Of the following statements concerning procainamide, which is TRUE?

• A. The primary toxicity of procainamide is bone marrow suppression.
• B. Procainamide is an antibiotic.
• C. N-Acetylprocainamide is an active product of procainamide metabolism.
• D. All of these are true.

Answer: (C)

Procainamide is a class IA antiarrhythmic that is metabolized in the liver by N-acetylation to N-acetylprocainamide (NAPA), an active metabolite with its own antiarrhythmic activity. This means the metabolite contributes to the overall effect of the drug, and in some patients—especially slow acetylators—NAPA can accumulate and influence both efficacy and toxicity. That makes the statement about N-Acetylprocainamide being an active product true. The other points aren’t correct: procainamide is not an antibiotic, and while bone marrow suppression can occur, it is not regarded as the primary toxicity of the drug (a lupus-like syndrome is a more characteristic adverse effect with long-term use).