Chapter 45: Gastrointestinal Disorder Drug Therapy

Gastrointestinal Disorder Drug Therapy begins by outlining the anatomy and physiology of the digestive system and the neurological regulation of emesis, detailing how the vomiting center in the medulla and the chemoreceptor trigger zone (CTZ) respond to various stimuli such as drugs, toxins, and vestibular changes. The text offers an in-depth classification of antiemetic agents, distinguishing between nonprescription antihistamines and prescription classes including anticholinergics, dopamine antagonists, benzodiazepines, serotonin antagonists, cannabinoids, and neurokinin receptor antagonists. Significant attention is given to the pharmacodynamics and safety profiles of key drugs like promethazine, which blocks H1 receptors but carries risks of sedation and extrapyramidal symptoms, and serotonin antagonists like ondansetron, which are highly effective for chemotherapy-induced nausea. The chapter then addresses the management of diarrhea, categorizing antidiarrheals into opiates and opiate-related agents—such as diphenoxylate with atropine and loperamide—that slow intestinal motility, and adsorbents like bismuth subsalicylate that coat the GI wall to bind toxins. Finally, the discussion on constipation delineates the mechanisms of various laxative classes, including osmotics (lactulose, magnesium citrate) that pull water into the colon, stimulants (bisacodyl, senna) that irritate sensory nerve endings to induce peristalsis, bulk-forming agents (psyllium) that naturally increase fecal volume, and emollients (stool softeners) like docusate. Throughout the text, the nursing process is emphasized, highlighting the critical need for monitoring fluid and electrolyte balance to prevent dehydration and metabolic acidosis, as well as patient education to avoid laxative dependence and ensure safe medication use.