Benzodiazepines and elderly drivers: a comparison of pharmacoepidemiological study designs

Contradictory results were published from two studies in the late 1990s about the effects of long half-life benzodiazepine use on the risk of motor vehicle crashes (MVCs) in the elderly. The use of different study designs could explain the differences observed in these studies.

The results of an unmatched case-control study were compared to those of a case-crossover study using the same prescription claims database to determine whether the current use of benzodiazepines increased the risk of MVCs.

There were 5579 cases and 12 911 controls identified between the years 1990 and 1993 in the province of Quebec, Canada. The case-control approach demonstrated an increased rate of injurious MVC associated with the current use of long-acting benzodiazepines [odds ratio (OR) 1.45; 95% confidence interval (CI): 1.12-1.88]. The case-crossover approach applied to all cases did not show any association [OR 0.99; 95%CI: 0.83-1.19]. However, among the cases restricted to subjects with four or less prescriptions filled in the previous year, corresponding more to transient exposures, the OR was elevated [OR 1.53; 95%CI: 1.08-2.16].

Differences in study design and analysis may explain some of the discrepancies in previous results. Both study designs provide evidence that long-acting benzodiazepines appear to be associated with an increased risk of MVC.