Emedastine- 13 C,d 3 (fumarate) is the 13 C- and deuterium labeled Emedastine. Emedastine is an orally active, selective and high affinity histamine H1 receptor antagonist with a Ki value of 1.3 nM. Emedastine is a benzimidazole derivative with potent antiallergic properties and used for allergic rhinitis, allergic skin diseases and allergic conjunctivitis.