Liposomes and Nanoparticles as Ocular Drug Delivery Systems

This chapter deals with liposomes and nanoparticles as novel dosage forms to prolong the residence time of the encapsulated drug within the eye, or used as drug carriers for targeting the drug to ocular tissues. Liposomes are microscopic vesicles composed of membrane-like lipid layers surrounding aqueous compartments. Depending on the composition, liposomes can have positive, negative, or neutral surface charge. The major components of liposomes are lipids, water, drug, and possibly electrolytes. Liposomes have been studied for ocular drug delivery by various ways of administration. Liposome-encapsulated dihydrostrep-tomycin sulfate, a hydrophilic compound, produced lower drug levels in ocular tissues compared to its solution form. The liposome preparation containing dexamethasone valerate provided the highest ocular drug levels, but in the cases of dexamethasone and dexamethasone palmitate, the liposomal form provided a lower drug level than the suspension form. The potential of targeting the delivery of dyes and drugs to specific sites in the eye was investigated using temperature-sensitive liposomes.