Academisch Ziekenhuis-VUB, Laarbeeklaan 101, 1090 Brussels*; pharmacist, Le Roeulx¹; CHU Sart Tilman Liège²; Poison Control Centre Brussels³; UZ Gent⁴; CU Luxembourg⁵

The classification was based on the system of Wolschrijn et al (1991): 7 categories ranging from no effect (I) over minor and moderate (II1,II2) to severe effects (III), completed with the respective * categories for assumed classes with insufficient scientific data. A total of 28/179 molecules (16%) were considered having no influence (I/I*): 1/33 hypnotics-sedatives (0/4 barbiturates and 1/25 benzodiazepines), 0/10 anticonvulsants, 0/25 antidepressants, 0/28 neuroleptics, 0/19 narcotic analgesics and antitussives, 6/24 antihistamines (4/20 H1 and 2/4 H2), 11/20 beta blockers, 3/10 antidiabetics and 7/10 central stimulants.

The categorization of the molecules proved to be problematic. The lack of study data is reflected in the number of * categories (50%), this fraction being variable in the different drug groups e.g. antihistamines 0%, benzodiazepines 32%, neuroleptics 71%. The diversity in the study protocols makes an unequivocal classification impossible and emphasizes the need for standardization. It is obvious that the effect on driving ability is dose-dependent and time-related, which makes the use of a single category inadequate; co-ingestion of other medicines or alcohol, and development of tolerance further complicate the problem. Moreover the study data seldom relate the observed psychomotor performances with measured plasma concentrations, while this relation may be important in future traffic legislation. Physicians and pharmacists should take these considerations into account when estimating the driving abilities of their patients.