Which statement about macrolides is true?

• A. They can prolong QT interval and increase torsades de pointes risk
• B. They always shorten QT interval
• C. They have no effect on heart rhythm
• D. They only affect QT when combined with NSAIDs

Answer: (A)

Macrolides can affect cardiac repolarization by blocking the delayed rectifier potassium current (the hERG channel), which lengthens the QT interval on the ECG. This extended repolarization can predispose to torsades de pointes, a dangerous form of ventricular tachycardia, especially in people with low potassium or magnesium, slow heart rate, congenital long QT, or those taking other drugs that prolong the QT interval. While not every patient will experience it, the potential risk is real with macrolide therapy.

The other statements don’t fit because macrolides do not shorten the QT interval, they can influence heart rhythm even without NSAIDs, and the effect is not limited to combinations with NSAIDs—QT prolongation can occur with macrolides alone or with other risk factors.