The Effects of Intravenous Levofloxacin on the QT Interval and QT Dispersion

The QT dispersion (QT(d)) is a non-invasive means of identifying those patients at an increased risk of developing sudden cardiac death (SCD). Although levofloxacin has a minimal effect on the QT(c) interval, isolated reports of QT prolongation, polymorphic ventricular tachycardia with a normalQTinterval and TdP have been reported. The purpose of this study was to examine the effect of intravenous levofloxacin on the QT interval and QTd. Of the 50 patients who were deemed candidates to receive intravenous levofloxacin, 29 met the eligibility criteria and were enrolled in this study. A 12-lead ECG was performed before the initiation of levofloxacin (baseline), and on days 3 and 5. The QT(c) min, QT(c) max and the QT(d) were calculated. Measurements where made by two independent observers blinded to the patients' clinical status. The QT(d) increased significantly on days 3 and 5 following the initiation of therapy [QT(d) (baseline) 33.3 +/- 20 ms, QT(d) (day 3) 64.4 +/- 31.3 ms (p = 0.023), QTd (day 5) 66.8 +/- 20.3 ms, (p = 0.008)]. The increase in the QT(d) was significantly longer in men than women. Although women had a shorter baseline QT(d) compared to men, this did not achieve statistical significance. Intravenous levofloxacin was found to significantly increase the QTd, which was more pronounced in men compared to women. Its effect on the QTd may increase the risk of developing a potentially fatal ventricular arrhythmia. Therefore, care must be taken when prescribing this medication to patients with a pre-existing risk of developing SCD.