A pharmacokinetic model to differentiate preabsorptive, gut epithelial, and hepatic first-pass metabolism.

A combined perfusion/compartmental pharmacokinetic model has been developed to describe the time course of drugs that are subject to preabsorptive, intestinal epithelial, and hepatic first-pass metabolism. Equations are derived to estimate the fraction of the administered dose which is metabolized at each of the three sites and to establish the limits of the true absorption rate constant. The model is tested using literature data for phenacetin.