Antibiotics that are known to cause prolongation of the QT interval include which class?

Antibiotics that are known to cause prolongation of the QT interval include which class?

• A. Fluoroquinolones
• B. Tetracyclines
• C. Penicillins
• D. Macrolides

Answer: (D)

Macrolides are known to prolong the QT interval. They can inhibit the cardiac IKr potassium channels, delaying ventricular repolarization and lengthening the QT on the ECG. This increases the risk of torsades de pointes, especially in people with electrolyte disturbances (low potassium or magnesium), bradycardia, congenital long QT, or when used with other QT‑prolonging drugs. While some fluoroquinolones can also affect the QT, the class most consistently linked to this effect in exams and guidelines is macrolides. Tetracyclines and penicillins do not have a meaningful impact on the QT interval. In practice, exercise caution with macrolides in patients with known QT prolongation or those on other QT‑prolonging medications, and correct electrolytes if needed if a macrolide must be used.

Macrolides are known to prolong the QT interval. They can inhibit the cardiac IKr potassium channels, delaying ventricular repolarization and lengthening the QT on the ECG. This increases the risk of torsades de pointes, especially in people with electrolyte disturbances (low potassium or magnesium), bradycardia, congenital long QT, or when used with other QT‑prolonging drugs. While some fluoroquinolones can also affect the QT, the class most consistently linked to this effect in exams and guidelines is macrolides. Tetracyclines and penicillins do not have a meaningful impact on the QT interval. In practice, exercise caution with macrolides in patients with known QT prolongation or those on other QT‑prolonging medications, and correct electrolytes if needed if a macrolide must be used.