The effects of single acute therapeutic doses of dexchlorpheniramine, alone and in combination with alcohol on human performance in driving-related tests: exploration of the relationships between performance impairment and blood concentrations of dexchlorpheniramine and alcohol

A placebo controlled study was carried out which examined the dose-response relationships for three therapeutic doses of the antihistamine, dexchlorpheniramine (1, 2 & 4 mg), alone and in combination with a 'social' dose of alcohol (0.75 g/kg). The study was designed to examine the relationships between impairment in psychomotor tasks which examine aspects of driving skills and the concentrations of dexchlorpheniramine and alcohol in the blood. Blood samples (to establish pharmacokinetic parameters) were taken at regular intervals across the 250 minute sessions and psychomotor testing (to determine pharmacodynamic parameters) was carried out at similar time intervals. The results of this study indicate that although some individuals may be significantly impaired after a single therapeutic dose of dexchlorpheniramine (2 or 4 mg), they do not necessarily experience subjective markers of impairment, such as sedation and a perceived reduction in coordination. This is likely to pose difficulties for some drivers in recognising dexchlorpheniramine induced driving impairment.