Relative Susceptibilities of Gard ne re1 I a vaginal is (Haemophilus vaginalis), Neisseria gonorrhoeae, and Bacteroides fragilis to Metronidazole and Its Two Major Metabolites

Abstract

The susceptibilities of strains of G. vaginalis (H. vaginalis), N. gonorrhoeae and B. fragilis to metronidazole and its principal oxidative metabolites (1-[2-hydroxyethyl]-2-hydroxymethyl-5-nitroimidazole) (hydroxy metabolite) and 1-acetic acid-2-methyl-5-nitroimidazole (acid metabolite), were compared by determinations of the minimal inhibitory concentrations (MIC) of these compounds. Against 10 strains of G. vaginalis, the hydroxy metabolite was the most active (median MIC, 2 .mu.g/ml); the median MIC of metronidazole and of the acid metabolite were 8 and 64 .mu.g/ml, respectively. The hydroxy metabolite was also the most active against 15 strains of N. gonorrhoeae (median MIC, 32 .mu.g/ml). Metronidazole was the most active against 10 strains of B. fragilis (median MIC, 1 .mu.g/ml); the hydroxy and acid metabolites had median MIC of 2 and 64 .mu.g/ml, respectively. In the treatment of G. vaginalis-associated vaginitis [in humans] with metronidazole, the hydroxy metabolite may contribute a significant antimicrobial effect, in view of its excellent activity in vitro.