Which fluoroquinolone is most commonly associated with QT prolongation and torsades de pointes?

Explanation

## QT Prolongation and Fluoroquinolones **Key Point:** Moxifloxacin carries the highest risk of QT prolongation among fluoroquinolones due to its potent inhibition of cardiac potassium channels (particularly hERG channels). ### Cardiac Safety Profile of Fluoroquinolones | Fluoroquinolone | QT Risk | Mechanism | Clinical Significance | |---|---|---|---| | **Moxifloxacin** | **Highest** | Strong hERG channel blockade | Avoid in QT prolongation, hypokalemia, bradycardia | | Levofloxacin | Moderate | Mild hERG channel blockade | Use with caution in cardiac risk patients | | Ciprofloxacin | Low | Minimal cardiac effects | Relatively safer option | | Norfloxacin | Low | Minimal cardiac effects | Relatively safer option | ### Why Moxifloxacin is High-Risk 1. **Potent potassium channel inhibition** → prolonged action potential duration 2. **Delayed repolarization** → QT interval prolongation 3. **Risk of torsades de pointes** in susceptible patients ### Risk Factors for QT Prolongation with Moxifloxacin - Pre-existing QT prolongation - Electrolyte abnormalities (hypokalemia, hypomagnesemia) - Bradycardia - Female gender - Concurrent use of other QT-prolonging drugs - Hepatic impairment **High-Yield:** Moxifloxacin is contraindicated in patients with known QT prolongation or significant cardiac risk factors. Always check baseline ECG in high-risk patients before prescribing. **Clinical Pearl:** Among fluoroquinolones, ciprofloxacin and norfloxacin have the best cardiac safety profiles and are preferred in patients with cardiac risk factors. [cite:KD Tripathi 8e Ch 48]