DÄ internationalArchive16/2012Risk Factors Need to Be Considered
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No information is provided by merely listing the occurrence of QT prolongation for different drugs without considering known risk factors, because in this way it is not possible to distinguish between the effects of either. The authors correctly state that QT prolongation is almost always affected by risk factors such as hypokalemia (30%) or hypomagnesemia. But these electrolyte imbalances still do not receive anywhere near enough attention. Magnesium, the second most common intracellular cation after potassium, is not usually included in the electrolyte status. Potassium deficiency, however, almost always goes hand in hand with magnesium deficiency and can be balanced only by administering magnesium simultaneously.

In conclusion: if the intention is to administer drugs with repolarizing or depolarizing effects, for example in potential QT prolongation, any existing hypokalemia and hypomagnesemia needs to be treated first. In acute cases, magnesium sulfate should be administered intravenously, in all other cases, oral administration of magnesium aspartate will suffice. What remains of interest subsequently is only the occurrence of Torsade de pointes in patients with balanced electrolytes, but this has to be investigated when testing a drug.

DOI: 10.3238/arztebl.2012.0300a

Dr. rer. nat. Dr. med. Armin Schroll

München

Conflict of interest statement
The author declares that no conflict of interest exists.

1.
Schroll A: Importance of magnesium for the electrolyte homeostasis—an overview. In Smetana R (ed.): Advances in magnesium research: magnesium in cardiology: Proceedings of the 5th European congress on magnesium. London: John Libbey & Company 1997: 463–72.
2.
Wenzel-Seifert K, Wittmann M, Haen E: QTc prolongation by psychotropic drugs and the risk of torsade de pointes. Dtsch Arztebl 2011; 108(41): 687–93. VOLLTEXT
1.Schroll A: Importance of magnesium for the electrolyte homeostasis—an overview. In Smetana R (ed.): Advances in magnesium research: magnesium in cardiology: Proceedings of the 5th European congress on magnesium. London: John Libbey & Company 1997: 463–72.
2.Wenzel-Seifert K, Wittmann M, Haen E: QTc prolongation by psychotropic drugs and the risk of torsade de pointes. Dtsch Arztebl 2011; 108(41): 687–93. VOLLTEXT