Urinary Excretion Half-life of Δ1-Tetrahydrocannabinol-7-oic Acid in Heavy Marijuana Users after Smoking

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Abstract
The urinary excretion of the total amount of Δ1-tetrahydrocannabinol (Δ1-THC) metabolites, with special emphasis on Δ1-tetrahydrocannabinol-7-oic acid (Δ1-THC-7-oic acid), was studied in thirteen heavy Cannabis users after smoking administration of Δ1-THC, followed by a four week discontinuation period. The total amount of Δ1-THC metabolites and the levels of Δ1-THC-7-oic acid could be followed up to 25 days after abstinence using EMIT d.a.u. cannabinoid assay and high-performance liquid chromatography (HPLC). The urinary excretion half-life, calculated from the concentrations of Δ1-THC-7-oic acid versus time, ranged from 0.8–9.8 days with a mean (± SD) of 3.0 ± 2.3 days. Most of the Δ1-THC-7-oic acid was excreted as conjugate and only trace amounts of unconjugated Δ1-THC-7-oic acid were detected. The total concentrations of Δ1-THC-7-oic acid in urine were compared to the concentrations of “cross-reacting cannabinoids”, within the linear range of 20–75 ng/mL, obtained in the semiquantitative EMIT d.a.u. cannabinoid assay. The average ratio of “EMIT concentrations”/Δ1-THC-7-oic acid concentrations obtained by HPLC analysis was 1.23 ± 84% (C.V.) for 78 urine samples. A total of 83% of the samples with positive EMIT levels (cutoff 20 ng/mL) was confirmed by HPLC analysis (cutoff 7 ng/mL).