Which antiarrhythmic drug has a metabolite with the same pharmacologic action?

Which antiarrhythmic drug has a metabolite with the same pharmacologic action?

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

Answer: (C)

Some antiarrhythmics are converted into active metabolites that continue to exert the same therapeutic effect. Procainamide is metabolized to N-acetylprocainamide (NAPA), an active metabolite that retains antiarrhythmic activity. NAPA contributes to the overall action by prolonging the action potential duration, mainly through potassium-channel effects, which is a shared aspect of suppressing abnormal rhythms. Because this metabolite remains pharmacologically active, it can influence both efficacy and risk (for example, QT prolongation and torsades de pointes), especially in individuals who acetylate slowly. This is why procainamide is the drug whose metabolite has the same antiarrhythmic action as the parent drug.

Some antiarrhythmics are converted into active metabolites that continue to exert the same therapeutic effect. Procainamide is metabolized to N-acetylprocainamide (NAPA), an active metabolite that retains antiarrhythmic activity. NAPA contributes to the overall action by prolonging the action potential duration, mainly through potassium-channel effects, which is a shared aspect of suppressing abnormal rhythms. Because this metabolite remains pharmacologically active, it can influence both efficacy and risk (for example, QT prolongation and torsades de pointes), especially in individuals who acetylate slowly. This is why procainamide is the drug whose metabolite has the same antiarrhythmic action as the parent drug.