title: Association of apixaban therapy and prothrombin time in patients with atrial fibrillation.
abstract: BACKGROUND
  This study evaluated whether measuring prothrombin time (PT) using particular reagents of interest predicted apixaban-associated anticoagulant activity in Japanese patients with non-valvular atrial fibrillation (NVAF). METHODS AND RESULTS: Two reagents, Shinplastin Excel S and Coagpia PT-N, were used to evaluate PT under apixaban therapy. From June 2013 to February 2014, 103 NVAF patients were recruited, and PT was measured at 3 time points: (1) anytime in the outpatient clinic, (2) at peak, and (3) at trough. In spike-in experiments using pooled citrated normal human platelet-poor plasma with these PT reagents, apixaban prolonged PT values in a concentration-dependent manner. PT values significantly correlated between both reagents (r=0.97) in outpatients. PT values in outpatients taking 5-mg apixaban bid were significantly prolonged and had wide inter- and intraindividual variability. Peak values were significantly higher than trough values, with both values higher than normal. The dose change of apixaban from 5 mg bid to 2.5 mg bid in outpatients halved the degree of PT prolongation in each NVAF patient.
  
  
  CONCLUSIONS
  The PT value measured by these specific reagents can predict apixaban-associated anticoagulant activity, although there is significant interpatient variability.
authors.affiliation: Department of Cardiology, Yamaguchi Grand Medical Center.
authors.forename: Masashi
authors.initials: M
authors.lastname: Kanemoto
authors.forename: Hiroko
authors.initials: H
authors.lastname: Kuhara
authors.forename: Toru
authors.initials: T
authors.lastname: Ueda
authors.forename: Takahiro
authors.initials: T
authors.lastname: Shinohara
authors.forename: Takamasa
authors.initials: T
authors.lastname: Oda
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Nakao
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Kamei
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Ikeda
authors.forename: Takashi
authors.initials: T
authors.lastname: Fujii
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001281:Atrial Fibrillation / Q000097:blood* / Q000188:drug therapy*; D015331:Cohort Studies; D065427:Factor Xa Inhibitors / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011517:Prothrombin Time; D011720:Pyrazoles / Q000008:administration & dosage*; D011728:Pyridones / Q000008:administration & dosage*
chemical_list: D065427:Factor Xa Inhibitors; D011720:Pyrazoles; D011728:Pyridones; C522181:apixaban