Magnesium Sulfate Infusion Rate for Correction
For torsades de pointes or life-threatening ventricular arrhythmias, administer 2 g IV magnesium sulfate over 1-4 minutes as a bolus, followed by continuous infusion of 1-2 g/hour if arrhythmias persist. 1, 2
Emergency/Acute Arrhythmia Management
For torsades de pointes with acquired QT prolongation:
- Initial bolus: 2 g IV over 1-4 minutes (some sources specify "over 30 seconds with extreme caution" for other arrhythmias) 1, 3
- Repeat 2 g boluses may be necessary if episodes persist 2
- The rate should generally not exceed 150 mg/minute (1.5 mL of 10% solution) except in severe eclampsia with seizures 3
For digoxin-induced ventricular arrhythmias:
- Administer magnesium intravenously (specific rate: 10-15 mL of 20% solution over 1 minute, followed by 500 mL of 2% magnesium sulfate in D5W over 4-6 hours) 4
- Recurrence is common and second infusion may be necessary 4
Severe Hypomagnesemia Correction
For severe magnesium deficiency:
- 5 g (approximately 40 mEq) added to 1 liter of fluid, infused over 3 hours 3
- Alternative: 250 mg/kg (0.5 mL of 50% solution) IM over 4 hours if necessary 3
For mild magnesium deficiency:
- 1 g (8.12 mEq) IM every 6 hours for 4 doses 3
Maintenance Therapy
For patients requiring sustained magnesium levels above 2.0 mg/dL (e.g., heart failure with arrhythmia risk):
- 2 g IV doses are needed at least twice daily (every 12 hours) to maintain levels above 2.0 mg/dL 5
- Average total serum magnesium drops below 2.0 mg/dL within 24 hours of a single dose, and below threshold at just 12 hours when adjusted for clinical factors 5
For short bowel syndrome/high-output stomas:
- 4-12 mmol magnesium sulfate added to saline bags for IV or subcutaneous infusion 1
- Subcutaneous administration: intermittent infusions are effective and safe for chronic management 6
Critical Safety Parameters
Maximum dosing limits:
- Do not exceed 150 mg/minute IV infusion rate (except severe eclampsia) 3
- Total daily dose should not exceed 30-40 g in 24 hours 3
- In severe renal insufficiency, maximum is 20 g/48 hours with frequent serum monitoring 3
Monitoring requirements during infusion:
- Check patellar reflexes (lost at 3.5-5 mmol/L) 7
- Monitor respiratory rate (paralysis at 5-6.5 mmol/L) 7
- Cardiac monitoring (conduction altered >7.5 mmol/L, arrest >12.5 mmol/L) 7
- Serum magnesium levels should be kept below 5.5 mEq/L to avoid toxicity 4
Common pitfall: Administering magnesium too rapidly can cause hypotension, respiratory depression, and cardiac conduction abnormalities. Always dilute to 20% concentration or less before IV administration. 3
Pregnancy consideration: Continuous maternal administration beyond 5-7 days can cause fetal abnormalities and neonatal hypotonia increases with higher maternal serum concentrations. 3, 8