The three-compartment open model is a pharmacokinetic model used to describe the distribution and elimination of drugs following extravascular administration. It comprises a central compartment representing the plasma and two peripheral compartments. The highly perfused peripheral compartment represents organs and tissues with a rich blood supply, such as the liver, kidneys, and lungs. The scarcely perfused peripheral compartment represents tissues with lower blood supply, such as adipose tissue and certain muscle groups. The plasma concentration of a drug in such models is described by a multi-exponential equation involving various exponents, each corresponding to the rate of drug transfer between compartments. The equation for the plasma concentration of a drug in three-compartment models defines α, β, and γ as the first-order rate constants representing elimination from the central compartment and drug distribution to and from the peripheral compartments.

Estimating the elimination rate constants involves mathematical modeling and regression analysis to fit the observed data to the multi-exponential equation. The resulting values of α, β, and γ provide insights into the drug's distribution and elimination kinetics, with potential clinical applications in determining dosing regimens and predicting drug concentrations over time. The three-compartment open model offers a comprehensive understanding of drug distribution and elimination following extravascular administration. Estimating elimination rate constants is crucial in optimizing therapeutic outcomes and ensuring patient safety.