Which H2 receptor antagonist has the longest half-life and allows once-daily dosing?

Explanation

## H2 Receptor Antagonists: Pharmacokinetic Comparison **Key Point:** Famotidine has the longest half-life (2.5–3.5 hours) among H2 blockers, allowing once-daily dosing and superior acid suppression. ### H2 Blocker Pharmacokinetics | H2 Blocker | Half-life (hours) | Dosing Frequency | Potency (relative) | Metabolism | | --- | --- | --- | --- | --- | | Cimetidine | 1.5–2 | TID–QID | 1× (reference) | Hepatic (CYP450 inhibitor) | | Ranitidine | 2–3 | BID–TID | 5–10× | Hepatic | | Famotidine | 2.5–3.5 | OD–BID | 20–50× | Renal (70%) | | Nizatidine | 1–2 | BID–TID | 4–10× | Hepatic | **High-Yield:** Famotidine is 20–50 times more potent than cimetidine and has the longest half-life, making it the preferred H2 blocker in modern practice. ### Clinical Advantages of Famotidine 1. **Once-daily dosing** — improves compliance 2. **Minimal drug interactions** — renal excretion, not hepatic metabolism (unlike cimetidine) 3. **No endocrine side effects** — does not cause gynecomastia or impotence (cimetidine does) 4. **Renal clearance** — requires dose adjustment in severe renal impairment **Clinical Pearl:** Although PPIs have largely replaced H2 blockers, famotidine is still used for stress ulcer prophylaxis in ICU patients and for breakthrough symptoms in PPI-treated patients. **Warning:** Cimetidine is a potent CYP450 inhibitor and causes multiple drug interactions — it is rarely used now in India.