Which antiarrhythmic drug has a metabolite with the same action?

Which antiarrhythmic drug has a metabolite with the same action?

• A. Quinidine
• B. Digoxin
• C. Procainamide
• D. Nortriptyline

Answer: (C)

Some antiarrhythmics have active metabolites that continue to produce the same type of antiarrhythmic effect as the parent drug. In this case, procainamide is metabolized to N-acetylprocainamide, which preserves antiarrhythmic activity. NAPA mainly behaves as a class III drug, blocking potassium channels and prolonging repolarization, which extends the effective refractory period much like procainamide does. This metabolite thus contributes to the overall rhythm-stabilizing action. The other drugs listed don’t have well-known active metabolites that share their exact antiarrhythmic mechanism to the same extent, so they don’t fit this pattern as clearly.

Some antiarrhythmics have active metabolites that continue to produce the same type of antiarrhythmic effect as the parent drug. In this case, procainamide is metabolized to N-acetylprocainamide, which preserves antiarrhythmic activity. NAPA mainly behaves as a class III drug, blocking potassium channels and prolonging repolarization, which extends the effective refractory period much like procainamide does. This metabolite thus contributes to the overall rhythm-stabilizing action.

The other drugs listed don’t have well-known active metabolites that share their exact antiarrhythmic mechanism to the same extent, so they don’t fit this pattern as clearly.