Which medication–drug interaction is associated with QT prolongation concerns in heart failure?

• A. Cilostazol
• B. Dextromethorphan-Quinidine
• C. Non-DHP CCBs (Diltiazem and Verapamil)
• D. Dronedarone

Answer: (B)

QT prolongation in heart failure is especially risky when two drugs interact to increase exposure to a QT-prolonging effect, or when a drug that extends repolarization is boosted by another. The dextromethorphan-quinidine combination fits this scenario: quinidine is a strong QT-prolonging agent and also inhibits metabolism (CYP2D6), which markedly raises levels of dextromethorphan. The paired effect significantly increases the risk of QT prolongation and torsades de pointes, making this interaction a key concern in heart failure patients who often have complex medication regimens. By contrast, the other options involve drugs whose QT effects are not primarily driven by a problematic interaction with a partner in this context, or, in the case of dronedarone, the QT risk is due to the drug itself rather than a specific interaction.