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Anti-emetics, antacids & GI motility drugs

Applied Sciences Lecture Course. Anti-emetics, antacids & GI motility drugs. Dr Cathy Armstrong SpR In Anaesthesia & Clinical Fellow in Undergraduate Medical Education Manchester Royal Infirmary April 2011. Aims and objectives. To categorise drugs acting on the gut

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Anti-emetics, antacids & GI motility drugs

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  1. Applied Sciences Lecture Course Anti-emetics, antacids & GI motility drugs Dr Cathy Armstrong SpR In Anaesthesia & Clinical Fellow in Undergraduate Medical Education Manchester Royal Infirmary April 2011

  2. Aims and objectives • To categorise drugs acting on the gut • Discuss relevant pharmacological aspects • Discuss common clinical uses • To categorise antiemetics • Discuss relevant pharmacological aspects • Discuss common clinical uses

  3. Drugs acting on the gut • Antacids • Drugs influencing gastric secretion • Drugs influencing gastric motility

  4. Antacids • Action based on physical properties of drug • Weak bases which neutralise gastric acid and increase pH. • Traditionally compounds containing aluminium or magnesium • Liquid preparations more effective than tablet preparations • Symptomatic relief in dyspepsia • Some promotion of ulcer healing but less effective than drugs that inhibit acid secretion

  5. Antacids • Magnesium containing • Laxative • Aluminium containing • Constipating • Interactions • May affect absorption of other drugs. • Avoid giving at same time

  6. Antacids • Examples • Aluminium hydroxide • Magnesium trisilicate • Over – the – counter • Gaviscon • Sodium alginate, sodium bicarbonate, calcium chloride • Peptac • Sodium alginate, calcium carbonate • Rennie Duo • Calcium carbonate, magnesium carbonate

  7. Drugs influencing gastric secretion

  8. Mechanism of gastric acid secretion H+ Apical Cell surface Proton pump ATP-ase K+ Parietal Cell Protein Kinases Cyclic AMP Ca2+ Ca2+ ATP Gs Ac Gi Muscarinic receptor H2 receptor Gastrin Acetylcholine Histamine PGE2

  9. Drugs influencing gastric secretion • H2 receptor antagonists • Proton pump inhibitors

  10. H2 receptor antagonists • Reduce basal and food stimulated gastric acid by 90% • Heal gastric and duodenal ulcers • Provide symptomatic relief in dyspepsia

  11. Which of the following is not an H2 antagonist? • Ranitidine • Zantac • Gavilast • Losec • cimetidine

  12. H2 receptor antagonists • Rantidine • Zantac, gavilast • Oral / IV preparations • Available over the counter • Side effects (rare) • Cardiac arrhythmias during rapid IV administration • Thrombocytopenia, leucopenia, liver dysfunction • anaphylaxis

  13. H2 receptor antagonists • Cimetidine • Hepatic enzyme inhibitor • Inhibits cytochrome P450 system • Can reduce metabolism of other drugs causing a rise in serum levels e.g.warfarin.

  14. Proton pump inhibitors • Cause irreversible inhibition of proton pump • Final common pathway of gastric acid production • Examples • Esomeprazole • Nexium • Lanzoprazole • Zoton • Omeprazole • Losec • Pantoprazole • Protium • Rabeprazole • pariet

  15. Proton pump inhibitors • Uses • Dyspepsia & GORD • Treatment of gastric & duodenal ulcers • H. pylori eradication • In combination with antibacterials • Bleeding peptic ulcers (IV) • To reduce further bleeding & need for surgery • Zollinger-Ellison syndrome • Gastrin producing tumour

  16. Proton pump inhibitors • Side effects • Inhibition of cytochrome p450 system • Limited. • Rarely substantial effect • Rarely rashes & GI disturbances

  17. Drugs influencing gastric motility

  18. Drugs influencing gastric motility • Reduce motility • Antispasmodics • Antimotility drugs • Codeine • loperamide • Increase motility • Prokinetics • Laxatives • Bowel cleansing solutions • Picolax • Klean-prep

  19. Antispasmodics • Antimuscarinics • Hyoscine butlybromide • Buscopan • (Atropine) • Uses • Symptomatic relief of gastro-intestinal or genito-urinary disorders characterised by smooth muscle spasm • IBS • (Excessive resp secretions)

  20. Antispasmodics • Other • Mebeverine • Peppermint oil • Thought to be direct relaxants of intestinal smooth muscle • May relieve pain & diverticular disease

  21. Prokinetics • Drugs which stimulate gastrointestinal motility

  22. Which of the following is not considered a prokinetic? • loperamide • Metoclopramide • Erythromycin • Domperidone

  23. Prokinetics • Dopamine antagonists • Stimulate gastric emptying and small intestinal transit • Examples • Metoclopramide • Domperidone • Uses • Functional dyspepsia • GORD • Gastroparesis in diabetes • Aid speed of transit of barium in follow through test

  24. Prokinetics • Erythromycin • Increases gastric & small bowel activity • Thought to act on motilin receptor

  25. Laxatives • Bulk-forming • Isaghula Husk • Fybogel • Stimulant • Docusate sodium • Senna • Glycerol suppositories • Osmotic • Lactulose • Movicol

  26. Anti-emetics

  27. Vomiting • Afferent pathway • Control centre • Efferent pathway • Vagus nerve • Phrenic nerve • Spinal motor neurones supplying abdo muscles

  28. Dopamine Drugs Gut D2 5HT3 Chemoreceptor Trigger Zone (Area Postrema, floor of 4th ventricle) Outside BBB H1 Vomiting Centre Peripheral pain pathways Vestibular apparatus & cerebellar nuclei ACh Limbic cortex medulla 5HT3 Chemoreceptors & baroreceptors Gut Vomiting

  29. Antiemetics • Dopamine Antagonists • Antihistaminines • Antimuscarinics • 5HT3 receptor antagonists • miscellaneous

  30. Dopamine antagonists • Metoclopramide • Phenothiazines • Prochlorperazine (Stemetil) • Chlorpromazine • Thoridazine • Domperidone

  31. Dopamine antagonists • Side effects • Extrapyramidal side effects • Acute dytonias, ocular gyric crises • Commoner in young women • Can trigger neuroleptic malignant syndrome

  32. Antihistamines • Cyclizine • Also has anticholinergic properties • Side effects • Pain on injection • Tachycardia (IV bolus) • Antimuscarinic effects • Dry mouth, blurred vision • Restlessness, excitation, nervousness

  33. Antimuscarinics • Hyoscine hydrobromide • Particularly effective in motion sickness • Atropine • Glycopyrrolate

  34. 5HT3 Antagonists • Ondansetron • Dolasetron • Granisetron

  35. Miscellaneous • Corticosteroids • Dexamethasone

  36. Dopamine Drugs Gut D2 5HT3 Chemoreceptor Trigger Zone (Area Postrema, floor of 4th ventricle) Outside BBB H1 Vomiting Centre Peripheral pain pathways Vestibular apparatus & cerebellar nuclei ACh Limbic cortex medulla 5HT3 Chemoreceptors & baroreceptors Gut Vomiting

  37. Commonest Antiemetics used in Hospital • Prochlorperazine (stemetil) • 12.5mg IM • 3mg Buccal (Buccastem) • Cyclizine • 50mg PO/IM/IV • Metoclopramide • 10mg PO/IM/IV • Ondansetron • 4-8mg PO/IM/IV

  38. Summary • Discussed Drugs affecting the GI tract • Antacids • Drugs inhibiting acid secretion • Antispasmodics • Prokinetics • Laxatives • Discussed antiemetics

  39. ?

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