Flagyl (metronidazole) is not usually used to treat a typical urinary tract infection (UTI), such as uncomplicated bladder infection (acute cystitis). Most uncomplicated UTIs are caused by aerobic bacteria like Escherichia coli that are not reliably covered by metronidazole. Flagyl (metronidazole) is an antibiotic that can help treat certain infections caused by bacteria or parasites that also cause diarrhea. It is not used to treat most cases of sudden (acute) diarrhea, such as viral “stomach flu” or mild food poisoning. Find patient medical information for Metronidazole (Flagyl, Likmez) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings Flagyl, Flagyl ER, and Flagyl Injection (metronidazole) are antimicrobial drugs used to treat bacterial vaginosis, trichomonas, amebiasis, and anaerobic bacterial infections. Flagyl (metronidazole) is used to treat infections caused by anaerobic bacteria and parasites — organisms that thrive in low-oxygen environments. It is not effective against viral infections like colds or flu. Metronidazole, sold under the brand name Flagyl and Metrogyl among others, is an antibiotic and antiprotozoal medication. [10] It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vaginosis. [10] It is also used to treat infections caused by protozoa (eg, trichomoniasis and amebiasis) and infections caused by bacteria that do not need oxygen to survive. The extended-release tablets are used to treat women with vaginal infections (bacterial vaginosis). Metronidazole belongs to the class of medicines known as antibiotics.