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The gastrointestinal (GI) tract is responsible for food digestion and the absorption of nutrients and water. Dietary constituents undergo a series of digestive processes as they progress through the GI system. Under normal conditions, the transit time of food and water is adequate to allow the processes of digestion and absorption to take place. Indigestible and nonabsorbable products are eliminated by defecation.
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This chapter discusses drugs that are used to treat specific problems in the GI system. The primary disorders that occur in the GI tract are related to damage from gastric acid secretion and abnormal food movement through the GI tract. Problems may develop if digestive secretions in the stomach begin to damage the upper GI mucosa and cause a peptic ulcer. Certain drugs attempt to prevent or heal peptic ulcers by controlling gastric acid secretion and protecting the mucosal lining. Problems with GI motility may also respond to pharmacological management or be the result of pharmacological interventions. Excessive motility (diarrhea) and inadequate bowel evacuation (constipation) are treated with various agents that normalize peristalsis and facilitate normal bowel movements. Drugs are also available to treat other problems with digestion and vomiting (emesis).
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The GI system is susceptible to various infectious and parasitic invasions. The drugs used to treat these disorders are presented in Chapters 33 through 35, which deal with the chemotherapy of infectious diseases.
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DRUGS USED TO CONTROL GASTRIC ACIDITY AND SECRETION
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The acidic nature of the gastric fluids is essential for activating digestive protease activity and controlling intestinal bacteria. The gastric acids can cause severe ulceration and hemorrhage of the stomach lining if excessive amounts of it are produced or if the normal protection of the stomach mucosa is disturbed by irritants, drugs, or bacterial infection.1 Consequently, several different types of drugs are available that attempt to control or prevent the detrimental effects of gastric acid. These agents are used to treat peptic ulcers—that is, ulcerations of the mucosal lining of the esophagus, stomach, and duodenum.1,2 These drugs may also be helpful in treating general problems related to indigestion and epigastric pain (dyspepsia) and to heartburn sensations caused by the leakage of gastric acid into the distal esophagus, called gastroesophageal reflux.3 Agents used to control gastric acidity and secretion are presented below.
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Antacids attempt to chemically neutralize stomach acids. These drugs typically contain a base such as carbonate or hydroxide combined with aluminum, magnesium, sodium, or calcium.4 The base combines with excess hydrogen ions (H+) in the stomach to increase intragastric pH. The basic strategy of this chemical neutralization is illustrated in Figure 27-1. There is some evidence that antacids containing aluminum may provide additional protection of the gastric mucosa by inhibiting Helicobacter pylori infection and by enhancing the ...