What is "pharmacodynamics"

n. (context pharmacology English) The branch of pharmacology that studies the effects and modes of action of drugs upon the body.

Pharmacodynamics is the study of the biochemical and physiologic effects of drugs. The effects can include those manifested within animals (including humans), microorganisms, or combinations of organisms (for example, infection). Pharmacodynamics is the study of how a drug modifies an organism, whereas pharmacokinetics is the study of how the organism absorbs, modifies or distributes a drug. Pharmacodynamics is sometimes abbreviated as PD and pharmacokinetics as PK, especially in combined reference (for example, when speaking of PK/PD models).

Pharmacodynamics places particular emphasis on dose–response relationships, that is, the relationships between drug concentration and effect. One dominant example is drug-receptor interactions as modeled by

$$L + R \ \rightleftharpoons \ L\! \cdot \!R$$

where L, R, and LR represent ligand (drug), receptor, and ligand-receptor complex concentrations, respectively. This equation represents a simplified model of reaction dynamics that can be studied mathematically through tools such as free energy maps.