LC-MS/MS Method for Quantification of Atorvastatin, o-Hydroxyatorvastatin, p-Hydroxyatorvastatin, and Atorvastatin Lactone in Rat Plasma

A simple and sensitive liquid chromatography-tandem mass spectrometry method was developed for the quantification of atorvastatin, ortho-hydroxyatorvastatin, para-hydroxyatorvastatin, and atorvastatin lactone in rat plasma. Solid-phase extraction was used for preparation of samples. Rosuvastatin was chosen as an internal standard. Chromatographic separation was achieved on ZORBAX Eclipse C-18 Analytical, 4.6 x 100 mm (3.5 mu m) column with a gradient mobile phase composed of acetonitrile and 0.1% acetic acid, at a flow rate of 400 mu L min(-1). The column was kept at constant temperature (25 degrees C), and autosampler tray temperature was set at 4 degrees C. The following selected reaction monitoring (SRM) transitions were selected: (m/z, Q1 -> Q3, collision energy) atorvastatin (559.47 -> 440.03, 22 eV), atorvastatin lactone (541.36 -> 448.02, 19 eV), orthohydroxyatorvastatin (575.20 -> 440.18, 20 eV), para-hydroxyatorvastatin (575.54 -> 440.18, 20 eV), and rosuvastatin (482.25 with selected combination of two fragments 257.77, 31 eV, and 299.81, 35 eV) in positive ion mode. The method was validated over a concentration range of 0.5-20 ng mL(-1) for ortho-hydroxyatorvastatin and para-hydroxyatorvastatin and 0.1-20 ng mL(-1) for atorvastatin and atorvastatin lactone with excellent linearity (r(2) >= 0.99). This method demonstrated acceptable precision and accuracy at four quality control concentration levels. The detection limits were 0.1 and 0.13 ng mL(-1) for orthohydroxyatorvastatin and para-hydroxyatorvastatin, respectively, and 0.05 ng mL(-1) for atorvastatin and atorvastatin lactone. All analytes were found to be stable at examined conditions. Validated method was applied for determination of atorvastatin and its metabolites in plasma of experimental animals