On-the-road driving performance after use of the antihistamines mequitazine and l-mequitazine, alone and with alcohol.

Objective: Previous studies demonstrated that mequitazine produces mild sedation after single doses. Its enantiomer, l-mequitazine, has a stronger potency for the H1 receptor. The aim of the current study was to assess the effects of l-mequitazine and mequitazine, alone and with alcohol, on driving.

Methods: Twenty-five healthy volunteers were treated with l-mequitazine 2.5, 5.0 and 10 mg, mequitazine 10 mg and placebo, alone and in combination with alcohol in a double-blind crossover design. Driving performance was assessed using the standardized highway driving test in normal traffic. Its primary measure is the Standard Deviation of the Lateral Position (SDLP). Secondary measures consisted of an auditory word learning test during driving, and subjective measures of driving performance.

Results: L-mequitazine 2.5 and 5.0 mg showed no effect on SDLP in the highway driving test, while SDLP significantly increased after l-mequitazine 10 mg (alone +1.59 cm; with alcohol +1.41 cm) and mequitazine 10 mg (with alcohol +1.17 cm). Alcohol significantly impaired all performance measures (SDLP +2.63 cm) but did not interact with the effects of treatment. Subjective measures indicated that participants were aware of the impairing effects of alcohol, but not of l-mequitazine and mequitazine.

Conclusion: L-mequitazine can be considered safe to drive in dosages of 2.5 and 5.0 mg. L-mequitazine 10 mg led to mild driving impairment. Alcohol impaired all performance measures and added to the effects of l-mequitazine and mequitazine.