Ketotifen

Ketotifen is a second-generation H1-antihistamine and mast cell stabilizer. It is most commonly sold in as a salt of Fumaric Acid, Ketotifen fumarate, and is available in two forms. In its ophthalmic form, it is used to treat allergic conjunctivitis, or the itchy red eyes caused by allergies. In its oral form, it is used to prevent asthma attacks. Side effects include drowsiness, weight gain, dry mouth, irritability, and increased nosebleeds.

The drug is marketed as ophthalmic solutions under the brand names Zaditor/Zaditen (Novartis), Alaway (Bausch and Lomb), Zyrtec Itchy-Eye Drops, and Claritin Eye. A generic version of Novartis' Zaditor, ketotifen fumarate ophthalmic solution, 0.025%, is available from Perrigo and distributed as store brands.

General information
Ketotifen relieves and prevents eye itchiness and/or irritation associated with most seasonal allergies. It starts working within minutes after administering the drops. The drug has not been studied in children under three. The mean elimination half life is 12 hours. Besides its anti-histaminic activity, it is also a functional leukotriene antagonist and a phosphodiesterase inhibitor.

Off-Label Use
Ketotifen is used to up-regulate beta-2 adrenergic receptors down-regulated by beta-2 adrenergic agonists. It upregulates adrenergic receptors due to its phosphodiesterase inhibition, since a phosphodiesterase enzyme is involved in their feedback/homeostatic pathway.