Sta apixaban calibrator

Apixaban and rivaroxaban concentrations were measured in plasma by anti-Xa assay with Berichrom Heparin on the CS-2500 coagulation analyser calibrated with the STA-Apixaban calibrator or STA-Rivaroxaban calibrator (Diagnostica Stago, France). Dabigatran concentration was assessed by an in-house method for determination of diluted thrombin time^{18 (link)}. Levetiracetam concentration was determined by HPLCMS/MS (LCQ Fleet, Thermo Scientific, USA). Creatinine was measured in serum by a routine biochemical method and creatinine clearance was calculated using the Cockcroft-Gault formula.

The anti-Xa activity of apixaban was measured in citrate-anticoagulated PPP by the Comparative Coagulation Laboratory in the Animal Health Diagnostic Center at Cornell University. The PPP was harvested from the supernatant of PRP after high-speed centrifugation (13,000 × g, Accuspin Micro, Thermo Scientific, Rockford, IL, USA) for 5 min. The PPP was frozen at −20°C and assays were performed in batches. The PPP was thawed at 37°C in a water bath before analysis with an automated coagulation analyzer (STA® Compact, Diagnostica Stago, Parsipanny, NJ, USA). The assay is configured with a bovine activated Factor X reagent added in excess to the test plasma and a chromogenic substrate of Factor Xa (STA®-Liquid anti-Xa, Diagnostica Stago). In this assay, residual, uninhibited Factor Xa cleaves the chromogenic substrate such that the inverse of the color change in the reaction mixture is proportional to the drug concentration in the test plasma. Results are expressed as ng/mL anti-Xa activity, based on the calibration standard containing known apixaban concentrations in human plasma (STA®-Apixaban Calibrator, Diagnostica Stago). Assay controls, consisting of apixaban spiked-human plasma (STA®-Apixaban Controls) were measured before each batch of test samples.