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H₂-Receptor Antagonist Pregnancy: Compatible — H₂ receptor antagonists considered safe in pregnancy (preferred over PPIs in first trimester).

Famotidine

Brand names: Pepcid, Antodine

Adult dose

Dose: Peptic ulcer: 40mg at night for 4–8 weeks (maintenance 20mg at night). GORD: 20mg BD for 6–12 weeks. Dyspepsia: 20mg BD.
Route: Oral
Frequency: Once at night (peptic ulcer) or twice daily (GORD/dyspepsia)
Max: 40mg twice daily (GORD — maximum)
H₂-receptor antagonist — second-line to PPIs. Fewer drug interactions than cimetidine. Useful when PPIs contraindicated or not tolerated. Onset within 1 hour; duration up to 10–12 hours.

Paediatric dose

Dose: 0.5 mg/kg
Route: Oral
Frequency: Twice daily
Max: 40mg per dose
BNF for Children: 1–17 years: 0.5mg/kg BD (max 20mg per dose). GORD: 1–3 months (unlicensed): 0.5mg/kg BD. Source: BNF for Children 2024.

Dose adjustments

Renal

eGFR <30: reduce dose to 20mg at night or every 36–48 hours. Risk of CNS side effects in severe renal impairment.

Hepatic

No dose adjustment required in hepatic impairment.

Paediatric weight-based calculator

BNF for Children: 1–17 years: 0.5mg/kg BD (max 20mg per dose). GORD: 1–3 months (unlicensed): 0.5mg/kg BD. Source: BNF for Children 2024.

Clinical pearls

  • Preferred H₂RA over cimetidine — fewer drug interactions (cimetidine inhibits CYP1A2, CYP2C9, CYP2D6, CYP3A4; famotidine does not).
  • H₂RA tolerance (tachyphylaxis): efficacy decreases with regular use after 2–4 weeks — not suitable for long-term acid suppression.
  • Useful as step-down from PPI when long-term acid suppression no longer required at full PPI level.
  • OTC-available in UK (Pepcid 10mg) for dyspepsia — prescribe generically.

Contraindications

  • Known hypersensitivity to H₂-receptor antagonists

Side effects

  • Headache, dizziness
  • Constipation or diarrhoea
  • Confusion (especially in elderly or renal impairment — CNS penetration)
  • QT prolongation (rare, at high doses)

Interactions

  • Atazanavir: reduced antiretroviral absorption — separate doses by ≥10 hours
  • Ketoconazole / itraconazole: reduced absorption (acid-dependent)
  • Warfarin: minimal interaction (unlike cimetidine)

Monitoring

  • Symptom response
  • Renal function (adjust dose if eGFR falls <30)

Reference: BNFc; BNF 90; NICE CG17 GORD; SPC Pepcid. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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