Since most first-generation
antihistamines have undesirable
sedative effects on the central nervous systems (CNS), newer (
second-generation) antihistamines have been developed to improve patients' quality of life. However, there are few reports that directly compare the antihistaminic efficacy and impairment of psychomotor functions. We designed a double-blind, placebo controlled, crossover study to concurrently compare the clinical effectiveness of
promethazine, a first-generation
antihistamine, and
fexofenadine and
olopatadine,
second-generation antihistamines, by measuring their potency as peripheral inhibitors of
histamine-induced wheal and flare. Further, we investigated their
sedative effects on the CNS using a battery of psychomotor tests. When single therapeutic doses of
fexofenadine (60 mg),
olopatadine (5 mg) and
promethazine (25 mg) were given in a double-blind manner to 24 healthy volunteers, all
antihistamines produced a significant reduction in the wheal and flare responses induced by
histamine. In the comparison among
antihistamines,
olopatadine showed a rapid inhibitory effect compared with
fexofenadine and
promethazine, and had a potent effect compared with
promethazine. In a battery of psychomotor assessments using critical flicker fusion, choice reaction time, compensatory tracking, rapid visual information processing and a line analogue rating scale as a subjective assessment of sedation,
promethazine significantly impaired psychomotor function.
Fexofenadine and
olopatadine had no significant effect in any of the psychomotor tests.
Promethazine,
fexofenadine and
olopatadine did not affect behavioral activity, as measured by wrist actigraphy. These results suggest that
olopatadine at a therapeutic dose has greater antihistaminergic activity than
promethazine, and
olopatadine and
fexofenadine did not cause cognitive or
psychomotor impairment.