Mechanism of Action

  • Covalently binds to anaerobic bacterial DNA (anaerobes are unable to reduce metronidazole to inactive form)- causes bacterial death (bacteriocidal)


  • Anaerobic bacterial infections e.g. dental/gum infections; intra-abdominal/biliary tree infections; occasionally aspiration pneumonia; abscesses/fistulating disease; bad skin infections
  • Protozoal infections e.g. Trichomonas vaginalis


  • Do not take with alcohol
  • In severe liver disease, reduce the dose to one-third (avoid if possible)
  • If used for long-period, it is recommended that blood monitoring (FBC, U&E and LFT)

Side effects

  • Common
    • GI disturbance (inc nausea and vomiting); taste disturbance; furred tongue; oral mucositis; anorexia
  • Very rare
    • Hepatitis; jaundice; pancreatitis;
    • drowsiness; dizziness; headache; ataxia; psychotic disorders;
    • Darkening of urine
    • Thrombocytopenia, pancytopenia
    • Myaligia, arthralgia
  • Prolonged intensive therapy
    • Peripheral neuropathy
    • Leucopenia
    • Seizures
    • Rarely aseptic meningitis; optic neuropathy


  • Alcohol
  • Warfarin – increases effect
  • May increase plasma levels of antiepileptics e.g. phenytoin

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