About Ranitidine A histamine H2-receptor antagonist, Furan derivative, Anti-secretory G.I agent,Anti ulcer. Mechanism of Action of Ranitidine Ranitidine is a H2 (Histamine) receptor antagonist. Histamine is the most potent stimulus of acid secretion and acts as the common mediator. H2 receptor is a G-protein coupled receptor. It induces adenylate cyclase which converts ATP to cyclic AMP. This cyclic AMP acts on proton pump and exchange extracellular potassium ion for intracellular hydrogen ion across the parietal cell membrane. Ranitidine reversibly competes with Histamine for binding to H2 receptors on the parietal cells and predominantly inhibits basal acid secretion. Anaesthetic adjuncts: It is used in patients undergoing prolonged operations, caesarian section,obese patients those are at increased risk of gastric regurgitation and aspiration pneumonia. It raises pH of gastric juice and also reduces its volume and thus chances of regurgitation.