IV Magnesium Sulfate Dosing for Severe Acute Asthma in Children
The recommended dose of intravenous magnesium sulfate for children with severe acute asthma is 25-75 mg/kg (maximum 2-2.5 g) administered over 20 minutes as a single dose. 1, 2
Indications for IV Magnesium Sulfate
IV magnesium sulfate should be administered to children with:
- Severe asthma exacerbations not responding to conventional treatment after 1 hour of intensive therapy
- Signs of impending respiratory failure
- FEV1 <30% of predicted value (especially <20%)
- Poor response to initial treatment with bronchodilators and systemic corticosteroids 1
Administration Protocol
Step 1: Initial Standard Treatment
- High-flow oxygen to maintain SaO2 >92%
- Short-acting beta-agonists (salbutamol 5 mg or terbutaline 10 mg) via oxygen-driven nebulizer (half doses for very young children)
- Systemic corticosteroids (IV hydrocortisone or oral prednisolone 1-2 mg/kg, maximum 40 mg)
- Ipratropium bromide 100 μg nebulized every 6 hours 3, 1
Step 2: Assessment for Magnesium Sulfate
If no improvement after 15-30 minutes of initial treatment:
- Continue oxygen and steroids
- Increase frequency of nebulized beta-agonist (up to every 30 minutes)
- Consider IV magnesium sulfate 3, 1
Step 3: Magnesium Sulfate Administration
- Dose: 25-75 mg/kg (maximum 2-2.5 g)
- Administration: Infuse over 20 minutes
- Target plasma concentration: >4 mg/dL 1, 2
Monitoring During Administration
- Continuous clinical assessment of respiratory status
- Oxygen saturation monitoring
- Blood pressure monitoring
- Heart rate monitoring
- Observe for signs of magnesium toxicity (hypotension, flushing, muscle weakness) 1
Evidence of Efficacy
IV magnesium sulfate has been shown to:
- Improve lung function parameters in children with acute asthma 4
- Reduce hospitalization rates in children with moderate to severe asthma exacerbations 2
- Help prevent intubation in critically ill patients 1
- Provide earlier improvement in clinical signs and symptoms in patients not responding to conventional therapy 5
Important Considerations
- IV magnesium sulfate should be used with caution in patients with renal disease
- Monitor for possible magnesium toxicity (levels 6-10 mmol/L)
- Consider transfer to ICU if there is deterioration of respiratory status despite treatment 1
Caution Against Prolonged Infusions
While some clinicians utilize prolonged magnesium sulfate infusions for children with refractory asthma, there is significant variability in dosing regimens and limited assessment of clinical outcomes. Adverse events including hypotension (16.6%), nausea/vomiting (7.8%), and muscle weakness (4.9%) have been reported with prolonged infusions. Until further research is conducted, prolonged magnesium sulfate infusions should be reserved for truly refractory cases 6.
The standard single-dose approach (25-75 mg/kg over 20 minutes) remains the evidence-based recommendation for most children with severe acute asthma not responding to initial therapy.