Background: Studies of the risk of motor vehicle crash associated with diabetes have produced conflicting results.
Objectives: To assess whether the use of anti-diabetic drugs among the elderly increases the risk of motor vehicle crash.
Methods: The computerized databases of the various universal insurance programs of Québec were linked to form a cohort of all 224,734 elderly drivers that was followed from 1990-1993. Using a nested case-control approach, all 5,579 drivers involved in an injurious crash (cases) and a random sample of 13,300 control subjects were identified. Exposure to anti-diabetic drugs was assessed in the year preceding the index date, namely the date of the crash for the cases and a randomly selected date during follow-up for the controls.
Results: The adjusted rate ratio of an injurious crash was 1.4 (95% CI: 1.0-2.0) for current users of insulin monotherapy relative to non-users and 1.3 (95% CI: 1.0-1.7) for sulfonylurea and metformin combined. Monotherapy, using either a sulfonylurea or metformin, was not associated with an increased risk. There was a dose-response effect in subjects using high doses of combined oral therapy (RR 1.4; 95% CI: 1.0-2.0). For users of insulin monotherapy or of high doses of combined oral therapy, the increase corresponds to an excess rate of 32 crashes per 10,000 elderly drivers per year.
Conclusions: L Elderly drivers treated with insulin monotherapy or a combination of sulfonylurea and metformin, especially at high doses, have a small increased risk of injurious crashes. There is no increased risk associated with any regimen of oral monotherapy.