Magnesium is considered a mainstay of treatment of prolonged QT syndrome leading to torsade de pointe, including those cases caused by drugs. The exact mechanism of action is unknown, though it is thought to stabilize the myocardium. Interestingly, magnesium infusions will not necessarily change the heart rate or QT interval on ECG.
The dose is 2 g IV followed by an infusion (similar to treatment of eclampsia/preeclampsia). The bolus should be given slowly if the patient is relatively stable, but can be pushed over 1 minute in a patient with ongoing torsade that is not responding to electricity.
References
Charlton NP, Lawrence DT, Brady WJ, et al. Termination of drug-induced torsades de pointes with overdrive pacing. Am J Emerg Med 2010;28:95-102.
