In vivo pharmacokinetics and in vitro production of cocaethylene in pregnant guinea pigs

Simultaneous exposure to cocaine and ethanol results in the formation of cocaethylene, an active metabolite of cocaine. The concurrent abuse of both cocaine and ethanol is common during human pregnancy, but the kinetics of elimination and formation of this ethyl ester of cocaine have not been studied during pregnancy in any species. In the late gestation guinea pig (61 to 63 days), cocaethylene, at doses of 2 to 4 mg · kg^?1, is rapidly eliminated with a half-life of 29 min and a total body clearance of 77 ml · min^?1 · kg^?1. It is formed enzymatically by hepatic microsomal preparations from fetal, neonatal and maternal guinea pigs. The maximum rate of cocaethylene production (apparent V_max) when either ethanol or cocaine are varied while the other substrate is held constant, increases with age, from the late fetal period (65 days gestation, term 70 days) to adulthood. However, the Michaelis-Menten constant (apparent K_M) does not change with age. The rapid elimination of cocaethylene, coupled with the slow rate of formation (apparent V_max of 140 pmol · min^?1 · mg microsomal protein^?1) and the small amount of plasma analyzed most likely explains the inability to detect cocaethylene in vivo after concomitant cocaine and ethanol administration.