Cimetidine 💊
🧪 Always test for and eradicate Helicobacter pylori in suspected peptic ulcer disease (PUD).
⚠️ Cimetidine was the first H2-receptor antagonist, revolutionary in its time, but now rarely used due to side effects and drug interactions.
📖 About
Always check the BNF link here.
- 💊 First H2-blocker introduced in the 1970s.
- ✅ Effective at reducing gastric acid, particularly nocturnal secretion.
- ⚠️ Rarely prescribed now – superseded by ranitidine (historically) and PPIs (current standard).
⚡ Mechanism of Action
- ⛔ Competitive antagonist at gastric parietal cell H2-receptors.
- ⬇️ Reduces basal and stimulated gastric acid secretion.
- 💤 Particularly suppresses nocturnal acid secretion.
🩺 Indications (historical/limited use today)
- Peptic ulcer disease (GU/DU).
- Gastro-oesophageal reflux disease (GORD).
- NSAID-associated gastritis (now PPI preferred).
- Stress ulcer prophylaxis in hospitalised patients.
💊 Dosing – Cimetidine (verify in BNF/datasheet)
| Indication |
Details |
| 🩹 Benign Gastric Ulcer |
Cimetidine 400 mg PO BD or 800 mg nocte × 6 weeks |
| 🔥 NSAID Gastritis |
Cimetidine 400 mg PO BD or 800 mg nocte × 8 weeks |
| ⬆️ Reflux Oesophagitis |
Cimetidine 400 mg PO QDS × 6 weeks |
| 🏥 Stress Ulcer Prophylaxis |
Cimetidine 200–400 mg PO/IV every 6 h |
🔄 Interactions
- ⚠️ Potent inhibitor of hepatic cytochrome P450 enzymes (esp. oxidation pathways).
- ⬆️ Toxicity risk with phenytoin, theophylline, warfarin, carbamazepine, lidocaine.
- Multiple interactions → one reason for decline in clinical use.
⚠️ Cautions
- 🏥 Always exclude gastric cancer before treating suspected ulcer disease.
- 👴 Elderly more prone to CNS side effects (confusion, delirium).
- 📉 Dose adjustment needed in renal impairment.
- Polypharmacy patients at high risk due to enzyme inhibition.
🚫 Contraindications
- Hypersensitivity to cimetidine or other H2-antagonists.
- Relative caution: severe renal/hepatic impairment (requires dose reduction).
- ⚠️ Avoid in patients on narrow therapeutic index drugs (e.g. warfarin, phenytoin) if safer acid suppression options available.
💥 Side Effects
- 🤢 GI: diarrhoea, nausea, constipation.
- 🧠 CNS: headache, dizziness, confusion (esp. elderly/renal impairment).
- ⚡ Endocrine: anti-androgenic effects → gynaecomastia, impotence, galactorrhoea (dose-dependent, chronic use).
- 🌡️ Malaise, fatigue.
- 🫀 Rare: arrhythmias (esp. with IV use).
- 🩸 Rare: bone marrow suppression (leucopenia, thrombocytopenia).
📑 References
