Pharmacodynamics
The study of what a drug does to the body — its biological effects, mechanism of action, and the relationship between drug concentration and therapeutic response. Pharmacodynamics complements pharmacokinetics and together they determine a drug's dosing regimen and clinical behaviour.
Technical Context
PD describes the concentration-effect relationship using key concepts: potency (EC50 — concentration producing 50% maximum effect), efficacy (Emax — maximum achievable effect), Hill coefficient (steepness of the concentration-response curve), and receptor occupancy theory (fraction of receptors occupied at a given drug concentration). For GLP-1 RAs, PD effects include insulin secretion (EC50 varies by compound), glucagon suppression, gastric emptying delay, and appetite reduction — each with potentially different concentration-response relationships. PK/PD modelling integrates pharmacokinetic data (how concentrations change over time) with pharmacodynamic data (how effects relate to concentrations) to optimise dosing regimens and predict clinical outcomes.