Metronidazole 400mg tablets are commonly prescribed to treat a wide range of bacterial and parasitic infections. These include conditions such as bacterial vaginosis, gastrointestinal infections, dental infections, and infections caused by anaerobic bacteria. The 400mg strength is often used for moderate to severe infections, depending on the doctors recommendation. Metronidazole works by stopping the growth of bacteria and parasites, helping the body eliminate the infection effectively. It is usually taken with or after food to reduce stomach upset.