3.14:
Compartment Models: Two-Compartment Model
The two-compartment model assumes that drugs are not uniformly distributed throughout the body because the blood perfusion rate varies among different organs and tissues. So, this model divides the body into central and peripheral compartments.
The central compartment comprises blood and highly perfused tissues where the drug is rapidly distributed.
The peripheral compartment consists of tissues where the drug distribution is slow.
Following a single IV bolus dose, the drug concentration is high in the plasma and low in the tissues.
The distribution of the drug between the compartments is a first-order process defined by rate constants, termed as transfer constant or micro constant.
Due to distribution, drug concentration rapidly declines in the plasma and increases in the tissues until an equilibrium is reached.
After this, the drug concentration slowly declines in both compartments due to elimination.
In short, the plasma drug concentration declines bi-exponentially, where the rapid initial decline is the distribution or ɑ phase, and the subsequent decline is the elimination or β phase.
3.14:
Compartment Models: Two-Compartment Model
The two-compartment model divides the body into central and peripheral compartments to account for varying blood perfusion rates among organs and tissues, affecting drug distribution. The central compartment includes blood and highly perfused tissues with rapid drug distribution, while the peripheral compartment contains tissues with slower drug distribution. After a single IV bolus dose, the drug concentration is high in plasma and low in tissues. The drug distribution between compartments follows a first-order process with rate constants known as transfer constants or micro constants. This leads to a rapid decline in plasma drug concentration and an increase in tissue concentration until equilibrium is reached. Following this, both compartments experience a slow decline in drug concentration due to elimination. The plasma drug concentration decline occurs in two phases: the rapid distribution or ɑ phase and the slower elimination or β phase.