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Nursing 3703 Pharmacology Digestive System Drugs
By Linda Self
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Effects of Drugs on the Digestive System
Digestive system and drug therapy have a reciprocal relationship Some medications cause GI symptoms (e.g. EES), conversely, some GI disorders alter the absorption and metabolism of drugs (e.g. liver failure)
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Effects of drugs on the digestive system
Drugs affecting the GI tract include: laxatives, antidiarrheals, antiemetics, and drugs used in acid/peptic ulcer disorders. Others include cholinergics (Aricept), anticholinergics (atropine), corticosteroids and anti-infectives.
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Cell protective mechanisms in the stomach
Secretion of mucous and bicarbonate Dilution of gastric acid by food and secretions Prevention of diffusion of HCL from the stomach lumen back into the gastric mucosal lining Presence of prostaglandin E Alkalinization of gastric secretions by pancreatic juices and bile
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Cell destructive effects in stomach
Gastric acid, secreted by parietal cells Parietal cells contain receptors for acetylcholine, gastrin and histamine. All of which stimulate gastric acid production Acetylcholine is released by vagus nerve endings in response to stimuli. For example, seeing or smelling certain foods or even thinking about food.
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Cell destructive effects cont.
Gastrin is a hormone released by the stomach and duodenum in response to food ingestion. Affects parietal cells which in trun causes gastric acid to be released in stomach. Histamine is released from cells in the gastric mucosa and diffuses into nearby parietal cells. Pepsin is a proteolytic enzyme that helps digest protein foods and also can digest the stomach wall.
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Cell destructive effects cont.
H. pylori is a gram negative bacterium found in the gastric mucosa of most clients with chronic gastritis In 75% of those with gastric ulcers and in 90% of patients with duodenal ulcers Spread by oral-fecal route or by iatrogenic spread Thought to affect mucosal function
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Peptic Ulcer Disease Gastric Ulcers
Associated with stress, NSAIDs or H. pylori Manifested by painless bleeding Take longer to heal than duodenal ulcers When associated w/stress, can occur at any age With H. pylori and NSAIDs, generally are in 6th or 7th decade Tend to be chronic
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PUD cont. Duodenal ulcers Can occur nearly at any age
Occur equally in men and women Manifested by abdominal pain Associated with cigarette smoking Also associated with NSAIDs and H. pylori
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Peptic Ulcer and Acid Reflux Disorders
Characterized by ulcer formation in the esophagus, stomach or duodenum Occurs in areas that are exposed to gastric acid and pepsin Gastric and duodenal ulcers are more common than esophageal ulcers Parietal cells contain receptors for acetylcholine-implication of which is stimulation by/of the vagus
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Other Upper GI Disorders
Gastritis—acute or chronic inflammatory reaction of gastric mucosa Often will see peptic ulcers with gastritis NSAID gastropathy: Chronic ingestion causes irritation of the gastric mucosa, inhibits the synthesis of prostaglandins (which protect mucosal lining) and increases synthesis of substances that can cause mucosal damage (leukotrienes)
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Gastroesophageal Reflux Disease (GERD)
Most common disorder of the esophagus Characterized by regurgitation of gastric contents into the esophagus Occurs most often after a meal Worse when recumbent Caused by incompetent lower esophageal sphincter
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GERD Foods that cause relaxation of the lower esophageal sphincter include: etoh, caffeine, fats, chocolate, cigarette smoking, gastric distention and certain medications (beta blockers, calcium channel blockers and nitrates)
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GERD Occurs in men, women and children Common during pregnancy
Traditionally more common in persons over 40 years of age
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Classifications and Individual Drugs
Antacids-alkaline substances that neutralize acids. Raising the pH to approximately 3.5 neutralizes more than 90% of gastric acid and inhibits conversion of pepsinogen to pepsin. Commonly used antacids are aluminum, magnesium and calcium compounds.
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Antacids Vary in onset of action and dosage needed for neutralization
Aluminum compounds require large doses for effectiveness. They can cause constipation, hypophosphatemia and osteomalacia. Magnesium based antacids have more rapid onset than Al++ but can cause diarrhea and hypermagnesemia
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Antacids Calcium compounds can cause hypercalcemia and hypersecretion of gastric acid==‘rebound’ May be in combinations such as aluminum and magnesium hydroxide Decreases the diarrhea and constipation
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Antacids Most are pregnancy category C May be used in children
Antacids with magnesium are contraindicated in renal failure because hypermagnesemia may result May contain additives such as simethicone Pills are as effective as liquids
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Antacids Some examples are: Amphogel (Al++) Maalox (Mg++ and Al++)
Mylanta (Mg++, Al++ and simethicone)
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Use of antacids in older adults
Need smaller dosages as they secrete less acid May have some pre-existing renal compromise Older adults often take large amounts of NSAIDs H2 receptor antagonists sometimes cause more side effects Sucralfate is well tolerated PPIs are drugs of choice in this population
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Helicobacter pylori Increasingly common
Requires combination of two antimicrobials and a PPI or H2 receptor antagonist Use amoxicillin, clarithromycin, metronidazole or tetracycline for antibiotic action More than one antimicrobial is indicated to prevent resistance
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H. pylori Bismuth compound is added for its antibacterial effects as well as increasing the HCO3- and mucous contents of the stomach Adding an H2RA or PPI decreases s/s and hastens healing
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Histamine 2 Receptor Antagonists (H2RAs)
Histamine release causes contraction of smooth muscle in bronchi, GI tract, increases permeability of capillaries, stimulates sensory nerve endings and causes strong stimulation of gastric acid secretion Vagal stimulation causes release of histamine from cells in stomach, acts on receptors in parietal cells>>>>>increases HCL production. Called H2 receptors.
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Histamine 2 Receptor Antagonists
Traditional antihistamines or H1 receptor antagonists generally reduce the effects of histamine in the body but do not block histamine effects on gastric acid production Have been replaced as first choice drugs by the PPIs Prototype is cimetidine Generally are pregnancy category B
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H2RA Often have multple drug interactions and SE
Available OTC and by prescription Reduce dosage in pregnancy Ranitidine is more powerful than cimetidine May use for up to 8 weeks Examples are: cimetidine, ranitidine, famotidine and nizatidine.
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H2RA Cimetidine affects the cytochrome p450 drug metabolizing system in the liver; may cause confusion and antiandrogenic effects (gynecomastia)
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Proton Pump Inhibitors (PPIs)
Very strong inhibitors of gastric acid secretion Bind irreversibly to the gastric proton pump to prevent the release of gastric acid from parietal cells Suppresses acid secretion in response to all primary stimuli including histamine, gastrin and acetylcholine. Are the drugs of first choice in erosive esophagitis, erosive gastritis and in Zollinger-Ellison (gastrin secreting tumors)
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PPIs More effective than H2RAs
Faster symptom relief and faster healing Used in prevention of esophagitis Tx H. pylori associated ulcers Side effects are nausea, diarrhea and HA Long term effects……..hypocalcemia, vitamin deficiencies, others
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Examples of PPIs Nexium (esmeprazole) Prevacid (lansoprazole
Prilosec (omeprazole) Protonix (pantoprazole) Aciphex (rabeprazole)
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Prostaglandin Naturally occurring prostaglandin E is produced by mucosal cells of the stomach and duodenum. It inhibits gastric acid secretion and increases mucous and bicarbonate, mucosal blood flow and mucosal repair. With inhibition of prostaglandin E, erosion and ulcerations can occur.
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Cytotec (misoprostol)
Synthetic form of prostaglandin E Indicated for clients at high risk for GI ulceration and bleeding and in those who take NSAIDs frequently Contraindicated in women of childbearing potential (unless effective birth control methods are being used) and during pregnancy as it can cause abortion.
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Cytotec May induce abortion
Side effects include diarrhea and abdominal cramping
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Sucralfate (carafate)
Preparation of sulfated sucrose and aluminum hydroxide that binds to normal and ulcerated mucosa Mechanism of action is unclear Thought to possibly bind to the ulcer and form a protective barrier between the mucosa and gastric acid, pepsin and bile salts; and stimulates prostaglandin synthesis Effective in treating duodenal ulcers and in preventing recurrences
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Sucralfate Side effects include constipation and dry mouth
Must be given BID Cannot be given with an antacid, H2RA or PPIs May bind other drugs and prevent their absorption Give 2 hours before or after other drugs
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Effects of acid suppressant drugs on nutrients
Dietary folate, iron and Vitamin B12 are better absorbed from an acidic environment Less acidic environment can cause defiencies of these nutrients Sucralfate interferes with the absorption of the fat soluble vitamins Magnesium containing antacids interfere with absorption of Vitamin A
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Antiemetics Vomiting is the expulsion of stomach contents through the mouth Used to prevent or treat nausea and vomiting Vomiting can occur w/o nausea
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Origin of vomiting Vomiting center is located in medulla oblongata
Stimuli are relayed to the vomiting center from the periphery (gastric mucosa, peritoneum, intestines, joints) and centrally (cerebral cortex, vestibular apparatus in the ear and from the chemoreceptor trigger zone in the 4th ventricle).
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Vomiting center, chemoreceptor trigger zone and the GI tract contain benzodiazepine, cholinergic, dopaminic, histaminic, opiate and serotonin receptors that are stimulated by emetogenic drugs and toxins For example, chemotherapy may stimulate the CTZ which then signals the vomiting center Motion sickness triggers receptors in inner ear>>CTZ and the vomiting center
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Triggering the vomiting center
Sequence goes as follows: Efferent impulses cause glottic closure Contraction of abdominal muscles and diaphragm Relaxation of the GI sphincter Reverse peristalsis Projection or expulsion
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Causes of nausea and vomiting
Pain Emotional disturbances Radiation therapy Motion sickness Drug therapy: especially w/alcohol, ASA, digoxin, anticancer drugs, antimicrobials, estrogen preparations and Opioids
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Causes of nausea and vomiting
GI disorders such as inflammation of the GI tract, liver, gallbladder, pancreas, impaired GI motility and muscle tone (gastroparesis) and ingestion of food that is irritating to the mucosa Cardiovascular, infectious, neurologic or metabolic disorders as well
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Antiemetic Drugs Most have anticholinergic, antidopaminergic, antihistaminic or antiserotonergic effects Generally are more effective in prophylaxis than treatment Most act on the vomiting center, the chemoreceptor trigger zone, the cerebral cortex, the vestibular apparatus or a combination of.
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Phenothiazines Are CNS depressants used in psychoses
Block dopamine from receptors sites in the brain Act on the CTZ and the vomiting center Not all phenothiazines are anti-emetics Compazine (prochlorperazine) and Phenergan (promethazine) are examples of phenothiazines Compazine and phenergan are Cat. C.
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Phenothiazines—side effects
Can cause extrapyramidal symptoms (EPS) which include: dyskinesias (rhythmic movements), dystonias (rhythmic jerks), and akathesia (inability to sit still) related to dopamine receptor blockade
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Antihistamines as antiemetics
Prevent histamine from exerting its widespread effects on the body Classic antihistamines or H1 receptor blocking agents are though to block the action of acetylcholine in the brain (anticholinergic) Indicated in motion sickness Examples are: Dramamine, Vistaril (hydroxyzine), Antivert (meclizine)
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Corticosteroids May affect prostaglandin activity in the cerebral cortex Dexamethasone and methylprednisolone are commonly used in the management of chemotherapy-induced emesis; usually in combination with other antiemetics
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Benzodiazepine antianxiety drugs
Not classic anti-emetics but often are used in multi-drug regimens to prevent nausea and vomiting associated with cancer chemotherapy Inhibit cerebral cortex input to the vomiting center May give to those with anticipatory nausea before chemotherapy Example is Ativan (lorazepam)
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5 Hydroxytryptamine (5-HT3 or Serotonin) Receptor Antagonists
Zofran (ondansetron) Kytril (granisetron) Anzemet (dolasetron) Are used to prevent or treat moderate to severe nausea and vomiting r/t cancer chemotherapy, radiation therapy and postoperatively Some anticancer drugs seem to affect a subset of 5 HT3 receptors in the CTZ and the GI tract
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5 HT3 receptor antagonists cont.
Can be given IV or orally Side effects are mild to moderate and include: diarrhea, headache, dizziness, constipation, muscle aches and transient liver enzymes elevation Zofran (ondansetron) is the prototype Are metabolized by the liver
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Miscellaneous antiemetics
Marinol (dronabinol) is a cannabinoid used in the management of nausea and vomiting associated with anticancer drugs and unrelieved by other drugs Schedule III under federal narcotic laws Withdrawal s/s may occur Can cause sleep disturbances
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Reglan (metoclopramide)
Prokinetic that increases GI motility and the rate of gastric emptying by increasing the release of acetylcholine from nerve endings in the GI tract Can cause decreased n/v associated with gastroparesis Has central antiemetic effects, antagonizes the action of dopamine Can be given IV, PO or IM
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Reglan cont. Side effects include sedation, restlessness and extrapyramidal reactions May increase the effects of alcohol and cyclosporine and decrease the effects of cimetidine and digoxin (decrease time for passage)
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Emetrol Also known as phosphorated carbohydrate solution
Is a hyperosmolar solution with phosphoric acid Is OTC If felt to work by reducing smooth muscle contraction in the GI tract
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Scopolamine Is an anticholinergic drug
Effective in relieving nausea and vomiting associated with motion sickness Often used a transdermal patch and place behind the ear
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Contraindications to use of anti-emetics
When s/s of toxicity can be masked When use can delay or prevent diagnosis Reglan is relatively contraindicated in Parkinson’s disease because it further depletes dopamine
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Management considerations
5HT3 antagonists are 1st choice in chemotherapy induced or postoperative nausea and vomiting Drugs with anticholinergic and antihistaminic properties are preferred for motion sickness If ambulatory, opt for drug that causes less sedation Phenergan is used for its antihistaminic antiemetic and sedative effects
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Management considerations cont.
Phenothiazines can have serious side effects Reglan may be preferred for non-obstructive gastric retention
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Herbals Efficacy still debated
Ginger may be helpful for tx of nausea and vomiting, studies not conclusive
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Chemotherapy-induced nausea and vomiting
Chemo may be given during sleeping hours Decrease food intake few hours before tx Antiemetics should be given before the emetogenic tx and may be given for 2-3 days 5-HT3 receptor antagonists are the drugs of choice for this indication Reglan is alternative but may need to give Benadryl to prevent the EPS Sometimes use combination of steroid and 5HT3 RA.
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Laxatives and Cathartics
When stomach and duodenum are distended with food, gastrocolic and duodenocolic reflexes are initiated Cerebral cortex controls the defecation reflex so that defecation can occur at acceptable times and places In people who inhibit the defecation reflex or fail to respond to the urge, constipation results
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Laxatives are chemical substances that act to facilitate passage of bowel contents
Cathartics—a purgative action of the bowels, action is stronger and generally produces elimination of liquid stools
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Indications for use Reduce cholesterol Obtain stool sample
Accelerate excretion of parasites after anthelminthics started Accelerate elimination of potentially toxic substances (Kayexalate) Pre-op Prevent straining at stool in those with CAD or hemorrhoids
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Indications cont. Relieve constipation in pregnancy, in the elderly; in children with megacolon, and in those w/decreased motility
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Contraindications Laxatives and cathartics should not be used in the presence of undiagnosed abdominal pain Could cause an inflamed organ to rupture Oral agents are contraindicated in intestinal obstruction and fecal impaction
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Laxatives Bulk-forming—Citrucel and Metamucil (psyllium)
Surfactant laxatives-mainly prevent straining. They allow water to penetrate stool and act as detergent to facilitate admixing of fat and water in the stool. Examples are Colace (docusate) and Surfak. Saline—magnesium citrate. Nulytely. Increase osmotic pressure in intestinal lumen. Can affect fluids and electrolytes.
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Cathartics Stimulant type are the strongest and most abused
Cascara, bisacodyl, castor oil and senna products comprise are examples Mineral oil is a lubricant laxative. It slows colonic absorption of water.
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Others Lactulose-a disaccharide that is not absorbed from the GI tract. Pulls water into intestinal lumen. Used to treat constipation and hepatic encephalopathy. Lactulose reduces production of ammonia in the intestine. Can affect electrolyte and water balance. Sorbitol-monosaccharide that pulls water into the intestinal lumen and has laxative effects. It is given with Kayexalate (potassium removing resin to treat hyperkalemia)
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Laxative Abuse Public health problem in the elderly
Use in patients with cancer What is normal? What are some measures to prevent constipation?
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Safety in Use Saline cathartics must be used cautiously in the renally impaired Lactulose may be indicated in those with hepatic encephalopathy Seen frequently in form of enemas in hyperkalemia in the hospital
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Antidiarrheals Diarrhea is a symptom of numerous conditions that increase bowel motility; cause secretion or retention of fluids in the intestinal lumen and cause inflammation or irritation of the GI tract. End result: bowel contents are rapidly propelled and absorption of fluids and electrolytes is limited.
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Causes of diarrhea Abuse of laxatives Inflammatory bowel diseases
Drug Therapy-pseudomembranous colitis-Clostridium difficile (anaerobic, spore forming rods) Intestinal infections-E. coli 0157:H7, Traveller’s diarrhea (E. coli, Campylobacter jejuni, Salmonella, Shigella, rotavirus
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Antidiarrheals Opiate related drugs Paregoric
Motofen (defenoxin with atropine) Lomotil (diphenoxylate with atropine)
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Antibacterials Zithromax (azithromycin) for Traveller’s diarrhea
Ciprofloxacin for E. coli, Campylobacter and Shigella EES-amebiasis Flagyl (metronidazole) for C. difficile Bactrim for Traveller’s diarrhea Vancomycin for C. diff; may even be in the form of enemas
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Miscellaneous Questran—useful in Crohn’s disease. Binds and inactivates bile salts in the intestine. Octreotide—diarrhea associated with HIV, carcinoid tumors, cancer therapies or intractable diarrhea caused by other drugs Pancreatin—pancreatic enzymes used for replacement in patients w/deficiency of pancreatic enzymes Zelnorm—is a 5HT4 receptor agonist. Use in IBS, constipation form.
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