Xterra ms column

Rifampin was administered to mice at 10 mg/kg/day for seven days to achieve CYP3A and P-glycoprotein induction (Matheny et al., 2004 (link)). Tofacitinib was then administered in two doses 6 h apart for a total dose of 15, 22.5 or 30 mg/kg; the second dose was co-administered with rifampin at 10 mg/kg. Blood was collected from mice at 1, 2, 3, 4, 6, 7, 8, 10, 12 and 24 h post-administration of the first dose of tofacitinib. Serum samples were separated by centrifugation and stored at − 80 °C until analysis. Drug levels were measured using an AB-Sciex QTrap 5500 LC/MS/MS (MA, USA) using 0.1% formic acid in deionized water (mobile phase A) and 0.1% formic acid in acetonitrile (mobile phase B) at a flow rate of 200 μl/min with an XTerra® MS column (C₁₈, 2.1 mm × 50 mm, particle size 3.5 μm, Waters Corporation, MA, USA). Quantitation of drug levels was performed using m/z transitions of 823.1/791.2 for rifampin and 313.4/149.1 for tofacitinib, and the chromatograms were analyzed using the Multiquant 2.1 software from AB-Sciex (MA, USA).