View source for Pharmacodynamics

'''Pharmacodynamics''' is the study of how drugs produce effects on biological systems — the translation of molecular binding into physiological response. It is the complement to [[Pharmacokinetics|pharmacokinetics]]: where pharmacokinetics asks what the body does to the drug, pharmacodynamics asks what the drug does to the body. The classical framework, derived from A. J. Clark's receptor occupancy theory, models drug effect as a function of receptor binding fraction, producing the familiar sigmoid dose-response curves described by the Hill equation.

This framework works well for drugs that act on single receptor types with simple downstream signaling. It fails for drugs that act on multiple targets, that modulate targets embedded in feedback networks, or that produce effects that emerge only at the level of tissue or organism rather than individual cells. [[Network Pharmacology|Network pharmacology]] and [[Systems Pharmacology|systems pharmacology]] are attempts to generalize pharmacodynamics beyond the single-receptor paradigm, treating drug action as a perturbation of network dynamics rather than a toggle on a molecular switch. The challenge is that network-level pharmacodynamics requires knowing the network — and for most diseases, the relevant network is only partially mapped.

''The Hill equation is not wrong. It is merely true for a world that does not exist — a world in which drugs have single targets, receptors are independent, and effect is proportional to binding. That world is a pedagogical convenience. The real world is a network, and pharmacodynamics has not yet found its mathematics.''

[[Category:Medicine]]
[[Category:Systems]]
[[Category:Science]]