Determination of edoxaban equivalent concentrations in human plasma by an automated anti-factor Xa chromogenic assay

The day 5 concentration estimates were significantly correlated between the 2 assays (P < 0.0001 for both edoxaban doses). The geometric least squares mean (GLSM) ratio (90% confidence interval) for edoxaban equivalent concentrations vs edoxaban + M-4 concentrations was 114.3% (108.2-120.8) for edoxaban 60 mg (P < 0.0001) and 113.0% (107.1-119.2) for edoxaban 90 mg (P = 0.0002). The GLSM ratio for edoxaban concentrations in sodium citrate vs lithium heparin tubes for 60-mg and 90-mg edoxaban doses were 82.8% (78.5-87.3) and 83.9% (79.1-89.0), respectively. In this study, an anti-FXa chromogenic assay with edoxaban-specific calibrators and controls demonstrated good accuracy in estimating edoxaban concentrations across a wide range of concentrations relative to LC/MS/MS at steady state following the administration of once-daily edoxaban for 5 days.