Double-masked, randomized, placebo-controlled clinical study of the mast cell-stabilizing effects of treatment with olopatadine in the conjunctival allergen challenge model in humans

Abstract

Objective: The purpose of this study was to assess the effects of olopatadine on the release of mast cell-derived mediators after conjunctival allergen challenge (CAC) in humans. Methods: This was a double-masked, randomized, placebo-controlled clinical trial. Subjects with a clinical history of seasonal allergic conjunctivitis (but no current symptoms or treatment at baseline) were studied. At visit 1, subjects underwent bilateral CAC with increasing doses of allergen every 15 minutes until a significant clinical reaction was obtained, then were evaluated at 15 minutes and 5 hours after CAC. At visit 2 (2 weeks later), subjects were rechallenged to confirm the allergic response. Subjects exhibiting positive reactions at both visits (at both 15 minutes and 5 hours) were randomized and instructed to treat 1 eye with olopatadine and the contralateral eye with placebo (commercially available artificial tears) in a double-masked fashion twice daily for the 5 days immediately preceding visit 3. At visit 3, bilateral CAC was performed with the same dose as at visit 2. Itching and redness were recorded. Tear cytology for inflammatory cell counts (ie, neutrophils, eosinophils, and lymphocytes) was carried out using precolored slides, and cell numbers were counted at 400x magnification. Tear histamine was assessed using radioimmunoassay histamine measurement. Intercellular adhesion molecule (ICAM)-1/CD54 monoclonal antibody was used for immunohistochemical staining of conjunctival epithelial cells obtained by impression cytology.