THE ROLE OF THE FIBROUS CAPSULE IN THE FUNCTION OF IMPLANTED DRUG-POLYMER SUSTAINED-RELEASE SYSTEMS

To gain a better understanding of the influence of the local tissue environment and implant site on release behavior, the authors have investigated the release behavior of a gentamicin-silicone rubber system implanted in canines. Particular attention has been directed toward investigating the role that the fibrous capsule which eventually surrounds the implant plays in determining the rate and pattern of drug release. The drug burst effect was decresed by the use of a drug-free silicone rubber membrane on the gentamicin-silicone rod implant. Analysis for gentamicin in the tissue adjacent to the implant for periods up to four weeks indicated that the release rate was retarded by the development of the fibrous capsule. The temporal and spatial variations in gentamicin levels in the tissue surrounding the rod implants were determined. In addition, the influence of implant coating and gentamicin loading level in the implant on local tissue concentrations with time were also investigated.