What are the emergency indications, dosing protocols, and crash‑cart stocking recommendations for magnesium sulfate (including dosage for torsades de pointes, severe refractory asthma, eclampsia, and acute symptomatic hypomagnesemia)?

Magnesium Sulfate Crash Cart Use: Emergency Indications and Dosing Protocols

Torsades de Pointes

For torsades de pointes associated with acquired QT prolongation, administer IV magnesium sulfate 1-2 g as a bolus over 5 minutes, even if serum magnesium is normal. 1

• This is a Class I recommendation for cardiotoxicity and cardiac arrest from severe hypomagnesemia or drug-induced torsades 2, 1
• Magnesium suppresses episodes of torsades without necessarily shortening the QT interval 3
• For recurrent torsades that cannot be suppressed with IV magnesium, increase heart rate with atrial/ventricular pacing or isoproterenol 4
• Maintain potassium ≥4.0-4.5 mmol/L and magnesium ≥2.0 mmol/L 4, 3
• Critical caveat: Magnesium has NOT been shown effective for polymorphic VT with normal QT interval 5
• The 2025 AHA guidelines confirm magnesium remains indicated only for torsades with long QT, not for routine ventricular arrhythmias 5

Severe Pre-eclampsia/Eclampsia

For severe pre-eclampsia with clinical signs of severity, administer a loading dose of 4-5 g IV over 3-4 minutes (or infused in 250 mL over 15-20 minutes), followed by maintenance of 1-2 g/hour by continuous infusion. 6

• Alternative loading: 4 g IV plus 10 g IM (5 g in each buttock), then 5 g IM every 4 hours 6
• Target serum magnesium level: 4.8-6 mg/dL (optimal for seizure control) 1, 6
• For obese women (BMI ≥35): Consider higher dosing—6 g IV loading dose followed by 2 g/hour maintenance, as standard Zuspan dosing achieves subtherapeutic levels in 100% of obese patients 7
• Monitor patellar reflexes and respiratory function before each dose 6
• Maximum dose: 30-40 g per 24 hours; in severe renal insufficiency, maximum 20 g per 48 hours 6
• Critical warning: Continuous use beyond 5-7 days in pregnancy can cause fetal abnormalities 6

Severe Refractory Asthma

For life-threatening asthma exacerbations that remain severe after 1 hour of intensive conventional treatment, consider IV magnesium sulfate 2 g (approximately 40 mEq) infused over 20 minutes. 8

• This is a conditional recommendation for patients failing standard therapy 8
• The National Asthma Education and Prevention Program states magnesium has "no apparent value" in lower severity exacerbations 8
• Pediatric dosing: 50 mg/kg over 1 hour (maximum 2 g) 9
• High-dose prolonged infusion (50 mg/kg/hour for 4 hours, max 8 g) shows superior efficacy in pediatric severe asthma, with 47% discharge rate at 24 hours versus 10% with bolus dosing 9
• Nebulized magnesium (isotonic solution) may provide additional benefit when combined with beta-agonists 10

Acute Symptomatic Hypomagnesemia

For severe hypomagnesemia with tetany or cardiac manifestations, administer 1-2 g (8-16 mEq) magnesium sulfate IV push over 5-15 minutes, followed by continuous infusion. 1, 6

• For mild deficiency: 1 g (8.12 mEq) IM every 6 hours for 4 doses 6
• For severe deficiency: Up to 250 mg/kg (approximately 2 mEq/kg) IM over 4 hours if necessary 6
• Alternative for severe cases: 5 g (40 mEq) in 1 L D5W or NS infused over 3 hours 6
• Caution: Do not exceed renal excretory capacity; monitor serum levels 6

Crash Cart Stocking Recommendations

Stock multiple 2 mL vials of 50% magnesium sulfate (1 g per 2 mL = 500 mg/mL) for immediate bolus administration. 6

• Pre-diluted solutions (10-20% concentration) should be available for slower infusions 6
• Maximum IV injection rate: 150 mg/minute (1.5 mL of 10% solution), except in severe eclampsia with seizures 6
• Solutions for IV infusion must be diluted to ≤20% concentration 6
• Store at room temperature (20-25°C); contains no preservative, discard unused portions 6

Critical Safety Monitoring

• Monitor for magnesium toxicity: Loss of patellar reflexes (8-12 mg/dL), respiratory depression (12-15 mg/dL), cardiac arrest (>15 mg/dL) 1
• Have calcium gluconate 10% (15-30 mL IV) or calcium chloride 10% (5-10 mL IV) immediately available as antidote for hypermagnesemia 1
• In cardiac arrest from suspected hypermagnesemia, empirical IV calcium may be reasonable 2

Common Pitfalls to Avoid

• Do NOT use magnesium for routine cardiac arrest—multiple RCTs show no benefit for undifferentiated arrest or VF/VT without long QT 11
• Do NOT use magnesium for polymorphic VT with normal QT—this is typically ischemia-driven and requires different management 5
• Do NOT give bolus potassium for cardiac arrest in suspected hypokalemia—this is potentially harmful (Class III: Harm) 2, 1
• Do NOT continue magnesium in pregnancy beyond 5-7 days—risk of fetal skeletal abnormalities 6