Scientific Glossary

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Pharmacodynamics is the flip side of pharmacokinetics: what the compound does to the body. Includes receptor binding (affinity, selectivity), downstream signaling, therapeutic effects, and side effects. The PK/PD relationship links compound exposure (concentration) to observed response. Understanding PD helps explain why two compounds with similar structures may have very different biological effects.

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Pharmacodynamics is the companion to pharmacokinetics. While PK asks "what does the body do to the drug?", PD asks "what does the drug do to the body?" Key PD parameters: Emax (maximum effect), EC50 (concentration producing 50% maximum effect), receptor binding affinity (Kd, Ki), and the dose-response relationship. Understanding PD requires knowing which receptors a compound engages, with what affinity, and what the downstream signaling consequences are. PK/PD modeling combines both to predict effects over time.