famotidine

Famotidine competitively inhibits H2 receptors on gastric parietal cells, reducing both basal and stimulated gastric acid secretion (by decreasing cAMP-mediated activation of the H+/K+ ATPase indirectly, unlike PPIs which directly inhibit the proton pump). It is less potent than proton pump inhibitors (PPIs) but has a faster onset, making it useful for rapid symptom relief in GERD and peptic ulcer disease. Clinical uses include treatment of GERD, peptic ulcer disease (gastric and duodenal), Zollinger-Ellison syndrome (adjunct), and prophylaxis against stress-related mucosal bleeding in ICU patients. Compared to cimetidine (another H2 blocker), famotidine has minimal effect on the cytochrome P450 system and does not cause antiandrogenic effects (gynecomastia), making it a preferred H2 blocker with fewer drug interactions. Adverse effects are generally mild and include headache, dizziness, and constipation/diarrhea; rare effects include thrombocytopenia and CNS effects (confusion) especially in elderly or renally impaired patients due to reduced clearance. Tolerance can develop with chronic use (tachyphylaxis), which is a key reason PPIs are often preferred for long-term acid suppression. It's important to note H2 blockers like famotidine can mask symptoms of gastric cancer, so alarm symptoms (weight loss, dysphagia, GI bleeding) warrant endoscopy before empiric treatment. Famotidine is renally excreted, requiring dose adjustment in renal insufficiency.