Residual effects and skills related to driving after a single oral administration of diazepam, medazepam or lorazepam

Abstract

Psychomotor skills and visual functions related to driving were measured double-blind cross-over in ten healthy volunteers before, and 1,3,5 and 7 h after a single oral administration of diazepam (10mg), medazepam (15 mg) or lorazepam (2.5 mg). The late effects of lorazepam were tested in seven other subjects 12 and 24 h after the administration. Lorazepam impaired almost all the measured skills more (P less than 0.05 to 0.001) than diazepam, medizepam or the placebo. The lorazepam impairment of reactive skills and flicker fusion discrimination remained statistically significant (P less than 0.05) for as long as 12 h. Medazepam impaired only reactive skills and flicker fusion, the latter remaining impaired (P less than 0.05) for as long a 5 h after the administration. The magnitude and duration of the effects of diazepam were intermediate between those of lorazepam and medazepam. Diazepam impaired perceptual speed and reactive and co-ordinative skills as well as flicker fusion discrimination and visual parameters related to driving. Slight impairments in performance were measurable for up to 5 h after administration but at 7 h the results resembled those measured after the placebo. The lack of alterations in adaptation to darkness, sensitivity to brightness or visual discrimination ability in bright counterlight at a time when flicker fusion discrimination was severely depressed suggests that an impaired ability to discriminate flickering light is of no or little clinical significance to driving ability. It is concluded that patients receiving a 2.5 mg dose of lorazepam should not drive or operate machinery for 24 h after the administration. After diazepam (10 mg) or medazepam (15 mg) patients should refrain from driving or participating inskilled performances for only 5 to 7 hours.