Cocaine and metabolite concentrations in plasma during repeated oral administration: Development of a human laboratory model of chronic cocaine use

Long-term use of cocaine may produce neurophysiological and metabolic alterations that differ from acute drug use. A laboratory model that was capable of evaluating the effects of chronic cocaine administration in human subjects was needed. Chronic oral administration of cocaine was considered a feasible route because of the ease of administration, control of dosing patterns, and possible reduction in medical risks compared with the intravenous and smoked routes. This clinical study was conducted to evaluate chronically administered oral cocaine as a means of studying cocaine addiction and withdrawal in humans. Cocaine-abusing volunteers were given multiple doses of oral cocaine each day in up to 16 daily sessions (including three placebo sessions). In each daily session, volunteers received five equal doses separated by hourly intervals. Across sessions, the dose was increased from an initial dose of 100 mg (500 mg/day) to 400 mg (2000 mg/day) in the last session. The dose for each consecutive cocaine session was increased by 25 mg/dose/session (125-mg total increase per session). Twelve subjects were enrolled in the study; however, three subjects dropped out prior to completion of at least three sessions. Two subjects completed all 13 cocaine sessions. The remaining seven subjects completed from 3 to 11 sessions; their participation was terminated early for safety and behavioral reasons. Plasma was collected during all sessions and analyzed for cocaine and metabolites by solid-phase extraction followed by gas chromatography- mass spectrometry. Oral cocaine administration resulted in peak plasma concentrations of cocaine approximately 1 h after administration. Accumulation of cocaine was evident between hourly doses and there was evidence of dose-proportional increases in area under the curve (AUC) measures across sessions. A variety of cocaine metabolites was measured in plasma including benzoylecgonine, ecgonine methyl ester, norcocaine, benzoylnorecgonine, and p- and m-hydroxy metabolites of cocaine and benzoylecgonine. During chronic oral dosing, there appeared to be a trend for AUC ratios (AUC(metabolite)/AUC(cocaine)) of benzoylecgonine and ecgonine methyl ester to decrease and norcocaine to increase, indicating the possibility of dose-, time-, or route-dependent changes in the absorption and/or metabolism of cocaine. Overall, this study demonstrated that chronic oral dosing of cocaine produced dose-related increases in plasma cocaine concentration, and this model could be useful for studying the effects of chronic cocaine use in human subjects.