PK and PD for Infectious Disease Therapies: Building the Right Data Package Before IND

When sponsors begin planning an IND-enabling strategy for an infectious disease therapy, pharmacokinetics (PK) and pharmacodynamics (PD) are often discussed early—but not always executed with the rigor they require. Too often, these studies are viewed as supporting data rather than as the scientific backbone of the entire preclinical program. In reality, PK and PD are the first studies that determine whether succeeding studies that follow will be interpretable, defensible, and regulatory-ready.

At Southern Research, PK and PD are treated as foundational studies that inform every following decision, from dose selection to IND-enabling toxicology study design to first-in-human starting doses.

Pharmacokinetics describes how a drug moves through the body; its absorption, distribution, metabolism, and excretion. Pharmacodynamics, by contrast, captures how the body responds to that drug. These two disciplines run hand in hand, and separating them too early in development often leads to incomplete conclusions.

What PK and PD Really Mean in Early Drug Development

From a practical standpoint, PK answers questions such as: How quickly does the drug reach peak concentration? How long does it remain in circulation? Which organs or tissues does it distribute into? How efficiently is it cleared? PD then overlays biological meaning on that exposure: Are we seeing target engagement? Is there a measurable therapeutic effect? Are there early signals of toxicity, and if so, what organs or organ systems?

Without this paired understanding, sponsors lack the context needed to design dose range finding studies or GLP toxicology studies.  Without PK/PD data, there is simply no rational basis for selecting dose levels. You may know you have a promising molecule, but you do not yet know how, or even whether, it behaves predictably in a living system.

These studies are therefore not optional precursors; they are the foundational studies that allow scientists to “get a handle on what’s happening” before advancing into more resource-intensive phases.

Why Infectious Disease Changes the PK/PD Equation

In infectious disease programs, PK and PD become even more critical. A compound may behave one way in a healthy subject and very differently once infection is introduced. Disease can alter metabolism, organ function, immune response, and susceptibility to toxicity. A dose that appears safe in a naïve or healthy subject may become intolerable in a diseased one, or may fail to achieve therapeutic exposure when it matters most.

This is the critical reason why PK/PD studies in infectious disease development cannot be limited to healthy populations alone. Evaluating exposure and response within the disease model itself provides insight into how infection alters drug behavior and informs realistic dose selection.

A common misconception: assuming that PK/PD data from healthy animals automatically translates to infected systems. In practice, this assumption frequently leads to failed studies, unexpected toxicities, or regulatory questions that could have been avoided with disease-relevant data generated earlier.

The Role of PK/PD in Downstream Study Design

PK and PD data serve as the bridge between discovery studies and regulatory toxicity and safety studies. They inform dose range finding studies by identifying exposure levels that appear therapeutic versus those that trend toward toxicity. They also guide the design of pivotal GLP toxicology studies, where regulators expect to see dose ranges that are scientifically justified.

Without PK/PD, sponsors often default to arbitrary dose selection, an approach that introduces unnecessary risk and frequently results in study redesigns or additional regulatory interactions.

By integrating PK, PD, infectious disease biology, and bioanalysis, Southern Research helps sponsors move into IND-enabling studies with confidence, clarity, and a data package that withstands regulatory scrutiny.