Lipophilic drugs corneal epithelium penetration

The molecular properties of drugs influence which tissues act as reservoirs for them and which act as barriers. Modeling parameters vary considerably for drugs with different penetration and partitioning properties. A lipophilic drug that is also water soluble penetrates the corneal epithelium more readily than does fluorescein, a more hydrophilic drug. 

The corneal epithelium (epithelium cornea anterior layer) is made up of epithelial tissue and covers the front of the cornea (Figure 51.4). It acts as a barrier to protect the cornea, resisting the free flow of fluids from the tears, and prevents bacteria and also therapeutic drugs from entering the epithelium and corneal stroma. The epithelium of the cornea consists of five to six layers of cells packed closely and connected by tight junctions. The cornea is composed of five layers epithelium, Bowman s membrane, stroma, Descemet s membrane, and endothelium, each of alternating polarity. This sandwich-like structure makes the cornea a crucial barrier to most lipophilic and hydrophilic drugs. To penetrate these layers, optimal lipophilicity for the permeant corresponds to log D values of 2-3. °... 

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