Metronidazole should be stored at room temperature and protected from light. Interactions may occur if other medication is taken while taking Flagyl. Metronidazole is an imidazole antibiotic that is used in the treatment of many protozoal and bacterial infections. It is important to maintain a constant level of Flagyl in the blood. Metronidazole is an antibiotic effective against anaerobic bacteria and certain parasites. Interactions may occur if other medication is taken while taking Flagyl.