Biodegradable intraocular therapies for retinal disorders: progress to date

In general, it is difficult to achieve effective levels of drugs in the vitreous and the retina via topical and/or systemic administration. Intraocular drug delivery systems that achieve longer duration of pharmacological effect with lower administration frequency are urgently needed. Intraocular sustained drug release via implantable devices or injectable particles has been investigated for the treatment of various vitreoretinal disorders. Several non-biodegradable implants are available in clinical practice or in the late developmental phase: Vitrasert (ganciclovir intravitreal implant) for cytomegalovirus retinitis, Retisert (fluocinolone acetonide intravitreal implant) for non-infectious uveitis, Iluvien (fluocinolone acetonide intravitreal implant) for diabetic macular oedema, and NT-501 (a polymer implant containing human retinal epithelial cells genetically modified to secrete ciliary neurotrophic factor) for non-neovascular (dry) age-related macular degeneration and/or retinitis pigmentosa. Many biodegradable formulations, including different shapes of rods, nail-like plugs, discs, or micro- or nanoparticles, have also been investigated, but are not available as yet for the treatment of vitreoretinal disorders. The most developed biodegradable device, Ozurdex (dexamethasone intravitreal implant), is approved as first-line therapy for the treatment of macular oedema following branch retinal vein occlusion or central retinal vein occlusion. In this article, we review the progress of major biodegradable drug delivery systems currently in clinical trials or in experimental stages for the treatment of vitreoretinal disorders.