A 'biorelevant' system to investigate in vitro drug released from a naltrexone implant

This research is based on the recognized need for an in vitro release method for drug implants that better simulate physiological conditions at the site of implantation ('biorelevance'). In this paper, we describe the evaluation of a 'biorelevant' approach for in vitro drug release testing of a biodegradable implant of naltrexone in a pre-clinical stage of development. A miniature, capillary cell culture device was modified and tested as a biorelevant alternative for a standard commercially available flow-through cell. The real-time data generated through 90 days indicated a 48% lower rate of release for the capillary system. The profiles using both systems followed zero-order kinetics after an initial period of burst release. In vitro release data from the capillary device resulted in a 1-to-1 correlation with dog plasma pharmacokinetic data, and furthermore, the capillary device potentially simulated the lag-time in absorption more effectively than the flow-through cell. Scanning electron micrographs revealed that the sheath was continuous with no signs of cracks at the end of in vitro and in vivo studies. However, at the interface of the sheath and the core, intercalating, "finger-like" projections were observed consistent with penetration of the medium. No macroscopic or clinical toxicity signs were observed during the in vivo implantation study.