Chapter 28: Pharmacological Treatment of Gastrointestinal Disorders

Pharmacological Treatment of Gastrointestinal Disorders details the mechanisms of action for acid-reducing drugs, specifically Histamine H2 receptor antagonists (such as famotidine) and the more potent Proton Pump Inhibitors (PPIs) like omeprazole, which irreversibly block the H+/K+-ATPase enzyme system. A significant portion of the discussion focuses on the necessity of eradicating Helicobacter pylori infections using combination antibiotic therapies to prevent ulcer recurrence, as well as the use of cytoprotective agents like sucralfate and the prostaglandin analog misoprostol for NSAID-induced damage. The chapter then shifts to the management of IBD, differentiating between ulcerative colitis and Crohn disease, and outlining treatments ranging from aminosalicylates (mesalamine) and glucocorticoids to advanced biologic therapies using monoclonal antibodies like infliximab that target tumor necrosis factor-alpha. Pharmacological interventions for motility disorders include prokinetic agents such as metoclopramide, which antagonizes dopamine D2 receptors to accelerate gastric emptying in conditions like diabetic gastroparesis. The section on constipation categorizes laxatives into bulk-forming, surfactant, osmotic, and stimulant types, while also introducing specific therapies for Irritable Bowel Syndrome with Constipation (IBS-C), such as the chloride channel activator lubiprostone and guanylate cyclase agonists like linaclotide. Conversely, the treatment of diarrhea and IBS with Diarrhea (IBS-D) is explored through opioids like loperamide, antibiotics like rifaximin, and serotonin 5-HT3 antagonists like alosetron. Finally, the chapter reviews antiemetic drugs for nausea and vomiting, explaining the neural pathways of the chemoreceptor trigger zone and vomiting center, and detailing the clinical use of serotonin antagonists (ondansetron), neurokinin-1 antagonists (aprepitant), and vestibular suppressants like scopolamine for indications ranging from chemotherapy-induced emesis to motion sickness.