(D) Routes of delivery: Case studies. (7) Ocular delivery of peptide and protein drugs

Researchers have identified a number of peptide and protein drugs which may be of benefit in treating conditions of the eye. However, the clinical use of these agents may be limited by their low bioavailabilities of ocular tissues following topical application. Few studies to date have addressed the issue of corneal penetration enhancement of peptides, not least perhaps because of concerns over the local toxicity of such agents. This paper reviews the ocular delivery of peptides and the ocular use of penetration enhancement. Further, it reports a general approach to corneal penetration enhancement based on the principle that epithelial tight junctions, modulated by the cell cytoskeleton, are a major component of the permeability barrier. The cytoskeletal modulator, cytochalasin B, has been shown to give a similar increase in permeability to other conventional penetration enhancers, but with substantially less disruption of epithelial cell membranes. This agent may act via a paracellular cytoskeletally modulated mechanism, which may form a basis for developing relatively specific, low-toxicity corneal penetration enhancers.