tailieunhanh - Color Atlas of Pharmacology (Part 15): Drugs for the Treatment of Peptic Ulcers

Drugs for the Treatment of Peptic Ulcers cipitated antacid or, phosphate depletion of the body with excessive intake of Al(OH)3. Na+ ions remain in solution even in the presence of HCO3–-rich pancreatic secretions and are subject to absorption, like HCO3–. Because of the uptake of Na+, use of NaHCO3 must be avoided in conditions requiring restriction of NaCl intake, such as hypertension, cardiac failure, and edema. Since food has a buffering effect, antacids are taken between meals (., 1 and 3 h after meals and at bedtime). Nonabsorbable antacids are preferred. Because Mg(OH)2 produces a laxative effect (cause: osmotic action,. | 166 Drugs for the Treatment of Peptic Ulcers Drugs for Gastric and Duodenal Ulcers In the area of a gastric or duodenal peptic ulcer the mucosa has been attacked by digestive juices to such an extent as to expose the subjacent connective tissue layer submucosa . This self-digestion occurs when the equilibrium between the corrosive hydrochloric acid and acid-neutralizing mucus which forms a protective cover on the mucosal surface is shifted in favor of hydrochloric acid. Mucosal damage can be promoted by Helicobacter pylori bacteria that colonize the gastric mucus. Drugs are employed with the following therapeutic aims 1 to relieve pain 2 to accelerate healing and 3 to prevent ulcer recurrence. Therapeutic approaches are threefold a to reduce aggressive forces by lowering H output b to increase protective forces by means of mucoprotectants and c to eradicate Helicobacter pylori. I. Drugs for Lowering Acid Concentration Ia. Acid neutralization. H -binding groups such as CO32- HCO3- or OH- together with their counter ions are contained in antacid drugs. Neutralization reactions occurring after intake of CaCO3 and NaHCO3 respectively are shown in A at left. With nonabsorbable antacids the counter ion is dissolved in the acidic gastric juice in the process of neutralization. Upon mixture with the alkaline pancreatic secretion in the duodenum it is largely precipitated again by basic groups . as CaCO3 or AlPO4 and excreted in feces. Therefore systemic absorption of counter ions or basic residues is minor. In the presence of renal insufficiency however absorption of even small amounts may cause an increase in plasma levels of counter ions . magnesium intoxication with paralysis and cardiac disturbances . Precipitation in the gut lumen is responsible for other side effects such as reduced absorption of other drugs due to their adsorption to the surface of pre cipitated antacid or phosphate depletion of the body with excessive intake of Al OH 3. Na ions remain in .