Quinolones: cardioprotective or cardiotoxic.

Quinolones block the rapid component of the delayed rectifier potassium current (Ik) in a dose dependent manner. This electrophysiological action translates into prolongation of the QT interval and may predispose to development of torsades de pointes. QT prolongation appears to be a class effect but there is a wide range of potency among class members. According to the available evidence, the fluoroquinolones that are currently on the market present a low risk of drug induced torsades de pointes, with a frequency of this adverse event occurring at a rate of approximately 0.2-2.7 per million prescriptions. The safest member of the class appears to be ciprofloxacin. ECG monitoring during initiation of quinolone treatment is indicated only in patients with conditions known to predispose to torsades or to those receiving concomitant medications that prolong the QT interval.