Routes for Drug Delivery: Sustained-Release Devices.

Several different technologies exist for sustained-release drug delivery devices, including: (1) nonbiodegradable implants; (2) biodegradable implants; (3) micro- and nanoparticles; (4) liposomes, and (5) encapsulated cell technology (ECT). Currently, the only sustained-release devices approved by the Food and Drug Administration are the ganciclovir implant for the treatment of cytomegalovirus retinitis, the fluocinolone acetonide implant for the treatment of noninfectious posterior uveitis and the dexamethasone implant for the treatment of diabetic macular edema or noninfectious posterior uveitis. The first two implants are nonbiodegradable and require surgical placement, whereas the dexamethasone implant is biodegradable, and can be shaped and injected using a small-gauge needle or applicator into the vitreous. ECT, currently in a phase II clinical trial, utilizes modified retinal pigment epithelium cells to produce protein drug molecules in the vitreous. The microparticle, nanoparticle and liposome technology currently in development may offer the most flexibility for prolonged drug release and combination therapy for retinal diseases.