Multi-compartment Pharmacokinetics

The observed plasma concentrations determine the compartmental model that describes the drug disposition.

When the plasma drug concentrations decline biexponentially, this means that the drug follows two-compartment pharmacokinetic model.

Peripheral
compartment

k21

k12

iv

Central
compartment

k10

The mathematical expression that describes the plasma concentration-time profile of drugs that follow the two-compartment pharmacokinetic model after single iv administration in terms of the macro-rate constants is:

Cp = A e -α t + B e -β t

In terms of the micro-rate constants the expression is:

Cp =

D(α-k21)

Vc(α-β) e -α t +

D(k21-β)

Vc(α-β) e -β t

Any change in the pharmacokinetic parameters will be reflected by a change in the drug plasma concentration which represents the drug profile in the central compartment, and also the drug tissue concentration which represents the drug profile in the peripheral compartment.