Cimetidine
Rx
Therapeutic ClassH₂ Receptor Antagonist
Common Dose400 mg / 800 mg
Max / 24h1600 mg
PregnancyCategory B
Indications ▼
Duodenal and gastric ulcer
Gastroesophageal reflux disease (GERD)
Zollinger–Ellison syndrome
Stress ulcer prophylaxis in hospitalized patients
Prevention of recurrent ulcer disease
Mechanism & Pharmacokinetics ▼
Mechanism: Competitively inhibits histamine H₂ receptors on gastric parietal cells, leading to reduced basal and stimulated gastric acid secretion.
Pharmacokinetics: Oral bioavailability ~60–70%. Peak plasma level in 1–2 hours. Partially metabolized in liver. Elimination half-life ~2 hours. Primarily excreted unchanged in urine.
Dosage & Administration ▼
| Indication | Dose | Max / Day |
|---|---|---|
| Peptic ulcer | 400 mg twice daily or 800 mg at bedtime | 1600 mg |
| GERD | 400 mg four times daily | 1600 mg |
| Zollinger–Ellison syndrome | 300 mg every 6 hours | Up to 2400 mg (specialist) |
Side Effects ▼
Common: Headache, dizziness, diarrhea, fatigue
Endocrine: Gynecomastia, impotence (long-term or high dose)
CNS: Confusion (especially in elderly or renal impairment)
Rare: Elevated liver enzymes, thrombocytopenia
Contraindications ▼
Hypersensitivity to cimetidine
Severe renal impairment without dose adjustment
Drug Interaction ▼
Inhibits CYP450 enzymes
Increases levels of warfarin, phenytoin, theophylline, diazepam
May enhance adverse effects of propranolol and lidocaine
Pregnancy & Lactation ▼
Pregnancy Category B
Generally considered safe when clearly indicated
Excreted in breast milk; caution advised
Clinical / Research Summary ▼
Mechanism-Based Efficacy: Cimetidine is a histamine H₂-receptor antagonist that reduces gastric acid secretion by blocking histamine stimulation of parietal cells, providing effective acid control in mild to moderate acid-related disorders.
Clinical Indications Evidence: Extensive clinical use supports its effectiveness in peptic ulcer disease, gastroesophageal reflux disease, and stress ulcer prophylaxis, particularly before the widespread use of proton pump inhibitors.
Onset and Duration: Cimetidine demonstrates a relatively rapid onset of action, though its duration of acid suppression is shorter compared with PPIs, often requiring multiple daily dosing.
Comparative Effectiveness: Studies indicate lower ulcer healing rates compared to PPIs, but adequate symptom control in patients with mild GERD or those intolerant to PPIs.
Drug Interaction Profile: Cimetidine is a strong inhibitor of multiple cytochrome P450 enzymes, leading to clinically significant interactions with drugs such as warfarin, phenytoin, theophylline, and diazepam.
Endocrine Effects: Long-term or high-dose therapy has been associated with reversible antiandrogenic effects including gynecomastia and impotence, supported by clinical observations.
Current Clinical Role: Due to interaction potential, cimetidine is now used selectively, often replaced by newer H₂ blockers or PPIs, but remains relevant where cost or availability is a concern.
Research Perspective: Ongoing research explores its immunomodulatory properties and potential adjunctive roles in certain dermatologic and oncologic settings.
Patient Counseling Points ▼
Take exactly as prescribed
Avoid smoking and alcohol
Report breast enlargement or sexual dysfunction
Do not stop abruptly without medical advice
Storage & Handling ▼
Store below 30°C
Protect from moisture and light
Keep out of reach of children
Brand Names (Bangladesh & Global) ▼
Bangladesh (Local Brands):
Global / International Brands:
Medical Disclaimer: This clinical summary is for informational purposes only. Always follow guidance from a qualified healthcare professional.
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