Recent advances in intraocular drug delivery systems.

Vitreoretinal diseases are refractory to both topical and systemic pharmacological approaches because of specific environment of the eye. That is, the cornea, the sclera, nasolacrimal drainage of tears, frontward stream of aqueous humor, blood-aqueous barrier, and blood-retinal barrier strictly limit penetration and diffusion of drug into the retina. However, recent advances in intraocular drug delivery systems (DDS) have enabled drug to be delivered effectively into the eye. Clinically successful or promising cases involve non-biodegradable implants and inserts, biodegradable inserts and microparticles, intravitreal or sub-Tenon's injection of triamcinolone acetonide, and a photodynamic therapy (PDT) with verteporfin, a photosensitizer. More recently, a variety of pharmacological challenges to treat exudative age-related macular degeneration and macular edema are proceeding into clinical trials, as soon as anti-vascular endothelial growth factor (anti-VEGF) therapies have been proved to be effective by repeated intravitreal injections. In the near future, DDS must be required not only to develop a new treatment modality but also to improve efficacy and/or reduce injection numbers of currently available drugs. Here we introduce controlled release of drug and discussion of recent patents with biodegradable or non-biodegradable implants and drug targeting by modification of systemically administered drug.