1. Clinical Overview
Famotidine is a competitive, reversible histamine H2-receptor antagonist. It is a potent antisecretory agent that significantly inhibits both basal and stimulated gastric acid secretion (including nocturnal and meal-stimulated secretion). It is widely used in the Indian market for the management of acid-peptic disorders due to its efficacy, safety profile, and cost-effectiveness.
| Onset | Duration | Bioavailability |
|---|---|---|
| Within 1 hour for symptom relief; peak antisecretory effect occurs in 1-3 hours. | 10-12 hours for a single 20mg dose. | 40-45% (Oral administration). Reduced by food but not clinically significant. |
2. Mechanism of Action
Famotidine competitively and reversibly inhibits the action of histamine at the histamine H2-receptors located primarily on the parietal cells of the gastric mucosa. This blockade prevents the activation of adenylate cyclase, leading to a decrease in intracellular cyclic AMP (cAMP). Reduced cAMP levels inhibit the activation of the proton pump (H+/K+ ATPase), resulting in a marked reduction in both the volume and hydrogen ion concentration of gastric acid secretion.
3. Indications & Uses
- Active Duodenal Ulcer
- Active Gastric Ulcer
- Gastroesophageal Reflux Disease (GERD)
- Pathological Hypersecretory Conditions (e.g., Zollinger-Ellison Syndrome, Multiple Endocrine Adenomas)
4. Dosage & Administration
Adult Dosage: Duodenal/Gastric Ulcer: 20 mg twice daily or 40 mg at bedtime. Maintenance: 20 mg at bedtime. GERD: 20 mg twice daily for up to 6 weeks. Hypersecretory conditions: Start at 20 mg every 6 hours, adjust as needed.
Administration: Can be taken with or without food. Tablet should be swallowed whole with a glass of water. For once-daily dosing, take at bedtime. For twice-daily dosing, take in the morning and at bedtime.
5. Side Effects
Common side effects may include:
- Headache
- Dizziness
- Constipation
- Diarrhea
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Ketoconazole, Itraconazole, Atazanavir | Famotidine increases gastric pH, which can significantly reduce the absorption of these drugs that require an acidic environment. Separate administration by at least 2 hours. | Major |
| Warfarin | Theoretical interaction due to altered absorption; however, clinically significant interaction is rare. Monitor INR periodically. | Moderate |
| Procainamide | Famotidine may reduce renal clearance of procainamide, increasing its plasma levels and risk of toxicity. | Moderate |
| Antacids | May reduce the absorption of Famotidine. Administer Famotidine at least 1-2 hours before or after antacids. | Minor |
7. Patient Counselling
- Do take the medication as prescribed, even if symptoms improve quickly.
- Do inform your doctor about all other medications, including OTC antacids and supplements.
- Don't crush or chew the tablet unless advised (some dispersible forms exist).
- Don't take a double dose to make up for a missed one.
8. Toxicology & Storage
Overdose: Symptoms are extensions of side effects: CNS effects (confusion, agitation, seizures - especially in renal failure), hypotension, bradycardia, arrhythmias, vomiting, diarrhea, muscle cramps.
Storage: Store below 30°C, in a cool, dry place, protected from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.