What is the dose of magnesium for torsades de pointes (TdP)?

From the Guidelines

For torsades de pointes, the recommended dose of magnesium sulfate is 1 to 2 g IV given as a bolus, as stated in the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1. This dose can be administered over 1-2 minutes, and the initial bolus can be repeated once after 5-15 minutes if torsades persists. The total dose should generally not exceed the recommended amount in the acute setting. Magnesium works by stabilizing the cardiac cell membrane and reducing early afterdepolarizations that trigger torsades. It's effective even in patients with normal magnesium levels. When administering, monitor for hypotension, flushing, and respiratory depression, especially in patients with renal impairment. Calcium gluconate should be available as an antidote for severe magnesium toxicity. Concurrent management should include identifying and correcting underlying causes such as QT-prolonging medications, electrolyte abnormalities (particularly potassium and calcium), and bradycardia, as suggested by the guidelines 1. Some key points to consider when administering magnesium sulfate include:

• Monitoring magnesium levels if frequent or prolonged dosing is required, particularly in patients with impaired renal function 1
• Being aware of the potential side effects of magnesium sulfate, such as hypotension, CNS toxicity, and respiratory depression 1
• Considering the use of other treatments, such as isoproterenol or ventricular pacing, in certain cases of torsades de pointes, such as those associated with bradycardia and drug-induced QT prolongation 1

From the Research

Dose of Magnesium for Torsades

• The optimal bolus dosage of magnesium sulfate for torsades de pointes is between 3 to 12 mg/kg, as determined in studies on children with congenital and acquired long QT syndrome 2, 3.
• In adults, a single bolus of 2 g of magnesium sulfate has been shown to completely abolish torsades de pointes within 1 to 5 minutes 4.
• The dose of magnesium sulfate can also be given as a continuous infusion, with rates ranging from 0.3 to 1.0 mg/kg/hr, to prevent recurrence of torsades de pointes 2, 4, 3.
• The serum magnesium concentration after bolus injection should be between 3 to 5 mg/dL, as observed in studies on children with long QT syndrome 2, 3.

Specific Studies

• A study published in 2004 found that a bolus injection of magnesium sulfate, followed by continuous infusion, effectively treated torsades de pointes in children with long QT syndrome, with an optimal bolus dosage of 3 to 12 mg/kg and infusion rates of 0.5 to 1.0 mg/kg/hr 2.
• Another study published in 1988 found that intravenous injections of magnesium sulfate, with a dose of 2 g, completely abolished torsades de pointes in 9 out of 12 patients, with no significant changes in the QT interval observed after treatment 4.
• A study published in 2006 found that intravenous infusion of magnesium sulfate was effective in treating torsades de pointes in children with long QT syndrome, with an optimal bolus dosage of 3 to 12 mg/kg and infusion rates of 0.5 to 1.0 mg/kg/hr 3.