Makindo Medical Notes

💡 Always test for and eradicate Helicobacter pylori in suspected peptic ulcer disease before or during acid-suppressive therapy. Famotidine is a well-tolerated H₂ receptor antagonist that reduces gastric acid secretion and is particularly effective at suppressing nocturnal acid output.

🧠 About

• Famotidine is a potent histamine H₂-receptor antagonist acting selectively on gastric parietal cells.
• It decreases both basal and stimulated gastric acid secretion, reducing hydrogen ion concentration and gastric volume.
• It is longer-acting and better tolerated than cimetidine or ranitidine, with fewer drug interactions.
• Effective for short-term ulcer healing, long-term prophylaxis, and symptom relief in reflux disease.

⚙️ Mechanism of Action

• Histamine released from enterochromaffin-like (ECL) cells binds to parietal cell H₂ receptors to stimulate the proton pump (H⁺/K⁺-ATPase).
• Famotidine competitively inhibits these H₂ receptors, blocking the histamine-mediated component of acid secretion.
• Also indirectly reduces acid stimulated by gastrin and vagal activity.
• Particularly suppresses nocturnal acid production, which is histamine-dominant.

🎯 Indications

• Peptic ulcer disease (gastric and duodenal).
• Gastro-oesophageal reflux disease (GORD) and reflux oesophagitis.
• Prevention of stress ulceration in critically ill patients (alternative to PPIs).
• Non-ulcer dyspepsia and Zollinger–Ellison syndrome (rare indication).

💊 Dosing (Adults)

• Benign gastric ulcer: 40 mg once daily for 4–6 weeks (before bedtime).
• Duodenal ulcer: 20 mg nocte for 4 weeks; may increase to 40 mg if needed.
• Reflux oesophagitis: 20–40 mg twice daily for 6–12 weeks, then 20 mg BD for maintenance.
• Stress ulcer prophylaxis: 20 mg twice daily (oral) or 20 mg IV every 12 hours if unable to take orally.

⚠️ Cautions

• Before treatment, exclude gastric malignancy in patients with alarm symptoms (anaemia, weight loss, vomiting, dysphagia).
• Reduce dose in severe renal impairment (risk of accumulation and CNS effects).
• Adjust therapy in elderly or frail patients.
• Use with caution in hepatic dysfunction, though mainly renally excreted.

🚫 Contraindications

• Known hypersensitivity to famotidine or other H₂ antagonists.
• Relative: pregnancy or breastfeeding (use only if benefit outweighs risk).

💊 Side Effects

• Generally well tolerated.
• Common: headache, dizziness, constipation, fatigue, dry mouth, flatulence.
• Occasional: diarrhoea, nausea, rash.
• Rare: confusion (especially elderly), myalgia, and transient ↑LFTs.

🔄 Interactions

• Far fewer drug interactions than cimetidine — famotidine does not inhibit CYP450 significantly.
• May reduce absorption of drugs requiring an acidic environment (e.g. ketoconazole, atazanavir).
• See full list in the BNF.

🤰 Pregnancy and Breastfeeding

• Limited human data suggest safety; use only if benefit justifies risk.
• Small amounts appear in breast milk — consider alternatives for prolonged use.

🩺 Clinical Pearls

• Ideal for patients intolerant of PPIs or in whom PPIs are contraindicated.
• Night-time dosing provides maximal suppression of nocturnal acid secretion.
• Symptom control is rapid, but ulcer healing may take 4–6 weeks.
• Do not combine routinely with antacids — separate by 1–2 hours to avoid reduced absorption.

💡 Teaching Tip

• H₂ antagonists reduce *acid secretion*, whereas sucralfate and alginates *protect mucosa*.
• They are less potent than PPIs but have a faster onset — useful for breakthrough or nocturnal acid symptoms.
• Mnemonic: “H₂ blockers = Histamine → Halt Hydrogen.”

📚 References

• BNF: Famotidine
• NICE CKS: Dyspepsia and Peptic Ulcer (2024)
• Howden CW. NEJM 1990;323:1749–1756 — H₂ blockers in acid-peptic disease.