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H2 Receptor Antagonist — Aspiration Prophylaxis Pregnancy: Famotidine: use with caution — limited safety data; omeprazole preferred in pregnancy

Ranitidine / Famotidine (H2 Antagonist — Aspiration Prophylaxis)

Brand names: Famotidine (generic), Pepcid

Adult dose

Dose: Famotidine: 20 mg oral 2 hours pre-operatively (aspiration prophylaxis). Ranitidine: withdrawn UK (NDMA contamination) — replaced by famotidine
Route: Oral
Frequency: Single pre-operative dose
Max: 40 mg
Aspiration prophylaxis: reduces gastric acid volume and pH before anaesthesia. Often combined with sodium citrate (30 mL oral immediately pre-induction) for rapid gastric neutralisation

Paediatric dose

Dose: 0.5-1 mg/kg oral (famotidine) mg/kg
Route: Oral
Frequency: Single pre-operative dose
Max: 20 mg
Seek specialist opinion for aspiration prophylaxis dosing in paediatric anaesthesia

Dose adjustments

Renal

Reduce famotidine dose in severe renal impairment (eGFR under 30): 20 mg every 48 hours

Hepatic

No dose adjustment required

Paediatric weight-based calculator

Seek specialist opinion for aspiration prophylaxis dosing in paediatric anaesthesia

Clinical pearls

  • Ranitidine was withdrawn from UK market in 2019 (MHRA) due to NDMA (N-nitrosodimethylamine) contamination — a probable human carcinogen; famotidine is the recommended alternative for aspiration prophylaxis
  • Aspiration risk reduction: H2 antagonist pre-operatively reduces gastric acid secretion for 6-8 hours; target gastric pH above 2.5 and volume below 25 mL to minimise aspiration pneumonitis risk (Mendelson criteria)
  • Rapid sequence induction (RSI) technique (cricoid pressure, rapid induction, immediate intubation) is the primary protection against aspiration — antacid prophylaxis is an adjunct
  • Sodium citrate (30 mL oral): immediate gastric pH neutralisation (alkaline buffer) given immediately before RSI induction — complements pre-operative H2 antagonist
  • NICE: Routine aspiration prophylaxis not required for all patients — reserve for high-risk groups (full stomach, emergency surgery, obesity, GORD, diabetes with gastroparesis, hiatus hernia)

Contraindications

  • Hypersensitivity to H2 antagonists

Side effects

  • Headache
  • Dizziness
  • Constipation or diarrhoea
  • Elevated liver enzymes (rare)
  • QT prolongation (famotidine — less than cimetidine)

Interactions

  • Antacids (reduce absorption — separate by 2 hours)
  • Ketoconazole / itraconazole (reduced absorption due to raised gastric pH)
  • Famotidine has fewer drug interactions than cimetidine (not a CYP inhibitor)

Monitoring

  • No specific monitoring required for single pre-operative dose

Reference: BNFc; BNF 90; MHRA Ranitidine Withdrawal 2019; AAGBI Preoperative Assessment Guidelines; Mendelson (1946) aspiration criteria. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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