Cocaine: pharmacokinetics and biotransformation in man

Pharmacokinetic studies of cocaine have been carried out only in the last decade, although its local anesthetic action and addictive properties have been known for almost 100 years. Elimination half-lives of cocaine in man estimated from serial plasma concentration are relatively short and range from 0.5 to 1.1 h after i.v. and 0.9-1.5 h after administration by the nasal or oral route. The bioavailability after nasal inhalation is about 60%. The bicyclic structure of cocaine is characterized by functional groups including N-methyl, carboxyl methyl ester, and benzoyl ester, which are susceptible to biotransformation. Hydrolysis of the benzoyl group to ecgonine methyl ester is catalyzed by plasma cholinesterase and is thus under monogenic control. The hydrolytic cleavage of the other ester group, methyl ester, to benzoyl ecgonine occurs spontaneously at body temperature. In contrast, N-demethylation of cocaine mediated by microsomal cytochrome P-450 produces norcocaine and this metabolite was shown to be pharmacologically active, the action being similar to cocaine.