IV Magnesium Sulfate Dosing for Pediatric Patients
For severe acute asthma in children, administer IV magnesium sulfate at 25-50 mg/kg (maximum 2 g) infused over 15-30 minutes, with the higher dose range (40-50 mg/kg) showing superior efficacy for moderate to severe exacerbations. 1, 2
Standard Dosing Regimens
Acute Severe Asthma (Primary Indication)
- Bolus dose: 25-50 mg/kg IV/IO over 15-30 minutes 1
- Maximum single dose: 2 g 1
- Timing: Administer after 1 hour of intensive conventional treatment (bronchodilators + corticosteroids) if exacerbation remains severe 1
The evidence strongly supports the higher end of this range. A controlled trial demonstrated that 40 mg/kg produced remarkable improvement in pulmonary function, with 50% of treated patients discharged home versus 0% in the placebo group 2. The 50 mg/kg dose has been validated in prospective pharmacokinetic studies and shown to be safe in pediatric cohorts 3.
Life-Threatening Presentations
- Torsades de pointes VT: 25-50 mg/kg IV/IO (maximum 2 g) given rapidly over several minutes for pulseless arrest, or over 10-20 minutes if pulses present 1
- Impending respiratory failure: Consider magnesium before intubation as a last-resort therapy 1
Administration Guidelines
Infusion Rate Considerations
- Standard bolus: Infuse over 15-30 minutes for asthma 1
- Rapid infusion (for torsades): Over several minutes when pulseless 1
- Slower infusion: Over 10-20 minutes for torsades with pulses to minimize hypotension 1
Critical caveat: Rapid infusion may cause hypotension and bradycardia 1. The American Heart Association guidelines emphasize monitoring during administration and having calcium chloride available to reverse magnesium toxicity if needed 1.
Continuous Infusion (Alternative Approach)
For refractory severe asthma, continuous infusion at 50 mg/kg/h over 4 hours has been studied and shown to be well-tolerated with improved respiratory status 4. However, this remains less commonly used than bolus dosing and should be reserved for intensive care settings with appropriate monitoring 5.
Clinical Context and Patient Selection
When to Administer
The National Asthma Education and Prevention Program recommends magnesium for 1:
- Life-threatening exacerbations
- Severe exacerbations remaining unresponsive after 1 hour of intensive conventional therapy
- Not indicated for mild-moderate exacerbations 1
Expected Therapeutic Effect
- Target peak plasma concentration: >4 mg/dL correlates with efficacy 6
- Clinical improvement typically seen within 20 minutes of infusion completion 2
- Maximal benefit at 110 minutes post-infusion 2
Safety Monitoring
Common Adverse Effects
- Hypotension (48% incidence, predominantly diastolic): Usually transient, limited to single measurements, rarely requires intervention 5
- Flushing and light-headedness: Minor effects, self-limited 1
- Nausea/emesis: 23% incidence 5
- Transient weakness: 15% incidence 5
Serious Considerations
Supratherapeutic levels (>6 mg/dL) are uncommon (2%) and not consistently associated with adverse events 5. Most patients achieve therapeutic levels by the second magnesium level check 5. Prolonged infusions beyond 24 hours have been shown safe in critically ill children, with median duration of 53 hours well-tolerated 5.
Have calcium chloride immediately available to reverse magnesium toxicity if severe bradycardia or hypotension develops 1.
Age-Specific Notes
This dosing applies to children over 2 years of age 4. For infants and toddlers under 2 years, data are extremely limited, and consultation with pediatric critical care is essential before administration.