Pharmacology: Pharmacodynamics: Ketotifen is a histamine H1-receptor antagonist. Ketotifen also inhibits the release of mediators (e.g. histamine, leukotrienes, prostaglandins, PAF) from cells involved in type 1, or immediate allergic reactions (mast cells, eosinophils, basophils and neutrophils). Ketotifen also reduces chemotaxis, activation and degranulation of eosinophils. cAMP levels increased by phosphodiesterase inhibition can contribute to the cell-stabilising effect of ketotifen.
The antihistamine effect of Zaditen/Zaditen SDU eye drops has a rapid onset following instillation into the eye and persists for 8-12 hours.
Zaditen/Zaditen SDU eye drops alleviate the symptoms of allergic conjunctivitis, such as pruritus and hyperaemia.
Pharmacokinetics: In a pharmacokinetics study conducted in 18 healthy volunteers with Zaditen/Zaditen SDU eye drops plasma levels of ketotifen after repeated ocular administration for 14 days were in most cases below the limit of quantitation (20 pg/ml).
After oral administration, ketotifen is eliminated biphasically with an initial half-life of 3 to 5 hours and a terminal half-life of 21 hours. About 1% of the substance is excreted unchanged in the urine within 48 hours and 60 to 70% as metabolites. The main metabolite is the practically inactive ketotifen N-glucuronide.