|Factor Xa Activity
||The activity of Rivaroxaban against purified serine proteases is measured using chromogenic or fluorogenic substrates in 96-well microtiter plates. The enzymes are incubated with Rivaroxaban or its solvent, dimethyl sulfoxide (DMSO), for 10 minutes. The reactions are initiated by the addition of the substrate, and the color or fluorescence is monitored continuously at 405 nm using a Spectra Rainbow Thermo Reader, or at 630/465 nm using a SPECTRAfluor plus, respectively, for 20 minutes. Enzymatic activity is analyzed in the following buffers (final concentrations): human FXa (0.5 nM), rabbit FXa (2 nM), rat FXa (10 nM), or urokinase (4 nM) in 50 mM Tris–HCl buffer pH 8.3, 150 mM NaCl, and 0.1% bovine serum albumin (BSA); Pefachrome FXa (50–800 μM) or chromozym U (250 μM) with thrombin (0.69 nM), trypsin (2.2 nM), or plasmin (3.2 nM) in 0.1 μM Tris–HCl, pH 8.0, and 20 mM CaCl2; chromozym TH (200 μM), chromozym plasmin (500 μM), or chromozym trypsin (500 μM) with FXIa (1 nM) or APC (10 nM) in 50mM phosphate buffer, pH 7.4, 150 mM NaCl; and S 2366 (150 or 500 μM) with FVIIa (1 nM) and tissue factor (3 nM) in 50 mM Tris–HCl buffer,pH 8.0, 100 mM NaCl, 5 mM CaCl2 and 0.3% BSA, H-D-Phe-Pro-Arg-6-amino-1-naphthalene-benzylsulfonamide-H2O (100 μM) and measured for 3 hours. The FIXaβ/FX assay, comprising FIXaβ (8.8 nM) and FX (9.5 nM) in 50 mM Tris–HCl buffer, pH 7.4, 100 mM NaCl, 5 mM CaCl2 and 0.1% BSA, is started by the addition of I-1100 (50 μM), and measured for 60 minutes. The inhibitory constant (Ki) against FXa is calculated according to the Cheng–Prusoff equation. The IC50 is the amount of inhibitor required to diminish the initial velocity of the control by 50%.