What medication is known to cause a prolonged QT interval when given simultaneously with ciprofloxacin?

The medication that is known to cause a prolonged QT interval when given simultaneously with ciprofloxacin is amiodarone. This is significant because both ciprofloxacin and amiodarone can affect the heart's electrical system, leading to an increased risk of arrhythmias. Amiodarone is a well-known antiarrhythmic medication that already has the potential to prolong the QT interval on its own. When it is administered with ciprofloxacin, which is in the fluoroquinolone class and also carries a risk for QT prolongation, the combined effect could further increase the risk of serious cardiac events.

The other medications listed, while they may have interactions with ciprofloxacin, do not share the same propensity for enhancing QT interval prolongation as amiodarone does. Phenytoin is an antiepileptic that does not typically have a significant impact on the QT interval. Levofloxacin and moxifloxacin, which are both fluoroquinolones, do carry some risk for inducing QT prolongation but do not interact in the same way with ciprofloxacin to exacerbate this effect. Therefore, amiodarone is the most relevant choice when considering the specific interaction that leads to a prolonged QT interval