Levocetirizine and cetirizine are powerful non-sedating antihistamines that potently inhibit or reduce histamine-induced weal and flare reaction.
Researchers at the University of Surrey, Guildford, England, compared the inhibitory effects of acute and sub-chronic doses of levocetirizine and cetirizine, as well as another antihistamine drug, loratadine, versus placebo.
So that psychometric assessments were sensitive to impairment, the antihistamine agent promethazine was used as a control, validating the sensitivity of various tests to the effects of the study drugs on the central nervous system.
Twenty healthy volunteers aged 18-50 years were recruited into this five-way, double-blind, crossover study. They received levocetirizine 5 mg, cetirizine 10 mg, loratadine 10 mg, promethazine 30 mg and placebo once daily for four days.
For each treatment condition, they were assessed by psychometric tests and a pinprick weal and flare response to 100 mg/ml histamine solution at baseline and at one, two, three, four, six, eight, 10 and 12 hours on days one and four. On days two and three, the volunteers took medication out of the unit at pre-designated times.
The psychometric tests comprised critical flicker fusion, choice reaction time, a continuous tracking task and subjective rating scales for sedation.
In this study, where psychometric assessments were sensitive to impairment, neither levocetirizine, cetirizine nor loratadine were distinguishable from placebo in any of the objective and subjective tests at any time on days one or four.