Epinastine (WAL801), a potent, selective, and orally-active antihistamine and mast cell stabilizer, functions as a histamine H1 receptor antagonist. It also inhibits IL-8 release from human eosinophils, showcasing antiallergic action [1] [2] [3] [4].

Epinastine can displace specific [ 3 H]NC-5Z binding at low concentrations in the locust nervous tissue. Epinastine binds to the honey bees neuronal octopamine receptor with K i of 1.1 nM. Epinastine antagonises octopamine-induced cAMP formation in the insect brain [2]. Epinastine results in an inhibition of histamine release from rat peritoneal mast cells induced by both antigen-antibody reaction and compound 48/80. Epinastine is similarly effective in inhibiting compound 48/80-induced histamine release not only from isolated rat peritoneal mast cells but also from rat mesenterial pieces. Epinastine is effective in inhibiting not only Ca 2+ uptake into lung mast cells in actively sensitized guinea pigs but also Ca 2+ release from the intracellular Ca store of rat peritoneal mast cells exposed to both compound 48/80 and substance P [3]. Epinastine shows a dose- and time-dependent suppressive effect on IL-8, one of the chemokines for eosinophils, released from eosinophils isolated from atopic diseases [4].

In receptor binding studies, Epinastine shows a high affinity to H1-receptors in the guinea pig ileum. Epinastine inhibits histamine-induced reactions in the skin or the lung of rats, dogs and guinea pigs [1].