Antiarrhythmic potency of N-acetylprocainamide.

Area of Science:

• Pharmacology
• Cardiology
• Clinical Therapeutics

Background:

• Procainamide is a widely used antiarrhythmic drug.
• Its N-acetylated metabolite, NAPA, is known to possess antiarrhythmic properties.
• The relative contribution of NAPA to the overall antiarrhythmic effect of procainamide therapy is not fully elucidated.

Purpose of the Study:

• To compare the antiarrhythmic potency of NAPA to procainamide in an animal model.
• To assess the antiarrhythmic effects of combined procainamide and NAPA administration.
• To evaluate the equipotency of procainamide and NAPA in patients and its implications for therapeutic drug monitoring.

Main Methods:

• An animal model of cardiac arrhythmia was utilized to compare drug potencies.
• Dose-response and plasma level-response relationships were established for procainamide and NAPA.
• Clinical measurements of procainamide and NAPA plasma levels were correlated with the suppression of ventricular extrasystoles.

Main Results:

• In an animal model, NAPA demonstrated 92% of procainamide's potency by dose and 70% by plasma level.
• The antiarrhythmic effects of procainamide and NAPA were found to be additive.
• In patients, procainamide and NAPA were nearly equipotent, with an average plasma level of 5.1 mcg/ml procainamide equivalent required for arrhythmia control.

Conclusions:

• NAPA is a potent antiarrhythmic agent, contributing significantly to the therapeutic effect of procainamide.
• Patients on long-term procainamide therapy often have substantial NAPA plasma concentrations.
• Therapeutic drug monitoring and dosing regimens for procainamide should incorporate NAPA plasma levels for optimal patient management.