New developments in posterior segment drug delivery

New extended delivery methods are under development and in the future should facilitate moreeffective administration of numerous types of ocular agents, said William F. Mieler, MD, professorand 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 theside 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 severaltypes of solid implants are on the market already, such as a fluocinolone acetonide intravitrealimplant (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 becapable of long-term sustained delivery.

Microspheres of biodegradable polymers are also being explored and could be a means of reducingtoxicity 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 alsobeing investigated.

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

At the University of Chicago and the Illinois Institute of Technology, investigators are studyingthermoresponsive hydrogels and have developed one product that becomes a gel at body temperature inless than 1 minute. They hope to design a product that can be placed in a 27- to 30-gauge needle anddelivered either intravitreally or in the juxtascleral space. The investigators are studying thedelivery 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 totransconjunctivally enter the vitreous; a 39-gauge cannula is then advanced to create theretinotomy.

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