In pediatric patients with severe asthma/respiratory distress, what magnesium sulfate dose is recommended?

• A. 50 mg/kg slow IV drip over 20 minutes. Do not exceed 2 gm total.
• B. 5 mg/kg slow IV drip over 20 minutes
• C. 20 mg/kg bolus
• D. 100 mg/kg slow IV drip over 30 minutes

Answer: (A)

Magnesium sulfate is used in severe pediatric asthma as an adjunct bronchodilator when initial treatments aren’t fully effective. The dosing that provides meaningful bronchodilation while keeping toxicity risk acceptable is 50 mg/kg given IV over about 20 minutes, with a maximum total of 2 g. This amount takes advantage of magnesium’s ability to relax airway smooth muscle by blocking calcium influx and reducing acetylcholine release, which helps open the airways without causing rapid toxicity.

Doses that are much smaller, like 5 mg/kg, are unlikely to provide clinically meaningful bronchodilation in severe distress. Very large doses or rapid bolus administration raise the risk of adverse effects such as hypotension, bradycardia, flushing, hyporeflexia, and potential respiratory depression. Therefore, 50 mg/kg capped at 2 g over 20 minutes is the balanced, evidence-based approach. Always monitor the patient for signs of magnesium toxicity and adjust if needed, especially in those with renal impairment.