Metronidazole

Nitroimidazole·Infectious Diseases - Other Antibiotics

Intra-abdominal sepsis, pelvic inflammatory disease, brain abscess, C. difficile, Trichomonas, Giardia

PBSNITROIMIDAZOLEFlagyl, Metrogyl200 mg tabletS4+1

Max Dose

2 g/day

Half-life

8 h

Disulfiram

ALCOHOL

Neuropathy

CHRONIC

Rapid Summary

Overview

Highly potent bactericidal agent against strict anaerobes and protozoa. Penetrates abscesses, bone, and the blood-brain barrier beautifully.

Maximum Dose

Max 2 g/day.

Clinical Focus

Interacts violently with alcohol. Prolonged courses cause peripheral neuropathy.

Bottom Line

Metronidazole is the first-line treatment for anaerobic infections and C. difficile, but causes a severe disulfiram-like reaction with alcohol and peripheral neuropathy with prolonged use.

Formulation & Access

Brand Names

Flagyl, Metrogyl

Oral Routes

Tablets (200 mg, 400 mg).

Parenteral

Pre-mixed infusion bags (500 mg/100 mL) for IV use. Suppositories for PR.

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Intra-abdominal sepsis, pelvic inflammatory disease, brain abscess, C. difficile, Trichomonas, Giardia.

Clinical Place

The foundational drug for any infection 'below the diaphragm' to cover gut anaerobes (Bacteroides).

Quick reference

Class & Role

Nitroimidazole — Highly potent bactericidal agent against strict anaerobes and protozoa.

Route / Formulation

Tablets (200 mg, 400 mg). (Flagyl, Metrogyl)

Usual Dose & Max

IV 500 mg q12h (or PO 400 mg q12h). Max 2 g/day.

Key Indication Doses

Anaerobic Sepsis / Abscess: IV 500 mg q12h (or PO 400 mg q12h). C. Difficile (Mild): PO 400 mg TDS for 10-14 days. Trichomoniasis / Giardia: PO 2 g STAT single dose. Hepatic Impairment: Reduce dose in severe liver disease (metabolised hepatically).

Best Uses

Metronidazole is the first-line treatment for anaerobic infections and C. difficile, but causes a severe disulfiram-like reaction with alcohol and peripheral neuropathy with prolonged use.

Avoid / Cautions

Active CNS disease (seizures). Pregnancy Category B2. Often avoided in 1st trimester but used if required.

Key Risks

Neurological: Peripheral neuropathy (usually with courses > 14 days), optic neuropathy. CRITICAL — Seizures, encephalopathy at massive doses. Gastrointestinal: Severe nausea, metallic taste in mouth, anorexia. Haematological: Mild, reversible neutropenia.

Key Interactions

Alcohol. Causes a severe 'Disulfiram-like' reaction (accumulation of acetaldehyde) resulting in violent vomiting, flushing, tachycardia, and hypotension. Must avoid alcohol during and for 48h after course. Warfarin. Metronidazole inhibits CYP2C9, drastically spiking INR. Halve the Warfarin dose proactively.

Monitoring

Warn patients about metallic taste and strict zero-alcohol rule. Monitor LFTs if prolonged course.

Clinical Pearl

Oral metronidazole has 100% bioavailability. If the patient can swallow, switch from IV to PO instantly to save money and protect their veins.

Access

Flagyl, Metrogyl200 mg tablet

Brand: Flagyl, Metrogyl
Formulation: Tablets (200 mg, 400 mg)

Metronidazole

Nitroimidazole·Infectious Diseases - Other Antibiotics

Intra-abdominal sepsis, pelvic inflammatory disease, brain abscess, C. difficile, Trichomonas, Giardia

PBSNITROIMIDAZOLEFlagyl, Metrogyl200 mg tabletS4+1

Max Dose

2 g/day

Half-life

8 h

Disulfiram

ALCOHOL

Neuropathy

CHRONIC

Rapid Summary

Overview

Highly potent bactericidal agent against strict anaerobes and protozoa. Penetrates abscesses, bone, and the blood-brain barrier beautifully.

Maximum Dose

Max 2 g/day.

Clinical Focus

Interacts violently with alcohol. Prolonged courses cause peripheral neuropathy.

Bottom Line

Metronidazole is the first-line treatment for anaerobic infections and C. difficile, but causes a severe disulfiram-like reaction with alcohol and peripheral neuropathy with prolonged use.

Formulation & Access

Brand Names

Flagyl, Metrogyl

Oral Routes

Tablets (200 mg, 400 mg).

Parenteral

Pre-mixed infusion bags (500 mg/100 mL) for IV use. Suppositories for PR.

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Intra-abdominal sepsis, pelvic inflammatory disease, brain abscess, C. difficile, Trichomonas, Giardia.

Clinical Place

The foundational drug for any infection 'below the diaphragm' to cover gut anaerobes (Bacteroides).

Quick reference

Class & Role

Nitroimidazole — Highly potent bactericidal agent against strict anaerobes and protozoa.

Route / Formulation

Tablets (200 mg, 400 mg). (Flagyl, Metrogyl)

Usual Dose & Max

IV 500 mg q12h (or PO 400 mg q12h). Max 2 g/day.

Key Indication Doses

Best Uses

Metronidazole is the first-line treatment for anaerobic infections and C. difficile, but causes a severe disulfiram-like reaction with alcohol and peripheral neuropathy with prolonged use.

Avoid / Cautions

Active CNS disease (seizures). Pregnancy Category B2. Often avoided in 1st trimester but used if required.

Key Risks

Key Interactions

Monitoring

Warn patients about metallic taste and strict zero-alcohol rule. Monitor LFTs if prolonged course.

Clinical Pearl

Oral metronidazole has 100% bioavailability. If the patient can swallow, switch from IV to PO instantly to save money and protect their veins.

Access

Flagyl, Metrogyl200 mg tablet

Brand: Flagyl, Metrogyl
Formulation: Tablets (200 mg, 400 mg)