Gastrointestinal Drug Introduction Gastrointestinal medications can be broken down into the following categores antidiarrheals antiemetics H2 antagonists proton pump inhibitors other antiulcer medications laxitives Omeprazole also lansoprazole Mechanism irreversibly inhibit H+/K+-ATPase in gastric parietal cells Clinical use peptic ulcer disease most effective drug gastritis GERD Zollinger-Ellison syndrome Eradication of H.pylori Toxicity P-450 inhibitor