The anti-allergic drug epinastine hydrochloride (Elestat, Allergan) is a prescription only medicine indicated for the treatment of allergic conjunctivitis. As with all medications, there are potential side effects - although uncommon (1 in 10 to 1 in 100 people), there may be a slight burning sensation on application but this temporary and subsides quickly. The epinastine formulation also contains preservatives called benzalkonium chloride and disodium edetate. As with fluorescein sodium, these may cause a self limiting mild allergic reaction. In the unlikely event this does happen the experienced optometrist is immediately available to manage the condition.