Application of model-based methods to characterize exenatide-loaded double-walled microspheres: in vivo release, pharmacokinetic/pharmacodynamic model, and in vitro and in vivo correlation.

The objective of this study was to characterize exenatide double-walled microspheres (DWMS) using model-based methods. Exenatide DWMS were prepared using oil-in-oil-in-water method, and physicochemical characterization and in vitro release and degradation of DWMS were evaluated. The pharmacokinetics (PK) and pharmacodynamics (PD) were investigated after subcutaneous injection to diabetic rats. Transit compartment model was used to describe the in vivo release of exenatide from DWMS successfully. On the basis of the insulinotropic effects of exenatide and hypoglycemic effects of insulin, PK/PD model was developed and nicely described the concentration-effect relationship of exenatide. Moreover, on the basis of the transit compartment model, a simulation method was applied to predict in vivo release, and in vitro and in vivo correlation was established. In conclusion, DWMS was a promising vehicle for delivery of exenatide, and the proposed PK/PD model allowed a better understanding of the pharmacological properties of exenatide DWMS. Transit compartment model-based modeling and simulation methods provided more options for the description and prediction of the in vivo exenatide release from DWMS.