Pharm 101: Metronidazole


Nitroimidazole antiprotozoal drug

  • Selectively absorbed by anaerobic bacteria and sensitive protozoa
  • Causes disruption of electron transport chain

  • PO/IV/suppository administration
  • Well absorbed
  • 99% bioavailability
  • Low protein binding 10-20%
  • Well distributed in tissues, including CSF
  • Hepatic metabolism
  • Renal excretion
    • Half-life 7.5 hours

Antimicrobial activity
  • Potent activity against anaerobes, including Bacteroides and Clostridium species
  • Clinical uses:
    • Anaerobic or mixed intra-abdominal infections
    • Vaginitis
    • Clostriudium difficile
    • Brain abscess

Adverse effects
  • Gastrointestinal
    • Nausea
    • Diarrhoea
    • Stomatitis
  • Neurological:
    • Headache
    • Metallic taste in mouth
    • Peripheral neuropathy with prolonged use
  • Thrombophlebitis
  • Disulfiram-like effect, therefore avoid alcohol
    • Inhibits aldehyde dehydrogenase and causes accumulation of acetaldehyde in blood
  • Inhibitions CYP 3A4 (responsible for metabolism of 50% of drugs)
    • Potentiates effect of warfarin

  • Hepatic insufficiency or renal failure require dose adjustment


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MBBS (UWA) CCPU Emergency Medicine Trainee with interests in medical education, ECG interpretation, and the use of point-of-care ultrasound in the undifferentiated patient. Co-author of the LITFL ECG Library | Twitter

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