Pharmacology · single question
DAY 2 — CASE 17: What is the mechanism of action of ranitidine?
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Correct answer: D. H2 receptor antagonist
- A. An H2 agonist would stimulate gastric acid secretion — the opposite of ranitidine's effect.
- B. H1 agonists are pharmacological tools, not therapeutic medications for GERD.
- C. H1 antagonists (antihistamines like diphenhydramine, loratadine) block allergic/inflammatory effects of histamine on H1 receptors — used for allergies, NOT for reducing gastric acid.
- D. Ranitidine (Zantac) is an H2 RECEPTOR ANTAGONIST. By blocking H2 receptors on gastric parietal cells, it reduces histamine-stimulated gastric acid secretion. Used for GERD, peptic ulcer disease, and Zollinger-Ellison syndrome. Note: Ranitidine was withdrawn from the market in 2020 due to NDMA contamination concerns; famotidine is the current preferred H2 blocker.