• Magnesium sulphate is an airway smooth muscle relaxant that is used in patients with acute severe asthma in conjunction with standard therapy. It is believed to potentiate the bronchodilatory effects of inhaled β-2 agonists. Evidence is less convincing for COPD exacerbations although it is widely used by emergency physicians.
  • Magnesium is also used in eclampsia to prevent/treat seizures.
  • Finally, magnesium has been found to have some utility in the treatment of acute atrial fibrillation to improve rapid ventricular response rate and convert to sinus rhythm.
  • Asthma (adults & paediatrics): For adults with acute severe asthma without a good initial response to inhaled bronchodilator therapy or those with life-threatening asthma
  • Eclampsia: Presence of one or more seizures superimposed on a history of pre-eclampsia
  • Atrial Fibrillation (with fast ventricular response rate): Atrial fibrillation with a ventricular response rate >100bpm
  • Known drug allergy
  • AV block
  • Renal failure
 Precautions / Notes
  • Rapid administration can cause hypotension
  • Common side effects include flushing, pain at cannula site
  • Magnesium Toxicity: loss of deep tendon reflexes, respiratory depression. This can be treated by administration of Calcium Gluconate (1g slow IV push over 2-3 minutes).
 Weight-based Calculations
Cefazolin for fractures/prophylaxis
Presentation: /mL
Calculated dose:  in

Critical Care


  • Dilute 10mmol (5mL) into 45ml 0.9% sodium chloride to give final concentration of 10mmol/50ml.
  • Administer over 20 minutes (1 ampule)


  • Dilute 0.2mmol/kg in 0.9% Saline to 50ml total volume.
  • Administer over 20 minutes (maximum of 10mmol)
  • Dilute 20mmol (10ml) into 40 ml 0.9% sodium chloride to give final concentration of 20mmol/50ml.
  • Administer over 20 minutes
Atrial Fibrillation
  • Dilute 10mmol (5mL) into 45ml 0.9% sodium chloride to give final concentration of 10mmol/50ml.
  • Administer over 20 minutes
 Special Considerations
  • Nil
  • 5mL ampoule containing 10mmol (2mmol/mL)
Current mode:
Extended Care:
Colour assist:


Lang E. ED use of magnesium sulphate improved rate control in atrial fibrillation with rapid ventricular response. BMJ Evidence-Based Medicine. 2005;10:139

Davey MJ, Teubner D. A randomized controlled trial of magnesium sulfate, in addition to usual care, for rate control in atrial fibrillation. Ann Emerg Med. 2005;45:347–53

Perth Childrens Hospital Clinical Guidelines. Asthma. https://www.pch.health.wa.gov.au/For-health-professionals/Emergency-Department-Guidelines/Asthma

SIGN Guidelines Asthma. 2019. https://www.bsuh.nhs.uk/library/wp-content/uploads/sites/8/2019/03/BTS-SIGN-Asthma-2016-Guidelines.pdf

Shivanthan MC, Rajapakse S. Magnesium for acute exacerbation of chronic obstructive pulmonary disease: A systematic review of randomised trials. Ann Thorac Med. 2014;9(2):77-80. doi:10.4103/1817-1737

Green RH. Asthma in adults (acute): magnesium sulfate treatment. BMJ Clin Evid. 2016:1513

Lu JF, Nightingale CH. Magnesium sulfate in eclampsia and pre-eclampsia: pharmacokinetic principles. Clin Pharmacokinet. 2000 Apr;38(4):305-14.

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