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  • antiemetics appear to be only marginally better than iv N Saline placebo for ED patients excluding those with hyperemesis gravidarum, chemotherapy, or vertigo aetiologies 1)2)
metoclopramide (Maxolon)
  • metoclopramide should not be used in children as the risk of dystonic reactions such as oculogyric crises is high.
  • there is little evidence that its routine use in preventing opiate-induced nausea is worth the incidence of dystonic reactions in adults, or that it is effective in post-op nausea or vomiting.
  • thus it should not be used as a prophylaxis routinely in patients receiving opiates unless vomiting would be particularly deleterious (eg after upper abdominal or intraocular surgery), in patients unable to protect their airways, or in patients known to vomit excessively after opioids.
  • it should be avoided in those with restless legs syndrome and those with hypersensitivity such as Lewy Body dementia
  • it should not be used long term (more than a week or two) without good reason as there is a risk of irreversible tardive dyskinesia, particularly in the elderly
  • it should not be used in those with possible bowel obstruction
  • it will generally cause increased abdominal flatus (due to undigested food being pushed into the colon) and potentially exacerbate bloating and cramps

physiology of nausea and vomiting

  • the brain stem “vomiting centre” is a loosely organised neuronal region within the lateral medullary reticular formation.
  • high concentrations of muscarinic M1, histamine H1, neurokinin NK1 and serotonin 5-HT3 receptors have been detected in this region.

introduction to anti-emetics

motion sickness

  • motion sickness is an autonomic syndrome similar to that which accompanies vertigo, except that it is due to real motion and not an illusion of motion.
  • prevention and Rx is usually best with medications which have anticholinergic activity
do not use anticholinergics in children under age 2 years as they are very sensitive to anticholinergics

prevention of motion sickness options include:

  • non-pharmacologic:
    • distraction - keep eyes on horizon where possible
    • avoid reading or playing games whilst traveling
    • avoid unnecssary head movements by using pillow as head rest
    • in a car try sitting towards the front
    • if flying, try sitting over the wing for better stability
    • in a boat, try to keep standing up with legs far apart and keep watching the horizon to help give your brain more stable inputs until it learns the new motions (this takes about 36hrs)
    • avoid heavy, greasy meals prior to travel
    • avoid overheating - allow adequate ventilation
    • keep calm - motion sickness tends to be worse with anxiety
    • ginger may help but no proof, and as it inhibits thromboxane synthetase, high doses may potentiate the effects of anticoagulants.
  • pharmacologic:
    • dimenhydrinate
      • take orally 30min before travel
      • dose: child 2-7yrs: 12.5-25mg; 8-12yrs: 25-50mg; adults 50-100mg;
    • hyoscine hydrobromide:
      • as effective as antihistamines, less sedating but more anticholinergic effects
      • take orally 30min before travel
        • dose: child 2-7yrs: 75mcg; 8-12yrs: 150-300mcg; adults 300-600mcg;
      • transdermal patches are available overseas for those above 10yrs of age.
    • promethazine:
      • take orally 1-2 hours before travel
      • dose: child 2-5yrs: 5-6.25mg; 6-10yrs: 10-12.5mg; adults 25mg;
    • NB. non-sedating antihistamines, such as loratadine and cetirizine, penetrate poorly into the central nervous system and are not

effective against motion sickness.

treatment options for motion sickness

  • dimenhydrinate:
    • dose:
      • children: 1 to 1.5 mg/kg orally, 6-hourly, up to 175 mg in any 24-hour period
      • adults: 50 to 100 mg orally, 4- to 6-hourly, up to 400 mg in any 24-hour period
  • hyoscine hydrobromide:
    • dose:
      • children: 6 to 8 micrograms/kg orally, 6-hourly, up to 600 micrograms in any 24-hour period
      • adults: 300 to 600 micrograms orally, 4- to 6-hourly, up to 1200 micrograms in any 24-hour period
  • promethazine:
    • dose:
      • children: 0.125 to 0.3 mg/kg orally, 6-hourly, up to 100 mg in any 24-hour period
      • adults: 25 to 50 mg orally, then 25 mg orally, 8- to 12-hourly, up to 100 mg in any 24-hour period.



hyperemesis gravidarum

post-operative nausea and vomiting (PONV)


  • regional anaesthesia
  • propofol for induction and maintenance of anaesthesia
  • supplementary oxygen
  • hydration
  • avoidance of nitrous oxide
  • avoidance of volatile anaesthetics
  • minimisation of intra- and postoperative opioid use
  • minimisation of neostigmine dose (ie. avoid doses > 2.5mg)
  • in high risk patients (eg. women non-smokers with PH motion sickness), consider:
    • dexamethasone 4-8mg (adults) prior to induction of anesthesia
    • low dose droperidol post-op, especially if using PCA - no more than 2.5mg droperidol with 100mg morphine in PCA infusion.
      • be aware of the warnings relating to prolonged QT and sudden death, although none have occurred at low dose for prevention of post-op nausea.
    • promethazine at the end of surgery is effective but causes sedation
    • iv cyclizine 25mg appears to decrease PONV by 55-65% but has the usual adverse effects of antihistamines (H1) including sedation and anticholinergic effects
    • NB. THERE IS NO EVIDENCE TO SUPPORT METOCLOPRAMIDE in 10mg IV doses is useful in preventing post-op nausea and vomiting.

a treatment regime for established post-op nausea and vomiting

  • exclude medication and mechanical causes (eg. swallowing blood, abdominal obstruction)
  • if using opioid via PCA, add droperidol as above
  • ondansetron 4-8mg (25-100mcg/kg up to 4mg in children) slow iv (although studies have shown doses as low as 1mg in adults may be effective), can repeat dose after 6hrs
  • if ongoing vomiting, use a different class agent:
    • dexamethasone 4mg iv (100-200mcg/kg up to 8mg in children) if not already given within past 8hrs
    • consider droperidol 0.625mg (adults) slow iv
  • if still vomiting:
    • promethazine 12.5mg (adults) iv
  • reference: Aust. Ther. Guidelines 2008

radiotherapy or chemotherapy-induced vomiting

  • first line tends to be a 5HT3 antagonist such as ondansetron
  • there is no evidence to support the use of 5-HT3–receptor antagonists 24 hours beyond the last dose of radiation therapy.

cannabinoid hyperemesis

  • classically associated with relief from hot showers resulting in compulsive showers/bathing
  • cyclical every 2-3weeks
  • anti-emetics generally do not work well
antiemetics.txt · Last modified: 2017/01/11 10:06 (external edit)