Epinastine (WAL801) is a selective and orally active histamine H1 receptor antagonist primarily used for treating allergic conjunctivitis. Epinastine also inhibits the release of IL-8 from human eosinophils and acts as a mast cell stabiliser to prevent the release of histamine.

Methods: Epinastine (1 nM-100 μM) was used to treat isolated human skin mast cells, basophils, and eosinophils induced by different secretagogues to investigate whether it could affect the in vitro activation of these cells. Results: Epinastine (1 nmol/l to 100 μmol/l) did not significantly inhibit histamine release from basophils induced by either immune (anti-IgE, leukocyte antigen A, interleukin-3 and interleukin-5) or non-immune (A23187, ionomycin, 12-o-tetradecanoyl-phorbol-13-acetate, C5a, methylformyl-leucyl-phenylalanine) stimulation. [1]

In receptor binding studies, Epinastine demonstrates high affinity for H1-receptors in the guinea pig ileum and effectively inhibits histamine-induced reactions in the skin and lungs of rats, dogs, and guinea pigs [1].