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.
