Defense Date


Document Type


Degree Name

Doctor of Philosophy



First Advisor

Dr. H. Thomas Karnes


Characterization of in vitro and in vivo drug release profiles constitutes an important step in developing and optimizing an effective, long acting delivery system for naltrexone. Accelerated in vitro methods are also important for quality assurance of manufactured dosage forms. For drug release testing of sustained release parenteral dosage forms, the modified USP Apparatus 4 (flow-through cell) has been recommended by the The Fédération Internationale Pharmaceutique/American Association of Pharmaceutical Scientists (FIP/AAPS) Guidelines. Details on such studies however, are generally not found in the literature. To incorporate 'biorelevance' to implant drug release studies, this research investigated an approach to apparatus design and media selection that is significantly different from conventional dissolution studies involving oral dosage forms.Biodegradable implants of naltrexone were obtained from Durect Corporation, USA. A modified Hanks' Balanced Salts Solution was characterized as a 'biorelevant' medium for in vitro drug release studies. Naltrexone was found to be sufficiently stable in the medium, as determined by a stability-indicating High Performance Liquid Chromatography (HPLC) assay. A miniature, cell-culture, capillary system was modified and tested as a 'biorelevant' alternative to the modified flow-through apparatus, to mimic significant barriers to drug release that would be expected in vivo. The in vitro release profiles generated up to 3 months using both devices indicated considerable (2-fold) variation in rates, as expected from the difference in media flow characteristics. An implantation study in a dog was conducted to determine which of the two devices could provide a better simulation of the in vivo conditions. Analysis of in vivo samples was carried out by a Liquid Chromatography-Tandem Mass Spectrometry (LC-MS-MS) method that also employed a molecular model approach to demonstrate the absence of Internal Standard Deuterium Isotope Effects. A good In vitro-In vivo Correlation (IVIVC) resulted from both devices; however, the capillary device provided a superior simulation for the lag-time in absorption. The accelerated study at 45°C and 55°C established a predictable increase in release rates (2-fold and 4-fold increases, respectively). The approach described in this work could provide the basis for future method modification of in vitro drug release tests of subcutaneous implants.


© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

June 2008