Antihistamines in ocular allergy: are they all created equal?

Use of topical antihistamines in the treatment of allergic conjunctivitis has evolved over the past several decades as our knowledge of the nature of the underlying disease has progressed. Formulations for the eye typically employ H(1)-receptor antagonists with a dual action, both directly as competitors for histamine receptor occupancy and as mast cell-stabilizing agents. Many of these compounds also display activity against late-phase allergic symptoms. Of the newest available drugs, several have a prolonged duration of action allowing once-daily dosing. Future development is likely to focus on long-acting agents such as these and on drugs that can target additional histamine receptor subtypes.