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  1. 1. Antiemetics Dr.S.Manikandan Department of Pharmacology Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), Pondicherry. INDIA.
  2. 2. Vomiting Centre (medulla) Cerebral cortex Anticipatory emesis Smell Sight Thought Vestibular nuclei Motion sickness Pharynx & GIT Chemo & radio therapy Gastroenteritis Chemoreceptor Trigger Zone (CTZ) (Outside BBB) Cancer chemotherapy Opioids Muscarinic, 5 HT 3 & Histaminic H 1 5 HT 3 receptors Dopamine D 2 5 HT 3, ,Opioid Receptors Muscarinic Histaminic H 1 Pathophysiology of Emesis
  3. 3. Now answer this question Which group of drugs can be used as antiemetics ? <ul><li>Serotonin 5 HT 3 Antagonists </li></ul><ul><li>Dopamine D 2 Antagonist </li></ul><ul><li>Anticholinergics </li></ul><ul><li>H 1 Antihistaminics </li></ul><ul><li>Cannabinoids </li></ul>
  4. 4. Serotonin 5 HT 3 Antagonist <ul><li>Potent antiemetics </li></ul><ul><li>Even though 5 HT 3 receptors are present in vomiting centre & CTZ, the antiemetic action is restricted to emesis caused by vagal stimulation. </li></ul><ul><li>High first pass metabolism </li></ul><ul><li>Excreted by liver & kidney </li></ul><ul><li>No dose reduction in renal insufficiency but needed in hepatic insufficiency </li></ul><ul><li>Given once or twice daily – orally or intravenously. </li></ul>
  5. 5. Drugs Available <ul><li>Ondansetron 32 mg / day </li></ul><ul><li>Granisetron 10  g / kg / day </li></ul><ul><li>Dolasetron 1.8 mg / kg / day </li></ul>Indications <ul><li>Chemotherapy induced nausea & vomiting – given 30 min. before chemotherapy. </li></ul><ul><li>Postoperative & postradiation nausea & vomiting </li></ul>
  6. 6. Adverse Effects <ul><li>Excellent safety profile </li></ul><ul><li>Headache & constipation </li></ul><ul><li>All three drugs cause prolongation of QT interval, but more pronounced with dolasetron. </li></ul>
  7. 7. Dopamine D 2 Antagonist <ul><li>Antagonise D 2 receptors in CTZ. </li></ul><ul><li>Drugs available </li></ul><ul><li>Metoclopramide 2.5 mg b.d </li></ul><ul><li>Domperidone 10 mg b.d </li></ul><ul><li>Both drugs are also prokinetic agents due to their 5 HT 4 agonist activity. </li></ul><ul><li>Domperidone – oral ; Metoclopramide – oral & i.v </li></ul><ul><li>Metoclopramide crosses BBB but domperidone cannot. </li></ul>
  8. 8. Now answer this question Which is a better antiemetic – Metoclopramide or Domperidone ? <ul><li>As CTZ is outside BBB both have antiemetic effects. </li></ul><ul><li>But as metoclopramide crosses BBB it has adverse effects like extrapyramidal side effects. . </li></ul><ul><li>Domperidone is well tolerated. </li></ul>
  9. 9. Phenothiazines & Butyrophenones <ul><li>Phenothiazines </li></ul><ul><li>Prochlorperazine </li></ul><ul><li>Promethazine </li></ul><ul><li>Phenothiazines are antipsychotics with potent antiemetic property due to D 2 antagonism. </li></ul><ul><li>Butyrophenone </li></ul><ul><li>Droperidol </li></ul><ul><li>Droperidol used for postop. nausea & vomiting, but cause QT prolongation. </li></ul>
  10. 10. H 1 Antihistaminics <ul><li>Most effective drugs for motion sickness </li></ul><ul><li>Drugs available </li></ul><ul><li>Meclizine </li></ul><ul><li>Cyclizine </li></ul><ul><li>Dimenhydrinate </li></ul><ul><li>Diphenydramine </li></ul><ul><li>Promethazine – Used in pregnancy, used by </li></ul><ul><li>NASA for space motion sickness </li></ul>
  11. 11. Anticholinergics <ul><li>Scopolamine (hyoscine) – used as transdermal patch for motion sickness </li></ul>Cannabinoids <ul><li>Dronabinol – used as adjuvant in chemotherapy induced vomiting.It is a psychoactive substance </li></ul><ul><li>Nabilone </li></ul>
  12. 12. Now answer this question <ul><li>A physician prescribed Tab.Ondansetron for prophylaxis of motion sickness. Even though ondansetron is a potent antiemetic it didn’t produce any effect in this patient. Can you explain why ? </li></ul>
  13. 13. <ul><li>Explanation : </li></ul><ul><li>Vestibular nuclei has only muscarinic and H 1 histaminic receptors. </li></ul>
  14. 14. Points to Ponder
  15. 15. <ul><li>Even though both atropine and scopolamine are antimuscarinic, only scopolamine is used in the treatment of motion sickness. Why ? </li></ul><ul><li>Generally transdermal patches are applied over the arm or chest. But scopolamine transdermal patch is applied behind the ear. Why? </li></ul>
  16. 16. Thank you