Quantitative determination of atorvastatin and ortho-hydroxy atorvastatin in human plasma by liquid chromatography tandem mass spectrometry and pharmacokinetic evaluation.

A specific, sensitive and simple method was developed to determine the levels of both atorvastatin and ortho-hydroxy atorvastatin in human plasma. The analytes and internal standard pitavastatin were extracted from plasma by liquid-liquid extraction, separated on a Zorbax SB-C18 column, eluted with a mobile phase of water:acetonitrile (45:55 v/v), both containing 5% methanol and 0.01% formic acid. Detection was performed with an electrospray ionization triple quadrupole mass spectrometer in positive ion mode using multiple reaction monitoring. The standard calibration curves of atorvastatin and ortho-hydroxy atorvastatin were linear in the concentration range of 0.2-20 and 0.1-20 ng/mL, respectively. The intra- and inter-day precisions were < 7.7% and the accuracy was within ± 5.9%. The method has been successfully used for the study of the pharmacokinetics of atorvastatin and ortho-hydroxy atorvastatin in Chinese patients with coronary heart disease after a single oral dose of 20 mg atorvastatin. The mean values for the area under the plasma concentration-time curve for atorvastatin and ortho-hydroxy atorvastatin were 63.1 and 46.9 ng.h/mL, respectively.