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Physiology of vomiting

  • Nausea and vomiting are protective reflexes that serve to rid the stomach and intestine of toxic substances and prevent their further ingestion. This is accompanied by multiple autonomic phenomena including salivation, shivering, and vasomotor changes.
  • Vomiting is complex, consisting of a pre-ejection phase (gastric relaxation and retroperistalsis), retching (rhythmic action of respiratory muscles preceding vomiting and consisting of contraction of abdominal and intercostal muscles and diaphragm against a closed glottis), and ejection (intense contraction of the abdominal muscles and relaxation of the upper esophageal sphincter).


  • Emesis center in the lateral reticular formation of the mid-brainstem adjacent to both the chemoreceptor trigger zone (CTZ) in the area postrema (AP) at the bottom of the fourth ventricle and the Solitary tract nucleus (STN) of the vagus nerve.
  • The lack of a blood–brain barrier allows the CTZ to monitor blood and cerebrospinal fluid constantly for toxic substances and to relay information to the emesis center to trigger nausea and vomiting.
  • The CTZ has high concentrations of receptors for serotonin (5-HT3), dopamine (D2), and opioids, while the STN is rich in receptors for enkephalin, histamine, and ACh, and also contains 5-HT3 receptors.


Apomorphine (Act on D-2 receptors on CTZ)

Ipecacuanha (Act reflexly and directly on CTZ)

a.  Given SC

b.  Ergot alkaloid

c.   Non-safe

a.  Given orally

b.  Safe to use


Vomiting should not be induced in:

  1. Opioid/ Morphine poisoning                    
  2. Phenothiazine /CNS stimulant poisoning  
  3. Corrosive (acid, alkali) poisoning          
  4. Kerosene poisoning               
  5. Unconscious patient







Cyclizine, Dimenhydrinate, Diphenhydramine,

Hydroxyzine, Promethazine

5-HT4 Agonist

Cisapride, Mosapride, Itopride


Dolasetron, Granisetron, Ondansetron, Palonosetron, Ramosetron

Benzamides (D-2 Agonist)

Domperidone, Metoclopramide


Droperidol, Haloperidol


Chlorpromazine, Fluphenazine, Perphenazine, Prochlorperazine


Betamethasone, Dexamethasone

  1. 5-HT3 blockers (e.g. Ondensetron)
    1. Short acting
    2. DOC
      1. Radiotherapy, chemotherapy, postoperative vomiting
    3. S/E
      1. Headache, constipation
  2. 5-HT4 agonists
    1. Cisapride is oldest
    2. Prokinetic
    3. Does not have anti-emetic activity
    4. S/E
      1. Abdominal cramps
      2. Diarrhea
      3. Prolonged QT syndrome, can lead to Torsades De Pointes

Drugs causing Torsades De pointes (APACHE)

Amiodarone, Procainamide, Arsenium, Cisapride, Haloperidol, Erythromycinv

  1. Metoclopramide
    1. D2 antagonist, Cholinergic (Dual action)
    2. Well absorbed
    3. Short acting
    4. High first pass metabolism
    5. DOC
      1. GERD
      2. Prokinetic
      3. Mendelson’s syndrome
      4. Shortening GET
      5. Enteric tube feeding


  1. Sedation
  2. Hyperprolactinemia (D-2 suppression on pituitary increasing Prolactin)
  3. Extra Pyramidal Syndrome (EPS)


Same as metoclopramide but Does not enter blood brain barrier

Free from EPS

Safe even in Parkinson’s disease 

  1. Antihistaminics
    - Motion sickness and postoperative emesis.
    - Act on vestibular afferents and within the brainstem
  2. Anticholinergics
    - Scopolamine Transdermal patches
    - No role in chemo-induced vomiting
    - Prevention and treatment of motion sickness, although it also has some activity in postoperative nausea and vomiting

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