Intravenous Magnesium Sulfate for Severe Asthma Exacerbations

Dosing Protocol

Adult dosing – A single intravenous infusion of 2 g magnesium sulfate administered over 20 minutes is the recommended regimen for adults with severe refractory asthma. 1
Pediatric dosing – For children, the dose is 25–75 mg/kg (maximum 2 g) infused over 20–60 minutes. 2

Severe refractory asthma – Magnesium sulfate should be given only to patients whose exacerbations have not responded adequately to initial bronchodilators and systemic corticosteroids. 1
Life‑threatening exacerbations – Indicated after at least 1 hour of intensive conventional therapy (β‑agonists + corticosteroids) when respiratory failure is imminent. 3

Magnesium sulfate produces rapid bronchial smooth‑muscle relaxation that is independent of serum magnesium concentrations, providing an immediate bronchodilating effect. 1

Reduced hospital admissions – A single 2 g dose lowers the odds of admission (OR ≈ 0.75). 1
Improved pulmonary function – Significant increases in FEV₁, peak expiratory flow, and forced vital capacity are observed within 50–110 minutes after infusion. 1
Higher emergency‑department discharge rates – More patients receiving magnesium are discharged home compared with placebo. 1

Common adverse effects – Flushing, light‑headedness, fatigue, nausea, headache, and transient hypotension are generally mild and self‑limited. 1

Do not repeat magnesium – If clinical improvement is absent after the single dose, additional magnesium should not be administered.
Escalate care – Transfer to intensive care for deteriorating peak flow, worsening hypoxia despite 60 % oxygen, hypercapnia (PaCO₂ > 6 kPa), exhaustion, or altered mental status. 4
Alternative therapies – Consider heliox‑driven albuterol nebulization as a next‑line bronchodilator strategy. 5
Prepare for intubation – If signs of impending respiratory failure develop (inability to speak, altered mental status, intercostal retractions, worsening fatigue, PaCO₂ ≥ 42 mmHg), initiate airway protection measures. 3

Mild‑to‑moderate exacerbations – Magnesium sulfate provides no measurable benefit in patients with lower‑severity attacks and should not be used in this setting. 3

Adults should receive 2 g of magnesium sulfate intravenously infused over 20 minutes as a single administration. 6
Children should receive 25–75 mg/kg (maximum 2 g) of magnesium sulfate intravenously infused over 20–60 minutes as a single administration. 6

The single dose is reserved for patients with severe refractory asthma who have failed to improve after at least 1 hour of intensive conventional therapy (continuous β‑agonists and systemic corticosteroids). 6

If the patient shows signs of impending respiratory failure (e.g., inability to speak, altered mental status, intercostal retractions, worsening fatigue), prepare for endotracheal intubation. 6
As an alternative bronchodilator strategy, consider heliox‑driven albuterol nebulization. 6

Continuous or prolonged magnesium infusions (4–24 hours) are not endorsed by national asthma guidelines and should be limited to specialized centers for refractory status asthmaticus. 6

Magnesium sulfate has no therapeutic value in mild‑to‑moderate asthma exacerbations and should be administered only once in severe cases that meet the above criteria. 6