During regulatory review of clinical pharmacology data in new drug applications and biologics license applications, questions are routinely asked about how intrinsic factors (e.g., organ dysfunction, age, and genetics) and extrinsic factors (e.g., drug-drug interactions) might influence dose-response and exposure-response and about the impact of these individual factors on the efficacy and safety of the candidate compound. Physiologically based pharmacokinetic (PBPK) modeling and simulation is one of the tools that can be used to address these critical questions.