Cyclodextrins in ocular drug delivery: theoretical basis with dexamethasone as a sample drug

Cyclodextrins are cyclic oligosaccharides that are able to form water-soluble complexes with many lipophilic drugs. Thus, through cyclodextrin complexation it is possible to formulate lipophilic water-insoluble drugs as aqueous eye drop solutions. The ocular barrier to topical drug delivery into the eye consists of the aqueous tear film and lipophilic epithelium, and most drugs permeate this barrier via passive diffusion. Cyclodextrins enhance permeation of lipophilic drugs through the aqueous tear film to the epithelial surface increasing drug availability immediately to the membrane surface. However, since hydrophilic cyclodextrins and cyclodextrin complexes do not readily permeate lipophilic membranes, excess amounts of cyclodextrin will hamper drug penetration into the eye. Cyclodextrins frequently reduce drug delivery of hydrophilic drugs.