The guidance to industry on population pharmacokinetics emphasizes the role of modeling and simulation  in designing trials and analyzing trial outcomes. The exposure-response guidance focuses on the design and analysis of data from studies characterizing the PK/PD of a drug.
The impact of the aforementioned regulatory recommendations issued by the FDA is obvious. With efficient planning, sponsors can economize drug development time and resources, and take full advantage of the incentives. Building a concentration (not dose)-biomaker/surrogate/clinical endpoint relationship during the development of a new drug for use in adults can readily facilitate design (using simulations), analysis, and dosing recommendations (labeling changes) for the drug's use in pediatrics. However, the ability of a concentration-effect relationship to support approval of a dose/regimen not directly studied in clinical trials is not being fully exploited. This is in fact one of the strongest uses of modeling and simulation. Usually doses/regimens "directly" studied in clinical trials are proposed in the labels. A model can effectively be used to explore the suitability of intermediate doses not directly studied but could potentially offer similar effectiveness as the other doses or dosing regimens. Extrapolating outside the studied range may not be possible.
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