Reliable approaches to predict clinical outcome during drug development are essential. Characterization of the potential of a drug to cause interactions relies initially on preclinical data, followed by clinical studies. Physiologically-based pharmacokinetic (PBPK) modeling and simulation (M&S) emerged as a powerful translational tool that aids in planning of clinical drugdrug interaction (DDI) studies and is often used to bridge gaps during regulatory filings. 1 Practical applications of PBPK in drug development will be discussed.
PBPK MODELING IN BRIDGING DRUG-DEVELOPMENT GAPSIdeally, characterization of the DDI potential for a new molecular entity (NME) is addressed through the conduct of clinical trials, commonly in healthy volunteer subjects, to provide the ultimate data package to inform dosing in patients. Clinical trials using healthy volunteers follow strict ethical criteria ensuring no to minimal risk given that no therapeutic benefit would be expected from participating in such studies. Therefore, exposing healthy volunteers to an experimental NME to evaluate its potential for DDI in the presence of alternative reliable approaches may be considered unethical. For example, if an NME is a substrate of cytochrome P450 (CYP)3A and a clinical DDI study with the potent CYP3A inhibitor ketoconazole was conducted, the magnitude of DDI with moderate or weak CYP3A inhibitors can be reliably predicted using PBPK modeling as the contribution of CYP3A has been clinically defined. This approach has been well documented in the literature and led to successful labeling of many NMEs. 1 Unfortunately, the results of PBPK modeling approaches may be considered less reliable or even ignored by some clinicians, who typically rely on empirical clinical evidence to inform dosing in patients and wrongfully argue that M&S is unreliable because it suffers from using assumptions and is a tedious approach that requires large amounts of physiological data, as well as intensive drug-dependent input data. 2 Despite these barriers, several successful examples have been reported where PBPK simulations were provided as evidence in lieu of clinical DDI studies to inform regulatory decisions and, ultimately, labeling. 1,3 Considering "totality of the scientific evidence" from PBPK, exposure-response analyses and risk-benefit evaluation enabled these successful examples to optimize drug development using a model-informed framework. For instance, PBPK modeling was used to inform dose adjustments of aripiprazole and eliglusat, as reflected in the labels of these drugs.In oncology drug development, the limited ability to conduct phase I healthy volunteer studies necessitates the use of reliable translational approaches such as in vitroin vivo extrapolation and PBPK for assessment of DDIs. Conducting DDI trials in oncology patients is possible but poses several challenges with respect to consent, ability to conduct multiple dose studies, and use of the clinical dose in patients. For these reasons, a fit-for-purpose use of PBPK offers a great v...