A histamine H1 receptor antagonist; selective over H3, α1-, α2-, and β-adrenergic, dopamine D2long, serotonin 5-HT2, muscarinic acetylcholine, and benzodiazepine receptors; reduces dye leakage from the nasal passages of sensitized rats (ED50 = 0.03 mg/kg); inhibits histamine-induced bronchoconstriction in the anesthetized dog (ED50 = 3.2 μg/kg); dose-dependently prevents conjunctival vascular hyperpermeability a in guinea pig model of conjunctivitis