Cannabinoidto Creatinine Ratio Studies

Regardless of the cutoff levels chosen for cannabinoids testing, substantial variabilities have been observed between subjects and between doses in the excretion profiles of THC-COOH. Huestis et al. (67) demonstrated that mean detection times in urine following smoking varied considerably between individuals even in highly controlled smoking studies. It has been documented that consecutive urine specimens may fluctuate below and above the cutoff during the terminal elimination phase when THC-COOH concentrations approach the cutoff (67,71). The normalization of drug excretion to urine creatinine concentration has been well documented not only to predict new drug use but also to reduce the variability of drug measurements attributable to urine dilution (146-150). Gustafson et al. (70) observed an up to fourfold intrasubject variation across doses and a sixfold intersubject variation for a single dose in terminal elimination half-lives. However, the authors found no significant effect of creatinine normalization on pharmacokinetic parameters, half-life, maximum excretion rate, and time to maximum excretion rate following oral THC administration. The authors also showed that the apparent urinary elimination half-life of THC-COOH prior to reaching 15 ng/mL concentration was significantly shorter than the terminal urinary elimination half-life.

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