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Antibiotic (Nitroimidazole)

Metronidazole

Brand names: Flagyl, Metrolyl

Metronidazole is a nitroimidazole antimicrobial active against anaerobic bacteria and certain protozoa, widely used for anaerobic infections, Clostridioides difficile infection, dental and intra-abdominal infections, and protozoal infections such as giardiasis and trichomoniasis.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

After reductive activation in anaerobic organisms it generates reactive intermediates that damage microbial DNA, leading to strand breakage and cell death.

Prescribing in practice

  • A disulfiram-like reaction can occur with alcohol, so patients should avoid alcohol during treatment and for a short period afterwards per the SPC.
  • Prolonged or high-dose courses carry a risk of peripheral neuropathy and, rarely, central nervous system effects, so duration should be no longer than necessary.
  • It interacts with warfarin and can enhance its anticoagulant effect, so the INR should be monitored when they are used together.

Monitoring

Monitor for neurological symptoms with prolonged courses and check the INR in patients taking warfarin.

Counselling the patient

  • Do not drink alcohol while taking this medicine or for a short time after finishing it.
  • Complete the full course even if you feel better.
  • Report any numbness, tingling or persistent unsteadiness.

Evidence & guidelines

Metronidazole is an established first-line agent for anaerobic and several protozoal infections, supported by long-standing clinical use and guideline recommendation.

Reference: PHE Antibiotic Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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