Context: Benzodiazepines, used by a sizable number of the elderly population, may affect the ability to drive and thus increase the risk of a motor vehicle crash. Epidemiologic studies of this question have produced inconsistent results that may be due to the different effects of long- and short-half-life benzodiazepines and variations in their duration of use.
Objective: To determine whether the use of benzodiazepines of either long- or short-elimination half-life is associated with the risk of injurious motor vehicle crash in the elderly.
Design and setting: Nested case-control design within a cohort of 224,734 drivers from the Canadian province of Quebec, aged 67 to 84 years, followed up from 1990 to 1993. Computerized data for the study were obtained from provincial driver's license files, police reports of injurious crashes, and health insurance records.
Patients: We identified all 5579 drivers involved in an injurious crash (cases) and a random sample of 10 controls per case selected from a subcohort of 13,256 subjects.
Main outcome: Involvement of a cohort member as a driver in a motor vehicle crash in which at least 1 person (not necessarily the driver) sustained bodily injury.
Results: The adjusted rate ratio of crash involvement within the first week of long-half-life benzodiazepine use was 1.45 (95% confidence interval [CI], 1.04-2.03). The rate ratio for continuous use of longer duration up to 1 year was slightly lower but remained significant (rate ratio, 1.26; 95% CI, 1.09-1.45). In contrast, there was no increased risk after the initiation of treatment with short-half-life benzodiazepines (rate ratio, 1.04; 95% CI, 0.81-1.34) or with their continued use (rate ratio, 0.91; 95% CI, 0.82-1.01).
Conclusions: Brief or extended periods of exposure to long-half-life benzodiazepines are associated with an increased risk of motor vehicle crash involvement in the elderly population. There is no such elevated risk for short-half-life benzodiazepines.