absolute oral bioavailability of approximately 50% or greater. The steady-state Vd of apixaban is approximately 0.5, 0.2, and 0.17 l/kg in rats, dogs, and chimpanzees, while CL is approximately 0.9, 0.04, and 0.018 l/h/kg, respectively. In vitro metabolic clearance of apixaban is also low. Renal clearance comprises approximately 10-30% of systemic clearance in rat, dog, and chimpanzee. Anti-fXa activity, prothrombin time (PT), and HEPTEST(®) clotting time (HCT) prolongation correlated well with plasma apixaban concentration in rat, dog and chimpanzee. There was no lag time between apixaban plasma concentration and the pharmacodynamic (PD) markers, suggesting a rapid onset of action of apixaban. The PK/PD analyses were performed using an inhibitory E (max) model for anti-fXa assay and a linear model for PT and HCT assays. The IC(50) values for anti-fXa activity were 0.73 ± 0.03 and 1.5 ± 0.15 μM for rat and dog, respectively. The apparent K ( i ) values for PT were approximately 1.7, 6.6, and 4.8 μM for rat, dog and chimpanzee, respectively. The apparent K ( i ) for HCT was approximately 1.3 μM for dog. Apixaban exhibits desirable PK and PD properties for clinical development with good oral bioavailability, small Vd, low CL, and direct, predictable, concentration-dependent PD responses.