What is the recommended dose of magnesium sulfate for a 3-year-old child weighing 14.8 kg with an asthma exacerbation?

Magnesium Sulfate Dosing for Pediatric Asthma Exacerbation

For a 3-year-old child weighing 14.8 kg with an asthma exacerbation, administer intravenous magnesium sulfate at 25-50 mg/kg (370-740 mg for this child, maximum 2 g) infused over 15-30 minutes. 1

Indication and Timing

• Magnesium sulfate is indicated when the child has life-threatening features or shows inadequate response to initial conventional therapy (oxygen, nebulized beta-agonists, and systemic corticosteroids) 1
• Life-threatening features in children include: too breathless to talk or feed, respirations >50 breaths/min, pulse >140 beats/min, PEF <33% predicted, poor respiratory effort, cyanosis, silent chest, fatigue/exhaustion, or altered consciousness 1
• Administer after the child has received at least 2-3 doses of nebulized salbutamol without adequate improvement 2

Specific Dosing for This Patient

• Weight-based dose: 25-50 mg/kg = 370-740 mg for a 14.8 kg child 1
• Infusion rate: Administer over 15-30 minutes for acute asthma exacerbation 1, 3
• Maximum single dose: 2 grams (this child is well below the maximum) 1
• For this specific patient, a practical dose would be 500-700 mg (approximately 35-47 mg/kg) infused over 20 minutes 1

Administration Details

• Dilute in D5W (dextrose 5% in water) for infusion 1
• Continue concurrent therapy with high-flow oxygen, nebulized beta-agonists, and systemic corticosteroids during magnesium infusion 1
• Monitor continuously during infusion for hypotension and bradycardia 1
• Have calcium chloride available to reverse magnesium toxicity if needed 1

Evidence Supporting Use

The evidence strongly supports intravenous magnesium sulfate in severe pediatric asthma:

• Efficacy: Multiple studies demonstrate significant improvement in pulmonary function (FEV1, PEF, FEF25-75) and clinical asthma scores within 30 minutes to 1 hour after infusion 2, 3
• Hospital admissions: Intravenous magnesium reduces hospital admissions in severe exacerbations 4, 5
• Safety profile: Adverse effects are rare in children, with the medication considered safe when properly administered 6, 2, 3

Monitoring Requirements

• Continuous monitoring of heart rate and blood pressure during infusion 1
• Oxygen saturation should be maintained >92% 1
• Assess clinical response at 30 minutes, 1,2, and 3 hours post-infusion through respiratory rate, work of breathing, oxygen saturation, and if age-appropriate, peak expiratory flow 2

Common Pitfalls to Avoid

• Do not delay administration in severe cases waiting for laboratory confirmation of hypomagnesemia—the therapeutic effect is independent of baseline magnesium levels 4
• Avoid rapid infusion (faster than recommended 15-30 minutes) as this significantly increases risk of hypotension and bradycardia 1
• Do not use as first-line therapy—ensure the child has received adequate conventional treatment first (oxygen, beta-agonists, corticosteroids) 1, 6
• Inhaled magnesium sulfate is NOT recommended—evidence shows it is less effective than intravenous administration and offers no advantage over standard beta-agonist therapy 4, 5

Contraindications

• Kidney failure (renal insufficiency) 6
• Atrioventricular heart block 6
• Known hypersensitivity to magnesium sulfate 1

Additional Considerations for Severe Cases

If life-threatening features are present at presentation, consider administering magnesium sulfate earlier in the treatment algorithm rather than waiting for failure of multiple rounds of bronchodilators 1

For children requiring transfer to intensive care, magnesium sulfate should be given before transfer if not already administered, as it may prevent progression to respiratory failure and need for intubation 6