MAY 19, 2009
The authors of this study described the creation and use in an animal model of a slow-release drug delivery system that incorporates mitomycin C into an Ahmed drainage implant. In vitro experiments demonstrated that Ahmed implants into which poly(2-hydroxyethyl methacrylate) disks containing mitomycin C were implanted released the drug when flushed with sterile water over an eight-day period, leaving some residual mitomycin C in the implant. In the in vivo portion of the study, rabbits implanted with mitomycin C-releasing drainage devices were found to have blebs that were thinner at the limbal edge, as well as in the bleb roof, compared with blebs from rabbits that received standard implants without mitomycin C. The study elegantly demonstrated the ability to add a drug release system to a glaucoma implant, that mitomycin C can be released through this system and that this can reduce capsule fibrosis in an experimental animal following drainage device implantation. However, as the authors pointed out, these results may not translate to humans.
The in vivo part of the study involved the implantation of standard Ahmed glaucoma valves (AGVs) without mitomycin C into the right eyes of four rabbits and modified AGVs with 0.17 mg, 0.35 mg or 0.8 mg of mitomycin C per gram of dry gel each into the right eyes of six rabbits. Histology of the blebs created over the implants three months after device implantation demonstrated a significant reduction in inflammatory reaction and fibrosis in the rabbits that received modified versus unmodified devices. However, no significant differences were noted between the rabbits implanted with different mitomycin C concentrations. The capsule floors were thick in all of the rabbits, which may have occurred because the implant's contact with the sclera prevents aqueous from reaching this area.
An important factor in glaucoma is that high eye pressure results in the formation of pro-inflammatory substances. This leads to a marked inflammatory response, seen as the hypertensive phase of the bleb cycle. This factor was not taken into account in the rabbit study and in humans certainly could decrease or negate mitomycin C's effects. Studies of the device's use in humans would be useful and informative.
Dr. Freedman is a consultant to Optonol Ltd. and IOP Inc.