Overview
Famotidine is a histamine-2 (H2) receptor antagonist that decreases gastric acid secretion. It is used for the treatment and prevention of acid-related gastrointestinal disorders.
Mechanism of Action
Famotidine competitively inhibits histamine at H2 receptors on gastric parietal cells. This results in: Decreased basal gastric acid secretion Decreased nocturnal acid secretion Reduced gastric volume and hydrogen ion concentration It does not significantly affect gastric emptying, pancreatic secretion, or lower esophageal sphincter pressure.
Indications
- Treatment of duodenal ulcer
- Treatment of gastric ulcer
- Gastroesophageal reflux disease (GERD)
- Maintenance therapy for healed duodenal ulcers
- Pathological hypersecretory conditions (e.g., Zollinger-Ellison syndrome)
- Relief of heartburn (OTC formulations)
Dosage
Duodenal Ulcer (Adults): 40 mg once daily at bedtime OR 20 mg twice daily Maintenance (Duodenal Ulcer): 20 mg once daily at bedtime Gastric Ulcer: 40 mg once daily at bedtime GERD: 20 mg twice daily (up to 6–12 weeks) Erosive Esophagitis: 20–40 mg twice daily Hypersecretory Conditions: Initial 20 mg every 6 hours; adjust as needed Renal Impairment (CrCl < 60 mL/min): Dose reduction required
Contraindications
- Hypersensitivity to famotidine or other H2 receptor antagonists
Side Effects
- Headache
- Dizziness
- Constipation
- Diarrhea
- Less common but serious: Confusion (especially elderly)
- Less common but serious: QT prolongation (rare)
- Less common but serious:Thrombocytopenia (rare)
- Less common but serious: Elevated liver enzymes
Interactions
- May alter absorption of drugs dependent on gastric pH (e.g., ketoconazole, atazanavir)
- Probenecid may increase famotidine levels
- Minimal CYP450 interaction compared to cimetidine
Counseling Points
- Prescription/OTC.