Driving and benzodiazepine use : Evidence that they do not mix

Although the data are sparse, epidemiological studies show that benzodiazepine use increases the relative risk of being involved in a traffic accident by a factor of from 1.5 to about 6.5, depending on dose, number of benzodiazepines used and recency of use. These risks are similar to those associated with blood alcohol concentrations of about 0.6 and 1 g/L, respectively. Experimental studies employing on-the-road driving, driving simulation and laboratory tests measuring skills related to driving have clearly established the dose-dependent performance- impairing effects of benzodiazepines. Benzodiazepine hypnotics vary considerably in their potential to produce residual effects in the morning after nocturnal use. The main determinants of the degree and duration of action after a single dose are size of dose, rate and extent of distribution, lipophilicity and receptor affinity. With repeated administration, compounds with a long elimination half-life (t) are likely to accumulate and produce increased sedation. Diazepam may have a rapid onset of action precipitating the risk of sudden intoxication, but its duration of action is relatively short after a single dose (acute tolerance). The impairing effects of diazepam on driving performance may persist at least during the first 3 weeks of daily administration. The issue of tolerance has not yet been adequately explored and patients should be warned that their performance may not return to the premedication level. Elderly patients may be more sensitive to the sedative and performance-impairing effects than the young, although the evidence is equivocal. Caution is warranted with concomitant use of CNS depressants, such as alcohol, and with drugs interfering with the metabolic pathways of benzodiazepines. Considerable interindividual differences in sensitivity to the behavioural effects of benzodiazepines warrant the careful monitoring of patients. Physicians should educate their patients about the risk of traffic accident during benzodiazepine use.