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.
Serum or plasma
Red-top tube or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.
Transfer separated serum or plasma to a plastic transport tube. Oral treatment: peak: 75 minutes after dose; trough: immediately before next dose. I.V. treatment: immediately after loading dose; 2, 6, 12, and 24 hours after starting I.V. maintenance.
Gel-barrier tube; severe hemolysis; lipemia; icteric specimen.