Procainamide, Serum or Plasma

The cardiac actions of this drug are similar to those of quinidine. It is used in a variety of arrhythmias. Procainamide usually is rapidly absorbed from the gastrointestinal tract. Peak blood levels are reached within one hour. Optimal plasma sampling time after oral dosage is one to two hours. Optimal sampling time after I.V. administration of dose is 30 minutes. The drug is converted by the liver to its active metabolite, N-acetyl procainamide (NAPA). The half-life of procainamide is two to six hours and for NAPA is eight hours. Rate of metabolism is genetically determined (slow and fast acetylator types) contributing to significant interindividual variability. Impairment of renal function has pronounced effect on drug disposition, especially for NAPA. Patients with severe renal dysfunction generally have prolonged and highly variable half-life characteristics. Elimination half-life may be prolonged in geriatric subjects.¹