Stereoselective analysis of fluvastatin in human plasma for pharmacokinetic studies

Fluvastatin, an inhibitor of cholesterol biosynthesis, is commercialized as a racemic mixture of the (+)-3R,5S and (−)-3S,5R stereoisomers, although inhibition of HMG-CoA reductase mainly resides in the (+)-(3R,5S)-fluvastatin isomer. The aim of the present study was to analyze fluvastatin isomers in human plasma with application to studies on kinetic disposition. Plasma samples of 1 ml were eluted into 3 ml LC-18 Supelclean (Supelco) columns equilibrated with methanol and water. The columns were washed with water and acetonitrile and then eluted with methanol containing 0.2% diethylamine. The (+)-3R,5S and (−)-3S,5R isomers were separated by HPLC on a Chiralcel OD-H chiral phase column and detected by fluorescence (λ_ex 305 nm; λ_em 390 nm). The quantification limit was 0.75 ng for each isomer/ml plasma and linearity was observed up to 625 ng/ml. The relative standard deviations obtained for intra- and inter-assay precision were lower than 10% and the recovery was higher than 80% for both enantiomers. Application of the method to a stereoselective study on the pharmacokinetics of fluvastatin administered as a single oral dose (Lescol, 20 mg) to a healthy volunteer revealed stereoselectivity, with the highest plasma concentrations being observed for the (−)-3S,5R isomer (C_max 92.4 vs. 60.3 ng/ml, AUC^0–∞ 133.3 vs. 97.4 ng h/ml, Cl/f 150.2 vs. 205.2 l h⁻¹ and V_d/f 4.4 vs. 6.0 l/kg).