Gastrointestinal Drug Introduction Gastrointestinal medications can be broken down into the following categores antidiarrheals antiemetics H2 antagonists proton pump inhibitors other antiulcer medications laxitives Ranitidine also cimetidine, famotidine, nizatidine Mechanism indirectly inhibits proton pump by blocking stimulation via H2 receptors on parietal cells and ECL cells leads to ↓ H+ secretion by parietal cells no effect on gastic emptying time Clinical use peptic ulcer gastritis GERD Zollinger-Ellison syndrome Toxicity cimetidine potent inhibitor of P-450 antiandrogenic effects results in gynecomastia, impotence, ↓ libido in males crosses blood-brain barrier results inconfusion, dizziness, headaches crosses placenta cimetidine and rantidine ↓ creatinine clearance other H2 blockers have fewer side effects