Quinidine inhibition of cocaethylene degradation in human serum in vitro: a preliminary study

Quinidine (QUINID) substantially inhibited the serum degradation of cocaethylene (CE), an important cocaine analog, when incubated for two hours at 37 degrees C with pooled human serum containing 1.58 micromol/L of CE. In the absence of QUINID, the CE concentration was only 49.4% of its original value after incubation. However, QUINID at subtherapeutic (3.08 micromol/L) and therapeutic (15.4 micromol/L) concentrations preserved 55.1% and 75.9% of the original CE concentration, respectively. At a QUINID concentration of 308 micromol/L, 89.2% of the CE concentration was preserved. There was a marked decrease in the serum cholinesterase (CHE) activity as QUINID concentrations were increased to 154 micromol/L (19.8% decrease in CHE) and to 308 micromol/L (36.8% decrease in CHE). These data suggest that QUINID inhibits the hydrolysis of CE in human serum by suppressing CHE activity. These findings are significant because QUINID may be used in patients who have abused cocaine with ethanol. They also have important implications for individuals receiving QUINID together with other drugs whose hydrolysis may be catalyzed by CHE.