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Single-compartment model

The simplest PK compartmental model is the one-compartmental PK model. This models an organism as one homogenous compartment. This monocompartmental model presupposes that blood plasma concentrations of the drug are the only information needed to determine the drug's concentration in other fluids and tissues. For example, the concentration in other areas may be approximately related by known, constant factors to the blood plasma concentration.

In this one-compartment model, the most common model of elimination is first order kinetics, where the elimination of the drug is directly proportional to the drug's concentration in the organism. This is often called linear pharmacokinetics, as the change in concentration over time can be expressed as a linear differential equation d C d t = − k el C {\textstyle {\frac {dC}{dt}}=-k_{\text{el}}C}. Assuming a single IV bolus dose resulting in a concentration C initial {\displaystyle C_{\text{initial}}} at time t = 0 {\displaystyle t=0}, the equation can be solved to give C = C initial × e − k el × t {\displaystyle C=C_{\text{initial}}\times e^{-k_{\text{el}}\times t}}.