Properties of Glycyrrhizin in Kampo Extracts Including Licorice Root and Changes in the Blood Concentration of Glycyrrhetic Acid after Oral Administration of Kampo Extracts

We investigated in vitro the properties of glycyrrhizin (GL), such as dissolution, absorption and resolution, using a Sho-Seiryu-To extract, a Sho-Saiko-To extract, both including a licorice root, and licorice extract. The dissolution of GL differed with the pH of the solvent. The absorption (partition coefficient) of GL decreased with an increase in pH, and increased in the presence of other active constituents, such as baicalin, baicalein, and ephedrine. In the case of the Sho-Saiko-To extract, the conversion from GL to glycyrrhetic acid (GA) by beta-glucuronidase originated from E. coli occurred slowly. It was also suppressed by adding baicalin. We determined in vivo the pharmacokinetics of GA after oral administration of Kampo extracts in healthy volunteers. In each Kampo extract, the time of administration had no influence on the mean maximum blood concentration (Cmax) and the area under the blood concentration-time curve (AUC). Tmax was delayed in the case of the administration after meal (p < 0.05).