BCNU in silicone oil in proliferative vitreoretinopathy: I. Solubility, stability (in vitro and in vivo), and antiproliferative (in vitro) studies

Safety and feasibility of a novel intravitreal tamponade using a silicone oil/acetyl-salicylic acid suspension for proliferative vitreoretinopathy: first results of the Austrian Clinical Multicenter Study

BACKGROUND

The safety and efficacy of a new surgical method of intravitreal tamponade using silicone oil suspended with aspirin (acetylsalicylic acid) was investigated for the treatment of proliferative vitreoretinopathy.

METHODS

The study was designed as a prospective, randomized, controlled, double-blind multicenter study. A total of 29 patients were included; 15 patients were treated with the silicone oil suspended with aspirin, and 14 patients represented the control group receiving only silicone oil. A standard three-port pars plana vitrectomy was performed in 29 eyes of 29 patients. In cases in which the natural lens was present, simultaneous phacoemulsification was required. The control group received as standard therapy a vitreous tamponade with pure 5000 mPas silicone oil and the treatment group received silicone oil containing 0.2 mg/ml aspirin (AS SiO). At 6 months after surgery, the tamponade was removed from all eyes. The main outcome measure was the incidence of retinal redetachment requiring reoperation. Secondary outcome measures were visual acuity and ophthalmic examination results.

RESULTS

The rate of redetachment, defined as the primary outcome parameter, was the same for both groups. The AS SiO was well tolerated and remained clear during the 6-month study period. Clinical examination revealed no signs of local or systemic adverse effects. The visual acuities were well matched before inclusion in the study and there were no significant differences during the follow-up period and in the final visual outcome between the two groups.

CONCLUSIONS

Aspirin delivery by intravitreal silicone oil in the human eye is safe and also may provide a delivery vehicle for other antiproliferative agents to the posterior pole.

Intravitreal injection of therapeutic agents

BACKGROUND

Intravitreal injection (IVI) with administration of various pharmacological agents is a mainstay of treatment in ophthalmology for endopthalmitis, viral retinitis, age-related macular degeneration, cystoid macular edema, diabetic retinopathy, uveitis, vascular occlusions, and retinal detachment. The indications and therapeutic agents are reviewed in this study.

METHODS

A search of the English, German, and Spanish language MEDLINE database was conducted. A total of 654 references spanning the period through early 2008 were individually evaluated.

RESULTS

The advantage of the IVI technique is the ability to maximize intraocular levels of medications and to avoid the toxicities associated with systemic treatment. Intravitreal injection has been used to deliver several types of pharmacological agents into the vitreous cavity: antiinfective and antiinflammatory medications, immunomodulators, anticancer agents, gas, antivascular endothelial growth factor, and several others. The goal of this review is to provide a detailed description of the properties of numerous therapeutic agents that can be delivered through IVI, potential complications of the technique, and recommendations to avoid side effects.

CONCLUSION

The IVI technique is a valuable tool that can be tailored to the disease process of interest based on the pharmacological agent selected. This review provides the reader with a comprehensive summary of the IVI technique and its multitude of uses.

Slow release of acetylsalicylic acid by intravitreal silicone oil

PURPOSE

To assess in vitro the potential of silicone oil as a delivery system for acetylsalicylic acid (ASA) and to evaluate in vivo the pharmacokinetic distribution of salicylic acid (SA) in the eye.

METHODS

In an experimental model ASA/silicone oil suspension mixed to a concentration of 1.67 mg/mL was investigated for release rate of ASA and SA. In vivo vitrectomy and intravitreal injection of two different ASA/silicone oil suspensions, both mixed to a concentration of 1.67 mg/mL, was performed on two groups, A and B, of New Zealand white rabbits. Salicylic acid concentrations in ocular tissues, aqueous, vitreous, and blood plasma were evaluated at 6 hours, 24 hours, and 5 days using high performance liquid chromatography.

RESULTS

Salicylic acid was detected in all tissues. The highest levels were obtained in the vitreous: 745.4 microg/mL (A) and 640.0 microg/mL (B) at 6 hours. The retina followed with 332.9 ng/mg (A) and 281.3 ng/mg (B) at 6 hours and 31.6 ng/mg (A) and 48.1 ng/mg (B) at day 5. The maximum blood plasma levels were 5.2 microg/mL.

CONCLUSION

Silicone oil is an efficacious delivery system of ASA in vitro and in vivo. Higher concentrations of SA were found in all ocular tissues and fluids when compared to intravenous administration of maximum doses.

Biomaterials used in the posterior segment of the eye

The treatment of posterior segment eye disease and related conditions has improved greatly in recent years with the advent of new therapies, materials and devices. Vitreoretinal conditions, however, remain significant causes of blindness in the developed world. Biomaterials play a major role in the treatment of many of these disorders and the success rate of vitreoretinal surgery, especially in the repair of retinal detachment and related conditions, would increase with the introduction of new and improved materials. This review, which focuses on disorders that feature retinal detachment, briefly describes the anatomy of the eye and the nature and treatment of posterior segment eye disorders. The roles, required properties and suitability of the materials used in vitreoretinal surgery as scleral buckles, tamponade agents or drug delivery devices, are reviewed. Experimental approaches are discussed, along with the methods used for their evaluation, and future directions for biomaterial research in the posterior segment of the eye are considered.

Chemotherapeutic drugs released from polymers: distribution of 1,3-bis(2-chloroethyl)-1-nitrosourea in the rat brain

PURPOSE

The distribution of [(3)H]BCNU following release from polymer implants in the rat brain was measured and evaluated by using mathematical models.

METHODS

[(3)H]BCNU was loaded into p(CPP:SA) pellets, which were subsequently implanted intracerebrally in rats; [(3)H]BCNU was also directly injected into the brains of normal rats and rats with intracranially transplanted 9L gliomas. Concentrations of [(3)H]BCNU on coronal sections of the brain were measured by autoradiography and image processing. For comparison, the kinetics of [(3)H]BCNU release from the p(CPP:SA) polymer discs into phosphate-buffered saline were also measured.

RESULTS

High concentrations of BCNU (corresponding to 1 mM) were measured near the polymer for the entire 30-day experiment. The penetration distance, defined as the distance from the polymer surface to the point where the concentration of [(3)H]BCNU in the tissue had dropped to 10 percent of the maximum value, was determined: penetration distance was 5 mm at day 1 and 1 mm at days 3 through 14. Local concentration profiles were compared with a mathematical model for estimation of the modulus phi (2), an indicator of the relative rate of elimination to diffusion in the brain. From day 3 to 14, phi(2) was 7, indicating that BCNU elimination was rapid compared to the rate of diffusive penetration into tissue. The enhanced penetration observed on day 1 appears to be due to convection of extracellular fluid caused by transient, vasogenic edema, which disappears by day 3.

CONCLUSIONS

Polymer implants produce very high levels of BCNU in the brain, but BCNU penetration into brain tissue is limited due to rapid elimination.