New developments in posterior segment drug delivery

New extended delivery methods are under development and in the future should facilitate more effective administration of numerous types of ocular agents, said William F. Mieler, MD, professor and chairman, department of ophthalmology and visual science, University of Chicago.

Speaking during Retina Subspecialty Day, Dr. Mieler said that new methods are needed to lessen the side effects and invasiveness of current methods as well as to reduce systemic side effects.

Listing delivery methods with potential to address these concerns, Dr. Mieler noted that several types of solid implants are on the market already, such as a fluocinolone acetonide intravitreal implant (Retisert, Bausch & Lomb) and a ganciculovir intravitreal implant (Vitrasert, Bausch & Lomb). A subretinal implant system (I-vation, SurModics) has been tested in rabbits and appears to be capable of long-term sustained delivery.

Microspheres of biodegradable polymers are also being explored and could be a means of reducing toxicity during drug delivery, Dr. Mieler said. Studies are under way of delivering pegaptanib sodium (Macugen, OSI/Eyetech/Pfizer), and the feasibility of delivering other products by this route is also being investigated.

Thermoresponsive gels are another promising delivery method; one such product is currently on the market, although not for ophthalmic use, Dr. Mieler said.

At the University of Chicago and the Illinois Institute of Technology, investigators are studying thermoresponsive hydrogels and have developed one product that becomes a gel at body temperature in less than 1 minute. They hope to design a product that can be placed in a 27- to 30-gauge needle and delivered either intravitreally or in the juxtascleral space. The investigators are studying the delivery of bevacizumab (Avastin, Genentech) by this method.

Surgical-based delivery techniques include microcannulation of the suprachoroidal space. In addition, SurModics has developed a subretinal cannula (RetinaJect). A 25-gauge needle is used to transconjunctivally enter the vitreous; a 39-gauge cannula is then advanced to create the retinotomy.

Encapsulated cell technology (Neurotech SA) is also being tested as a novel means of drug delivery and has been shown to be safe and effective in early studies.