Magnesium Sulfate Dosing in Pediatric Asthma
For pediatric patients with severe asthma exacerbations, intravenous magnesium sulfate should be administered at 50 mg/kg (maximum 2 grams) as a single dose over 20 minutes. This dosing regimen is recommended for children with life-threatening exacerbations or those whose exacerbations remain severe after one hour of intensive conventional treatment 1.
Indications for Magnesium Sulfate in Pediatric Asthma
Magnesium sulfate should be used as an adjunctive therapy in the following scenarios:
- Severe asthma exacerbations not responding to first-line treatments
- Life-threatening asthma exacerbations
- Patients with FEV1 or PEF <40% of predicted after initial bronchodilator therapy
- Persistent hypoxemia despite oxygen supplementation
Administration Protocol
Standard Single Dose Approach:
- Dose: 50 mg/kg (maximum 2 grams)
- Administration: Intravenous infusion over 20 minutes
- Timing: After failure of first-line treatments (inhaled β2-agonists, anticholinergics, and systemic corticosteroids)
Monitoring During Administration:
- Vital signs (heart rate, blood pressure, respiratory rate)
- Oxygen saturation
- Clinical asthma severity scores
- Side effects (flushing, hypotension, muscle weakness)
Mechanism and Benefits
Magnesium causes relaxation of bronchial smooth muscle independent of serum magnesium level 1. When combined with nebulized β-adrenergic agents and corticosteroids, IV magnesium sulfate can moderately improve pulmonary function in patients with asthma, with only minor side effects such as flushing and light-headedness 1.
A Cochrane meta-analysis concluded that IV magnesium sulfate improves pulmonary function and reduces hospital admissions, particularly for patients with the most severe exacerbations of asthma 1.
Alternative Dosing Approaches
While the standard single-dose approach is most commonly recommended in guidelines, some research suggests alternative dosing regimens:
Continuous Infusion: Some studies have explored continuous infusion at 50 mg/kg/hour for 4 hours in severe cases 2, 3. This approach showed improvement in respiratory status with good tolerability 2.
Pharmacokinetic studies suggest that doses between 50-75 mg/kg are required to achieve serum concentrations within the hypothesized therapeutic range of 25-40 mg/L 4.
Important Caveats and Considerations
- Magnesium sulfate has no apparent value in patients with exacerbations of lower severity 1.
- The serum half-life of magnesium is relatively short (approximately 2.7 hours) in children 4.
- Potential side effects include hypotension, flushing, nausea/vomiting, and mild muscle weakness 3.
- Continuous infusions beyond 24 hours have been associated with more adverse events and should be reserved only for refractory cases 3.
Integration with Other Asthma Treatments
Magnesium sulfate should be administered after or concurrent with:
- Inhaled short-acting β2-agonists (e.g., albuterol 0.15 mg/kg every 20 minutes)
- Systemic corticosteroids (e.g., methylprednisolone 1-2 mg/kg IV)
- Ipratropium bromide (if indicated)
- Oxygen supplementation to maintain saturation >92-95%
In a recent study comparing magnesium sulfate to aminophylline as second-line treatment, magnesium sulfate (50 mg/kg single dose) proved more effective and safer, with significant improvements in clinical scores and reduced hospitalization rates 5.