Chapter 57: Drugs Affecting Gastrointestinal Secretions

PUD is described as an erosion of the GI lining resulting from an imbalance between corrosive acid levels and the protective mucous layer, frequently exacerbated by infection from Helicobacter pylori bacteria or by the erosive effects of Nonsteroidal Anti-inflammatory Drugs (NSAIDs) which inhibit the formation of protective mucus. Stress-induced ulcers occur when acute physiological stress decreases blood flow to the GI tract, weakening the mucosal layer. Drug classes targeting these conditions function by either reducing acid secretion, neutralizing acid already present, or forming a protective barrier over injured tissue. Histamine-2 (H2) Antagonists such as ranitidine and cimetidine work by selectively blocking H2 receptor sites on the gastric parietal cells, thereby decreasing the release of hydrochloric acid and pepsin. Antacids, which are inorganic chemicals, offer rapid relief by chemically neutralizing stomach acid. However, chronic use carries the risk of acid rebound, a reflex response where the stomach increases gastrin production to restore normal acidity. The most potent class, Proton Pump Inhibitors (PPIs) including omeprazole and lansoprazole, function by blocking the hydrogen–potassium adenosine triphosphatase (H+ K+–ATPase) enzyme system, which is the final step in acid production. Due to the resulting change in GI acidity, long-term PPI use has been linked to serious adverse effects, including an increased risk of bone fractures and osteoporosis, lowered serum magnesium levels, and heightened susceptibility to Clostridium difficile infections. The Gastrointestinal Protectant sucralfate forms a barrier that adheres to ulcer sites, protecting them from acid and pepsin to promote healing. Prostaglandins, specifically misoprostol, are primarily used to prevent gastric ulcers caused by NSAID use, acting by inhibiting acid secretion and increasing the production of protective mucus. Misoprostol is strictly contraindicated in pregnancy due to its classification as an abortifacient. Finally, replacement Digestive Enzymes, such as saliva substitute for dry mouth conditions or pancrelipase for pancreatic enzyme deficiency, are necessary for patients unable to produce sufficient enzymes for normal nutrient digestion and absorption.