Editor—Yap and Camm emphasise the risk of torsades de pointes associated with non-cardiac drugs that prolong the QT interval.1 They comment on the fluoroquinolone antimicrobial agents grepafloxacin and sparfloxacin causing QT prolongation but also the apparent lack of this effect with levofloxacin. We recently cared for a patient who developed torsades de pointes while taking levofloxacin, which prompted us to examine retrospectively paired electrocardiograms in other patients to compare QTc intervals before and after they started treatment with this drug.
Twenty three patients who received a standard dose of 500 mg levofloxacin daily had cardiograms that could be compared for QTc prolongation. Prolongation of >30 ms was found in four patients and of >60 ms in two patients. Absolute QT interval prolongation of >500 ms was present in four, one of whom developed torsades de pointes. This patient was also receiving amiodarone, which is known to prolong the QTc interval but not commonly associated with pro-arrhythmia when used alone.
The United States Food and Drug Administration's spontaneous reporting system documents 11 other cases of torsades de pointes in patients receiving levofloxacin, and Samaha reported on an additional patient who also was receiving amiodarone.2 Studies in rabbit Purkinje fibres have shown a concentration-dependent prolongation of the maximal rate of depolarisation at concentrations of ofloxacin up to 100 μmol/l, but the trend did not achieve significance.3 Serum concentrations of 8 μmol/l are achieved by levofloxacin, but the affinity for cardiac tissues is unknown. The Food and Drug Administration has recently requested studies of levofloxacin on cardiac electrophysiology.
Our data indicate that prolongation of the QT interval is probably a class effect of the fluoroquinolones including levofloxacin. Care should be taken when this agent is used with type IA and type III antiarrhythmic agents and in situations such as hypokalaemia and hypomagnesaemia that increase the risk of pro-arrhythmic events.
Footnotes
Competing interests: PBI is a consultant for Bristol-Myers Squibb, Aventis, SmithKline Beecham, Bayer, Roche, Glaxo, TAP, and Abbott pharmaceutical companies. None declared for SD, EB, IC, and HK.
References
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