Determination of intestinal absorption

Study of the absorptive function of the intestinal tract can be carried out with numerous methods. Among the primary considerations in choosing an experimental technique to assess an aspect of the absorption process are the following  

The test species to be used that is, must the study be conducted in humans with all the accompanying complications, or is there an appropriate experimental animal model  

The aspect of the absorption process of interest for example, is it the overall absorption from the gut lumen to the systemic circulation and tissues, or is it the process of transport across the brush border or basolateral membrane of the intestinal mucosal cell  

Which experimental or physiological variables should be controlled, for example, the presence of anesthetic agents, the electrochemical potential difference across the gut wall, or the pH of the luminal gut contents  

The answers to these questions will determine the particular method that may be chosen from among the in vitro methods available for studying absorptive function [15,16]. These methods can be categorized according to (a) the method by which the test substance is administered, and (b) the method for assessing the extent and/or rate of absorption. 

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Since experimental determination of intestinal absorption is quite demanding, Caco-2 cell monolayers have been successfully used to model passive drug absorption. Several models for the prediction of Caco-2 permeability using PSA were developed, including those of van de Waterbeemd et al. [5] and Palm et al. [22] who found that relationships between Caco-2 permeability and PSA is stronger than with Clog D, Krarup et al. [23] who used dynamic PSA calculated for water accessible molecular surface and Bergstrom et al. [24]. 

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