Cannabinoid Test System

Cannabis is by far the most widely cultivated, trafficked, and abused illicit drug in the world (1-3). According to the recent Drug Abuse Warning Network update (51), the rate of drug abuse-related emergency department visits involving marijuana rose 139% nationally from 1995 to 2002. As reported in the Drug Testing Index series published by Quest Diagnostics (52), cannabinoid analysis has always had the highest "drug positivity rate by drug category" among all of the abused drugs tested in workplace drug-testing programs. Likewise, cannabinoid assays are among the most frequently performed tests in society drug testing, behavior toxicology, and criminal justice testing.

Cannabinoid is a term originally used to denote the unique C21 compounds found in the plant Cannabis sativa L. (53,54). Recent progress in cannabinoid research has been extended to various ligands of the cannabinoid receptors and related compounds, including the transformation products of cannabinoids, synthetic cannabinoid analogs, and the endocannabinoids, namely, the endogenous ligands of the cannabinoid receptors (55-58). As reflected by the profuse publications in cannabinoid chemistry, tremendous efforts have been invested in the isolation of the chemical constituents and the investigation of the structure-activity relationships of the cannabinoids.

The Cannabis plant contains more than 400 chemical compounds belonging to 18 different classes, including more than 60 phytocannabinoids that contain a typical C21 structure with pyran and phenolic rings (53-60). Most of the phytocannabinoids belong to several subclass types, including the tetrahydrocannabinol (A9-THC and A8-THC), cannabinol (CBN), cannabidiol (CBD), cannabichromene (CBC), and cannabigerol types (Fig. 1). The main active constituent of cannabis, and the primary psychoactive cannabinoid is A9-THC (55-59). The nomenclature A9-THC is based on the dibenzopyran numbering system; the same compound can also be called A1-THC according to the monoterpene numbering system (54). Immunoassays for detecting cannabis abuse in urine have been designed to detect THC metabolites and are generally referred to as the cannabinoid assay or THC assay.

In The Federal Register (21 CFR 862.3870), the cannabinoid test system is identified as "a device intended to measure any of the cannabinoids, hallucinogenic compounds endogenous to marihuana, in serum, plasma, saliva, and urine. Cannabinoid compounds include A9-THC, CBD, CBN, and CBC. Measurements obtained by this device are used in the diagnosis and treatment of cannabinoid use or abuse and in monitoring levels of cannabinoids during clinical investigational use." Quantitatively, the most important cannabinoids present in the cannabis plant are THC and the much less prominent constituents CBD, CBN, and CBC (58-60). Immunoassays developed to detect THC metabolites usually have certain degrees of cross-reactivity with CBN but have minimal or no detectable level of cross-reactivity with the ring-opened compounds such as CBD, CBC, and cannabigerol.

In analyzing 35,312 cannabis preparations confiscated in the United States between 1980 and 1997 (59), ElSohly et al. reported that the average concentrations for THC were 3.1% in marijuana (herbal cannabis), 5.2% in hashish (cannabis resin), 15.0% in hash oil (liquid cannabis), and 8.0% in sinsemilla (unfertilized flowering tops from the female Cannabis plant). The average THC content of these cannabis preparations all showed significant increase over the years. The outcome of a cannabinoid test can be affected not only by the analytical performance but also by drug-administration factors such as the potency (%THC) of the drug consumed, the route of administration, the methods, vehicles, and frequency of drug intake, the timing of drug use and sample collection, the type of samples tested, and the pharmacokinetics and pharmacodynamics of cannabinoids (23,61-73).

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