WHAT IS PROCAINAMIDE TEST?
Procainamide is an antidysrhythmic used in the treatment of atrial and ventricular dysrhythmias. It is most commonly administered as an oral or intravenous drug and metabolized by the liver. 25% of procainamide is metabolized to N–acetylprocainamide (NAPA) by the liver; 60% of the dose is excreted via the kidneys, with a half-life of 3-4 hours. Procainamide’s primary metabolite is NAPA, which has similar antidysrhythmic properties and a half-life of approximately 6 hours but is not metabolized by the liver. The differences in the half-lives result in slightly high NAPA levels until both reach stabilization approximately 18 hours after initiation of therapy. At this time, a 1 : 1 ratio exists between procainamide and NAPA. An increase or decrease in this ratio can alter the therapeutic effectiveness or result in toxicity. Therefore, when procainamide is assayed, NAPA levels should be monitored simultaneously. Steady-state levels of procainamide are reached after 11-20 hours. Steady-state levels of NAPA are reached after 22-40 hours.