Development and validation of two liquid chromatography–tandem mass spectrometry methods for the determination of silibinin and silibinin hemisuccinate in human plasma

To investigate the pharmacokinetics of silibinin and silibinin hemisuccinate in human plasma, two high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) methods were developed and validated. The methods require a small volume of sample (100 μL), and the recovery of the analytes was complete with a good reproducibility (CV% 1.7–9.5), after a simple protein precipitation. Naringenin was used as internal standard. The chromatographic methods provided a good separation of diastereoisomers A and B of both silibinin and silibinin hemisuccinate onto a Chromolith Performance RP18e 100 mm × 3 mm column, with a resolution of peaks from plasma matrix in less than 6 min. The methods precision values expressed as CV% were always ≤6.2% and the accuracy was always well within the acceptable 15% range. Quantification was performed on a triple-quadrupole tandem mass spectrometer by Selected Reaction Monitoring (SRM) mode, in a negative ion mode, via electrospray ionization (ESI). The lower limit of quantitation was set at 5.0 ng/mL (silibinin) and 25.0 ng/mL (silibinin hemisuccinate), and the linearity was validated up to 1000.0 and 12,500.0 ng/mL, for silibinin and silibinin hemisuccinate, respectively, with correlation coefficients (R2) of 0.991 or better. The methods were suitable for pharmacokinetic studies and were successfully applied to human plasma samples from subjects treated intravenously with Legalon® SIL at the dose of 20 mg/kg, expressed as silibinin.