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Antibiotic — Anaerobic Coverage Pregnancy: Use if clinically indicated — caution in first trimester; risk of ENT infection usually outweighs theoretical risk

Metronidazole

Brand names: Flagyl

Adult dose

Dose: 400 mg
Route: Oral
Frequency: Three times daily for 5–7 days
Max: 800 mg three times daily (severe infection)
Used in ENT for anaerobic cover in: peritonsillar abscess (quinsy), dental-origin ENT infections, Ludwig's angina, necrotising fasciitis (combined with other antibiotics), and aspiration pneumonia complicating ENT procedures. IV route for severe infections.

Paediatric dose

Dose: 7.5 mg/kg mg/kg
Route: Oral
Frequency: Three times daily
Max: 400 mg per dose
BNFc: 1 month–11 years 7.5 mg/kg TDS; 12–17 years 400 mg TDS. IV formulation for severe infections.

Dose adjustments

Renal

No dose adjustment in mild-moderate impairment; reduce dose frequency in severe impairment

Hepatic

Reduce dose in severe hepatic impairment

Paediatric weight-based calculator

BNFc: 1 month–11 years 7.5 mg/kg TDS; 12–17 years 400 mg TDS. IV formulation for severe infections.

Clinical pearls

  • Essential anaerobic cover for peritonsillar abscess — combined with benzylpenicillin IV (or co-amoxiclav) for drainage + antibiotic therapy
  • Ludwig's angina: life-threatening submandibular space infection — IV antibiotics (penicillin/metronidazole + gentamicin), airway management paramount, ITU involvement
  • Counsel about alcohol avoidance — disulfiram-like reaction (flushing, nausea, tachycardia) occurs even with small amounts of alcohol
  • Warfarin interaction clinically significant — check INR within 3–5 days of starting course
  • IV metronidazole 500 mg every 8 hours for severe ENT/orofacial infections or when oral route not possible

Contraindications

  • Hypersensitivity to nitroimidazoles
  • Disulfiram within 2 weeks

Side effects

  • Metallic taste
  • Nausea
  • Disulfiram-like reaction with alcohol
  • Peripheral neuropathy (prolonged use)
  • QT prolongation (high dose IV)

Interactions

  • Alcohol — disulfiram-like reaction; abstain during and 48h after
  • Warfarin — significantly increased INR
  • Lithium — increased toxicity

Monitoring

  • Symptom response
  • Peripheral neuropathy (prolonged use)
  • INR (if on warfarin)

Reference: BNFc; BNF 90; BNFc; NICE NG84; ENT-UK Ludwig's Angina guidance. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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