Benzodiazepines are among the most frequently prescribed classes of medications in elderly patients, primarily for treatment of anxiety and insomnia. The many adverse side effects of benzodiazepines, including drowsiness, sedation, confusion and impaired motor function, may have a serious effect on a patient's ability to operate a motor vehicle. Hemmelgarn and colleagues reviewed the association between the type of benzodiazepine used (long- or short-acting) and the risk of injury in a motor vehicle accident.

Individuals were included in the study if they had been driving when an accident occurred that injured at least one person. All study subjects lived in Quebec and were between the ages of 67 and 84 years. Prescription use of a benzodiazepine was confirmed by a review of Quebec province health care service records. Benzodiazepines were classified as having a long half-life (clonazepam, diazepam, clorazepate, chlordiazepoxide, flurazepam or nitrazepam) or a short half-life (alprazolam, bromazepam, lorazepam, oxazepam, temazepam or triazolam). Study subjects were selected from a cohort of those who met the criteria, and 10 control subjects were randomly selected for each study subject. A total of 5,579 study subjects and 18,490 control subjects were selected for the study.

Regardless of the duration of use, individuals who were currently taking long-acting benzodiazepines had an increased risk of involvement in a motor vehicle accident with injury. However, for those who had just begun taking long-acting benzodiazepines within the last seven days, the risk was even higher (risk ratio: 1.45). The risk dropped to nonsignificant levels if the individual had been taking the drug between eight and 30 days. The risk significantly increased again in study subjects who had used a benzodi-azepine for more than 61 days. Those taking short-acting benzodiazepines had no similar risk of involvement in motor vehicle accidents with injury.

The authors conclude that use of long-acting benzodiazepines, particularly within seven days of initiation of treatment, is associated with a significantly high risk of involvement in a motor vehicle accident with injury. Tolerance to the psychomotor effects of long-acting benzodiazepine use does not seem to develop, as had previously been proposed.