Ketotifen Fumarate USP For Compounding (API)Ketotifen Fumarate USP is an active pharmaceutical ingredient primarily used to treat asthma and allergies. It belongs to a class of drugs called mast cell stabilizers, which work by preventing the release of certain chemicals in the body that cause inflammation and allergy symptoms. Ketotifen fumarate is available in both oral and ophthalmic forms and is also used to relieve symptoms such as itchy or watery eyes associated with allergy