Journal article
Effect of Blood Collection Time on Measured Δ9-Tetrahydrocannabinol Concentrations: Implications for Driving Interpretation and Drug Policy
Clinical chemistry (Baltimore, Md.), Vol.62(2), pp.367-377
02/2016
DOI: 10.1373/clinchem.2015.248492
PMID: 26823611
Abstract
In driving-under-the-influence cases, blood typically is collected approximately 1.5-4 h after an incident, with unknown last intake time. This complicates blood Δ(9)-tetrahydrocannabinol (THC) interpretation, owing to rapidly decreasing concentrations immediately after inhalation. We evaluated how decreases in blood THC concentration before collection may affect interpretation of toxicological results.
Adult cannabis smokers (≥1×/3 months, ≤3 days/week) drank placebo or low-dose alcohol (approximately 0.065% peak breath alcohol concentration) 10 min before inhaling 500 mg placebo, 2.9%, or 6.7% vaporized THC (within-individuals), then took simulated drives 0.5-1.3 h postdose. Blood THC concentrations were determined before and up to 8.3 h postdose (limit of quantification 1 μg/L).
In 18 participants, observed Cmax (at 0.17 h) for active (2.9 or 6.7% THC) cannabis were [median (range)] 38.2 μg/L (11.4-137) without alcohol and 47.9 μg/L (13.0-210) with alcohol. THC Cmax concentration decreased 73.5% (3.3%-89.5%) without alcohol and 75.1% (11.5%-85.4%) with alcohol in the first half-hour after active cannabis and 90.3% (76.1%-100%) and 91.3% (53.8%-97.0%), respectively, by 1.4 h postdose. When residual THC (from previous self-administration) was present, concentrations rapidly decreased to preinhalation baselines and fluctuated around them. During-drive THC concentrations previously associated with impairment (≥8.2 μg/L) decreased to median <5 μg/L by 3.3 h postdose and <2 μg/L by 4.8 h postdose; only 1 participant had THC ≥5 μg/L after 3.3 h.
Forensic blood THC concentrations may be lower than common per se cutoffs despite greatly exceeding them while driving. Concentrations during driving cannot be back-extrapolated because of unknown time after intake and interindividual variability in rates of decrease.
Details
- Title: Subtitle
- Effect of Blood Collection Time on Measured Δ9-Tetrahydrocannabinol Concentrations: Implications for Driving Interpretation and Drug Policy
- Creators
- Rebecca L Hartman - Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, NIH, Baltimore, MDTimothy L Brown - National Advanced Driving Simulator, University of Iowa, Iowa City, IAGary Milavetz - College of Pharmacy, University of Iowa, Iowa City, IAAndrew Spurgin - College of Pharmacy, University of Iowa, Iowa City, IADavid A Gorelick - Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, NIH, Baltimore, MD; Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MDGary R Gaffney - Carver College of Medicine, University of Iowa, Iowa City, IAMarilyn A Huestis - Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, NIH, Baltimore, MD; mhuestis@intra.nida.nih.gov
- Resource Type
- Journal article
- Publication Details
- Clinical chemistry (Baltimore, Md.), Vol.62(2), pp.367-377
- DOI
- 10.1373/clinchem.2015.248492
- PMID
- 26823611
- NLM abbreviation
- Clin Chem
- ISSN
- 0009-9147
- eISSN
- 1530-8561
- Publisher
- England
- Grant note
- Intramural NIH HHS
- Language
- English
- Date published
- 02/2016
- Academic Unit
- Pharmacy; Psychiatry; Industrial and Systems Engineering; Pharmacy Practice and Science; Injury Prevention Research Center
- Record Identifier
- 9984065694902771
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