famotidine
H2 receptor antagonist· Brands: Pepcid, PepcidineIVPO
Mechanism of action
Famotidine is a competitive antagonist of histamine H2 receptors on gastric parietal cells, reducing basal and stimulated gastric acid secretion. It does not affect H1 receptors or muscarinic receptors.
Pharmacokinetics
Famotidine is administered orally or intravenously. Its bioavailability is about 40-50% after oral administration. It is poorly protein bound and undergoes minimal hepatic metabolism, with approximately 65-70% excreted unchanged in the urine. The elimination half-life is about 2.5 to 4 hours, prolonged in renal impairment.
Indications & dosing
Gastro-oesophageal reflux disease (GERD)
Non-erosive GERD: 20 mg twice daily. Erosive oesophagitis: 40 mg twice daily for up to 12 weeks.
- adult · PO: 20–40 mg twice daily · Non-erosive GERD: 20 mg twice daily. Erosive oesophagitis: 40 mg twice daily for up to 12 weeks.
Duodenal ulcer (active)
Take at bedtime. Treatment usually continued for 4-8 weeks.
- adult · PO: 40 mg once daily · Take at bedtime. Treatment usually continued for 4-8 weeks.
Gastric ulcer (benign)
Take at bedtime. Treatment usually continued for 4-8 weeks.
- adult · PO: 40 mg once daily · Take at bedtime. Treatment usually continued for 4-8 weeks.
Zollinger-Ellison syndrome
Initial dose; adjust based on acid output. Doses up to 480 mg/day may be required.
- adult · PO: 20 mg every 6 hours · Initial dose; adjust based on acid output. Doses up to 480 mg/day may be required.
Stress ulcer prophylaxis in critically ill patientsoff-label
For patients on enteral feeding, oral route may be used. Use is not routine; follow institutional protocol.
- adult · IV: 20 mg every 12 hours · For patients on enteral feeding, oral route may be used. Use is not routine; follow institutional protocol.
Contraindications & precautions
- Hypersensitivity to famotidine or other H2-receptor antagonists · Cross-sensitivity may occur.
- Severe renal impairment (creatinine clearance < 30 mL/min) · Dose reduction required; consider alternate H2 blocker.
- Severe hepatic impairment · Use with caution; monitor for adverse effects.
- Adjust dose in renal impairment; reduce to 20 mg once daily or 10 mg twice daily if creatinine clearance < 30 mL/min.
- Use with caution in elderly patients, as confusion and hallucinations are more likely.
- Avoid in pregnancy and breastfeeding unless clearly needed; seek specialist advice.
- May interfere with gastric pH-dependent absorption of drugs such as ketoconazole, atazanavir, and iron salts; monitor effectiveness.
- Monitor patients with a history of gastric ulcer for malignancy before starting therapy, as symptoms may mask gastric cancer.
Adverse effects
- Headache
- Dizziness
- Constipation
- Diarrhoea
- Confusionserious
- Hallucinationsserious
- Thrombocytopeniaserious
- Anaphylaxisserious
Renal & hepatic adjustment
- eGFR 0–50: Reduce dose to half or increase the dosing interval to 36-48 hours.
Monitoring, pregnancy & toxicity
- Clinical response (symptom relief) · Periodically, at follow-up
- Renal function (serum creatinine, eGFR) · Before initiation and periodically in patients with renal impairment
- Neurological symptoms (confusion, hallucinations) · In patients with severe renal impairment or high doses
- Pregnancy: Famotidine is generally considered safe during pregnancy; available data do not indicate an increased risk of congenital anomalies. It may be used for GERD or peptic ulcer disease when clinically indicated.
- Toxicity: Overdose may cause hypotension, bradycardia, lethargy, or confusion. · Supportive care; monitor vital signs; consider activated charcoal if recent ingestion; approximately 25-30% is removed by haemodialysis.
Clinical notes
Use for peptic ulcer disease, gastro-oesophageal reflux disease, and prevention of stress ulcers. Also used for dyspepsia and heartburn. It is generally well tolerated; common adverse effects include headache, dizziness, constipation, and diarrhoea. Adjust dose in renal impairment. It can be used in pregnancy and breastfeeding if needed.
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BNF; local formulary