Developing a Method to Determine Salivary THC Concentration

Introduction: Cannabis impairs cognitive and psychomotor performance, which can negatively affect driving skills. The main psychoactive ingredient in cannabis is ∆9-tetrahydrocannabinol (THC). Due to the recent legalization of cannabis in Canada, there is an urgent need for a roadside test to identify THC impaired drivers. The legal limit while driving is calculated based on blood THC concentration, but saliva samples are the most convenient to collect roadside. Thus, the objectives of this study are to (1) determine the relationship between salivary and serum THC concentration and (2) develop a suitable roadside method to determine salivary THC concentration. Methods: THC doses between 0.2 mg/Kg to 100 mg/Kg will be orally administered to 36 mice (18 female, 18 male) in a repeated-measures design. Saliva and blood samples will be collected in 15 min intervals from 0 to 6 hours after administration. Gas chromatography (GC) and liquid chromatography (LC) coupled to mass spectrometry (MS) will be used to determine THC concentration in the saliva and blood samples. The relationship between salivary and serum THC concentration will be modelled. In addition, a series of azo dyes will be applied to the saliva samples to determine salivary THC concentrations in a simple and rapid manner. The samples will be dissolved in NaOH, and various dyes will be added. An acid-base reaction will create a phenolate anion from the phenolic group of the ∆9-THC molecule, which will then attack the diazo group of the azo dye to produce a coloured end-product. Expected Results: We expect a positive linear relationship between the logged salivary and blood serum THC concentrations. We predict that each azo dye will produce a single colour within a specific and different range of THC concentration, so a distinct set of colours produced from many dyes can be associated with a narrow range of salivary THC concentration. Discussion: The colours produced from the azo dye reactions can be associated with salivary THC concentrations, which can then be correlated to serum THC concentrations. We use a mouse model in this study to have a more controlled investigation of the relationship between salivary and serum THC concentration, but future investigations should apply the results to humans. Conclusion: This study aims to determine salivary THC concentration in a suitable roadside method and correlate the results to serum THC concentration. The implications of this study are to be able to detect THC impaired drivers in a simple and rapid manner.