Integrating In Vitro Dissolution and Physiologically Based Pharmacokinetic Modeling for Generic Drug Development: Evaluation of Amorphous Solid Dispersion Formulations for Tacrolimus

<b>Objectives</b>: Tacrolimus, a Biopharmaceutics Classification System (BCS) class II drug, is widely used for transplant patients to prevent graft rejection. To enhance its bioavailability, amorphous solid dispersion (ASD) formulations were developed and evaluated. The release properties of several ASD-based tacrolimus formulations were studied using an in-house USP IV dissolution method. <b>Methods</b>: The pharmacokinetics of a promising test product were compared with the commercially available Advagraf^® in a pilot clinical bioequivalence study with 12 healthy subjects. A previously published PBPK model for tacrolimus was validated using in vivo data and then applied to predict the human pharmacokinetics of several ASD-based tacrolimus formulations. <b>Results</b>: This study compares the pharmacokinetic (PK) parameters-AUC, Cmax, and Tmax-of Advagraf^® and a test formulation using two methodologies: one incorporating the dissolution profile directly into the PBPK model and the other utilizing the DLM approach. The results show that both methods provided accurate predictions for Cmax and Tmax, with the dissolution profile approach underestimating AUC slightly, while the DLM method predicted AUC adequately. Sensitivity analysis refining the DLM scalars in the Ileum and Colon led to optimized predictions of PK parameters. Furthermore, this study explores the use of PBPK modeling to predict in vivo behavior for additional tacrolimus formulations, highlighting the influence of formulation composition, such as the inclusion of Eudragit-S100, on dissolution profiles and bioavailability. <b>Conclusions</b>: This study evaluates formulations with different compositions and manufacturing characteristics; key factors that could influence their performance in the body were identified. These insights-spanning qualitative, quantitative, and manufacturing aspects-can greatly simplify the development of generic drugs, offering strong evidence of the critical role that physiologically based pharmacokinetic (PBPK) modeling can play in the early phases of generic drug development, especially in designing and assessing biopredictive dissolution methods.