Dosage of 50% Magnesium Sulfate IV in ml/kg
For 50% magnesium sulfate IV administration, the dose is 0.1-0.2 ml/kg (maximum 2-2.5 g) when used for severe conditions such as torsades de pointes. 1, 2
Calculation Explanation
The dosing calculation is based on the following:
- 50% magnesium sulfate solution contains 500 mg/ml
- The recommended dose range is 25-75 mg/kg (maximum 2-2.5 g) 3
- Therefore, 25-75 mg/kg ÷ 500 mg/ml = 0.05-0.15 ml/kg
Clinical Applications
Torsades de Pointes
- When VF/pulseless VT cardiac arrest is associated with torsades de pointes, administer 1-2 g IV/IO bolus of magnesium sulfate (equivalent to 2-4 ml of 50% solution) 1
- For an adult, this typically translates to 0.1-0.2 ml/kg of 50% solution
Severe Asthma
- For severe asthma exacerbations, 2 g IV (4 ml of 50% solution) is recommended 3, 4
- This should be diluted in 10 ml D5W or more and administered over 15-30 minutes
Pre-eclampsia or Eclampsia
- Initial dose of 4-5 g IV (8-10 ml of 50% solution) 2
- The 50% solution must be diluted to 20% or less prior to administration
Important Administration Considerations
Dilution Requirements
- Solutions for IV infusion must be diluted to a concentration of 20% or less prior to administration 2
- Common diluents include 5% Dextrose Injection and 0.9% Sodium Chloride Injection
Rate of Administration
- IV injection rate should generally not exceed 150 mg/minute (0.3 ml/minute of 50% solution) 2
- For severe conditions like eclampsia with seizures, faster rates may be used
Monitoring
- Continuous clinical assessment is essential during administration 3
- Monitor for signs of magnesium toxicity, which can occur at serum levels of 6-10 mmol/L 3
- Monitor vital signs, especially blood pressure and respiratory rate
Cautions and Contraindications
- Use with caution in patients with renal disease due to renal excretion of magnesium 3
- Maximum dosage in severe renal insufficiency is 20 g/48 hours with frequent serum magnesium monitoring 2
- Continuous use in pregnancy beyond 5-7 days can cause fetal abnormalities 2
Common Side Effects
- Flushing, fatigue, nausea, headache, and hypotension are commonly reported adverse events 5
- Most side effects are mild and do not necessitate discontinuing treatment 6
Remember that 50% magnesium sulfate is a highly concentrated solution (500 mg/ml), and proper dilution before administration is critical to prevent adverse effects related to rapid infusion.