SOFT - TIAFT 1998 Poster Session 1 Wednesday October 7, 1998

Anne Smith-Kielland, Bjørn Skuterud and Jørg Mørland

National Institute of Forensic Toxicology, Oslo, Norway.

The present study was undertaken to obtain detailed information concerning the urinary excretion profiles of cannabinoids and the main urinary tetrahydrocannabinol (THC) metabolite, 11-nor-9-carboxy-D9-tetrahydrocannabinol (THCCOOH), in drug users. Informed consent was obtained from subjects starting to serve their prison sentence.

Drug habits were assessed by means of a questionnaire. Subjects were classified as infrequent users (cannabis use < once a week), or frequent users (cannabis use > once a week). The subjects agreed to give up to 5 urinary specimens daily until negative. The specimens were analysed semi-quantitatively by EMIT® (cut-off 20 ng/ml, representing cannbinoids). Positive specimens and several negative ones were analysed for THCCOOH by a gas chromatography using EC-detector with a limit of detection 1.4 ng/ml, considerably lower than cut-offs according to NIDA (15 ng/ml), and our institute (10.3 ng/ml). Creatinine was measured in all specimens.

All 21 participants (1 participated twice) admitted to having used cannabis, but not all went through the whole follow-up period. A total of 78% of the EMIT positive specimens were confirmed by GC analysis (THCCOOH cut-off 10.3 ng/ml). Relating THCCOOH concentration to creatinine generally gave a smoother time curve than the THCCOOH concentration itself.

Infrequent users had a mean apparent THCCOOH urinary elimination t1/2of about 1.3 days (pooled data). Frequent users had urinary elimination t1/2 from 1 day up to about 10 days. In infrequent users the median time from last reported intake until the last positive observed was 12 days (cannabinoids), 5 days (THCCOOH 10.3 ng/ml) and 4 days (THCCOOH 15 ng/ml), respectively. In frequent users the median time from last reported intake until last positive observed was 27 days (cannabinoids), 22 days (THCCOOH 10.3 ng/ml) and 17 days (THCCOOH 15 ng/ml). In one subject 16 negative gaps (THCCOOH positive specimen followed by a negative and again a positive specimen) were observed.

The study of the urinary excretion profiles of illegal drugs in prison inmates is a method of obtaining data that cannot ethically be obtained from healthy volunteers. The present results may aid in the interpretation of urinary THCCOOH and cannabinoid drug testing results.

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