A highly sensitive LC-MS/MS method for simultaneous determination of glycyrrhizin and its active metabolite glycyrrhetinic acid: application to a human pharmacokinetic study after oral administration

A highly sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of glycyrrhizin (GL) and its active metabolite, glycyrrhetinic acid (GA) from human plasma was validated and applied to a human pharmacokinetic study. The analytes were extracted from human plasma using an Oasis MAX cartridge and chromatographic separation was performed on an Inertsil ODS-3 column. The detection was performed using an API 4000 mass spectrometer operating in the positive electrospray ionization mode. Selected ion monitoring transitions of m/z 823→453 for GL and m/z 471→149 for GA were obtained. The response was a linear function of concentration over the ranges of 0.5–200 ng/mL for GL and 2–800 ng/mL for GA (both R2 > 0.998). Using this method, pharmacokinetics of GL after single oral administration of a clinical dose (75 mg) to six healthy male Japanese volunteers were evaluated. GL was detected in the plasma of all subjects and the average Cmax was 24.8 ± 12.0 ng/mL. In contrast, Cmax of GA was 200.3 ± 60.3 ng/mL, i.e., ~8-fold higher than that of GL. This is the first report clarifying pharmacokinetic profiles of GL and GA simultaneously at a therapeutic oral dose of a GL preparation.