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Pharmacology · single question

A patient taking a proton pump inhibitor asks about its mechanism of action. You correctly explain that omeprazole works by:

  1. Stimulating prostaglandin production to protect mucosa
  2. Irreversibly inhibiting the H+/K+ ATPase proton pump
  3. Blocking H2 receptors on parietal cells
  4. Neutralizing gastric acid directly
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Correct answer: B. Irreversibly inhibiting the H+/K+ ATPase proton pump

Omeprazole (and all PPIs) work by irreversibly binding to and inhibiting the H+/K+ ATPase (proton pump) in gastric parietal cells. This blocks the final step of acid secretion. PPIs are prodrugs activated in the acidic environment of the secretory canaliculi. They provide more complete and prolonged acid suppression than H2 blockers.
  • A. ❌ Misoprostol (a prostaglandin analog) protects gastric mucosa — not the MOA of PPIs.
  • B. ✅ CORRECT – PPIs like omeprazole irreversibly inhibit the H+/K+ ATPase proton pump, blocking acid secretion at the source.
  • C. ❌ H2 receptor blockers (e.g., ranitidine, famotidine) block histamine H2 receptors — not PPIs.
  • D. ❌ Antacids (e.g., calcium carbonate, aluminum hydroxide) directly neutralize acid — not PPIs.

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