Metronidazole is a drug effective against bacteria, amoeba and other protozoans like Trichomonas.

Mechanism of Action:

Metronidazole inhibits nucleic acid synthesis by disrupting DNA and causing strand breakage.


The metabolism of Metronidazole is mainly in the liver. It is mainly excreted in the urine and a small proportion in the feces.

Indications for use and dosages:

  1. Anaerobic bacterial infections: In oral or dental infections, as a part of antibiotic regimen in sepsis, urogenital infections etc. Given intravenously 15mg/kg as loading dose and half of it as maintenance.
  2. In colorectal surgeries. Dosage is same as anaerobic infections.
  3. In hepatic encephalopathy suspected due to bacterial overgrowth, for gut sterilization.
  4. Bacterial vaginosis: Orally 500 mg twice daily for one week
  5. Amebiasis: 500-750 mg thrice daily for 5-10 days.
  6. Trichomonas: 250 mg thrice daily for one week
  7. Giardiasis: 500 mg twice a day for one week
  8. Pelvic Inflammatory Disease: 500 mg twice daily for 2 weeks with quinolones
  9. H.Pylori infection: 250-500 mg once daily for 2 weeks as a part of combination protocol.
  10. Inflammatory bowel disease: Crohns disease and ulcerative colitis.

Adverse Effects:

  1. Gastrointestinal: Nausea, vomiting, diarrhea, decreased appetite, metallic taste
  2. Neurological: headache, dizziness, ataxia, seizures, aseptic meningitis
  3. Allergy related: hypersensitivity, Steven Johnson syndrome, toxic epidermal necrolysis
  4. Hematological such as neutopenia
  5. Disulfiram like reaction to ethanol.


Serious interactions are with drugs like Disulfiram, Cisapride, Erythromycin, Warfarin etc

Use in Pregnancy:

It is a category B drug in pregnancy, that is no significant teratogenicity found hence may be used if absolutely necessary

Use in Lactation:

It is secreted in milk hence not advisable during lactation.

Common brand names in India:

Flagyl, Metrogyl



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