Breakout session summary from AAPS/CRS joint workshop on critical variables in the in vitro and in vivo performance of parenteral sustained release products.

Parenteral drug delivery systems can be designed to provide the flexible delivery characteristics needed in an evolving therapeutic landscape. The goal of some parenteral formulations is to maintain effective drug concentrations over a period of months or years, thereby enhancing patient compliance. When functioning as intended, these formulations can be used to minimize undesirable effects that may occur in response to the fluctuating drug concentrations effected by immediate release products. In other cases, targeted parenteral delivery systems allow for the deposition of drug directly to its site of action, thereby minimizing systemic toxicity. While these novel formulations can be beneficial to both human and veterinary patients, disastrous effects can occur if there is an unanticipated change in product quality or performance. With these thoughts in mind, the Controlled Release Society (CRS) hosted a 2007 workshop entitled "In Vitro and In Vivo Considerations Associated with Parenteral Sustained Release Products". The objective of that workshop was to explore the physicochemical properties of parenteral products and the factors that could alter their in vitro and in vivo performance characteristics. The outcomes of that workshop were summarized in a Journal of Controlled Release article. In response to questions raised during that workshop, the CRS and the American Association of Pharmaceutical Scientist (AAPS) co-hosted the follow-up 2008 workshop entitled "Critical Variables in the In Vitro and In Vivo Performance of Parenteral Sustained Release Products". This 2008 workshop provided a platform for exploring the application of design space concepts to these complex pharmaceuticals, and to consider the corresponding in vitro test methods that can be used to set batch release specifications. To foster discussion, the workshop provided two afternoon breakout sessions where critical questions were explored. This manuscript captures the results of those discussions. Published by Elsevier B.V.