title: Measurement of rivaroxaban and apixaban in serum samples of patients.
abstract: BACKGROUND
  The determination of rivaroxaban and apixaban from serum samples of patients may be beneficial in specific clinical situations when additional blood sampling for plasma and thus the determination of factor Xa activity is not feasible or results are not plausible.
  
  
  METHODS
  The primary aim of this study was to compare the concentrations of rivaroxaban and apixaban in serum with those measured in plasma. Secondary aims were the performance of three different chromogenic methods and concentrations in patients on treatment with rivaroxaban 10 mg od (n = 124) or 20 mg od (n = 94) or apixaban 5 mg bid (n = 52) measured at different time.
  
  
  RESULTS
  Concentrations of rivaroxaban and apixaban in serum were about 20-25% higher compared with plasma samples with a high correlation (r = 0·79775-0·94662) using all assays (all P < 0·0001). The intraclass correlation coefficients were about 0·90 for rivaroxaban and 0·55 for apixaban. Mean rivaroxaban concentrations were higher at 2 and 3 h compared with 1 and 12 h after administration measured from plasma and serum samples (all P-values < 0·05) and were not different between 1 vs. 12 h (plasma and serum).
  
  
  CONCLUSIONS
  The results indicate that rivaroxaban and apixaban concentrations can be determined specifically from serum samples.
authors.affiliation: Department of Clinical Pharmacology, Medical Faculty Mannheim, Ruprecht-Karls University Heidelberg, Mannheim, Germany.
authors.forename: Job
authors.initials: J
authors.lastname: Harenberg
authors.forename: Sandra
authors.initials: S
authors.lastname: Krämer
authors.forename: Shanshan
authors.initials: S
authors.lastname: Du
authors.forename: Shabnam
authors.initials: S
authors.lastname: Zolfaghari
authors.forename: Astrid
authors.initials: A
authors.lastname: Schulze
authors.forename: Roland
authors.initials: R
authors.lastname: Krämer
authors.forename: Christel
authors.initials: C
authors.lastname: Weiss
authors.forename: Martin
authors.initials: M
authors.lastname: Wehling
authors.forename: Gregory Y H
authors.initials: GY
authors.lastname: Lip
mesh_terms: D000284:Administration, Oral; D019644:Arthroplasty, Replacement, Hip; D019645:Arthroplasty, Replacement, Knee; D001281:Atrial Fibrillation / Q000188:drug therapy; D001681:Biological Assay / Q000379:methods; D016022:Case-Control Studies; D002863:Chromogenic Compounds; D065427:Factor Xa Inhibitors / Q000008:administration & dosage / Q000097:blood*; D006801:Humans; D009025:Morpholines / Q000008:administration & dosage / Q000097:blood*; D011183:Postoperative Complications / Q000517:prevention & control; D011720:Pyrazoles / Q000097:blood* / Q000627:therapeutic use; D011728:Pyridones / Q000097:blood* / Q000627:therapeutic use; D000069552:Rivaroxaban; D044967:Serum / Q000737:chemistry; D013048:Specimen Handling / Q000379:methods; D013876:Thiophenes / Q000008:administration & dosage / Q000097:blood*; D013923:Thromboembolism / Q000517:prevention & control
chemical_list: D002863:Chromogenic Compounds; D065427:Factor Xa Inhibitors; D009025:Morpholines; D011720:Pyrazoles; D011728:Pyridones; D013876:Thiophenes; C522181:apixaban; D000069552:Rivaroxaban
keywords: Apixaban; chromogenic substrate methods; direct oral anticoagulants; plasma; rivaroxaban; serum