title: Quantitation of simvastatin and its beta-hydroxy acid in human plasma by liquid-liquid cartridge extraction and liquid chromatography/tandem mass spectrometry.
abstract: A sensitive and reliable procedure for the simultaneous determination of simvastatin (SV) and its active beta-hydroxy acid metabolite (SVA) in human plasma was developed and validated. The analytes were extracted simultaneously from 0.5 ml aliquots of human plasma samples by methyl tert-butyl ether (MTBE) via Chem Elut cartridge extraction [also called liquid-solid extraction (LSE) or liquid-liquid cartridge extraction (LLCE)], separated through a Kromasil C(18) column (50 x 2 mm i.d. 5 microm) and detected by tandem mass spectrometry with a turbo ionspray interface. Stable isotope-labeled SV and SVA, (13)CD(3)-SV and (13)CD(3)-SVA, were used as internal standards. SV and SVA were detected in positive and negative ion modes, respectively, via within-run polarity switching. The use of Chem Elut cartridges not only provided a simple and efficient means of plasma sample extraction but also successfully reduced the interconversion between SV and SVA to an undetectable (for lactonization of SVA) or negligible (<0.07%, for hydrolysis of SV) level. The method showed excellent reproducibility, with intra- and inter-assay precisions <4.5% (RSD), and intra- and inter-assay accuracy between 94% and 107% of nominal values, for both analytes. The extraction recoveries were 78% and 87% on average for SV and SVA, respectively. The analyte was found to be stable in plasma through three freeze (-70 degrees C)-thaw (4 degrees C) cycles and for at least 3 h under bench-top storage condition in an ice-bath (4 degrees C), and also in the reconstitution solution at 4 degrees C for at least 24 h. The method has a lower limit of quantitation (LOQ) of 50 pg ml(-1) with a linear calibration range of 0.05-50 ng ml(-1) for both analytes, and has proved to be very reliable for the analysis of clinical samples.
authors.affiliation: Department of Drug Metabolism, Merck Research Laboratories, WP75A-303, West Point, Pennsylvania 19486, USA. jamie_zhao@merck.com
authors.forename: J J
authors.initials: JJ
authors.lastname: Zhao
authors.forename: I H
authors.initials: IH
authors.lastname: Xie
authors.forename: A Y
authors.initials: AY
authors.lastname: Yang
authors.forename: B A
authors.initials: BA
authors.lastname: Roadcap
authors.forename: J D
authors.initials: JD
authors.lastname: Rogers
mesh_terms: D000924:Anticholesteremic Agents / Q000097:blood*; D002138:Calibration; D002853:Chromatography, Liquid; D006801:Humans; D007202:Indicators and Reagents; D013058:Mass Spectrometry; D011786:Quality Control; D012015:Reference Standards; D015203:Reproducibility of Results; D019821:Simvastatin / Q000031:analogs & derivatives* / Q000097:blood*
chemical_list: D000924:Anticholesteremic Agents; D007202:Indicators and Reagents; C063287:simvastatin acid; D019821:Simvastatin