Indications for Metronidazole and Tinidazole Metronidazole is active against All obligate anaerobic bacteria (it is inactive against facultative anaerobic and aerobic bacteria) Certain protozoan parasites (eg, Trichomonas vaginalis, Entamoeba histolytica, Giardia intestinalis [lamblia]) Metronidazole is used primarily for infections caused by obligate anaerobes, often with other antimicrobials.