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PHARMACOLOGY • Gastrointestinal drugs OBJECTIVES • Identify classes of drugs used to improve GI function. • Identity uses and varying actions of these drugs. • Identify how these drugs are absorbed, distributed, metabolized, and excreted. • Identify drug interactions and adverse reactions to these drugs. DRUGS AND THE GI SYSTEM • Classes of drugs used to improve GI function include: • Peptic ulcer drugs • Adsorbent, antiflatulent, and digestive drugs • Antidiarrheal and laxative drugs • Antiemetic and emetic drugs PEPTIC ULCER DRUGS • Aimed at either eradicating H. pylori or restoring balance between acid and pepsin secretions and the GI mucosal defense. • These drugs include: systemic antibiotics, antacids, Histamine-2 (H2)-receptor antagonists, proton pump inhibitors, and other peptic drugs such as misoprostol and sucralfate. SYSTEMIC ANTIBIOTICS • Treatment of peptic ulcers caused by H. pylori include the use of at least two antimicrobial drugs and an antacid for two weeks. • Systemic antibiotics used to treat H. pylori include: metronidazole, tetracycline, clarithromycin, and amoxicillin. SYSTEMIC ANTIBIOTICS • Pharmacokinetics: • Vary in absorption; tetracycline’s absorption is decreased when taken with dairy products; distributed widely; excreted primarily in the urine. • Pharmacodynamics: • Act by treating the infection. SYSTEMIC ANTIBIOTICS • Pharmacotherapeutics: • Combined with either an H2-receptor antagonist or a proton pump inhibitor to decrease stomach acid and promote healing. • Drug interactions: • Tetracycline increases digoxin levels and the risk of bleeding when taken with oral anticoagulants. SYSTEMIC ANTIBIOTICS • Adverse reactions: • GI disturbances ANTACIDS • Over-the-counter medications that include: • Magnesium hydroxide and aluminum hydroxide • Simethicone • Magaldrate • Calcium carbonate ANTACIDS • Pharmacokinetics: • Work locally in the stomach by neutralizing gastric acid. • Distributed throughout the GI tract; eliminated primarily in the feces. • Pharmacodynamics: • Reduces the total amount of acid in the GI tract. ANTACIDS • Pharmacotherapeutics: • Prescribed to relieve pain and promote healing in peptic ulcer disease. • Also used to relieve symptoms of acid indigestion, heart-burn, dyspepsia, or GERD. • Also used to prevent stress ulcers, GI bleeding, and hyperphosphatemia in kidney failure. ANTACIDS • Drug interactions: • All antacids can interfere with the absorption of oral drugs given at the same time. • Adverse reactions: • Diarrhea, constipation, electrolyte imbalances H2-RECEPTOR ANTAGONISTS • Commonly prescribed anti-ulcer drugs include: • Cimetidine (Tagamet) • Nizatidine (Axid) • Ranitidine (Zantac) • Famotidine (Pepcid) H2-RECEPTOR ANTAGONISTS • Pharmacokinetics: • Absorbed rapidly and completely except for famotidine; food and antiacids may reduce absorption; distributed widely throughout the body; metabolized by the liver; excreted primarily in the urine. • Pharmacodynamics: • Block histamine from stimulating the acid- secreting parietal cells of the stomach. H2-RECEPTOR ANTAGONISTS • Pharmacotherapeutics: • Used therapeutically to: • Promote healing of duodenal and gastric ulcers. • Provide long-term treatment of pathological GI hypersecretory conditions. • Reduce gastric acid production and prevent stress ulcers. H2-RECEPTOR ANTAGONISTS • Drug interactions: • Cimetidine inhibits metabolism of ethyl alcohol in the stomach resulting in higher blood alcohol levels. • Adverse reactions: • Headache, diarrhea, and rash PROTON PUMP INHIBITORS • Disrupt chemical binding in stomach cells to reduce acid production, lessening irritation and allowing peptic ulcers to heal. • These drugs include: • Rabeprazole (Aciphex) • Pantoprazole (Protonix) • Omenprazole (Prilosec) • Lansoprazole (Previcid) PROTON PUMP INHIBITORS • Pharmacokinetics: • Given orally in enteric-coated form to bypass the stomach and are dissolved and absorbed in the small intestine. • Highly protein-bound and are extensively metabolized by the liver; eliminated in the urine. PROTON PUMP INHIBITORS • Pharmacodynamics: • Block the last step in the secretion of gastric acid by combining with hydrogen, potassium, and adenosine triphosphate in the parietal cells of the stomach. PROTON PUMP INHIBITORS • Pharmacotherapeutics: • Indicated for: • Short term treatment of gastric ulcers • Active duodenal ulcers and peptic ulcers (H. pylori) • Erosive esophagitis • GERD • Hypersecretory states PROTON PUMP INHIBITORS • Drug interactions: • May interfere with the metabolism of diazepam, phenytoin, and warfarin. • May also interfere with drugs that depend on gastric pH for absorption. • Adverse reactions: • Abdominal pain, diarrhea, nausea, and vomiting OTHER PEPTIC ULCER DRUGS • Misoprostol (Cytotec) - Protects against peptic ulcers caused by NSAIDs by reducing the secretion of gastric acid and by boosting the production of gastric mucus. • Sucralfate (Carafate) - Works locally in the stomach by rapidly reacting with hydrochloric acid to form a thick, paste-like substance that adheres to the gastric mucosa. ADSORBENT DRUGS • Prescribed as antidotes for the ingestion of toxins which are substances that can lead to poisoning or overdose. • Most commonly used adsorbent drug is activated charcoal. • Pharmacokinetics: • Must be given soon after toxic ingestion; not absorbed or metabolized; excreted unchanged in feces. ADSORBENT DRUGS • Pharmacodynamics: • Inhibits toxins from being absorbed in the GI tract by attracting and binding with them. • Pharmacotherapeutics: • A general purpose antidote used for many types of acute oral poisoning. ADSORBENT DRUGS • Drug interactions: • Drugs to induce vomiting that had been given before administration, now are discouraged so administration is not delayed. • Adverse reactions: • Black stools and constipation. ANTIFLATULANT DRUGS • Disperse gas pockets in the GI tract. • Simethicone is the major drug currently used. • Pharmacokinetics: • Not absorbed in the GI tract; distributed to the intestinal lumen; eliminated in the feces. ANTIFLATULANT DRUGS • Pharmacodynamics: • Provide de-foaming action in the GI tract. • Pharmacotherapeutics: • Used to treat conditions in which excess gas is a problem such as: functional gastric bloating, postop gaseous bloating, diverticular disease, spastic or irritable colon, and air swallowing. ANTIFLATULANT DRUGS • Drug interactions: • Don’t interact significantly with other drugs. • Adverse reactions: • None known. DIGESTIVE DRUGS • Aid digestion in patients who are missing enzymes or other substances needed to digest food. • Include: • Dehydrocholic acid • Pancreatin and pancrelipse. DIGESTIVE DRUGS • Pharmacokinetics: • Aren’t absorbed; act locally in the GI tract; excreted in the feces. • Pharmacodynamics: • The action of digestants resembles the action of the body substances they replace. • Dehydrocholic acid - bile • Pancreatin and pancrelipase - pancreatic enzymes. DIGESTIVE DRUGS • These drugs contain: • Trypsin to digest proteins • Amylase to digest carbohydrates • Lipase to digest fats DIGESTIVE DRUGS • Pharmacotherapeutics: • Each digestant has its own indication: • Dehydrocholic acid provides temporary relief of constipation. • Pancreatic enzymes are given to patients with pancreatitis, cystic fibrosis, and steatorrhea. DIGESTIVE DRUGS • Drug interactions: • Antacids reduce the effects of pancreatic enzymes. • Adverse reactions: • Diarrhea ANTIDIARRHEAL & LAXATIVE DRUGS • Antidiarrheals include: opioid-related drugs and kaolin and pectin. • Laxatives include: hyperosmolar drugs, dietary fiber and related bulk-forming substances, emollients, stimulants, and lubricants. OPIOID-RELATED DRUGS • Decrease peristalsis in the intestines. • Include: • Difenoxin • Diphenoxylate (Lomotil) • Loperamide (Imodium) OPIOID-RELATED DRUGS • Pharmacokinetics: • Loperamide isn’t absorbed well; distributed in the serum; metabolized in the liver; excreted in the feces. • Pharmacodynamics: • Slow GI motility by depressing the circular and longitudinal muscle action in the small and large intestines. OPIOID-RELATED DRUGS • Pharmacotherapeutics: • Used to treat acute, nonspecific diarrhea. • Loperamide is also used to treat chronic diarrhea. • Drug interactions: • May enhance the depressant effects of barbiturates, alcohol, narcotics, tranquilizers, and sedatives. OPIOID-RELATED DRUGS • Adverse reactions: • GI distress KAOLIN & PECTIN • Locally acting OTC antidiarrheals that work by adsorbing irritants and soothing intestinal mucosa. • Pharmacokinetics: • Aren’t absorbed or distributed; excreted in the feces. KAOLIN & PECTIN • Pharmacodynamics: • Bind with bacteria, toxins, and other irritants on the intestinal mucosa. • Pectin decreases the pH in the intestinal lumen which provides a soothing effect on the irritated mucosa. • Pharmacotherapeutics: • Used to relieve mild to moderate diarrhea. KAOLIN & PECTIN • Drug interactions: • Can interfere with the absorption of digoxin or other drugs from the intestinal mucosa if administered at the same time. • Adverse reactions: • Constipation HYPEROSMOLAR LAXATIVES • Work by drawing water into the intestine promoting bowel distention and peristalsis. • Include the following drugs: • Glycerin • Lactulose • Saline compounds HYPEROSMOLAR LAXATIVES • Pharmacokinetics: • Glycerin is administered into the colon and isn’t absorbed systemically. • Lactulose is administered orally; is minimally absorbed; distributed in the intestine; metabolized by bacteria in the colon; excreted in the feces. HYPEROSMOLAR LAXATIVES • Saline compounds are administered orally and rectally; some ions are absorbed and excreted in the urine; the unabsorbed drug is excreted in the feces. • Polyethylene glycol (PEG) or “GoLytely” act as an osmotic drug but is not absorbed so it doesn’t alter electrolyte balance. HYPEROSMOLAR LAXATIVES • Pharmacodynamics: • Produce a bowel movement by drawing water into the intestine. • Pharmacotherapeutics: • Glycerin is used in bowel retraining. • Lactulose is used to treat constipation and decrease ammonia production and absorption from the intestines in liver disease. HYPEROSMOLAR LAXATIVES • Saline compounds are used when prompt and complete bowel evacuation is required. • Drug interactions: • Don’t interact significantly with other drugs except for PEG. • Adverse reactions: • Electrolyte imbalances DIETARY FIBER & RELATED BULK-FORMING LAXATIVES • A high fiber diet is the most natural way to prevent or treat constipation. • Include the following drugs: • Methylcellulose (Citrucel) • Polycarbophil (Fiberall) • Psyllium hydrophilic mucilloid (Metamucil) DIETARY FIBER & RELATED BULK-FORMING LAXATIVES • Pharmacokinetics: • Not absorbed systemically; polysaccharides in these drugs are converted into osmotically active metabolites that draw water into the colon; excreted in the feces. • Pharmacodynamics: • Increase stool mass and water content promoting peristalsis. DIETARY FIBER & RELATED BULK-FORMING LAXATIVES • Pharmacotherapeutics: • Used to: • Treat simple constipation. • Aid patients recovering from acute MI’s, cerebral aneurysms, or eye surgery who need to avoid the Valsalva maneuver. • Manage patients with irritable bowel syndrome and diverticulosis. DIETARY FIBER & RELATED BULK-FORMING LAXATIVES • Drug interactions: • Decreased absorption of digoxin, warfarin, and salicylates if taken within two hours of these laxatives. • Adverse reactions: • Gas, distention, obstruction, impaction EMMOLIENT LAXATIVES • Also known as stool softeners. • Include the calcium, potassium, and sodium salts of docusate. • Pharmacokinetics: • Administered orally; absorbed and excreted through the bile in the feces. EMMOLIENT LAXATIVES • Pharmacodynamics: • Soften the stool and make bowel movements easier by allowing water and fats to penetrate the stool. • Also stimulate electrolyte and fluid secretion from the intestinal mucosal cells. EMMOLIENT LAXATIVES • Pharmacotherapeutics: • The drug of choice for patients who should avoid straining during bowel movements including those with: • Recent MI or cardiac surgery • Disease of the anus or rectum • Increased ICP • Hernias EMMOLIENT LAXATIVES • Drug interactions: • May enhance the absorption of many oral drugs, therefore, drugs with a narrow therapeutic index should be administered cautiously. • Adverse reactions: • Seldom occur. STIMULANT LAXATIVES • Also known as irritant cathartics. • Include the following drugs: • Bisacodyl (Dulcolax) • Cascara sagrada • Castor oil • Phenolphthalein (Ex-Lax) • Senna (Senokot) STIMULANT LAXATIVES • Pharmacokinetics: • Minimally absorbed; metabolized in the liver; excreted in the urine and feces. • Pharmacodynamics: • Stimulate peristalsis and produce a bowel movement by irritating the intestinal mucosa or stimulating nerve endings of the intestinal smooth muscle. STIMULANT LAXATIVES • Pharmacotherapeutics: • The preferred drugs for emptying the bowel before general surgery, endoscopic procedures, and radiologic procedures. • Also used to treat constipation caused by prolonged bedrest, neurologic dysfunction of the colon, and constipating drugs such as narcotics. STIMULANT LAXATIVES • Drug interactions: • Reduce the absorption of other oral drugs when administered at the same time. • Adverse reactions: • Weakness, nausea, abdominal cramps, mild rectal and anal inflammation. LUBRICANT LAXATIVES • Mineral oil is the main lubricant laxative in current clinical use. • Pharmacokinetics: • Administered orally or rectally; minimally absorbed; distributed to the mesenteric lymph nodes, intestinal mucosa, liver, and spleen; metabolized by the liver; excreted in the feces. LUBRICANT LAXATIVES • Pharmacodynamics: • Lubricates the stool and the intestinal mucosa and prevents water reabsorption from the lumen of the bowel which increases peristalsis as well. • Pharmacotherapeutics: • Used to treat constipation and maintain soft stools when straining is contraindicated. LUBRICANT LAXATIVES • Also used to treat patients with fecal impactions. • Drug interactions: • May impair the absorption of many oral medications such as fat-soluble vitamins, oral contraceptives, and anticoagulants. • Adverse reactions: • GI distress ANTIEMETIC DRUGS • Derived from plants. • Prevent vomiting. • Include: • Antihistamines - dimenhydrate (Dramamine), meclizine hydrochloride (Antivert) • Phenothiazines - prochlorperazine (Compazine), promethazine hydrochloride (Phenergan) ANTIEMETIC DRUGS • Serotonin receptor antagonists - ondansetron (Zofran) antiemetic of choice in the U.S., granisetron (Kytril) • Pharmacokinetics: • Absorbed well; metabolized by the liver; excreted in the urine and/or feces. ANTIEMETIC DRUGS • Phenothiazines block the vomiting center in the medulla of the brain. • Serotonin receptor antagonists block serotonin stimulation centrally in the chemoreceptor trigger zone and peripherally in the vagal nerve terminals, both of which stimulate vomiting. ANTIEMETIC DRUGS • Pharmacotherapeutics: • Antihistamines prevent or treat motion sickness. • Phenothiazines and serotonin receptor antagonists control severe nausea and vomiting post-surgery, viral-related, during chemotherapy, and radiation therapy. ANTIEMETIC DRUGS • Drug interactions: • Many significant interactions and adverse reactions may occur, therefore, the nurse should always consult a drug handbook prior to administration. EMETIC DRUGS • Used to induce vomiting in a person who has ingested toxic substances. • Syrup of Ipecac is the drug of choice because it is the most effective and the least likely to cause problems. • It has become controversial because it delays the use of charcoal. EMETIC DRUGS • Pharmacokinetics: • Little is known about its properties. • Vomiting occurs within 10 to 30 minutes. • Pharmacodynamics: • Induces vomiting by stimulating the vomiting center located in the medulla of the brain. EMETIC DRUGS • Pharmacotherapeutics: • Considered the therapy of choice for emptying the stomach because of its effectiveness and low incidence of adverse effects. • Drug interactions: rarely occur. • Adverse reactions: rarely produced.
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