Pharmaceutical Delivery Systems
Drug delivery through the eye is made complicated by physiological barriers. Blinking of the eye, tears and their discharge through the nasolacrimal drainage apparatus add to the impermeability of the cornea. Three delivery routes are basically available: Topical creams and eye drops, systemic delivery through the blood stream and intraocular injection. All three have shortcomings. After administration of eye drops, they remain on the surface of the cornea for a very short time. Only in this period the drug may penetrate the cornea, but poor corneal permeability will allow only a very small portion of active pharmaceutical ingredient to cross it. Only about 1 % of applied drug reaches its target and the rest will be metabolized.
One idea to overcome this is the use of solubility enhancers, such as Phospholipids. It remains to be proven that also hard membranes can be penetrated by them. Some other recent developments in treatment of eye infections and other diseases are described in scientific literature. The most promising solution is the use of drug-charged contact lenses, where the inner layer is coated with drugs in liposomal formulations.