Pharmacokinetics (PK) describes how the body affects an administered drug in terms of absorption, distribution, metabolism, and excretion. Pharmacodynamics (PD) describes how a drug affects the body by relating the drug concentration to an efficacy metric or response.
PKPD modeling (pharmacokinetic/pharmacodynamic modeling) combines dose-concentration relationships (pharmacokinetics) and concentration-effect relationships (pharmacodynamics) into one set of mathematical expressions. These can be used to establish and evaluate dose-concentration-response relationships and therefore, to describe and predict the effect-time courses resulting from a drug dose.
Image credit: Yin-Cheong (Eric) Wong (Quantitative Clinical Pharmacology, UCB Pharma).