Mechanistic Model for Drug Release from PLGA-Based Biodegradable Implants for <i>In Vitro</i> Release Testing: Development and Validation

Several factors can affect drug release from polylactide coglycolide (PLGA)-based formulations, including polymer and drug properties, formulation components, manufacturing processes, and environmental <i>in vitro</i> or <i>in vivo</i> conditions. To achieve optimal release profiles for specific drug delivery applications, it is crucial to understand the mechanistic processes that determine drug release from PLGA-based formulations. In the current study, we developed a mechanistic model for the <i>in vitro</i> drug release of PLGA-based solid implants. The model accounts for all known critical quality attributes (CQAs) and considers the most important release rate processes, including water or dissolution medium influx into the porous structure of the implant, initial noncatalytic hydrolysis of PLGA, autocatalytic hydrolysis, dissolution of oligomers and monomers into the aqueous medium, the liberation of the trapped solid drug from the polymer matrix, dissolution of the solid drug into the wetted pore network, diffusion of the dissolved drug out of the implant, and distribution of the dissolved drug into the dissolution medium. The model has been validated using <i>in vitro</i> release data obtained from implants of four drugs (buserelin, afamelanotide, brimonidine, and nafarelin). The model presented in this manuscript provides valuable insights into the kinetics and mechanism of drug release from PLGA-based solid implants and has demonstrated the potential for optimizing formulation design. The <i>in vitro</i> release model, coupled with physiologically based pharmacokinetic (PBPK) modeling, can predict the <i>in vivo</i> performance of implants and can be used to support bioequivalence studies in a drug development program.