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 normal QT interval and TdP have been reported. The purpose of this study was to examine the effect of intravenous levofloxacin on the QT interval and QT d . 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), QT d (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 QT d , which was more pronounced in men compared to women. Its effect on the QT d 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. List of Abbreviations QT c max : Maximum corrected QT interval on the 12-lead electrocardiogram QT c min : Minimum corrected QT interval on the 12-lead electrocardiogram QT d : Difference between the maximum and minimum QT interval SCD: Sudden cardiac death VT: Ventricular tachycardia TdP: Torsade de Pointes