A sensitive LC-MS/MS method to quantify loureirin B in rat plasma with application to preclinical pharmacokinetic...

A novel method for the quantification of loureirin B in rat plasma using high-performance liquid chromatography/tandem mass spectrometry (LC-MS/MS) was developed. Loureirin B and internal standard (buspirone) were extracted by liquid-liquid extraction and separated on a Agilent XDB C18 column (50 mm x 4.6 mm, 5 microm). As mobile phase a binary mixture of methanol (containing 0.1% formic acid)-water (containing 0.1% formic acid) was delivered by a Shimadzu LC-20AD pump in gradient mode at a flow rate of 0.4 ml/min in a run time of 5.0 min. The detector was a Q-trap mass spectrometer with an electrospray ionization (ESI) interface operating in the multiple reaction monitoring (MRM) mode. The calibration curve of loureirin B in plasma showed good linearity over the concentration range of 0.08-100 ng/ml. The limit of detection and limit of quantification were 0.03 ng/ml and 0.08 ng/ml, respectively. Intra- and inter-day precisions (as relative standard deviation) in all samples were both within 15%. The validated method was successfully applied to a preliminary pharmacokinetic study of loureirin B in rats. After oral administration of 16 g/kg longxuejie to rats, the main pharmacokinetic parameters tmax, Cmax, t(1/2), Ke and AUC(0-T) were 0.8 h, 7.99 microg/l, 1.94 l h, 0.365/h, and 22.21 microg h/l, respectively.