What is the recommended dose of magnesium sulfate (MgSO4) for a child?

Magnesium Sulfate Dosing in Children

For acute severe asthma or life-threatening conditions like torsades de pointes, administer 25-50 mg/kg IV/IO (maximum 2 g) over 10-30 minutes depending on the indication. 1

Clinical Context-Specific Dosing

Acute Asthma/Status Asthmaticus

• Single bolus dose: 25-50 mg/kg IV (maximum 2 g) infused over 15-30 minutes 1
• Continuous infusion (for refractory cases): Following a bolus of 25-75 mg/kg, infuse at 18.4-50 mg/kg/hour depending on severity 2
  • For infusions lasting 4-5 hours: 40-50 mg/kg/hour 2
  • For prolonged infusions (>24 hours): 18.4-25 mg/kg/hour 2
• Target serum magnesium concentration: 4-6 mg/dL 2
• This approach reduces hospital admission odds by 68% in moderate-to-severe exacerbations 3

Life-Threatening Arrhythmias

• Torsades de pointes or refractory ventricular tachycardia: 25-50 mg/kg IV/IO (maximum 2 g) 1
• Administer as rapid bolus for pulseless torsades 1
• Infuse over 10-20 minutes for torsades with pulses 1

Hypomagnesemia Treatment

• Severe hypomagnesemia: Up to 250 mg/kg IM within 4 hours if necessary 4
• Mild deficiency: Dosing extrapolated from adult regimens; use caution 4

Parenteral Nutrition (Long-term)

• Infants: 2-10 mEq (0.25-1.25 g) daily 4
• Specific recommendations reference Table 1 in ESPGHAN/ESPEN guidelines for age-specific dosing in mmol/kg/day 1

Critical Safety Considerations

Administration Guidelines

• Maximum infusion rate: Do not exceed 150 mg/minute (1.5 mL of 10% solution) except in severe eclampsia with seizures 4
• Dilution requirement: Solutions must be diluted to ≤20% concentration for IV use in children 4
• IM administration: Dilute 50% solution to ≤20% concentration before IM injection in children 4

Monitoring Requirements

• Monitor deep tendon reflexes before each dose; absent reflexes indicate toxicity 4
• Maintain urine output ≥100 mL in the 4 hours preceding each dose 4
• Monitor respiratory rate (should be ≥16 breaths/minute) 4
• Check serum magnesium concentrations regularly, especially with continuous infusions 2

Toxicity Thresholds

• Therapeutic range: 1.8-3.0 mmol/L (3-6 mg/100 mL) 5, 4
• Loss of patellar reflex: 3.5-5 mmol/L 5
• Respiratory paralysis: 5-6.5 mmol/L 5
• Cardiac conduction alterations: >7.5 mmol/L 5
• Cardiac arrest risk: >12.5 mmol/L 5

Special Populations

• Neonates exposed to maternal magnesium therapy: Limit magnesium intake and adjust based on postnatal serum concentrations due to impaired renal excretion 1
• Renal impairment: Use with extreme caution; maximum 20 g/48 hours with frequent serum monitoring 4

Common Adverse Effects

Adverse events are more common with prolonged infusions (>24 hours) and include 2:

• Hypotension (16.6% in prolonged infusions)
• Nausea/vomiting (7.8%)
• Mild muscle weakness (4.9%)
• Flushing (2.2%)
• Sedation (0.4%)

Antidote

Have calcium chloride immediately available (20 mg/kg or 0.2 mL/kg of 10% solution IV) to reverse magnesium toxicity 1, 4