Emedastine is a specialty pharmaceutical chemical and selective H1 antihistamine used as an active pharmaceutical ingredient (API) in the treatment of allergic conjunctivitis. It works by blocking histamine H1 receptors, helping to reduce symptoms such as itching, redness, swelling, and tearing of the eyes. Typically formulated into eye drops, it provides rapid onset of action and long-lasting relief with minimal side effects. It is particularly effective for seasonal allergies and other allergic eye conditions.