Mode of action of metronidazole on anaerobic bacteria and protozoa.

Metronidazole and related 5-nitroimidazoles are relatively nontoxic. Reduction of their nitro group, however, leads to the production of short-lived cytotoxic intermediates, which finally decompose into nontoxic end products. The toxicity of the intermediates is due to their interaction with deoxyribonucleic acid and possibly with other macromolecules. Metabolic pathways of low redox potential that are linked to ferredoxin or flavodoxin-like electron transport components reduce nitroimidazoles with great efficacy. Such pathways are characteristic of susceptible anaerobic protozoa and bacteria and are absent in nonsusceptible aerobic cells of the host.