Why PK/PD matters

Common misconceptions

Many teams assume that running a wide dose range is enough to support registration or dose selection. Regulators and guidance documents say otherwise:

• Dose range ≠ exposure–response. A dose range tells you what you gave; it does not by itself tell you how exposure (e.g. concentration) related to efficacy or safety. Without exposure–response, you cannot robustly justify dose selection or interpret outcomes.
• If you don't measure or plan for exposure, you can't interpret outcomes. Without planned sampling and a clear link from exposure to response, positive or negative results are hard to interpret—and agencies may ask for more data or a better rationale.

Reframing "just run a wide dose range" as a risk (underestimating PK/PD) helps teams plan for valid study design and exposure–response from the start.

Exposure → response (conceptual)

A simple way to think about what regulators expect—without prescribing specific doses or designs:

PK/PD and exposure–response

Pharmacokinetics describes what the body does to the drug (absorption, distribution, metabolism, excretion). Pharmacodynamics describes what the drug does to the body (effect, efficacy, safety). Linking exposure (e.g. concentration) to response is central to dose selection and justification for regulators. Well-designed protocols and PK/PD plans reduce the risk of under- or over-dosing and support IND and later-stage decisions.

FDA exposure–response guidance

The FDA's guidance on exposure–response relationships emphasizes valid study design and planning for E–R modeling and decision-making:

• Characterizing exposure–response for efficacy and safety
• Using PK/PD to support dose selection and labeling
• Integrating exposure–response into trial design and analysis

FDA: Exposure-Response Relationships — Study Design, Data Analysis, and Regulatory Applications

ICH E4

ICH E4 ("Dose-Response Information to Support Drug Registration") is explicitly about dose–response information supporting registration. It outlines how dose-response and exposure-response information should be generated and used, and reinforces the need for well-defined PK/PD rationale and dose selection in protocols.

FDA adoption: E4 Dose-Response Information to Support Drug Registration · ICH E4 Guideline (PDF)

EMA and early human studies

EMA guidance focuses on risk mitigation when transitioning to early human studies. Aligning your protocol and PK/PD plan with FDA, ICH, and (as applicable) EMA expectations helps avoid delays and questions at the agency.

EMA: ICH E4 Dose-Response Information to Support Drug Registration

What we do

Aquarius provides an independent review of your protocol and PK/PD dosing plan—identifying gaps, assumptions, and regulatory risks before you lock the plan. We don't provide dosing recommendations; we help you strengthen your rationale and documentation so you can ship with confidence.