Major
amiodarone × ciprofloxacin
Class III antiarrhythmics (Vaughan Williams)×Fluoroquinolone antibacterials
Mechanism
Additive QT prolongation: amiodarone strongly blocks IKr potassium channels and ciprofloxacin does the same more mildly. Risk of torsades de pointes. FDA black-box warning for all fluoroquinolones regarding QT prolongation (2016 update).
Management
Avoid the combination where possible. If ciprofloxacin is essential, obtain an ECG at baseline and on day 2–3 and keep potassium above 4.0 mmol/L and magnesium in the upper-normal range. Alternatives are non-fluoroquinolone antibiotics where susceptibility allows.
Sources
- FDA: FDA Drug Safety Communication: FDA updates warnings for oral and injectable fluoroquinolone antibiotics due to disabling side effects (2016)— FDA Drug Safety Communication, July 26, 2016
- Lexicomp: Lexicomp Drug Interactions (2024)— Wolters Kluwer Clinical Drug Information, Inc. Lexi-Interact Online, 2024
- Pharmaceutical Press: Stockley's Drug Interactions, 12th edition (2024)— Preston CL (ed.). Stockley's Drug Interactions. 12th ed. London: Pharmaceutical Press; 2024