A Physiologically Based Model for Gastrointestinal Absorption and Excretion of Chemicals Carried by Lipids

Pharmacokinetic models which incorporate independently measured anatomical characteristics and physiological flows have been widely used to predict the pharmacokinetic behavior of drugs, anesthetics, and other chemicals. Models appearing in the literature have included as many as 18,⁽¹⁾ or as few as 5 tissue compartments.⁽²⁾ With the exception of the multiple-compartment delay trains used by Bischoff⁽³⁾ to model the delays inherent to the appearance of drug metabolites in bile and segments of the intestinal lumen, very little effort has been made to incorporate the available information on gastrointestinal anatomy and physiology into more accurate gastrointestinal absorption/enterohepatic recirculation submodels. Since several authors have shown that the lymphatic system is the most significant route of absorption for highly lipophilic chemicals, we have constructed a model of gastrointestinal absorption that emphasizes chylomicron production and transport as the most significant route of absorption for nonvolatile, lipophilic chemicals. The absorption and distribution of hexachlorobenzene after intravenous vs. oral dosing are used to demonstrate features of this model.