Epinastine HCl is primarily used as an antihistamine in ophthalmic solutions to treat allergic conjunctivitis. It works by blocking histamine H1 receptors, reducing symptoms like itching, redness, and swelling in the eyes. The application involves administering the solution directly into the eyes, typically one or two drops per affected eye, twice daily. It is suitable for both seasonal and perennial allergic conjunctivitis, providing relief without significant drowsiness, as it has limited penetration into the central nervous system. Additionally, its mast cell-stabilizing properties help prevent the release of histamine, offering a dual mechanism of action for effective allergy management.