Does Ciprofloxacin Really Prolong QT Intervals?

Because it can inhibit cardiac potassium channels, ciprofloxacin has the potential to prolong the QT interval and subsequently raise the risk for torsades de pointes, a life-threatening cardiac arrhythmia (Figure 1). However, these effects have only been seen at serum drug concentrations that far exceed those achieved with typical therapeutic doses.

To evaluate whether QT prolongation occurs with oral ciprofloxacin therapy, researchers retrospectively compared electrocardiograms (ECGs) obtained from 88 patients immediately before they initiated ciprofloxacin and at least 2 days after. The median daily dose of ciprofloxacin was 1000 mg; about 40% of patients were also taking other drugs known to prolong the QT interval.