Huestis Marilyn A, Cone Edward J
Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, USA.
J Anal Toxicol. 2004 Sep;28(6):394-9. doi: 10.1093/jat/28.6.394.
Understanding the relationship of Delta(9)-tetrahydrocannabinol (THC) concentrations in oral fluid and plasma is important in interpretation of oral fluid test results. Current evidence suggests that THC is deposited in the oral cavity during cannabis smoking. This "depot" represents the primary or sole source of THC found when oral fluid is collected and analyzed. In this research, oral fluid and plasma specimens were collected from six subjects following smoking of cannabis cigarettes containing 1.75% and 3.55% THC. There was at least one week between each cannabis administration. Plasma specimens were analyzed by gas chromatography-mass spectrometry (GC-MS) and paired oral fluid specimens were analyzed by radioimmunoassay (RIA). In addition, one individual's oral fluid specimens were also analyzed by GC-MS. These data are unique in that they represent simultaneous or near simultaneous collection of oral fluid and plasma specimens in subjects following controlled cannabis dosing. The first oral fluid specimen, collected from one subject at 0.2 h following initiation of smoking, contained a THC concentration of 5800 ng/mL (GC-MS). By 0.33 h, the THC concentration in oral fluid had fallen to 81 ng/mL. From approximately 0.3 h through 4.0 h, the mean (+/- SD) THC ratio of oral fluid to plasma THC concentrations was 1.18 (0.62) with a range of 0.5 to 2.2. Within 12 h, both oral fluid and plasma THC concentrations generally declined below 1 ng/mL. RIA analyses of oral fluid specimens for six subjects demonstrated the same pattern of initial high levels of contamination immediately after smoking, followed by rapid clearing, and a slower decline over 12 h. Mean THC oral fluid concentrations by RIA at 0.2 h were 864 ng/mL and 4167 ng/mL compared to plasma concentrations of 52 ng/mL and 230 ng/mL at 0.27 h following the low- and high-dose cannabis cigarettes, respectively. The similarity in oral fluid and plasma THC concentrations following the dissipation of the initial "contamination" indicates the likelihood of a physiological link between these specimens. Recent studies have shown that sublingual or transmucosal administration of pure THC results in direct absorption of intact THC into the bloodstream, thereby bypassing the gastrointestinal tract. The current study demonstrates that THC is deposited in the oral cavity and remains for up to 24 h following cannabis smoking. The decline in THC oral fluid concentration over this time suggests that there may be absorption of THC into blood as previously shown with pure THC. Passive cannabis exposure studies appear to indicate that positive oral fluid tests for THC can occur shortly after cannabis smoke exposure, but results were negative within 1 h. Consequently, when very recent passive exposure to cannabis smoke can be ruled out, it is concluded that a positive oral fluid test provides credible evidence of active cannabis use.
了解口腔液和血浆中Δ⁹-四氢大麻酚（THC）浓度之间的关系对于解释口腔液检测结果至关重要。目前的证据表明，吸食大麻期间THC会沉积在口腔中。这种“储存库”是收集和分析口腔液时发现的THC的主要或唯一来源。在本研究中，从6名受试者吸食含1.75%和3.55%THC的大麻香烟后采集口腔液和血浆样本。每次吸食大麻之间至少间隔一周。血浆样本通过气相色谱-质谱联用仪（GC-MS）分析，配对的口腔液样本通过放射免疫分析（RIA）分析。此外，还对一名个体的口腔液样本进行了GC-MS分析。这些数据具有独特性，因为它们代表了在受控大麻给药后同时或近乎同时采集的受试者口腔液和血浆样本。从一名受试者在开始吸烟后0.2小时采集的第一份口腔液样本中，THC浓度为5800 ng/mL（GC-MS）。到0.33小时，口腔液中的THC浓度降至81 ng/mL。从大约0.3小时到4.0小时，口腔液与血浆THC浓度的平均（±标准差）比值为1.18（0.62），范围为0.5至2.2。在12小时内，口腔液和血浆中的THC浓度通常都降至1 ng/mL以下。对6名受试者口腔液样本的RIA分析显示，吸烟后立即出现相同的初始高污染水平模式，随后迅速清除，并在12小时内缓慢下降。低剂量和高剂量大麻香烟后，RIA法测得的口腔液中THC平均浓度在0.2小时分别为864 ng/mL和4167 ng/mL，而血浆浓度在0.27小时分别为52 ng/mL和230 ng/mL。初始“污染”消散后口腔液和血浆中THC浓度的相似性表明这些样本之间存在生理联系的可能性。最近的研究表明，舌下或经粘膜给予纯THC会导致完整的THC直接吸收进入血液，从而绕过胃肠道。当前的研究表明，THC会沉积在口腔中，并在吸食大麻后持续长达24小时。这段时间内口腔液中THC浓度的下降表明，可能如先前对纯THC的研究所示，THC会吸收进入血液。被动接触大麻的研究似乎表明，接触大麻烟雾后不久口腔液中THC检测可能呈阳性，但1小时内结果为阴性。因此，当可以排除近期被动接触大麻烟雾的情况时，可以得出结论，口腔液检测呈阳性为主动使用大麻提供了可靠证据。
