Nystagmus among amphetamine-impaired drivers

Abstract

Clinical signs of drug use can be helpful to identify which drug has been used. Amphetamine intake has traditionally not been considered to cause nystagmus; however, there is a lack of evidence for this claim. The aim of this study was to find a relationship between amphetamine use and nystagmus in a population of apprehended drivers. We evaluated cases of drivers suspected of drugged driving where blood samples were collected and a clinical test of impairment (CTI) was performed. Evaluation of nystagmus is one of the CTI subtests. The samples were analysed for alcohol and psychoactive drugs. Cases with nystagmus were recorded and amphetamine-only cases were compared with alcohol-only cases and with cases where alcohol or drugs were not detected, respectively. Samples from 509 amphetamine-only cases were compared to 519 alcohol-only cases and 205 drug negative cases. The mean blood amphetamine concentration was 0.533 mg/L (range 0.027–3.650 mg/L) and the mean alcohol concentration was 1.57 g/kg (range 0.05–3.97 g/kg). The number of cases with nystagmus was similar in amphetamine-only cases (21%) and drug-negative controls (25%), P = 0.273. The number of cases with nystagmus was higher in alcohol-only cases (53%), than in amphetamine-only cases (21%), P < 0.001, and drug-negative controls (25%), P < 0.001. No association was found between the blood amphetamine concentration and nystagmus, whereas an association between blood alcohol concentration and nystagmus was demonstrated (Pearson's r = 0.252, P = 0.01). In our study, we did not find that apprehended drivers using amphetamine had more frequently nystagmus than a control group that tested negative for alcohol and drugs. One implication is that nystagmus is not a sensitive test to identify amphetamine-induced impairment.