Metronidazole kills a wide variety of bacteria that are known collectively as anaerobic bacteria. This means that they do not need oxygen to grow and multiply. Anaerobic bacteria can cause infections in areas of the body such as the bones, gut, pelvic cavity and gums. Metronidazole is used to treat these types of infections, as well as leg ulcers and pressure sores that are infected with anaerobic bacteria. Metronidazole is used as part of triple therapy to eradicate a type of bacteria called Helicobacter pylori (H pylori) from the gut. The presence of these bacteria in the gut is associated with ulcers.