Gastrointestinal  drugs
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  • 1. Pharmacology Drugs that Affect the Gastrointestinal System
  • 2. Topics• Peptic Ulcer Disease• Constipation• Diarrhea• Emesis• Digestion
  • 3. Peptic Ulcer Disease Factors that Factors that Protect AgainstIncrease Acidity Acidity
  • 4. Peptic Ulcer Disease• Factors Increasing • Factors Decreasing – H. pylori – Mucus production – NSAIDs – Buffers – Acidic agents – Blood flow – Pepsin – Prostaglandins – Smoking
  • 5. Regulation of Gastric AcidSecretion
  • 6. H2 Receptor Antagonists• Inhibits gastric acid secretion• No effect on H1 receptors• cimetidine (Tagamet®)• ranitidine (Zantac®)• famotidine (Pepcid®)• nizatidine (Axid®)
  • 7. H2 Receptor Antagonists• Indications: – PUD – GERD – Prevention of aspiration pneumonia
  • 8. Proton Pump Inhibitors• K+H+ATPase (Proton Pump)• Irreversible inhibition – Must synthesize new enzyme – Long duration• omeprazole (Prilosec®)• lansoprazole (Prevacid®)
  • 9. Anticholinergics• pirenzepine (Gastrozepine®)• Other anticholinergics have too many side effects and are not used
  • 10. Prostaglandin Analog• misoprostol (Cytotec®) – Approved for treating PUD due to long term NSAID use
  • 11. Antacids• Increase pH of gastric environment• Hydroxides – Aluminum – Magnesium• Carbonates – Calcium
  • 12. Antacids• Most OTC drugs are combinations – DiGel® – Amphojel® – Maalox® – Milk of Magnesia® – Mylanta®
  • 13. Antibiotics• Aimed at eliminating H. pylori• bismuth (Pepto-Bismol®)• metronidazole (Flagyl®)• amoxicillin (Amoxil®)• tetracycline (Achromycin V®)
  • 14. Stool FormationWater absorbed in colon (~90%) – Excessive absorption • Constipation: hard, dehydrated stool • Increases strain on defecation • Harmful for subset of patients – Recent episiotomy, colostomy, hemorrhoids, cardiovascular disease – Inadequate absorption • Diarrhea: soft, non-formed, liquid stool
  • 15. TermsLaxative Production of soft, formed stool over 1 or more daysCathartic Rapid, intense fluid evacuation of bowel.
  • 16. Laxatives• Bulk forming• Surfactants• Stimulants• Osmotics
  • 17. Bulk Forming Laxatives• Absorb water • methylcellulose• Soften and enlarge (Citrucel®) stool • psyllium (Metamucil®)• Fecal swelling • Polycarbophil promotes peristalsis
  • 18. Surfanctant Laxatives• Lowers surface • Docusate salts tension – Colace® – Facilitates water – Modane Soft®) penetration
  • 19. Stimulant Laxatives• Stimulate peristalsis • Phenylolpthalein• Increases water and – (Ex-Lax®, Feen-a- electrolytes secretion Mint®, Correctol®) into intestinal lumen • bisacodyl (Ducolax®)• Decreases water and electrolyte reabsorption
  • 20. Osmotic Laxatives• Poorly absorbed salts • Magnesium hydroxid remain in fecal matter (Milk of Magnesia®)• Pull water into lumen
  • 21. Antidiarrheal• Diarrhea is usually a compensatory action… – Treatment aimed at cause, no symptom• Opioid receptors in GI tract decrease motility – Increase time for water reabsorbtion
  • 22. Antidiarrheal Agents• paregoric/opium tincture• diphenoxylate (Lomotil®)• defenoxin (Motofen®)• loperamide (Imodium®)
  • 23. Vomiting Stimulus
  • 24. Antiemetics• Serotonin (5HT) Antagonists• Dopamine (DA) Antagonists• Anticholinergics (muscarinic blockers)• Cannabinoids
  • 25. Serotonin Antagonists• Used to treat side effects of chemotherapy- induced emesis• condansetron (Zofran®)• Doesn’t affect dopamine receptors ∴no extrapyramidal effects• Granisetron (Kytril®)
  • 26. Dopamine Antagonists• Phenothiazines – prochloraperazine (Compazine®) – promethazine (Phenergan®)• Butyrophenones – haloperidol (Haldol®) – droperidol (Inapsine®)• metoclopramide (Reglan®)
  • 27. Cannabinoids• Tetrahydrocannabinol (THC) – Active ingredient in marijuana – Dronabinol (Marinol®) – Nabilone (Cesamet®)
  • 28. Digestion Aids• Useful for inactive vagal stimulus/bypassed duodenum• Pancreatin (Entozyme®)• Pancrelipase (Viokase®)