LC-MS quantification and pharmacokinetics of the multi-constituents of Huangqin Tang in rat plasma after different single oral doses

The current study aims to investigate the pharmacokinetic properties of Huangqin Tang on different oral doses.  An LC-MS method for simultaneous determination of flavonoids and terpenoids in rat plasma was developed and validated.  Plasma samples were treated with hydrochloric acid (containing 1% ascorbic acid), precipitated with acetonitrile, separated on a Zorbax SB-C18 column, detected by single quadruple mass spectrometry with an electrospray ionization interface, and quantified using selected ion monitoring mode.  All pharmacokinetic parameters were processed by non-compartmental analysis using WinNonlin software.  The results of specificity, linearity, intra-day and inter-day precisions, accuracy, and stability for LC-MS assay were suitable for the quantification of paeoniflorin, baicalin, wogonoside, baicalein, wogonin, oroxylin A, glycyrrhizic acid and glycyrrhetinic acid in rat plasma.  The concentration–time profiles of baicalin, wogonoside, baicalein, wogonin, oroxylin A and glycyrrhizic acid showed double-peak phenomenon after Huangqin Tang was orally administered at 40 g?kg⁻¹ dose; all eight constituents in rat plasma showed good dose-exposure relationship within the dosage of 10-40 g?kg⁻¹; although plasma concentrations were different, the flavonoids with the same backbone showed the similar fate in the body with the corresponding dosage.  In conclusion, the LC-MS assay was successfully applied for the pharmacokinetic study of multi-constituents of Huangqin Tang with different doses.  Additionally, these constituents demonstrated good pharmacokinetic properties in the body.