Simultaneous quantitation of rosuvastatin and ezetimibe in human plasma by LC-MS/MS: Pharmacokinetic study of fixed-dose formulation and separate tablets

A simple, high-throughput and highly sensitive liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method has been developed for the simultaneous estimation of rosuvastatin and free ezetimibe. Liquid-liquid extraction was carried out using methyl-tert butyl ether after prior acidification from 300 mu L human plasma. The recovery for both the analytes and their deuterated internal standards (ISs) ranged from 95.7 to 99.8%. Rosuvastatin and ezetimibe were separated on Symmetry C-18 column using acetonitrile and ammonium formate buffer, pH3.5 (30:70, v/v) as the mobile phase. The analytes were well resolved with a resolution factor of 3.8. Detection and quantitation were performed under multiple reaction monitoring using ESI(+) for rosuvastatin (m/z 482.0 -> 258.1) and ESI(-) for ezetimibe (m/z 407.9 -> 271.1). A linear response function was established in the concentration ranges of 0.05-50.0 ng/mL and 0.01-10.0 ng/mL for rosuvastatin and ezetimibe, respectively, with correlation coefficient, r(2)>= 0.9991. The IS-normalized matrix factors for the analytes ranged from 0.963 to 1.023. The developed method was successfully used to compare the pharmacokinetics of a fixed-dose combination tablet of rosuvastatin-ezetimibe and co-administered rosuvastatin and ezetimibe as separate tablets to 24healthy subjects. The reliability of the assay was also assessed by reanalysis of 115 subject samples.