Mark Klimek Blue Book Part 1 Exam 2026 – 400 Free Practice Questions to Pass the Exam

Ranitidine is a histamine H2 receptor antagonist. It works by selectively blocking H2 receptors on gastric parietal cells, preventing histamine from binding. When histamine would normally bind, it increases cAMP and activates the proton pump that secretes acid into the stomach. By occupying the receptor, ranitidine reduces both basal and meal-stimulated acid secretion, creating a less acidic environment that helps ulcers heal and GERD symptoms improve. It’s different from proton pump inhibitors, which shut down the final acid pump itself, and from antacids, which neutralize acid rather than stopping its production.