ABSTRACT
As discussed in Chapters 1, 2, and 7, the absorption of xenobiotics via an extravascular route of administration involves permeation through a physiological barrier before reaching the systemic circulation. The barriers can be as complex as the gastrointestinal wall (Chapter 8) or as simple as a capillary wall in the intramuscular, rectal, or sublingual route of administration (Chapters 1 and 2). The PK/TK prole of the compounds absorbed through extravascular routes involves all four biological processes of absorption, distribution, metabolism, and excretion. These processes occur simultaneously and not sequentially. The physicochemical characteristics of the xenobiotic and behavior of the body in dealing with the compound, inuences the data which in return inuences the selection of the PK/TK model. The general approaches in PK/TK modeling are discussed in Chapter 9. The focus of the current chapter is to evaluate the application and practicality of the models used in PK/TK analysis of compounds absorbed from an extravascular route of administration. Although the focus of discussion is on the oral administration, the models and parameters are applicable to the other extravacular route of administration, except for percutaneous absorption, which will be discussed in Chapter 13.
