PATANOL® (olopatadine hydrochloride ophthalmic solution) 0.1 % is a sterile ophthalmic solution containing olopatadine, a relatively selective H1-receptor antagonist and inhibitor of histamine release from the mast cell for topical administration to the eyes. Olopatadine hydrochloride is a white, crystalline, water-soluble powder with a molecular weight of 373.88. The chemical structure is presented below: