Cimetidine
H2 Blocker · Histamine Antagonist · GERD / Peptic Ulcer
-TIDINE = dining
+
CIME = "see me"
Picture yourself DINING at a restaurant. You wave to the waiter: "See me!" — CIME-tidine. The waiter rushes over and blocks the chef from sending out any more acid. The suffix -tidine sounds like dining, and every drug ending in -tidine is an H2 blocker. The restaurant's table number? H2. Parietal cells can't secrete acid when their H2 receptor is blocked. Less acid, fewer ulcers.
H2 blocker
-tidine = dining = H2
How Step Tests It
1
Treats GERD and peptic ulcer disease by blocking H2 receptors on gastric parietal cells, reducing acid secretion. Step loves asking which receptor class is blocked.
2
Inhibits CYP450 — cimetidine is the classic drug interaction culprit. Step will give you a patient on warfarin or theophylline whose levels spike after adding cimetidine. Know this cold.
3
Gynecomastia and anti-androgenic effects — cimetidine blocks androgen receptors. A man on long-term cimetidine develops breast tenderness. Step loves this side effect.
This Week's Practice Question
A 58-year-old man on warfarin for atrial fibrillation is started on cimetidine for GERD. Two weeks later his INR has risen from 2.4 to 5.1. What is the most likely mechanism?
A) Cimetidine increases warfarin absorption in the gut
B) Cimetidine inhibits CYP450 enzymes, decreasing warfarin metabolism
C) Cimetidine displaces warfarin from plasma proteins
D) Cimetidine directly activates clotting factor inhibition
Answer: B. Cimetidine inhibits hepatic CYP450 enzymes. Warfarin is metabolized by CYP2C9 — when that pathway is blocked, warfarin accumulates and the INR rises. This is cimetidine's most tested drug interaction. Remember: -tidine = dining, and at this restaurant, cimetidine controls who gets to leave (CYP450 slows down).