In vitro activity: Metronidazole is relatively inactive until it is metabolized within host or microbial cells. Metronidazole is activated when it receives an electron from ferredoxin or fla vodoxin that is reduced by POR in anaerobic or microaerophilic bacteria or luminal parasites. Metronidazole damages cells by forming protein and DNA adducts. Metronidazole has activity against protozoans like Entamoeba histolytica, Giardia lamblia and Trichomonas vaginalis, for which the drug is first approved as an effective treatment. The activity of metronidazole against anaerobic bowel flora has been used for prophylaxis and treatment of patients with Crohn's disease who might develop an infectious complication. Metronidazole has played an important role in anaerobic-related infections. Metronidazole has notable effectiveness in treating anaerobic brain abscesses. Metronidazole resistance tends to result from de novo mutation in the resident rdxA gene, rather than from lateral transfer of mutant rdxA (or other) genes from unrelated but Mtzr strains. Metronidazole partially inhibits growth stimulate forward mutation to rifampin resistance in rdxA(+) (Metronidazole(s)) and also in rdxA (Metronidazole(r)) H. pylori strains, and that expression of rdxA in Escherichia coli results in equivalent Mtz-induced mutation. Metronidazole leads to apoptosis-like features in growing cultures of axenic B. hominis, including key morphological and biochemical features of programmed cell death (PCD), viz. nuclear condensation and nicked DNA in nucleus, reduced cytoplasmic volume, externalization of phosphatidylserine and maintenance of plasma membrane integrity with increasing permeability.

Infect Control Hosp Epidemiol. 2010 May;31(5):431-55; Antimicrob Agents Chemother. 1999 Jul;43(7):1533-41; Drugs. 1991 Sep;42(3):428-67.