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Drugs Acting On Gastrointestinal Tract

Drugs Acting On Gastrointestinal Tract. Professor Kassim Al-Saudi, M.B.,Ch.B.,Ph.D. OBJECTIVES. Identify classes of drugs used to improve GI function. Identify uses and varying actions of these drugs.

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Drugs Acting On Gastrointestinal Tract

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  1. Drugs Acting On Gastrointestinal Tract Professor Kassim Al-Saudi, M.B.,Ch.B.,Ph.D.

  2. OBJECTIVES • Identify classes of drugs used to improve GI function. • Identify 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. • Be familiar with drug-induced hepatotoxicity

  3. DRUGS AND THE GI SYSTEM Classes of drugs used to improve GI function include: • Peptic ulcer drugs • Antiemetic and emetic drugs • Antidiarrheal drugs • Laxative drugs

  4. PepticUlcer • The term “peptic ulcer” refers to an ulcer in the lower Oesophagus, stomach, duodenum (commonly), jujenum and ileum (rarely) • Gastric and duodenal ulcers may be acute • or chronic • Acute ulcer shows no evidence of fibrosis • Both penetrate the muscularis mucosae • Erosions do not penetrate the muscularis • mucosae

  5. Aetiology: 1- Infection – Helicobacter pylori (Gm –ve) - 50% Industrialized - 90% Developing (Childhood) - Majority symptoms free - 90% of DU patients and 70% of GU patients are infected with H. pylori 2- Acid and Pepsin secretion 3- Mucosal defensive mechanism

  6. Pathogenesis of Ulcers Therapy is directed at enhancing host defense or eliminating aggressive factors; i.e., H. pylori. Defensive Factors • Mucus, bicarbonate layer • Blood flow, cell renewal • Prostaglandins • Phospholipid • Free radical scavengers Aggressive Factors • Acid, pepsin • Bile salts • Drugs (NSAIDs) • H. pylori

  7. Aim of Treatment • Relief Symptoms • Heal Ulcer • Prevent recurrence • Prevent complications

  8. Lifestyle measures • Raise the head of the bed • Decrease fat intake • Avoid certain foods • Avoid lying down for 3 hours after eating • Stop smoking • Lose weight if appropriate

  9. 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.

  10. Eradication of H. pylori

  11. Tests For Initial Diagnosis of Infection • Urea Breath Test and Stool Assay • Non-invasive, sensitive and specific • Serology • O.K. for initial diagnosis • Fair sensitivity and specificity • Endoscopy Not necessary for diagnosis

  12. Who Should Be Treated For H. pylori Infection? • Patients who have documented H. pylori infection and: • Definitely had or has a duodenal or stomach ulcer • Have had stomach lymphoma or family hx of stomach cancer • Consider treatment if: • Presence of “severe histologic” gastritis and H. pylori infection • Ulcer-like dyspepsia in the absence of an ulcer or prior to endoscopy in a young patient

  13. FDA-Approved Treatment Regimes for H. pylori Infection • Omeprazole 20 mg BID + Clarithromycin 500 mg BID + Amoxicillin 1 g BID for 10 days • Lansoprazole 30 mg BID +Clarithromycin 500 mg BID + Amoxicillin 1 g BID for 10 days • Bismuth subsalicylate (Pepto Bismol) 525 mg QID + Metronidazole 250 mg QID + Tetracycline 500 mg QID X 14 days + H2 receptor antagonist x 4 wks

  14. Known Factors Which Determine Success of H. pylori Therapy • Patient compliance or non-compliance • Medicine complications or side effects • Antimicrobial resistance of infecting H. pylori strains • Duration of Therapy • Correct dosing Clearance of H. pylori infection is not equivalent to eradication.

  15. Drugs Affecting Gastric Acid Secretion

  16. PROTON PUMP INHIBITORS • Disrupt chemical binding in stomach cells to reduce acid production, lessening irritation and allowing peptic ulcers to heal. • These drugs include: • Omeprazole (Prilosec) • Rabeprazole (Aciphex) • Pantoprazole (Protonix) • Lansoprazole (Previcid) • Esomaprazole (Nexium)

  17. 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.

  18. 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.

  19. 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

  20. 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

  21. Pharmacological therapy – PPIs • Significantly more effective than H2RAs for both symptom resolution and healing of erosive esophagitis • Also effective in more severe cases of GERD • Most patients respond well to standard therapy, but some require prolonged and/or high-dose treatment

  22. PPIs are the most effective drugs for the initial treatment of GERD 100 PPIs 80 p < 0.0005 60 H2RAs % esophagitis cases healed 40 Placebo 20 0 12 2 4 6 8 10 Weeks of treatment

  23. H2-RECEPTOR ANTAGONISTS • Commonly prescribed anti-ulcer drugs include: • Cimetidine (Tagamet) • Ranitidine (Zantac) • Famotidine (Pepcid) • Nizatidine (Axid)

  24. 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.

  25. 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.

  26. 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

  27. Prevention of ulcers in NSAID Users * * p< 0.05 *

  28. Antimuscarinic drugs • Pirenzepine, telenzepine • • M1 receptors antagonists : • Pirenzepine, telenzepine (a more potent analog), reduce gastric acid secretion with fewer adverse effects than atropine and others. • • Contraindicated in some gastric ulcers as they • may slow gastric emptying and prolong the • exposure of the ulcer bed to acid.

  29. ANTACIDS • Over-the-counter medications that include: • Magnesium hydroxide and aluminum hydroxide • Sodium bicarbonate • Calcium carbonate • Simethicone

  30. ANTACIDS Pharmacokinetics: • Work locally in the stomach by neutralizing gastric acid. • Distributed throughout the GI tract; eliminated primarily in the feces. Pharmacodynamics: • Reduce the total amount of acid in the GI tract.

  31. 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.

  32. ANTACIDS Drug interactions: • All antacids can interfere with the absorption of oral drugs given at the same time. Adverse reactions: • Diarrhea, constipation, electrolyte imbalances

  33. Antacids

  34. Mucosal Protective Agents

  35. Bismuth Compounds: • Tripotassium dicitratobismuthate is a bismuth chelate effective in healing gastric & duodenal ulcers. • Low absorption has been reported • Colloidal Bismuth Subcitrate (CBS) is used in the management of gastric and duodenal ulcers, and in combination with two antibacterials for the eradication of H. pylori.

  36. Sucralfate • • It is a complex of aluminium hydroxide • and sulphated sucrose but has minimal • antacid properties. • May act by protecting the mucosa from • acid-pepsin attack in gastric and duodenal • ulcers.

  37. 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.

  38. NSAID Use in the Arthritis Patient with a History of Bleeding Ulcer • Treating H. pylori is likely to be of benefit if there was a duodenal ulcer; test and treat for H. pylori is recommended. • Use COX2 Inhibitor • Add a PPI or Misoprostol

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