Pharmacodynamics (PD)

Pharmacodynamics (PD) refers to the study of the biochemical and physiological effects of a drug on the body, including its mechanism of action, dose-response relationship, and therapeutic effects.

Essentially, PD explains "what the drug does to the body", in contrast to pharmacokinetics (PK), which describes "what the body does to the drug." PD assessments are critical throughout all phases of clinical trials, but are particularly important in Phase I and Phase II trials. Early studies evaluate whether a drug produces the desired biological response before moving to larger efficacy and safety trials.