The use of bioerodible polymers and daunorubicin in glaucoma filtration surgery

Oxidized porous silicon particles covalently grafted with daunorubicin as a sustained intraocular drug delivery system

PURPOSE

To test the feasibility of covalent loading of daunorubicin into oxidized porous silicon (OPS) and to evaluate the ocular properties of sustained delivery of daunorubicin in this system.

METHODS

Porous silicon was heat oxidized and chemically functionalized so that the functional linker on the surface was covalently bonded with daunorubicin. The drug loading rate was determined by thermogravimetric analysis. Release of daunorubicin was confirmed in PBS and excised rabbit vitreous by mass spectrometry. Daunorubicin-loaded OPS particles (3 mg) were intravitreally injected into six rabbits, and ocular properties were evaluated through ophthalmic examinations and histology during a 3-month study. The same OPS was loaded with daunorubicin using physical adsorption and was evaluated similarly as a control for the covalent loading.

RESULTS

In the case of covalent loading, 67 ± 10 μg daunorubicin was loaded into each milligram of the particles while 27 ± 10 μg/mg particles were loaded by physical adsorption. Rapid release of daunorubicin was observed in both PBS and excised vitreous (~75% and ~18%) from the physical adsorption loading, while less than 1% was released from the covalently loaded particles. Following intravitreal injection, the covalently loaded particles demonstrated a sustained degradation of OPS with drug release for 3 months without evidence of toxicity; physical adsorption loading revealed a complete release within 2 weeks and localized retinal toxicity due to high daunorubicin concentration.

CONCLUSIONS

OPS with covalently loaded daunorubicin demonstrated sustained intravitreal drug release without ocular toxicity, which may be useful to inhibit unwanted intraocular proliferation.

Drug delivery systems for the eye

Topical and systemic administration of drugs to the eye is highly inefficient and there is a need for controlled, sustained release, particularly for conditions that affect the posterior segment. Various nonimplantable and implantable drug delivery devices have been developed. Colloidal carriers may allow targeted drug delivery and afford protection to substances that are sensitive to degradation, particularly RNA/DNA-based treatments. Gene therapy and cell transplantation are also starting to emerge as alternatives to conventional pharmacological treatment. There is the potential to use existing ocular devices to deliver drugs. In order to exploit this opportunity, modifications to drugs and devices, along with clarification of the appropriate drug dose, must be undertaken. This review will describe some of the treatment options for ocular disease and barriers to drug delivery, discuss the design of existing drug delivery systems and highlight some of the research into combining drug delivery with existing ocular medical devices.

Modulation of wound healing during and after glaucoma surgery

Following all types of glaucoma filtration surgery (GFS), scarring still poses the major threat to long-term success. The healing and scarring determine the percentage of patients achieving low final intraocular pressures (IOPs) that are associated with virtually no glaucoma progression. The use of antifibrotic agents to inhibit scarring of trabeculectomy blebs is now a well-established clinical practice. Unfortunately, severe complications such as leakage, infection, hypotony, and endophthalmitis with complete loss of vision may occur. In addition, surgery still fails in some individuals despite maximal doses of current antifibrotics. Better therapeutic agents are needed. Many promising new agents are being evaluated clinically and in vitro. In this chapter, we will discuss our current understanding of the wound healing process after glaucoma surgery and promising new treatment modalities.

Intraocular implants for extended drug delivery: therapeutic applications

An overview of ocular implants with therapeutic application potentials is provided. Various types of implants can be used as slow release devices delivering locally the needed drug for an extended period of time. Thus, multiple periocular or intraocular injections of the drug can be circumvented and secondary complications minimized. The various compositions of polymers fulfilling specific delivery goals are described. Several of these implants are undergoing clinical trials while a few are already commercialized. Despite the paramount progress in design, safety and efficacy, the place of these implants in our clinical therapeutic arsenal remains limited. Miniaturization of the implants allowing for their direct injection without the need for a complicated surgery is a necessary development avenue. Particulate systems which can be engineered to target specifically certain cells or tissues are another promising alternative. For ocular diseases affecting the choroid and outer retina, transscleral or intrasscleral implants are gaining momentum.

Evaluation of efficacy and safety of daunorubicin in glaucoma filtering surgery

PURPOSE

To evaluate the intraocular pressure (IOP)-lowering effect and ocular side effects of daunorubicin (DNR) in drug-modulated trabeculectomy.

METHODS

A prospective pilot study was conducted in which 21 Asian patients of Indian origin with high risk factors for failure of trabeculectomy were recruited. An approval from research ethics committee and an informed consent from every patient included in the study were obtained. DNR, an antimetabolite with known antifibroblastic action was used intraoperatively. A limbus-based conjunctival flap followed by conventional trabeculectomy was performed in all eyes. During trabeculectomy, a cellulose sponge soaked in 0.2 mg/ml DNR was applied for 3 min at the proposed site of trabeculectomy before preparation of the partial thickness scleral flap. A regular follow-up was carried out for 1 year where parameters including visual acuity, IOP by applanation tonometry, and slit lamp examination were performed on each visit. An IOP of 21 mmHg or less was taken as criteria for success.

RESULTS

Following DNR trabeculectomy, the IOP was lowered from baseline preoperative value of 36.19+/-5.9 to 16.05+/-2.52 mmHg at the end of 1 year. Success rate of 81% (17 out of 21 patients) was noted. None of the patients developed corneal epithelial toxicity, hypotony maculopathy, or choroidal detachment.

CONCLUSION

The authors feel that intraoperative daunorubicin is safe and effective in lowering IOP in high-risk surgical cases of glaucoma. However, a much larger cohort study over a considerable number of years will eventually demonstrate its safety.

Formulation factors for preparing ocular biodegradable delivery system of 5-fluorouracil microparticles

Microparticles containing 5-fluorouracil (5-FU) were prepared using poly(DL-lactide-co-glycolide) with an oil-in-oil emulsion/solvent extraction technique. Particle characteristics including size distribution, 5-FU loading efficiencies, in vitro release and degradation were investigated. The dispersed phase was composed of PLG dissolved in dichloromethane, and the continuous phase was paraffin oil containing lecithin. 5-FU was successfully entrapped in the microparticles with trapping efficiencies up to 76%, loading level 10% w/v, and particle size 3 microm. Release profiles of 5-FU loaded microparticles were determined to follow a first-order-time relationship. An optimized preparation of 5-FU microparticles was achieved and was capable of controlling the release of 5-FU over 21 days with an in vitro delivery rate of 0.4 microg 5-FU/mg particles/day in the study. Preliminary animal studies indicated that the 5-FU loaded microparticles as an ocular delivery system showed no ocular toxicity and no significant inflammatory response in rabbits for 2 months. The 5-FU loaded microparticles approach, with PLG, might be a potential for the application of long-term delivery of hydrophilic drugs in the eye.