Hair analysis for drugs of abuse. VII. The incorporation rates of cocaine, benzoylecgonine and ecgonine methyl ester into rat hair and hydrolysis of cocaine in rat hair.

We studied the incorporation rates of cocaine and its major metabolites, benzoylecgonine (BE) and ecgonine methylester (EME), into hair from blood. It was demonstrated in our previous report (Nakahara et al. 1992a) that the incorporation rate of cocaine from blood into hair was much higher than those of BE and EME following administration of cocaine. In this study, the incorporation rates of these drugs into rat hair were investigated following independent administration of BE and EME at 10 mg/kg per day for 5 days, and co-administration of cocaine, BE-d3 and EME-d3 at 3, 0.5 and 0.5 mg/kg per day for 10 days. When BE and EME were administered to rats independently, levels of both these drugs were hardly detectable or quite low in hair, though their AUCs in plasma were very high. On co-administration of cocaine, BE-d3 and EME-d3, the deuterium labeled metabolites in hair were negligibly lower in comparison with the unlabeled ones and in particular the concentration of BE in rat hair was significantly higher than that of BE-d3 although the AUC of BE-d3 was higher than that of BE. It was concluded that the incorporation rates of BE and EME into hair were very low in comparison with that of cocaine and most of the BE detected in hair would be a hydrolytic product derived from cocaine in hair matrix after incorporation.