Urinary excretion of ecgonine methyl ester, a major metabolite of cocaine in humans.

In this study, cocaine, benzoylecgonine, and ecgonine methyl ester excretion in urine was measured after intravenous and intranasal administration of cocaine at 16, 32, 48, and 96 mg doses to healthy cocaine users. Ecgonine methyl ester and cocaine were analyzed by gas chromatography/mass spectrometry. Benzoylecgonine was measured by immunoassay (EMIT) and liquid chromatography. Urinary ecgonine methyl ester accounted for 26 to 60% of the cocaine dose. Ecgonine methyl ester had an elimination halflife of 4.2 hr, compared with 5.1 hr for benzoylecgonine. These results indicate that ecgonine methyl ester accounts for most of the previously unidentified urinary metabolic products of cocaine. The time course of ecgonine methyl ester excretion is such that its detection can substitute for benzoylecgonine detection as a marker of cocaine use.