Cases of ketamine consumption in driving under the influence of drugs (DUID) were evaluated with regard to recorded psychomotor impairments and possible co-consumption of drugs of abuse or other substances.

Ketamine is a substance that is used e.g. as an anaesthetic or for analgesics in medical treatment. Due to its dissociative effects, ketamine abuse has increased in the past years leading to several drug-impaired driving cases. According to literature, ketamine plasma concentrations above 50ng/mL are associated with significant psychomotor impairments, whereby mind-altering effects can be expected at plasma concentrations of ketamine between 50 and 200ng/mL. They seem to be concentration dependent. The most commonly described impairments comprise a slurred speech, drowsiness, confusion and vomiting as well as lack of coordination and dystonia, blurred vision or visual field narrowing, dissociation, referential thinking, euphoria, depersonalization and anxiety. Moreover, pupil dilatation, a lack of convergence, horizontal gaze nystagmus, elevated pulse rate and failure of divided attention tests like walk-and-turn and one-leg stand test were observed.

DUID cases from two institutes of legal medicine from the years 2021 to early 2022 were evaluated with regard to drug-impaired drivers who consumed ketamine. The cases were compared with regard to psychomotor impairments, salience in driving and co-consumption of drugs. Technical devices for the analyses of drug concentrations in blood were drug-dependent and therefore either performed by GC-MS/MS, LC-MS/MS or HPLC-DAD.

Five cases of drivers (all male, between 21 and 44 years old) were collected. Ketamine consumption was admitted in two out of five cases. Indications for a medical application were not given in the other three cases without confessed consumption. Ketamine concentrations of approx. 165ng/mL, 245ng/mL, 610ng/mL, 676ng/mL and 3800ng/mL were detected in the serum samples. Moreover, co-consumption of either one or multiple substances like cannabis (n=2), amphetamine (n=4), 3,4-methylenedioxymethamphetamine (MDMA) (n=1), cocaine (n=2) and clonazepam (n=1) could be ascertained in all cases. The recorded psychomotor impairments of the drivers comprised e.g. dilated pupils (n=2), missing or delayed pupil reactions (n=3), as well as aggressive behaviour (n=3), a slurred or decelerated speech (n=2), a delayed reaction (n=2), lack of concentration (n=2) or vertigo (n=3).

The observed psychomotor impairments correlated with literature data. However, the assessment and differentiation of impairments with regard to ketamine consumption is aggravated due to co-consumption of other drugs of abuse or substances. In literature, co-consumption of e.g. alcohol, cannabis, MDMA, amphetamine, benzodiazepines or cocaine is also described when ketamine is abused, which is also in line with the collected data. The extremely high concentration of ketamine (approx. 3800ng/mL) in one case from the present case series, might allow the supposition that the recorded impairments are most likely due to ketamine consumption, although cocaine and its metabolite benzoylecgonine (BE) were also detected in moderate concentrations (cocaine=32ng/mL, BE=729ng/mL) as well. However, a decent distinction of the impairments is not possible.

The presented case series provides additional data on psychomotor impairments observed in DUID cases after the consumption of ketamine, although the results have to be regarded critically due to co-consumption of other substances and the limited case number. Nevertheless, correlation between existing literature data could be observed. Since the abuse of ketamine has increased in the past years, those data can support the assessment of cases, where ketamine abuse is in question.