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Intravenous MgSO4 Decreases the Number of Hospital Admissions for Children With Moderate to Severe Asthma Exacerbations


  • In pediatric patients with moderate to severe acute asthma, does intravenous magnesium sulfate therapy, compared to placebo, decrease the rate of hospital admissions?

Clinical Bottom Lines

  1. In pediatric patients with moderate to severe asthma, who fail to improve after three NMTs, 40mg/kg (max dose 2g) IV MgSO4 quickly improves PEFR, FEV1, FVC, and decreases the hospital admission rate.
  2. NNT to prevent one hospital admission for a moderate to severe asthma exacerbation is two.
  3. Intravenous MgSO4 should be considered as part of the treatment plan for patients who fail to improve after several NMTs and can be thought of as a bridge until the steroids can have their impact.

Summary of Key Evidence

  1. Thirty children (age 6-17.9) experiencing a moderate-severe asthma exacerbation who failed to improve significantly after three NMTs were randomized in a double blind fashion to receive 40mg/kg IV MgSO4 (16 patients) or similar volume of normal saline (14 patients).(1)
  2. The study excluded patients who had fever, recent use of theophyline, cardiac, renal or pulmonary disease other than asthma. Patients under the age of six or who were too severely distressed to perform PFTs were also excluded.
  3. All patients in the treatment and control groups were similar (see table 1) The only significant difference between the two groups was slightly higher systolic blood pressure in the MgSO4 treatment group.
  4. All patients were treated equally other than the MgSO4 treatment. Each patient received three NMTs (albuterol, atrovent, or combination) and continued to have PEFR < 70% predicted. All patients received 2mg/kg IV methylprednisolone, and continued to receive NMTs at the discretion of the ED team.
  5. The PEFR, FEV1, and FVC all improved significantly in the MgSO4 treatment group compared with the control group. The improvements were noted immediately after completing the MgSO4 infusion, and continued to improve throughout the study.
  6. None of the patients in the MgSO4 treatment group were admitted to the hospital. In the control group 7/14 patients required admission to the hospital. (ARR 0.5, NNT 2)
  7. There were no changes in blood pressure or other significant side effects in the MgSO4 treated group.

Additional Comments

  • MgSO4 proposed method of action is as a calcium antagonist or as a cofactor in enzyme systems involved in the movement of sodium and potassium across membranes, resulting in smooth muscle relaxation and mast cell stabilization.
  • Several other studies looking at the benefits of MgSO4 in acute asthma in children have had conflicting results.(2) This study was done in a more heterogenous group of patients seen in the ER and was not powered to detect a difference in hospitalization rates. MgSO4 seems to be the most beneficial in moderate to severe asthma patients who fail to improve with b-agonist therapy.
  • The clinical effect of the MgSO4 infusion, while statistically significant at an absolute increase of 25% in the peak flows, was still relatively moderate with the peak flows still being only about 55% of predicted.
  • MgSO4 infusion has minimal if any side effects, and the cost is certainly less than a hospital admission.


  1. Ciarallo L, et al. Higher-dose intravenous magnesium therapy for children with moderate to severe acute asthma. Arch Pediatr Adolesc Med 2000; 154: 979-983.
  2. Scarfon R, et al. A randomized trial of magnesium in the emergency department treatment of children with asthma. Annals of Emergency Medicine 2000; 36(6):572-8.

CAT Author: Amy Benzing, MD

CAT Appraisers: John G. Frohna, MD

Date appraised: February 12, 2001

Last updated February 14, 2001
Department of Pediatrics and Communicable Diseases
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