In PK, what is meant by central and peripheral compartments?

• A. Central and peripheral compartments are conceptual but have identical perfusion and exchange.
• B. Peripheral compartments are the site of distribution to blood.
• C. Distribution between compartments occurs instantaneously.
• D. Central contains blood and highly perfused organs; peripheral compartments are less well perfused with slower exchange.

Answer: (D)

Understanding how distribution occurs between fast and slow tissues is the idea behind central and peripheral compartments. The central compartment represents the blood and other tissues that are highly perfused, so the drug is present there soon after administration. The peripheral compartments are tissues with lower blood flow, where the drug moves more slowly and exchange with the central compartment happens at a limited rate.

Distribution between these compartments is governed by kinetic transfers, not instantaneous mixing. Rate constants determine how quickly the drug moves from the central to the peripheral space and back, so concentrations change over time rather than jumping to equilibrium.

This is why the correct statement describes the central as containing blood and highly perfused organs, with peripheral compartments being less well perfused and exchanging more slowly. The other ideas don’t fit: identical perfusion would not require separation into central and peripheral; distribution to blood is not a separate peripheral site; and assuming instantaneous distribution ignores the time-dependent exchange that defines a two-compartment model.