Disease - Anti-emetics

From CambridgeNotes

Nausea and vomiting are common and distressing complaints. The causes are often multifactorial so a careful history and examination are important. Common causes include:

  • Drugs: opioids, cytotoxic chemotherapy
  • GI causes: gastritis, ulceration, functional gastric stasis, external pressure, carcinoma of stomach, gastroduodenal obstruction, intestinal obstruction
  • Constipation due to drugs, cancer, immobility
  • Biochemical causes: renal failure, hypercalcaemia, infection, tumour toxins
  • Raised intracranial pressure (RICP)
  • Vestibular disturbance
  • Radiotherapy
  • Anxiety, cough, pain


  • Non-drug methods: acupuncture, ginger, small meals, hypnotherapy, avoid certain foods/smells
  • Oral drugs can be used but for severe vomiting alternative routes are needed
    • IM is suitable for a single episode but it is too painful for persistent use
    • subcutaneous route: via a syringe driver, for persistent nausea and vomiting
    • rectal
  • Ensure the anti-emetic is given regularly for maximum effects, not prn
  • If the first drug used is ineffective, try higher doses then a drug from a different group
  • The following classes of anti-emetic drugs are available:
  • Anti-histamines: cyclizine, promethazine
    • Action: inhibit vestibular and vomiting centres
    • Indications: vestibular disturbance, RICP, unknown cause
    • Side effects: antimuscarinic: sedation, constipation, dry eyes/skin, urinary retention
  • Anti-muscarinics: hyoscine
    • Action: reduces gastrointestinal secretions and motility
    • Indications: intestinal obstruction
    • Side effects: sedation, constipation, dry eyes/skin, urinary retention, may antagonise metoclopramide and other pro-kinetic drugs
  • Anti-dopaminergics: metoclopramide, domperidone, haloperidol, chlorpromazine
    • Action: block D2 receptors in the chemoreceptor trigger zone, increase peristalsis in the gut (pro-kinetic)
    • Indications: opioid induced vomiting, renal failure, functional gastric stasis, in combination with cyclizine, contra-indicated in GI obstruction
    • Side effects: sedation, parkinsonism, anti-muscarinic, neuroleptic malignant syndrome
  • 5-HT3 receptor antagonists: ondansetron, granisetron
    • Indications: chemotherapy induced vomiting (expensive, however)
    • Side effects: constipation, headache, sedation, dizziness, flushing
  • Corticosteroids: dexamethasone.
    • Indications: RICP, chemotherapy induced vomiting
  • Benzodiazepines : diazepam.
    • Action: GABA agonist in cerebral cortex
    • Indications: anxiety induced vomiting
    • Side effects: respiratory depression, drowsiness