A histamine H1 receptor antagonist (Ki = 1.3 nM); selective for histamine H1 over H2 and H3 receptors (Kis = 49 and 12.43 µM, respectively), as well as α1-, α2-, and β1-adrenergic and dopamine D1 and D2 receptors, and the serotonin (5-HT) receptor subtypes 5-HT1 and 5-HT2 at 10 µM; inhibits histamine-induced phosphoinositide turnover and intracellular calcium mobilization in primary HCECs (IC50s = 1.6 and 2.9 nM, respectively); inhibits histamine-stimulated secretion of IL-6, IL-8, and GM-CSF by primary HCECs (IC50s = 2.23, 3.42, and 1.50 nM, respectively); ocular application of emedastine prior to histamine challenge inhibits vascular permeability in guinea pigs