Kompartimentmodell

The kompartimentmodell is a mathematical framework used to describe how substances such as drugs, tracers, or pollutants distribute within a biological system or physical environment and how they are eliminated over time. The system is divided into discrete compartments that are assumed to be homogeneous and well mixed.

Transfers between compartments are governed by rate constants, typically assumed to be first-order, and elimination is modeled as loss from one or more compartments. The resulting dynamics are described by ordinary differential equations. In practice, the model is expressed in terms of amounts or concentrations, often using volumes to relate the two.

Common levels of complexity include the one-compartment model, which assumes instantaneous distribution and a single elimination pathway, and the two-compartment model, which adds a peripheral compartment to capture slower distribution. More compartments can be used when necessary to fit data, at the cost of identifiability and interpretability.

Such models are widely used in pharmacokinetics to describe drug concentration in plasma and tissues, in toxicokinetics, PET and SPECT tracer kinetics, and environmental fate studies. Parameters are typically estimated by fitting model predictions to concentration-time data using nonlinear regression or maximum likelihood methods.

Limitations include simplifications such as linear, first-order kinetics, homogeneous mixing within compartments, and constant physiology. They may fail for saturable or nonlinear processes, time-varying volumes, or highly heterogeneous tissues. More complex approaches, such as physiologically based pharmacokinetic (PBPK) models, address some of these issues.