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Pharmacology · single question

What is the mechanism of action of omeprazole?

  1. H2 receptor antagonist (blocks histamine)
  2. Antacid (neutralizes stomach acid)
  3. Proton pump inhibitor (irreversibly blocks H+/K+-ATPase)
  4. Inhibits serotonin reuptake (SSRI)
Show answer and explanation

Correct answer: C. Proton pump inhibitor (irreversibly blocks H+/K+-ATPase)

  • A. Incorrect. H2 receptor antagonists (ranitidine, famotidine) block histamine receptors on parietal cells — this is a different mechanism from omeprazole.
  • B. Incorrect. Antacids (calcium carbonate, Tums) chemically neutralize existing acid — they do not inhibit acid production like PPIs.
  • C. Correct. Omeprazole is a PROTON PUMP INHIBITOR (PPI). It irreversibly inhibits the H+/K+-ATPase enzyme (proton pump) on parietal cells, blocking the final step of gastric acid secretion. It is used for GERD, peptic ulcers, and H. pylori eradication.
  • D. Incorrect. SSRIs (fluoxetine, sertraline) inhibit serotonin reuptake in the CNS — completely different mechanism from omeprazole.

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