A zero-concentration limit for controlled scheduled drugs in the blood of motorists was introduced in Sweden in 1999 and the annual number of arrests for driving under the influence of drugs (DUID) has since increased eight-fold. However, for prescription drugs that might cause impairment (e.g. benzodiazepines) additional proof is needed to justify prosecution, such as whether the medication was being misused. Over a 2-year period, we found 94 cases of DUID in which the concentrations of diazepam in blood was 1.1 μg/g or more. Diazepam (D) and nordiazepam (ND) were determined in whole blood by capillary gas chromatography with a limit of quantitation of 0.05 μg/g for each compound. The mean (median) and maximum concentrations of D were 2.0 μg/g (1.7 μg/g) and 7.8 μg/g and the corresponding ND concentrations were 1.5 μg/g (1.0 μg/g) and 7.6 μg/g, respectively. The concentration of D in blood exceeded 2 μg/g in 21% of cases and was over 3.0 μg/g in 11% of cases. D and ND were the only drugs present in eight cases (seven men and one women) and in another five cases ethanol was present at concentrations ranging from 0.81 to 1.98 mg/g. Polydrug use was very common in these DUID suspects and D and ND coexisted with amphetamine in 20% of cases, tetrahydrocannabinol in 18% of cases and with both these illicit drugs in 12% of cases. The next most prevalent drug combination was D, ND and morphine (mostly derived from heroin), seen in 13% of cases. Other psychoactive prescription drugs were identified in blood including alprazolam, flunitrazepam, oxazepam, zolpidem and zopiclone. This case series of DUID suspects demonstrate the high frequency of polydrug use showing preference for illicit drugs like amphetamine, cannabis and heroin, in that order. Furthermore, Swedish traffic delinquents frequently overdose with prescription drugs as exemplified here by unusually high concentrations of D and its active metabolite ND.
2004. Vol. 146, no 1