Simultaneous Quantification of Oroxylin A and Its Metabolite Oroxylin A-7-O-Glucuronide: Application to a Pharmacokinetic Study in Rat

Oroxylin A shows reversal activity on multidrug resistance and has an attractive safety profile. A highly sensitive and specific method based on liquid chromatography coupled with tandem mass spectroscopy was developed and validated for simultaneous determination of oroxylin A and its major metabolite, oroxylin A-7-O-glucuronide in rat plasma. The assay procedure involved precipitation of plasma samples with acetonitrile after adding luteolin as an internal standard. Chromatographic separation was achieved on a C-18 column using methanol and 0.5% formic acid as the mobile phase, eluting in a gradient system. Detection was achieved with selected reaction monitoring using the electrospray ionization technique. The method was validated by evaluation of selectivity, linearity, precision, accuracy and limit of quantification. Its applicability was demonstrated through the quantification of oroxylin A and oroxylin A-7-O-glucuronide in plasma after intravenous administration of oroxylin A at a dose of 20 mg kg(-1) to rats. The developed quantification method can now be used for pharmacokinetic studies after intravenous infusion of oroxylin A injection in rats.