Effect of loratadine on human eosinophil function in vitro.

We investigated the in vitro effect of loratadine, a new nonsedating H1 histamine antagonist, on the eosinophil functions of chemotaxis, superoxide anion (O2-) generation and eosinophil cationic protein (ECP) release, using purified eosinophils obtained from allergic patients. Loratadine significantly attenuated platelet-activating factor (PAF)-induced eosinophil chemotaxis and O2- generation at therapeutic concentrations (equivalent to serum concentrations after single oral administration of 20 mg or 40 mg). Loratadine, however, had no effect on PAF-induced ECP release. These findings suggest that loratadine has a direct inhibitory effect on eosinophil activation and may be beneficial in the therapy of allergic disorders with its anti-allergic properties.