Sustained release of 5-fluorouracil from ethylene acetate copolymer

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.

Maintaining a near zero-order drug delivery from minidose reservoirs: simultaneous drug diffusion and binary vehicle evaporation

The purpose of this study was to develop a new design for transdermal system that provides a nearly constant drug delivery rate for the desired period of time in the absence of a large excess of drug in the donor reservoir. Simultaneous drug diffusion and aqueous binary vehicle evaporation has been investigated as a means of maintaining constant drug delivery from minidose reservoirs. Benzocaine was used as the model drug and water-ethanol mixtures as the binary vehicles. Benzocaine is much more soluble in ethanol than in water. Simultaneous diffusion-evaporation experiments were conducted using the water-ethanol mixture saturated with benzocaine as the minidose-reservoir. The reservoir vehicle was allowed to evaporate through a permselective membrane so as to maintain drug saturation in the vehicle even though the drug mass in the donor reservoir was constantly decreasing. Saturation activity of drug is maintained during donor depletion of drug by the selective loss of alcohol from the donor solvent, which concomitantly lowers the solubility. The superiority of the evaporable binary vehicle over a conventional sealed system was demonstrated by achieving near zero-order drug delivery with minimum drug remaining. A theoretical model was developed to predict drug flux, drug amount delivered, reservoir solvent volume and composition, and drug solubility during the two simultaneous processes of drug release and preferential solvent evaporation. Experimental data are in good agreement with theoretical calculations.

In vitro and in vivo studies of subcutaneous hydromorphone implants designed for the treatment of cancer pain

Unrelieved cancer pain remains a significant problem worldwide. Patients receive inadequate analgesia for a variety of complex and multifactorial reasons. Limited availability of opioids secondary to concerns about potential diversion of these medications for illicit use and poor compliance with oral regimens are significant factors in many countries. This study was designed to develop and test an implantable opioid delivery device capable of releasing a potent opioid subcutaneously at a continuous rate for 4 weeks. A low temperature solvent casting technique was used to formulate ethylene vinyl acetate (EVA) copolymer disks containing 50% hydromorphone by weight. The release characteristics of disks of different height and diameter, coated and uncoated, and with and without a central uncoated channel were studied. The effect of temperature and pH were also evaluated. In vitro assessments were conducted in phosphate buffer using UV spectrophotometry. In vivo studies employed New Zealand White Rabbits and a radioimmunoassay. Plasma levels following hydromorphone delivery by polymer, osmotic pump, and intravenous administration were compared. In vitro, uncoated EVA polymer disks measuring 1.05 cm in diameter and 0.27 cm in height released an initial large burst of hydromorphone. Coating the disks with 100-200 microM of poly(methyl-methacrylate) prevented drug egress from the polymer. A central uncoated channel measuring 1.25 mm in diameter in an otherwise coated polymer virtually eliminated the initial burst of drug release and provided near zero-order hydromorphone release at an average rate of 164 micrograms per hour for 4 weeks. Doubling the height of the polymer approximately doubled the release rate while doubling the diameter of the polymer extended the duration of drug release to over 8 weeks. In rabbits, stable plasma hydromorphone concentrations (23-37 ng/ml) were sustained for 4 weeks following implantation of 2 polymers with an uncoated central channel. No initial burst of hydromorphone release was noted. Increasing the number of polymers produced sustained and predictable increases in plasma hydromorphone concentrations. Plasma levels were similar with subcutaneous hydromorphone delivered by polymer and osmotic pump and much less variable than with intravenous bolus hydromorphone. A uniquely configured implantable drug delivery device has been developed using materials which are approved for human use. It safely and reproducibly releases hydromorphone for weeks in vitro and in vivo without an initial burst of drug release. Varying the thickness, diameter, and number of implants provides flexibility in the release rate and duration of release. This implantable opioid delivery device could provide a sustained subcutaneous infusion of hydromorphone to patient with cancer pain in developed and developing nations without pumps, catheters, or extensive outpatient support services. In addition, it should improve compliance and reduce concern regarding illicit diversion of opioids.

Manufacture and release characteristics of Elvax polymers containing glutamate receptor antagonists

Implantable sustained-release polymers offer an alternative to osmotic minipumps for the local delivery of drugs to specific brain areas. Here we describe the production of Elvax polymers containing a range of glutamate receptor antagonists and the quantitative characterization of their release properties. Sections of Elvax (200 or 400 microns), prepared by a dimethyl sulphoxide-based method, containing the NMDA antagonist MK-801 or the non-NMDA antagonist CNQX exhibited similar release profiles: an initial 2-week burst followed by a slow decline in release rate over the next 6 weeks. Differences in slice preparation method and thickness or drug concentration and solubility all led to alterations in the level of drug release, but not the overall exponential nature of the release curve. Elvax sections prepared by an aqueous method containing the NMDA antagonists CPP or APV displayed more constant but much lower levels of release than those from the dimethyl sulphoxide-based method. The in vitro release characteristics were compared with in vivo release of MK-801 and the close correspondence observed indicates that the in vitro release data is an accurate predictor of the drug release behaviour of implanted Elvax slices.

Corneal penetration of 5-fluorouracil and its improvement by prodrug derivatization in the albino rabbit: implication in glaucoma filtration surgery

The objective of this study was to determine whether the corneal penetration of 5-fluorouracil (5-FU) could be altered by prodrugs. The prodrugs studied included various 1-alkoxy-carbonyl 5-FU derivatives as well as an 1-acyloxymethyl and an 3-acyl derivative. Corneal penetration of 5-FU and its prodrugs was evaluated over 180 min using the isolated albino rabbit cornea in the modified Ussing chamber. 5-FU and its prodrugs were analyzed by reversed phase HPLC. Corneal penetration of 5-FU was very poor due to its low lipophilicity and extensive metabolism during penetration. There was no conclusive evidence for carrier-mediated transport. The corneal epithelium offered the main diffusional and metabolic resistance. Prodrugs of 5-FU with improved lipophilicity dramatically increased the corneal penetration of 5-FU, suggesting that a much reduced dose of 5-FU could be used if corneal penetration and aqueous levels are necessary. It is anticipated that a similar lower dose of prodrug would be required should the prodrug also improve the diffusion of 5-FU across the sclera following subconjunctival injection. Whether dose reduction will lead to reduced corneal toxicity in glaucoma filtration surgery following topical or subconjunctival dosing is an interesting therapeutic opportunity that remains to be determined. In addition to enhancing 5-FU penetration, prodrugs also protected 5-FU from metabolism even though they were rapidly and quantitatively converted to 5-FU during penetration. Protection of 5-FU from metabolism in the cornea may be advantageous from the standpoint of sparing the cornea from toxicity caused by 5-FU, be it from topical or subconjunctival dosing.