A 21-year-old woman comes with her parents to discuss therapeutic options for her Crohn's disease. She was diagnosed with Crohn's disease 2 years ago, and it involves her terminal ileum and proximal colon, as confirmed by colonoscopy and small bowel radiography. She was initially treated with mesalamine and budesonide with good response, but over the last 2 months, she has had a relapse of her symptoms. She is experiencing fatigue, cramping, abdominal pains, and nonbloody diarrhea up to 10 times daily, and she has had a 15-lb weight loss.
She has no other significant medical or surgical history. Her current medications are mesalamine 2.4 g/d and budesonide 9 mg/d. She appears thin and tired. Abdominal examination reveals tenderness without guarding in the right lower quadrant; no masses are palpable. On perianal examination, there is no tenderness, fissure, or fistula. Her laboratory data are notable for anemia and elevated C-reactive protein. What are the options for immediate control of her symptoms and disease? What are the long-term management options?
Many of the drug groups discussed elsewhere in this book have important applications in the treatment of diseases of the gastrointestinal tract and other organs. Other groups are used almost exclusively for their effects on the gut; these are discussed in the following text according to their therapeutic uses.
Acid-peptic diseases include gastroesophageal reflux, peptic ulcer (gastric and duodenal), and stress-related mucosal injury. In all these conditions, mucosal erosions or ulceration arise when the caustic effects of aggressive factors (acid, pepsin, bile) overwhelm the defensive factors of the gastrointestinal mucosa (mucus and bicarbonate secretion, prostaglandins, blood flow, and the processes of restitution and regeneration after cellular injury). Over 90% of peptic ulcers are caused by infection with the bacterium Helicobacter pylori or by use of nonsteroidal anti-inflammatory drugs (NSAIDs). Drugs used in the treatment of acid-peptic disorders may be divided into two classes: agents that reduce intragastric acidity and agents that promote mucosal defense.
Agents that Reduce Intragastric Acidity
Physiology of Acid Secretion
The parietal cell contains receptors for gastrin (CCK-B), histamine (H2), and acetylcholine (muscarinic, M3) (Figure 62–1). When acetylcholine (from vagal postganglionic nerves) or gastrin (released from antral G cells into the blood) bind to the parietal cell receptors, they cause an increase in cytosolic calcium, which in turn stimulates protein kinases that stimulate acid secretion from a H+/K+-ATPase (the proton pump) on the canalicular surface.
Schematic model for physiologic control of hydrogen ion (acid) secretion by the parietal cells of the gastric fundic glands. Parietal cells are stimulated to secrete acid (H+) by gastrin (acting on gastrin/CCK-B receptor), acetylcholine (M3 receptor), and histamine (H2 receptor). Acid is secreted across the parietal cell canalicular ...