Magnesium Sulfate Dosing for Severe Asthma
Recommended Dose
For adults with severe asthma exacerbations, administer 2 grams of intravenous magnesium sulfate over 20 minutes as an adjunct to standard therapy. 1, 2
For pediatric patients, the recommended dose is 25-75 mg/kg IV (maximum 2 grams) administered over 20 minutes. 3
When to Administer
Give IV magnesium sulfate to patients whose severe exacerbations persist after 1 hour of intensive conventional treatment with inhaled β2-agonists, anticholinergics, and systemic corticosteroids. 1, 2
Strongly consider IV magnesium for life-threatening exacerbations regardless of response to initial therapy, as recommended by the American Academy of Allergy, Asthma, and Immunology. 1
The greatest benefit occurs in patients with FEV1 <20% predicted or those presenting with FEV1/PEF <40% predicted after initial treatments. 1
Administration Details
Administer the full 2-gram dose over exactly 20 minutes to avoid hypotension and bradycardia that can occur with rapid infusion. 1, 3
Use IV magnesium as an adjunct to—not a replacement for—standard therapy including inhaled bronchodilators and systemic corticosteroids. 1, 2
Monitor for minor side effects including flushing and light-headedness during administration. 1
Have calcium chloride available to reverse potential magnesium toxicity if needed. 3
Route Comparison: IV vs. Nebulized
Intravenous administration is significantly more effective than nebulized magnesium sulfate for acute severe asthma. 1, 4
While some studies show nebulized magnesium (3 ml of 260 mmol/L solution every 20-60 minutes) may reduce admissions and improve outcomes, 5, 6 the evidence for inhaled formulations is less convincing than for IV administration. 1, 4
Nebulized magnesium may be considered as an additional adjunct in select cases but should not replace IV administration for severe exacerbations. 3
Mechanism and Evidence Base
Magnesium causes bronchial smooth muscle relaxation independent of serum magnesium levels, providing complementary bronchodilation to β-agonists. 1, 3
A Cochrane meta-analysis demonstrated that IV magnesium improves pulmonary function and reduces hospital admissions, particularly in patients with the most severe exacerbations. 1
Multiple guideline organizations including the American Heart Association, American Academy of Allergy, Asthma, and Immunology, and British Thoracic Society recommend this approach. 1
Common Pitfall to Avoid
Do not use magnesium sulfate for mild or moderate asthma exacerbations—reserve it specifically for severe cases that remain refractory after 1 hour of standard intensive treatment or for life-threatening presentations. 1, 3