What magnesium sulfate dose is recommended for torsades de pointes?

• A. 2–4 g IV bolus
• B. 0.5 g IV bolus
• C. 10 g IV bolus
• D. 1–2 g IV bolus (often 2 g), may repeat if needed

Answer: (D)

Magnesium sulfate works in torsades de pointes by stabilizing the cardiac membrane and suppressing the early afterdepolarizations that drive this polymorphic VT during QT prolongation. This effect is achieved rapidly with a bolus dose, which is why a fast IV bolus of 1–2 g (often given as 2 g) is recommended to promptly terminate or prevent recurrence. If the arrhythmia persists or recurs, the bolus can be repeated. After the acute event, an infusion may be used to maintain magnesium levels and reduce the chance of recurrence. Doses like 2–4 g or 10 g are too large for the initial bolus and increase toxicity risk, while 0.5 g is generally too small to achieve the needed antiarrhythmic effect quickly. Monitor for toxicity, especially in renal impairment, and adjust as needed.