title: Apixaban, an oral, direct and highly selective factor Xa inhibitor: in vitro, antithrombotic and antihemostatic studies.
abstract: BACKGROUND
  Apixaban is an oral, direct and highly selective factor Xa (FXa) inhibitor in late-stage clinical development for the prevention and treatment of thromboembolic diseases.
  
  
  OBJECTIVE
  We evaluated the in vitro properties of apixaban and its in vivo activities in rabbit models of thrombosis and hemostasis.
  
  
  METHODS
  Studies were conducted in arteriovenous-shunt thrombosis (AVST), venous thrombosis (VT), electrically mediated carotid arterial thrombosis (ECAT) and cuticle bleeding time (BT) models.
  
  
  RESULTS
  In vitro, apixaban is potent and selective, with a K(i) of 0.08 nm for human FXa. It exhibited species difference in FXa inhibition [FXa K(i) (nm): 0.16, rabbit; 1.3, rat; 1.7, dog] and anticoagulation [EC(2x) (microm, concentration required to double the prothrombin time): 3.6, human; 2.3, rabbit; 7.9, rat; 6.7, dog]. Apixaban at 10 microm did not alter human and rabbit platelet aggregation to ADP, gamma-thrombin, and collagen. In vivo, the values for antithrombotic ED(50) (dose that reduced thrombus weight or increased blood flow by 50% of the control) in AVST, VT and ECAT and the values for BT ED(3x) (dose that increased BT by 3-fold) were 0.27 +/- 0.03, 0.11 +/- 0.03, 0.07 +/- 0.02 and > 3 mg kg(-1) h(-1) i.v. for apixaban, 0.05 +/- 0.01, 0.05 +/- 0.01, 0.27 +/- 0.08 and > 3 mg kg(-1) h(-1) i.v. for the indirect FXa inhibitor fondaparinux, and 0.53 +/- 0.04, 0.27 +/- 0.01, 0.08 +/- 0.01 and 0.70 +/- 0.07 mg kg(-1) day(-1) p.o. for the oral anticoagulant warfarin, respectively.
  
  
  CONCLUSIONS
  In summary, apixaban was effective in the prevention of experimental thrombosis at doses that preserve hemostasis in rabbits.
authors.affiliation: Thrombosis Research, Bristol-Myers Squibb Company, Pennington, NJ 08534, USA. pancras.wong@bms.com
authors.forename: P C
authors.initials: PC
authors.lastname: Wong
authors.forename: E J
authors.initials: EJ
authors.lastname: Crain
authors.forename: B
authors.initials: B
authors.lastname: Xin
authors.forename: R R
authors.initials: RR
authors.lastname: Wexler
authors.forename: P Y S
authors.initials: PY
authors.lastname: Lam
authors.forename: D J
authors.initials: DJ
authors.lastname: Pinto
authors.forename: J M
authors.initials: JM
authors.lastname: Luettgen
authors.forename: R M
authors.initials: RM
authors.lastname: Knabb
mesh_terms: D000818:Animals; D002341:Carotid Artery Thrombosis; D004195:Disease Models, Animal; D004285:Dogs; D065427:Factor Xa Inhibitors; D006487:Hemostasis / Q000187:drug effects; D006801:Humans; D010974:Platelet Aggregation / Q000187:drug effects; D011720:Pyrazoles / Q000008:administration & dosage / Q000494:pharmacology*; D011728:Pyridones / Q000008:administration & dosage / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats; D013927:Thrombosis / Q000188:drug therapy* / Q000517:prevention & control; D020246:Venous Thrombosis
chemical_list: D065427:Factor Xa Inhibitors; D011720:Pyrazoles; D011728:Pyridones; C522181:apixaban