A three-compartment open model with first order absorption.

Many drugs confer upon the body the characteristics of a three-compartment model. This paper deals with the estimation of pharmacokinetic parameters of a three-compartment open model, with first order absorption from plasma level data. The central compartment (e.g. plasma) is connected to two other peripheral compartments, and (elimination occurs from only the central compartment. The method of solution involves an optimization method which provides a global minimum of delta, the deviation of plasma concentration from the observed values. The distribution volume of the central compartment and the lag time are also identified. The uniqueness of the absorption rate constant is obtained by the minimum energy principle. The model is tested for different sets of data for the drug Guanfacine (Sandoz laboratories), and the results are compared to those obtained by the generalised least square method.