What is the dosage of magnesium sulfate (MgSO4) for treating torsades de pointes?

Magnesium Sulfate Dosage for Torsades de Pointes

For torsades de pointes, administer magnesium sulfate 1-2 g IV over 1-2 minutes as initial therapy, even when serum magnesium is normal. 1

Adult Dosing

• For adults with pulseless torsades de pointes, administer 1-2 g IV magnesium sulfate as a bolus 1, 2
• For adults with torsades de pointes with pulses, administer 1-2 g IV magnesium sulfate over 1-2 minutes 1, 2
• If torsades persists after initial bolus, consider a second 1-2 g bolus 5-15 minutes later 2
• Following successful conversion, continue with maintenance infusion of 3-20 mg/min for 7-48 hours until QT interval normalizes (below 0.50 sec) 2

Pediatric Dosing

• For children with torsades de pointes, administer 25-50 mg/kg IV magnesium sulfate (maximum: 2 g) 3
• For pulseless torsades, give as a bolus 3
• For torsades with pulses, administer over 10-20 minutes 3
• Optimal bolus dosage for children is 3-12 mg/kg 4, 5
• For neonates with congenital LQTS and refractory torsades, higher doses up to 30 mg/kg total may be required 4, 5
• Following successful conversion, continue with maintenance infusion at 0.5-1.0 mg/kg/hour 4, 5

Monitoring and Precautions

• Target serum magnesium concentration of 3-5 mg/dL during therapy 4, 5
• Monitor for potential adverse effects including hypotension and bradycardia during rapid infusion 3
• Have calcium chloride available to reverse potential magnesium toxicity if needed 3
• Magnesium typically abolishes torsades without immediate shortening of the QT interval 6, 2, 5

Treatment Algorithm

1. Identify torsades de pointes and assess hemodynamic stability 1
2. Administer magnesium sulfate as first-line therapy (doses as above) 1
3. Simultaneously withdraw any QT-prolonging medications 7, 1
4. Correct electrolyte abnormalities, particularly maintaining serum potassium between 4.5-5 mEq/L 7, 1
5. If torsades persists after magnesium:
   • Consider temporary cardiac pacing 7, 1
   • Or isoproterenol infusion (2-10 mcg/min) if temporary pacing unavailable (contraindicated in congenital LQTS) 7

Clinical Pearls

• Magnesium is effective even when serum magnesium levels are normal 1, 2
• Magnesium can be safely administered even in patients with acute myocardial infarction, angina, or hypertension (conditions where isoproterenol is contraindicated) 6
• Magnesium is specifically effective for torsades de pointes but not for polymorphic ventricular tachycardia with normal QT intervals 2
• For pediatric patients, continuous monitoring of cardiac rhythm and serum magnesium levels is essential during therapy 4, 5