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UCSD BIMM 118 - Lecture 10

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Gastrointestinal PharmacologySlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19BIMM118Gastrointestinal Pharmacology•Antacids–Peptic ulcer therapy•Antiemetics•Laxatives•Antidiarrheal drugsBIMM118Gastrointestinal PharmacologyAcid production:•2.5 L per day•Isotonic HCl solution•pH < 1•Produced by parietal cellsMucus production:•Produced by mucus-secreting cells•Also produce bicarbonate, which becomes trapped in the mucus layer => pH gradient across the mucus layer (can become destroyed by alcohol)BIMM118Gastrointestinal PharmacologyAntacids:Weak bases:•Aluminum hydroxide–Cause constipation•Magnesium hydroxide–Cause diarrhea=> often combinedUsally taken 5-7 times per dayBIMM118Gastrointestinal PharmacologyAntacids:•Histamine stimulates acid production by parietal cells•Mast cells produce a steady basal level of histamine, which increases in response to gastrin or acetylcholine•Parietal cells express histamine H2 receptors =>H2 receptor blockers:•Cimetidine (Tagamet®)–First H2-blocker available–Inhibits P450 => Drug interaction•Ranitidine (Zantac®)–Does not inhibit P450 => fewer side effects•Nizatidine (Axid®)•Famotidine (Pepcid®)BIMM118Gastrointestinal PharmacologyAntacids:Proton pump inhibitors:–Irreversibly inhibit the H+/K+ - ATPase in gastric parietal cells–Drugs are inactive at neutral pH, but since they are weak bases,are activated in the acidic stomach milieu => restricted activity–Acid production abliterated for 24-48 hours•Omeprazole (Prilosec®)•Lansoprazole (Prevacid®)•Esomeprazole (Nexium®)•RabeprazoleBIMM118Gastrointestinal PharmacologyGastroesophageal reflux disease (GERD):–Backflow of stomach acid into the esophagus–Esophagus is not equipped to handle stomach acid => scaring–Usual symptom is heartburn, an uncomfortable burning sensation behind the breastbone (MI often mistaken for GERD !)–More severe symptoms: difficulty swallowing, chest pain–Reflux into the throat can cause sore throat–Complications include esophageal erosions, esophageal ulcer and narrowing of the esophagus (esophageal stricture)–In some patients, the normal esophageal lining or epithelium may be replaced with abnormal (Barrett's) epithelium. This condition (Barrett's esophagus) has been linked to cancer of the esophagus.–Primary treatment option are proton pump inhibitorsBIMM118Gastrointestinal PharmacologyMucosal protective agents:•Misoprostol–Prostaglandin E1 analog (PG stimulate mucus and bicarbonate production)–Used when treatment with NSAIDs inhibits endogenous PG synthesis•Sucralfate–Complex of aluminum hydroxide and sulfated sucrose–Forms complex gels with mucus => mucus stabilized => diffusion of H+ impaired–Not absorbed => essentially free of side effects–Must be taken every 6 hoursBIMM118Gastrointestinal PharmacologyPeptic Ulcer DiseaseImbalance between defenses and aggressive factors•Defensive factors:Prevent the stomach and duodenum from self-digestion–Mucus: continually secreted, protective effect–Bicarbonate: secreted from endothelial cells–Blood flow: good blood flow maintains mucosal integrity–Prostaglandins: stimulate secretion of bicarbonate and mucus, promote blood flow, suppress secretion of gastric acid•Aggressive factors:–Helicobacter pylori: gram negative bacteria, can live in stomach and duodenum, may breakdown mucus layer => inflammatory response to presence of the bacteria also produces urease – forms CO2 and ammonia which are toxic to mucosa–Gastric Acid: needs to be present for ulcer to form => activates pepsin and injures mucosa–Decreased blood flow: causes decrease in mucus production and bicarbonate synthesis, promote gastric acid secretion–NSAIDS: inhibit the production of prostaglandins–Smoking: nicotine stimulates gastric acid productionBIMM118Gastrointestinal PharmacologyPeptic Ulcer Disease(~25 mill. Americans will have an ulcer in their life)Most common cause (> 85%): Helicobacter pylorii(not stress or hot sauce!)Treatment options:•Antibiotics•Antisecretory agents•Mucosal protectants•Antisecretory agents that enhance mucosal defenses•AntacidsBIMM118Gastrointestinal PharmacologyAntibiotic ulcer therapy:Combinations must be used:•Bismuth (PeptoBismol®) – disrupts cell wall of H. pylori•Clarithromycin – inhibits protein synthesis•Amoxicillin – disrupts cell wall •Tetracyclin – inhibits protein synthesis•Metronidazole – used often due to bacterial resistance to amoxicillin and tetracyclin, or due to intolerance by the patientStandard treatment regimen for peptic ulcer:Omeprazole + amoxicillin + metronidazoleBIMM118Gastrointestinal PharmacologyAntiemetic drugs:Vomiting: –Infection, pregnancy, motion sickness, adverse drug effects,…–Triggered by the “vomiting center” or “chemoreceptor trigger zone (CTZ)” in the medulla (CTZ is on the ‘blood side’ of the blood-brain barrier).Treatment options:–H1 antagonists: Meclizine, promethazine, dimenhydramine…–Muscarinic receptor antagonists: Scopolamine (motion sickness)–Benzodiazepines: Lorazepam (during chemotherapy)–D2 antagonists: have also peripheral prokinetic effects => increase motility of the GI tract => increases the rate of gastric emptying. Caution in patients with Parkinson’s disease! MetoclopramideDomperidone–Cannabinoids:Marihuana ?Synthetic cannabinoids: during chemotherapyNabiloneDronabinolBIMM118Gastrointestinal PharmacologyLaxatives:•Laxative – production of a soft formed stool over a period of 1 or more days•Catharsis – prompt, fluid evacuation of the bowel, more intenseIndications for laxative use:•Pain associated with bowel movements•To decrease amount of strain under certain conditions•Evacuate bowel prior to procedures or examinations•Remove poisons•To relieve constipation caused by pregnancy or drugsContraindications:•Inflammatory bowel diseases•Acute surgical abdomen•Chronic use and abuseBIMM118Gastrointestinal PharmacologyLaxatives:•Stimulate peristalsis•Soften bowel contentClassification:•Bulk laxatives–Non-absorbable carbohydrates–Osmotically active laxatives•Irritant laxatives = purgatives–Small bowel irritants–Large bowel irritants•Lubricant laxatives–Paraffin–GlycerolBIMM118Gastrointestinal PharmacologyLaxatives:Bulk laxatives:Increase in bowel content volume triggers stretch


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UCSD BIMM 118 - Lecture 10

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