amiodarone and ciprofloxacin

MajorAvoid this combination where possible.

Mechanism

Additive QT interval prolongation. Both amiodarone and ciprofloxacin can prolong the QT interval by blocking cardiac repolarisation. Ciprofloxacin inhibits the rapid delayed rectifier potassium current (Ikr), while amiodarone blocks multiple ion channels including the potassium channel. Co-administration produces a greater effect on ventricular repolarisation.

What it means clinically

Increased risk of life-threatening ventricular arrhythmias, including torsades de pointes. The risk is higher in patients with existing risk factors such as bradycardia, hypokalaemia, hypomagnesaemia, or other QT-prolonging drugs. Symptoms may include palpitations, syncope, and sudden cardiac death in severe cases.

What to do

Consider alternative antibiotics with less QT prolonging activity, such as doxycycline, if clinically appropriate.

Evidence

Well-established in the literature and reflected in manufacturer prescribing information and major cardiology guidelines. Multiple case reports and observational studies have documented QT prolongation and associated arrhythmias with this combination.

The two drugs

amiodaroneClass III antiarrhythmicRead the monograph ciprofloxacinfluoroquinolone antibioticRead the monograph

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Other interactions involving amiodarone or ciprofloxacin

Educational reference for students and clinicians in training. It does not replace professional judgement, local protocols or current prescribing information.