Oral fluidplasma cannabinoid ratios following controlled oral THC and smoked cannabis administration.
Oral fluid (OF) is a valuable biological alternative for clinical and forensic drug testing. Evaluating OF to plasma (OFP) cannabinoid ratios provides important pharmacokinetic data on the disposition of drug and factors influencing partition between matrices. Eleven chronic cannabis smokers resided on a closed research unit for 51 days. There were four 5-day sessions of 0, 30, 60, and 120 mg oral ∆(9)-tetrahydrocannabinol (THC)day followed by a five-puff smoked cannabis challenge on Day 5. Each session was separated by 9 days ad libitum cannabis smoking. OF and plasma specimens were analyzed for THC and metabolites. During ad libitum smoking, OFP THC ratios were high (median, 6.1 range, 0.2-348.5) within 1 h after last smoking, decreasing to 0.1-20.7 (median, 2.1) by 13.0-17.1 h. OFP THC ratios also decreased during 5-days oral THC dosing, and after the smoked cannabis challenge, median OFP THC ratios decreased from 1.4 to 5.5 (0.04-245.6) at 0.25 h to 0.12 to 0.17 (0.04-5.1) at 10.5 h post-smoking. In other studies, longer exposure to more potent cannabis smoke and oromucosal cannabis spray was associated with increased OFP THC peak ratios. Median OFP 11-nor-9-carboxy-THC (THCCOOH) ratios were 0.3-2.5 (range, 0.1-14.7) ngμg, much more consistent in various dosing conditions over time. OFP THC, but not THCCOOH, ratios were significantly influenced by oral cavity contamination after smoking or oromucosal spray of cannabinoid products, followed by time-dependent decreases. Establishing relationships between OF and plasma cannabinoid concentrations is essential for making inferences of impairment or other clinical outcomes from OF concentrations.