Pharmacokinetics and Metabolism of the Plant Cannabinoids 679Fig. 6.Urine concentrations of 11-nor-9-carboxy-∆^9 -tetrahydrocannabinol (THCCOOH; ng/ml, and ng/mg
creatinine) for one subject after smoking a single 3.55% THC cigarette. (Reproduced from theJournal of
Analytic Toxicologyby permission of Preston Publications, a division of Preston Industries; Huestis and Cone
1998b, Fig. 3 therein)
200%. The most accurate ratio (85.4%) was 50%, with a sensitivity of 80.1% and
a specificity of 90.2%, with 5.6% false-positive and 7.4% false-negative predictions.
If the previously recommended increase of 150% was used as the threshold for new
use, sensitivity of detecting new use was only 33.4%, specificity was high at 99.8%,
and there was an overall accuracy prediction of 74.2%. To further substantiate
the validity of the derived ROC curve, urine cannabinoid metabolite and creati-
nine data from another controlled clinical trial that specifically addressed water
dilution as a means of specimen adulteration were evaluated (Cone et al. 1998).
Sensitivity, specificity, accuracy, percentage false positives, and percentage false
negatives were 71.9%, 91.6%, 83.9%, 5.4%, and 10.7%, respectively, when the 50%
criterion was applied. These data indicate selection of a threshold to evaluate se-
quential creatinine-normalized urine drug concentrations can improve the ability
to distinguish residual excretion from new drug usage.
5.3
Oral Fluid Testing
Oral fluid is also a suitable specimen for monitoring cannabinoid exposure and is
beingevaluatedfordrivingundertheinfluenceofdrugs,drugtreatment,workplace
drug testing, and for clinical trials (Cairns et al. 1990; Gross and Soares 1978; Gross
et al. 1985; Mura et al. 1999; Soares et al. 1976, 1982). Adequate sensitivity is best
achieved with an assay directed toward detection of THC, rather than 11-OH-
THC or THCCOOH. The oral mucosa is exposed to high concentrations of THC
during smoking and serves as the source of THC found in oral fluid. Only minor
amounts of drug and metabolites diffuse from the plasma into oral fluid (Hawks
1983). Following intravenous administration of radiolabeled THC, no radioactivity
could be demonstrated in oral fluid (Hawks 1982). No measurable 11-OH-THC or
THCCOOH was found in oral fluid collected immediately following and up to