In vitro susceptibility of Helicobacter pylori to several antimicrobial combinations

Synergy between metronidazole and its hydroxymetabolite and between each compound and amoxicillin or tetracycline-HCl was determined against Helicobacter pylori. Metronidazole plus its hydroxymetabolite and either compound combined with amoxicillin showed synergism against all 10 strains of H. pylori tested. Metronidazole plus tetracycline-HCl or the hydroxymetabolite plus tetracycline-HCl acted synergistically against seven and six strains, respectively, acted additively against three strains, and had no additional effect against one strain. These results may help to explain the in vivo efficacies of metronidazole combinations in the treatment of H. pylori-associated gastritis.