Although very useful agents, fluoroquinolones are associated with a number of adverse events, some with considerable clinical significance. Prolongation of the QT interval, for example, is an adverse effect associated with the use of fluoroquinolones. Fluoroquinolones prolong the QT interval by blocking voltage-gated potassium channels, especially the rapid component of the delayed rectifier potassium current IKr, expressed by HERG (the human ether-a-go-go-related gene). According to the available case reports and clinical studies, moxifloxacin carries the greatest risk of QT prolongation from all available quinolones in clinical practice and it should be used with caution in patients with predisposing factors for Torsades de pointes (TdP). Although gemifloxacin, levofloxacin, and ofloxacin are associated with a lower risk of QT prolongation compared with moxifloxacin, they should also be used with caution in patients at risk for QT prolongation. Ciprofloxacin appears to be associated with the lowest risk for QT prolongation and the lowest TdP rate. The overall risk of TdP is small with the use of fluoroquinolones. Clinicians can minimize that risk by avoiding prescriptions of multiple medications associated with QT-interval prolongation, especially in high-risk patients.

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