Physiologically-based pharmacokinetic modeling and bioactivation of xenobiotics

This paper describes the development and implementation of physiologically-based pharmacokinetic (PB-Pk) models to examine the disposition of xenobiotics and their bioactivation. In a PB-Pk model, the structure of the model is based, to as great extent as practicable, on the actual physiological and biochemical structure of the animal system being described. This paper provides an overview of the PB-Pk modeling approach using a series of models as examples. PB-Pk models for styrene and the dihalomethanes are discussed in relation to their ability to predict the kinetics of uptake, distribution, metabolism (bioactivation), and elimination in both rodents and humans. Three models are discussed which demonstrate the process of describing increasing complexity in bioactivation with reference to saturation of metabolism (methylene chloride), suicide enzyme inactivation (trans-1,2-dichloroethylene), and glutathione depletion (allyl chloride). Experimental studies to quantify these particular examples of non-linear kinetics were conducted by closed chamber gas uptake techniques. All of these behaviors can be quantitatively expressed within the framework of a PB-Pk model.