3.13:
Compartment Models: Single-Compartment Model
The single-compartment model assumes the human body is a single well-stirred open compartment.
When a drug administered through IV bolus enters the body, it distributes instantaneously without barriers and leaves the body through biotransformation and elimination.
The volume of the compartment is the apparent volume of distribution—a theoretical volume that the administered dose can rapidly and uniformly distribute into.
Drug clearance from the body follows first-order kinetics, where the elimination rate is directly proportional to the drug concentration in the body.
With time, drug plasma concentration declines exponentially with a proportional decline in the tissue drug concentration.
A continuous infusion of a given dose attains a steady-state value exponentially. If infusion stops, the concentration falls exponentially.
If the same dose is administered in multiple equal doses, the mean steady-state concentration and the time required to reach the steady state are similar to that of a continuous infusion.
3.13:
Compartment Models: Single-Compartment Model
The single-compartment model serves as a simplified representation of the human body. This model assumes that the body functions as a single, well-mixed open compartment. When a drug is administered intravenously, it enters the body and quickly distributes uniformly. The drug then undergoes biotransformation and elimination, ultimately leaving the body. The volume of this compartment is referred to as the apparent volume of distribution into which the drug can uniformly distribute. In this model, drug clearance from the body follows first-order kinetics, meaning that the elimination rate is directly proportional to the drug concentration in the body. With time, the drug plasma concentration declines exponentially, leading to a similar decline in tissue drug concentration. When a continuous infusion of a drug occurs, a steady-state value is reached exponentially. However, if the infusion stops, the concentration of the drug in the body falls exponentially. On the other hand, when a drug is administered in multiple equal doses, the average steady-state concentration and the time required to reach this steady state are comparable to those achieved with continuous infusion.