Exposure to THC in Dutch suspected impaired drivers

摘要

Aim of this presentation is first to describe the legal procedure, sampling and analytical methods that are used to detect exposure to THC in suspected impaired drivers and second, to explain the scientific base of the proposed legal limits for THC. According to the Dutch Road Traffic Act, it is forbidden to drive under the influence of a substance of which a driver ought to know that it can affect the driving performance negatively. For alcohol, legal limits, related to accident risk, have been laid down. For drugs, no legal limits have been laid down and driving impairment has to be evaluated case-by-case, based on the results of blood analysis. In 2015, the Dutch Road Traffic Act was changed; it is expected to come into force in 2017. The new law comprises limits for the nine most frequently detected drugs in blood as well as the use of oral fluid tests as a screening for drugs. The results of this oral fluid test will have to be confirmed in blood. After alcohol, the next most frequently detected drug in drivers is cannabis. Based on scientific literature, the proposed legal limit for single cannabis use is 3.0 ng THC/ml whole blood (impairment limit). In case of multi-drug use, the proposed legal limit for THC is 1.0 ng/ml in whole blood (analytical limit). These limits take into consideration that THC may come from passive inhalation of cannabis smoke. The prevalence of THC in blood of suspected impaired drivers was investigated by reviewing the results of the Netherlands Forensic Institute (NFI) during the years 2009-2012. The identification and quantification of THC and metabolites was performed by using a validated UPLC-MS/MS (ultra performance liquid chromatography-tandem mass spectrometry) method. The limit of quantification was 1 ug/L THC was demonstrated in 36% (1085/3038) of the blood samples of suspected impaired drivers. In 69% (748/1085) of the cases, no other illicit drug was detected. The most frequently detected combinations of THC and other illicit drugs in drivers were THC and amphetamines 14% (153/1085), THC and cocaine 5.7% (62/1085), THC and GHB 2.7% (29/1085). Alcohol was not included in the review of the cases because the results of the alcohol breath test (if performed) were unknown. Introduction of threshold values in the law is expected to make prosecution of an impaired driver more efficient, because it will obviate discussions on e.g. circumstances, tolerance and passive inhalation of cannabis.