Pharm 101: Metronidazole

Class

Nitroimidazole antiprotozoal drug

Pharmacodynamics

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

Pharmacokinetics

• 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

Precautions/contraindications

• Hepatic insufficiency or renal failure require dose adjustment

References

• Katzung BG. Basic and Clinical Pharmacology. 14e. 2018: 895-896, 929-930