Topical drug delivery to the posterior segment of the eye: The effect of benzalkonium chloride on topical dexamethasone penetration into the eye in vivo

Benzalkonium chloride (BAC) is a quaternary ammonium compound with antibacterial properties. It is used as preservative in aqueous eye drops but studies have shown that it can also act as a penetration enhancer increasing drug permeation from the eye surface into the eye. Here the effect of BAC on dexamethasone permeation into the eye was investigated in vivo. Dexamethasone in aqueous cyclodextrin-based eye drops with and without BAC, were administered to rabbits and the dexamethasone concentration in several eye tissues determined 2 h after the administration. The study shows that BAC has no effect on the drug penetration from the eye surface into the eye. The penetration enhancing effect of BAC is mainly based on in vitro observations where BAC is in contact with isolated epithelial membrane (e.g., cornea) for several hours. Under in vivo conditions, BAC is rapidly washed from the eye surface with the tear fluid before it can penetrate into the epithelia and disrupt its structure sufficiently to allow for enhanced drug permeation into the eye.