Development and validation of a liquid chromatography-tandem mass spectrometry method for simultaneous determination of amlodipine, atorvastatin and its metabolites ortho-hydroxy atorvastatin and para-hydroxy atorvastatin in human plasma and its application in a bioequivalence study.

A sensitive, simple and rapid high-performance liquid chromatography coupled with positive ion electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) method was developed for the simultaneous determination of amlodipine, atorvastatin and its metabolites ortho-hydroxy atorvastatin and para-hydroxy atorvastatin in human plasma. The analytes were extracted from human plasma through liquid-liquid extraction method. A mixture of methyl tert-butyl ether and ethyl acetate (50:50, v/v) was used as the extractant. The chromatographic separation was achieved on a CAPCELLPAK CR 1:4 (5 μm, 150 mm × 2.0 mm i.d.) column within 6.0 min with the mobile phase consisted of acetonitrile and ammonium acetate buffer (20mM) containing 0.3% formic acid (50:50, v/v). Data acquisition was carried out in multiple reaction monitoring (MRM) mode. The method was validated and was successfully applied to the bioequivalence study of combination tablets containing AM and AT with coadministered individual drugs in 50 healthy Chinese male volunteers.