Efficacy of the topical antihistamine olopatadine in dogs with experimentally induced allergic conjunctivitis.

OBJECTIVE: The objective of the study was to evaluate the efficacy of a once a day, over the counter antihistamine eye drop, 0.7% olopatadine hydrochloride, in treating or preventing experimentally induced allergic conjunctivitis in dogs. ANIMALS STUDIED: Twelve systemically healthy pet dogs with no known history of allergies or atopic dermatitis, and in the past 12 months had no known ocular abnormalities. PROCEDURES: Dogs were randomly assigned to two groups: "Treatment" which received topical 0.7% olopatadine hydrochloride and "Control" which received artificial tears. Dogs received the antihistamine eye drops before (Phase 1) or after (Phase 2) receiving a compounded ophthalmic histamine solution to induce clinical signs of allergic conjunctivitis. Conjunctival hyperemia, chemosis, follicles, ocular discharge, and ocular pruritus were graded, and photographs were used to document changes. Schirmer tear test values, fluorescein staining, and intraocular pressures were monitored throughout. RESULTS: In both Phase 1 and Phase 2, conjunctival scores increased 10 min after histamine administration (p < .05). There was no difference between maximum overall conjunctival scores between treatment and control groups in either phase or when comparing treatment groups of Phase 1 to Phase 2 (p > .05). However, treatment groups in Phase 2 did have a higher maximum conjunctival chemosis score and spent more time at their maximum chemosis score when compared to Phase 1 (p < .05). CONCLUSION: Olopatadine may be beneficial as prophylaxis to reduce the degree and duration of clinical signs of allergic conjunctivitis.