One-compartment versus two-compartment model
The difference between one-compartment and two-compartment pharmacokinetic models can be illustrated by the following example:
Suppose that a drop of dye is added to the liquid in a beaker that is coated with a porous material that can adsorb the dye. If the dye distributes rapidly into the coating material the equilibrium between the liquid and the coating material is achieved rapidly.
The concentration of the dye in the liquid (the sampling site) will be constant since the equilibrium between the liquid and the coating materials is achieved rapidly.
Any change in the dye conc in the liquid due to the addition of more dye will result in spontaneous increase in the dye conc in the coating material.
The beaker behaves as a single kinetically homogenous vessel or one compartment.
Suppose that when the dye is added to the beaker, the dye is distributed slowly into the coating material. The conc of the dye in the liquid (the sampling site) will be high initially because the dye is distributed only into the liquid in the center of the beaker. Then the dye conc in the liquid decreases due to its distribution into the coating material. When equilibrium is achieved between the liquid and the coating material, the conc remains constant.
Changing the dye conc in the liquid will lead to the distribution of more dye to the coating material. This distribution process has to be completed before a new equilibrium is established.
The beaker behaves as a two-compartment vessel. The liquid in the center represents one compartment and the coating material represents the second compartment.
Equilibrium
Distribution process
