A repeated dose comparison of the side effects of five antihistamines on objective assessments of psychomotor performance, central nervous system arousal and subjective appraisals of sleep and early morning behaviour.

The side effects of five antihistamines (chlorpheniramine maleate, mebhydrolin, clemastine hydrogen fumarate, Tavegil; ketotifen, and promethazine hydrochloride) were measured on subjective assessments of sleep and the integrity of early morning behaviour and objective assessments of complex psychomotor behaviour and central nervous system arousal. Fifty consenting volunteers each received one of the five preparations for a period of four days with the subjective effects being reported on a set of 10 cm line visual analogue scales and the objective assessments being made via a computer assisted reaction time task and critical flicker fusion thresholds. Chlorpheniramine, 4 mg t.d.s. for four days, produces a significant impairment in critical flicker fusion thresholds with respect to pretreatment baselines but none of the preparations showed any significant impairment in complex reaction time assessments. The subjective assessments of sleep and early morning hangover showed mebhydrolin and clemastine to be free from detrimental side effects, but promethazine and chlorpheniramine produce significant impairments in the integrity of early morning behaviour.