Elimination of 11-nor-9-carboxy-delta-9-tetrahydrocannabinol when normalized to urinary creatinine

Gas chromatography mass/spectrometry quantitative analysis of 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THCCOOH), the major metabolite of delta-9-tetrahydrocannabinol (THC) found in urine following marijuana use, was performed on serial urine specimens collected from an inpatient adolescent population of marijuana users. Creatinine normalization of THCCOOH was used to compensate for dilute or concentrated urine specimens. The urinary terminal elimination rate constant and terminal half-life was calculated for each subject. The mean urinary elimination rate constant for THCCOOH normalized to creatinine was 0.08433 days(-1) (range 0.05408-0.16544) reflecting a 8.22 day terminal half-life. A half-life of 1.15 days was observed for the initial decline phase of THCCOOH corrected by creatinine suggesting that reuse of marijuana can be detected after this phase ends. The creatinine normalized THCCOOH level was a better indicator for predicting reuse of marijuana than urinary concentrations of THCCOOH. The Mean Residence Time (MRT) of THCCOOH/Cr (5.7 days) correlated well with the length of time a subject will have detectable urinary THCCOOH concentrations (20.8 days).