Commentary on Fit-For-Purpose Models for Regulatory Applications.

Model-based analyses have been applied to influence various drug development and regulatory decisions in the last 2 decades. Applied models range from empirical models to highly complex mechanistic models. "Fit-for-purpose" has been the principle to determine the level of model complexity. While numerous case studies have been published to highlight the impact and value of model-based analyses, more experience and lessons are being accumulated to address new challenges and create more opportunities. The inclusion of Model-Informed Drug Development in the Prescription Drug User Fee Act (PDUFA) VI represents a new landmark for the field of quantitative clinical pharmacology.