Cimetidine
Summary
First-generation H2-receptor antagonist that reduces gastric acid secretion. Notable for potent CYP450 inhibition, antiandrogenic effects, and numerous drug interactions; largely replaced by famotidine and PPIs.
Detail
Cimetidine reversibly blocks H2 histamine receptors on parietal cells, reducing both basal and stimulated gastric acid secretion; used for peptic ulcer disease, GERD, and stress ulcer prophylaxis. It is a potent inhibitor of multiple CYP450 enzymes (CYP1A2, 2C9, 2D6, 3A4), raising levels of warfarin, phenytoin, theophylline, and many others. Unique antiandrogenic effects: gynecomastia, galactorrhea, impotence, and decreased libido (blocks androgen receptors and inhibits estradiol metabolism). Also crosses the BBB and can cause confusion in the elderly. Famotidine and ranitidine lack these effects and have replaced cimetidine clinically (ranitidine withdrawn for NDMA contamination). Boards: H2 blocker + gynecomastia + drug interactions = cimetidine.
Sources
- First Aid for USMLE Step 1 2024
- Sketchy Pharmacology
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.