Driving under the influence of drugs: prevalence in road traffic accidents in Italy and considerations on "per se" limits legislation.

OBJECTIVE: To present the prevalence and concentrations of drugs in blood samples of drivers involved in road traffic accidents (RTA) and to discuss the effects of adopting different concentration cut-off values proposed or applied in other European countries on the number of driving under the influence of drugs (DUID) offences.

METHODS: Blood samples from drivers involved in RTA in the Padova province, from 2014 to 2017, were analysed for the presence of alcohol and drugs. The prevalence of positive subjects was reported for each substance adopting the limits of quantification (LOQs) of our laboratory and the concentration cut-off values proposed and/or used in other European countries. The reduction of cases of driving under the influence of illicit drugs in applying different cut-offs was calculated.

RESULTS: 4443 blood samples were analysed: 23.7% were positive for alcohol and 19.9% for psychoactive drugs, with a prevalence of poly-drug and alcohol-drug abuse of 4.5% and 6% respectively. The most frequently detected drugs were cannabinoids (9.7%) and cocaine (7.2%) followed by benzodiazepines (4.1%), opiates (1.9%) and other opioids (1.7%). Barbiturates, amphetamines and ketamine have been identified in a much smaller number of cases. The overall decrease of DUID cases when adopting different cut-offs with respect to the cases "above the LOQs" was between 8% and 84%. The adoption of high LOQs such as those used in the "European Union's research project on Driving Under the Influence of Drugs, Alcohol and Medicines" (DRUID), decreases the hypothetical number of DUID offences by a quarter, while per se limits proposed as broadly equivalent to a blood alcohol concentration (BAC) between 0.2 and 0.8 g/L dramatically reduce the cases of DUID (cocaine -81%, cannabis -79%, opioids -97%, opiates -96%, and amphetamines -77%) and no ketamine positive samples were above the cut-off.

CONCLUSIONS: The implementation of high analytical limits or of per se limits based on impairing concentrations in the Italian legislation could result in the persecution of a much lower number of drugged drivers involved in RTA, with a decrease from 25% to more than 80% depending on the limits.