Macrolide antibiotics can cause which serious cardiac adverse effect?

• A. Prolonged QT interval leading to torsades de pointes
• B. Hypotension
• C. Renal toxicity
• D. Hyperkalemia

Answer: (A)

Macrolide antibiotics have the potential to prolong the heart’s repolarization, shown as a longer QT interval on the ECG. This occurs because these drugs can block the cardiac IKr potassium channel, which delays ventricular repolarization. When the QT interval is extended, it creates a substrate for a dangerous rhythm called torsades de pointes, a form of polymorphic ventricular tachycardia that can degenerate into sudden cardiac arrest if not addressed.

The risk is higher in people with low potassium or magnesium, those with congenital long QT syndrome, the elderly, and when a macrolide is taken with other drugs that prolong the QT interval or raise macrolide levels (for example via CYP3A4 inhibition). While macrolides can cause other adverse effects, the most serious cardiac concern is QT prolongation leading to torsades de pointes, not hypotension, renal toxicity, or hyperkalemia. In practice, monitor at-risk patients, correct electrolytes, and avoid combining with other QT-prolonging medications.