DRIVING AND BENZODIAZEPINE USE - EVIDENCE THAT THEY DO NOT MIX

Although the data are sparse, epidemiological studies show that benzod iazepine use increases the relative risk of being involved in a traffi c accident by a factor of from 1.5 to about 6.5, depending on dose, nu mber of benzodiazepines used and recency of use. These risks are simil ar to those associated with blood alcohol concentrations of about 0.6 and 1 g/L, respectively. Experimental studies employing on-the-road dr iving, driving simulation and laboratory tests measuring skills relate d to driving have clearly established the dose-dependent performance-i mpairing effects of benzodiazepines. Benzodiazepine hypnotics vary con siderably in their potential to produce residual effects in the mornin g after nocturnal use. The main determinants of the degree and duratio n of action after a single dose are size of dose, rate and extent of d istribution, lipophilicity and receptor affinity. With repeated admini stration, compounds with a long elimination half-life (t1/2 beta) 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 perform ance may persist at least during the first 3 weeks of daily administra tion. 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 se dative and performance-impairing effects than the young, although the evidence is equivocal. Caution is warranted with concomitant use of CN S depressants, such as alcohol, and with drugs interfering with the me tabolic pathways of benzodiazepines. Considerable interindividual diff erences in sensitivity to the behavioural effects of benzodiazepines w arrant the careful monitoring of patients. Physicians should educate t heir patients about the risk of traffic accident during benzodiazepine use.