Use of olopatadine ophthalmic solution and reactivity of histamine skin testing

The significant morbidity of allergic rhinitis and allergic conjunctivitis necessitates that diagnosis must be as accurate as possible. However, the very drugs used to treat allergic symptoms have been found to suppress histamine-induced skin testing, making the diagnosis very challenging. Oral formulations of antihistamines are well known to diminish skin test reactivity, but ocular application has never been studied to our knowledge. This study was performed to evaluate whether olopatadine hydrochloride 0.2% ophthalmic solution suppressed histamine-induced wheals and flares on skin-prick testing. A randomized, double-blinded, placebo-controlled, single-center, cross-over pilot study was performed that compared histamine-induced wheal and flare areas after 7-10 days of treatment with both olopatadine 0.2% ophthalmic solution and artificial tears, allowing for a 7- to 10-day washout period between medications. From a total of 24 patients randomized, 21 subjects completed the study, 86% of whom were female. There were no statistically significant differences among both the wheal and the flare areas when comparing treatment with olopatadine and placebo, under the 5% significance level. Although characterized by a small sample size and a preponderance of female subjects, our data suggest that olopatadine does not suppress wheal and flare areas during allergy testing, and discontinuation in preparation for skin-prick testing does not appear to be necessary.