Development and Validation of an LC–MS-MS Method for Determination of Simvastatin and Simvastatin Acid in Human Plasma: Application to a Pharmacokinetic Study

A liquid chromatography–tandem mass spectrometry method was developed and validated for the simultaneous determination of simvastatin (SV) and simvastatin acid (SVA) in human plasma. To improve assay sensitivity and achieve simultaneous analysis, SVA monitored in (−)ESI (electrospray ionization) mode within the first 4.5 min and SV thereafter in (+)ESI mode. The separation of all compounds was achieved in about 6.2 min using a C18 reverse-phase fused-core® column (Ascentis® Express C18) and a mobile phase, which was composed of 2.00 ± 0.05 mM ammonium acetate buffer titrated to pH 3.8 with glacial acetic acid–acetonitrile (25:75, v/v), in isocratic mode at a flow rate of 0.500 mL/min. Additionally, a solid-phase extraction step was performed to reduce any ion-suppression and/or enhancement effects. The developed method was linear in the concentration range of 0.100–74.626 ng/mL for SV, and 0.100–48.971 ng/mL for SVA, with correlation coefficient greater than 0.99 for both analytes. The method has shown tremendous reproducibility, with intra- and inter-day precision