Establishment of a liquid chromatographic/mass spectrometry method for quantification of tetrandrine in rat plasma and its application to pharmacokinetic study

A rapid and sensitive liquid chromatography-tandem mass spectrometric method (LC/MS/MS) for the determination of tetrandrine in rat plasma has been developed, fully validated and successfully applied to pharmacokinetic study in Sprague–Dawley (SD) rats after a single oral administration. Sample preparation involves a liquid–liquid extraction with n-hexane–dichlormethane (65:35, containing 1% 2-propanol isopropyl alcohol, v/v). Tetrandrine and brodimoprim (internal standard) were well separated by LC with a Dikma C18 column using acetonitrile–methanol–ammonium formate aqueous solution (20 mM) containing 0.3% formic acid (20:30:50, v/v/v) as mobile phase. Detection was performed on a triple quadrupole mass spectrometer in multiple reaction monitoring mode. The ionization was optimized using ESI(+) and selectivity was achieved using MS/MS analysis, m/z 623.0 → 381.0 and m/z 339.0 → 281.0 for tetrandrine and I.S., respectively. The present method exhibited good linearity over the concentration range of 5–2000 ng/mL for tetrandrine in rat plasma with a lower limit of quantification of 5 ng/mL. The intra- and inter-day precision were 2.0–9.2% and 4.5–9.4%, and the intra- and inter-day accuracy ranged from −7.6 to 10.3% and −6.0 to 5.3%, respectively. No endogenous compounds were found to interfere with the analysis, and tetrandrine was stable during the whole assay period. The method was successfully applied to a pharmacokinetic study after an intragastric administration (i.g.) of tetrandrine to SD rats with a single dose of 50 mg/kg. The results confirm that the assay is suitable for the pharmacokinetic study of tetrandrine.