A 74-year-old man with heart failure taking sotalol is prescribed moxifloxacin for acute exacerbation of COPD. His cardiologist objects to this prescription. The specific concern is:
- A Moxifloxacin prolongs the QT interval, adding to sotalol's QT effect and risking torsades de pointes ✓
- B Moxifloxacin accelerates sotalol clearance, causing loss of antiarrhythmic control
- C Moxifloxacin increases digoxin levels through P-glycoprotein inhibition
- D Moxifloxacin causes hyperkalemia that potentiates sotalol toxicity
Correct answer: A. Moxifloxacin prolongs the QT interval, adding to sotalol's QT effect and risking torsades de pointes
Explanation
Moxifloxacin prolongs cardiac repolarization by blocking delayed rectifier potassium channels, and it carries one of the largest QT-prolonging effects among fluoroquinolones. Sotalol is a class III antiarrhythmic that also markedly prolongs QT. Combining them stacks two QT-prolonging drugs and substantially raises the risk of torsades de pointes, which is why moxifloxacin is avoided in patients on other QT-prolonging agents. Fluoroquinolone-related tendinopathy and aortic events are separate concerns unrelated to this combination.
Reference: Katzung Basic and Clinical Pharmacology, 16th ed.
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Written and medically reviewed by the StethoPrep medical team.