The effect of procainamide on plasma cholinesterase activity.

The in vitro effect of procainamide on plasma cholinesterase (PCHE) activity in the plasma of ten normal ASA physical status I patients was studied using a kinetic method. The mean plasma cholinesterase activity without procainamide (control) was 0.90 +/- 0.09 units.ml-1. The dibucaine numbers of all the samples were in the normal range of 78 to 86, indicating normal genotypes. The mean plasma cholinesterase activity, in the presence of procainamide in concentrations of 5.0, 10.0, 20.0 and 40.0 micrograms.ml-1, was reduced to 0.73 +/- 0.04, 0.61 +/- 0.03, 0.45 +/- 0.02, and 0.36 +/- 0.01 units.ml-1, respectively. At therapeutic concentrations of 4 to 12 micrograms.ml-1, procainamide inhibited cholinesterase activity 15 to 30 per cent. The authors also showed that the concentration of procainamide required to inhibit 50 per cent of plasma cholinesterase activity was 20 micrograms.ml-1 (I50). The authors conclude that procainamide when tested in vitro had a statistically significant depressant effect on plasma cholinesterase activity at all the concentrations studied.