Epinastine HCl is primarily used as an antihistamine in ophthalmic formulations to treat allergic conjunctivitis. It works by blocking H1 histamine receptors and stabilizing mast cells, which helps prevent the release of histamine and other mediators of allergic reactions. This dual action reduces symptoms such as itching, redness, and swelling of the eyes caused by allergens like pollen, dust, or pet dander. It is commonly administered as eye drops, providing fast relief with once or twice-daily dosing. Due to its selective action and low systemic absorption, it has a favorable safety profile with minimal side effects, making it suitable for both short-term and long-term management of ocular allergies.