Delivery systems for intraocular routes

Intravitreal drug delivery has been developed to treat posterior segment diseases because the blood-ocular barrier prevents treatment by topical, systemic, or subconjunctival routes from attaining therapeutic levels in the vitreous. Endophthalmitis, uveitis, proliferative vitreoretinopathy, and viral retinitis are treated by intravitreal injection. Efforts to sustain drug delivery have included encapsulation of drugs in liposomes (made of lipids) or microspheres (made of polymers). In many instances the drug's toxicity to the retina was reduced and the clearance time was slowed. However, these methods cause clouding of the vitreous and can prolong drug delivery for only one month. Implantable devices have been used, such as an osmotic minipump, a drug pellet coated with polyvinyl alcohol and ethylene vinyl acetate, and polysulfone capillary fiber. Biodegradable devices are under investigation, including a drug matrix and a porous reservoir system, both made of polymers; these devices would not require surgical removal.