In vitro anti-Helicobacter pylori activity of Extractum liquiritiae, glycyrrhizin and its metabolites.

OBJECTIVES To investigate the in vitro activity of Extractum liquiritiae (EL), glycyrrhizic acid (GL), glycyrrhetinic acid (GA) and a novel lipophilic derivative of glycyrrhetinic acid monoglucuronide (GAMG), acetylated GAMG (aGAMG), against 29 Helicobacter pylori strains. METHODS The MIC of each compound was determined by the agar dilution method, and the killing kinetics were monitored in brain heart infusion broth ( approximately 10(6)-10(7) cfu/mL) at 0, 4, 24, 48, 72 and 96 h. RESULTS GA was the most potent compound (MIC(50 /90), 50/100 mg/L), inhibiting 79.3% of the strains at MIC < or =50 mg/L. Clarithromycin-resistant strains were susceptible at 12.5 and 25 mg/L, and metronidazole-resistant strains at 25-50 and at 200 mg/L. The MIC distribution (mg/L) of aGAMG was < or =6.25 (29.2%), 50 (4.2%), 100-200 (12.5%) and > or =400 (54.1%). EL and GL were less active (MICs >400 mg/L). GA exhibited rapid, concentration and strain-dependent bactericidal activity. CONCLUSIONS The potent in vitro activity of GA against H. pylori provides a further explanation for its beneficial effect on peptic ulcers. Its effectiveness against clarithromycin-resistant strains provides hope that it can form the basis for an alternative therapeutic agent against H. pylori.