Inhibitory effect of epinastine on bronchoconstriction induced by histamine, platelet activating factor and serotonin in guinea pigs and rats.

Effects of epinastine ((+/-)-3-amino-9,13b-dihydro-1H-dibenz[c,f]imidazo[1,5-a]azepine hydrochloride, WAL 801 CL, CAS 80012-43-7) and reference drugs on bronchoconstriction induced by histamine, platelet activating factor (PAF) and serotonin were studied in guinea pigs and rats. Oral administration of epinastine resulted in a potent inhibition on bronchoconstriction induced by all three bronchoconstrictor agents, and especially, an inhibitory effect on histamine-induced response was remarkable. The effect of epinastine was stronger than that of ketotifen in inhibiting the responses induced by both PAF and serotonin. However, the extent of inhibition in the latter was less remarkable than that seen after histamine. Azelastine was 1.36-4.57 times less potent than epinastine in inhibiting the bronchoconstriction induced by either bronchospasmogen. Although promethazine displayed inhibitory effects on the responses induced by histamine, PAF and serotonin, the inhibiting potency was distinctly inferior to that of epinastine.