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Anti-emetics

Anti-emetics. Two centres: Emetic centre (EC) and chemoreceptor trigger zone (CTZ) Both near the floor of the fourth ventricle, close to the vital centres EC is within the blood brain barrier (BBB) CTZ outside in the area postrema They are connected together. Anti-emetics: Teleology.

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Anti-emetics

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  1. Anti-emetics • Two centres: Emetic centre (EC) and chemoreceptor trigger zone (CTZ) • Both near the floor of the fourth ventricle, close to the vital centres • EC is within the blood brain barrier (BBB) • CTZ outside in the area postrema • They are connected together

  2. Anti-emetics: Teleology • Rational reflex • prevention of ingestion of noxious substances (sight, smell, taste, texture) • local gut reflexes stimulate vomiting e.g. toxins • backup blood monitoring system, should former two protective reflexes be breached • Irrational reflexes • labyrinth • pregnancy • ‘visual nasties’!

  3. Dopamine Opioids Chemotherapy Anaesthetics Hormones Azotaemia Diabetes CTZ BBB 5 HT3 Acetylcholine Emetic Centre Vestibular Sights Smell Taste Histamine Hypotension Hypoxaemia Gut Vomiting

  4. Anti-emetic agents Chemoreceptor trigger zone • Anti-dopaminergic agents • phenothiazines e.g. chlorpromazine • butyrophenones e.g. droperidol • procainamide derivs. e.g. metoclopramide • benzimidazole derivs. e.g. domperidone

  5. Anti-emetic agents at CTZ Anti-dopaminergic agents … uses • Chemotherapy • Drug induced N and V e.g. opioids and chemotherapy • Parkinson’s disease (domperidone) • Postoperative N and V • Motion sickness ?

  6. Anti-emetic agents at CTZ Anti- 5 HT3 agents • Ondansetron • Granisetron Uses • Chemotherapy (cis-platin) • Postoperative • Expensive !!-

  7. Anti-emetic agents at EC Anticholinergics • Atropine and hyoscine • Glycopyrrolate ? Uses • Travel sickness • Postoperative N and V (combined with opioids)

  8. Anti-emetic agents at EC Anti-histamines • Cyclizine • Promethazine (other actions?) Uses • Postoperative N and V • Sedation (combined with opioids)

  9. Anti-emetic agents: Side effects • Extra-pyramidal effects • Dry mouth and blurred vision • Sedation • Tachycardia • Hypotension

  10. Anti-emetic agents: Choice • Postoperative • Chemotherapy • Travel sickness • Parkinson’s disease (especially apomorphine) • Pregnancy

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