Procainamide

Specimen:

5 mL blood in plain tube, collected as a trough level immediately prior to next dose.

Method:

Chromatography or immunoassay.

Therapeutic Interval:

Procainamide: 17-42 mmol/L (4-10 mg/L)

N-acetylprocainamide: 36-87 mmol/L (10-24 mg/L).

Application:

Therapeutic drug monitoring.

Interpretation:

Both procainamide and its major metabolite N-acetyl procainamide are active pharmacologically and should be measured as the relative levels differ in slow or fast acetylators.

Procainamide half-life is about 3 h, whereas N-acetylprocainamide has a half-life of about 6-9 h.

Reference:

Karlsson E. Clin Pharmcokinet 1978; 3: 97-107.