In vivo evaluation of a dexamethasone/PLGA microsphere system designed to suppress the inflammatory tissue response to implantable medical devices.

The purpose of this research effort was to evaluate in vivo a newly developed dexamethasone/PLGA microsphere system designed to suppress the inflammatory tissue response to an implanted device, in this case a biosensor. The microspheres were prepared using an oil/water (O/W) emulsion technique. The microsphere system was composed of drug-loaded microspheres (including newly formulated and predegraded microspheres) and free dexamethasone. The combination of the drug and drug-loaded microspheres provided burst release of dexamethasone followed by continuous release from days 2-14. Continuous release to at least 30 days was achieved by mixing predegraded and newly formulated microspheres. The ability of our mixed microsphere system to control tissue reactions to an implant then was tested in vivo using cotton thread sutures to induce inflammation subcutaneously in Sprague-Dawley rats. Two different in vivo studies were performed, the first to find the dosage level of dexamethasone that effectively would suppress the acute inflammatory reaction and the second to show how effective the dexamethasone delivered by PLGA microspheres was in suppressing chronic inflammatory response to an implant. The first in vivo study showed that 0.1 to 0.8 mg of dexamethasone at the site minimized the acute inflammatory reaction. The second in vivo study showed that our mixed microsphere system suppressed the inflammatory response to an implanted suture for at least 1 month. This study has proven the viability of microsphere delivery of an anti-inflammatory to control the inflammatory reaction at an implant site.