Most Commonly Prescribed H2 Blockers
The four main H2-receptor antagonists available for clinical use are famotidine, ranitidine, cimetidine, and nizatidine. 1, 2
The Four Primary H2 Blockers
- Famotidine is the most potent H2 blocker available, approximately 8 times more potent than ranitidine and 40 times more potent than cimetidine on a weight basis 3, 4
- Ranitidine is a furan-based H2 blocker that is approximately 7 times more potent than cimetidine with a longer duration of action 2
- Cimetidine is an imidazole derivative and was the first widely used H2 blocker, though it has fallen out of favor due to drug interactions and side effects 3, 4
- Nizatidine belongs to the thiazole class and demonstrates the most complete absorption among H2 blockers 5
Equivalent Dosing Across H2 Blockers
The following doses are considered therapeutically equivalent 1:
- Famotidine: 20 mg twice daily
- Ranitidine: 150 mg twice daily
- Cimetidine: 300 mg three to four times daily
- Nizatidine: 150 mg twice daily
Clinical Considerations for Selection
Famotidine is generally preferred because it does not interact with the cytochrome P-450 hepatic enzyme system, unlike cimetidine which can impair oxidative drug metabolism 3, 4
- Cimetidine carries unique risks including increased risk of liver disease, gynecomastia, and cognitive decline (especially in elderly patients) due to anticholinergic effects 2, 6
- Famotidine does not interfere with antiplatelet activity of clopidogrel, making it preferable in patients on dual antiplatelet therapy 2
- All H2 blockers are equally effective at standard doses for mild GERD (>70% symptomatic improvement), but show limited efficacy in erosive esophagitis (40-50% healing rates) 7
Important Limitations
- Tachyphylaxis develops within 6 weeks of H2 blocker initiation, limiting long-term effectiveness 2, 6
- H2 blockers work better as prophylactic treatment rather than acute treatment, as they prevent histamine from binding to receptors 2
- The overall incidence of side effects across all H2 blockers is 2-3%, with no known irreversible adverse effects 3, 4