[Bioavailability of drugs applied to the eye externally]

There are following forms of the most frequently used ocular therapeutics: eye drops, ointments and inserts. In dependence on the physico-chemical properties of the therapeutical substance and the kind of disease one has to formulate the form of the drug in the manner to obtain its maximal bioavailability. By increasing their viscosity one can keep the watery solutions in the conjunctival sac for around 60 min. The time of the contact of the drug given in the form of suspension is limited mainly by the viscosity of the solution and the size of the molecules suspended in it. The ointments stay on the surface of the eye up to 2 hours. The ocular inserts secure a steady flow of the therapeutical substance up to 7 days. The compounds penetrate to the anterior chamber aqueous mainly through the cornea. Therefore the physiological factors of the lacrimal fluid, the properties of the cornea are influencing the penetration of the corneo-chamber barrier by the therapeutical substance.