What is the recommended dose of magnesium sulfate (MgSO4) for a 4-year-old male weighing 16 kg with an asthma exacerbation?

Magnesium Sulfate Dosing for Pediatric Asthma Exacerbation

For a 4-year-old male weighing 16 kg with an asthma exacerbation, the recommended dose of intravenous magnesium sulfate is 25-50 mg/kg (400-800 mg) administered over 10-20 minutes, with a maximum dose of 2 grams. 1

Indications for IV Magnesium Sulfate

Magnesium sulfate is indicated for:

• Severe asthma exacerbations that do not respond to conventional treatment after 1 hour
• Potentially life-threatening asthma exacerbations 1

It has no apparent value in mild asthma exacerbations, so clinical severity assessment is crucial before administration.

Administration Protocol

1. Dosing calculation:

   • At 25 mg/kg: 16 kg × 25 mg/kg = 400 mg
   • At 50 mg/kg: 16 kg × 50 mg/kg = 800 mg
   • Choose dose based on severity (closer to 50 mg/kg for more severe cases)

2. Administration rate:

   • Administer over 10-20 minutes as a single infusion 1
   • Slower administration reduces risk of adverse effects

3. Monitoring during administration:

   • Vital signs (blood pressure, heart rate, respiratory rate)
   • Oxygen saturation
   • Deep tendon reflexes (loss may indicate magnesium toxicity)
   • Signs of magnesium toxicity (flushing, sweating, hypotension, respiratory depression) 1

Clinical Considerations

• Magnesium sulfate should be used after first-line treatments (oxygen, nebulized short-acting beta2-agonists, and systemic corticosteroids) have been initiated 1, 2

• The intravenous route is more effective than inhaled magnesium sulfate for treating acute asthma exacerbations 2, 3

• Baseline vital signs, deep tendon reflexes, and if possible, serum magnesium and renal function tests should be obtained before administration 1

• Have calcium salts available to counteract potential magnesium toxicity 1

Efficacy and Safety

• Intravenous magnesium sulfate has been shown to reduce hospital admissions and improve lung function in severe asthma exacerbations 1, 4

• Common adverse events include flushing, fatigue, nausea, headache, and hypotension 4

• Caution: Higher doses (>27 mg/kg) in children weighing <40 kg have been associated with increased need for escalation in therapy, including mechanical ventilation or additional adjunctive therapies 5

Important Caveats

• Avoid exceeding the maximum dose of 2 grams, regardless of weight calculation 1

• Use with caution in patients with renal insufficiency 1

• Magnesium sulfate should be used with caution if the patient is receiving other medications that could interact with it, such as neuromuscular blocking agents 1

• While continuous infusion protocols exist (50 mg/kg/h for 4 hours), the single bolus approach is more commonly recommended in guidelines 6

By following these evidence-based recommendations, you can safely administer magnesium sulfate to this pediatric patient with an asthma exacerbation while minimizing risks and optimizing potential benefits.