Q:  Fluoroquinolones are of considerable clinical importance because of their ability to cause prolongation of the QT interval and consequently causing Torsades de pointes (TdP). Which Fluoroquinolone is known to be the least and which Fluoroquinolone is known to be the worst offender?

Answer: Ciprofloxacin appears to be associated with the lowest risk for QT prolongation and the lowest TdP  occurrence. And, moxifloxacin carries the greatest risk of QT prolongation. Fluoroquinolones prolong the QT interval by blocking voltage-gated potassium channels.

Reference:

Briasoulis A1, Agarwal V, Pierce WJ.- QT prolongation and torsade de pointes induced by fluoroquinolones: infrequent side effects from commonly used medications - Cardiology. 2011;120(2):103-10