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Developed in collaboration with five major pharmaceutical companies, the Absorption Model in iDEA pkEXPRESS™ predicts human intestinal absorption.  The systems patented dispersed plug flow model of absorption, simulates human physiology and accounts for the regional solubility, regional permeability, intestinal surface area and fluid flow in the gastrointestinal tract.  Optimized using internally generated in vitro data, intravenous and oral pharmacokinetic clinical data, and chemical structures, the 62 drugs in the Absorption Model training set span 19 different therapeutic classes and include development successes as well as drugs that failed clinical trials.  Compounds in the training set were selected so that a broad range of solubility, permeability, transport properties and extent of absorption was represented. 



Using dose, chemical structure, solubility, Caco-2 permeability, and efflux (optional input), the Absorption Model predicts the extent of absorption, absorption rate, mass absorbed, soluble mass, insoluble mass, and intestinal drug concentration of potential drugs.


The physiological absorption model is based on a multi-compartment representation of the human gastro-intestinal tract.  The model is physiologic, using human intestinal flow rates, surface areas and luminal pH values gathered from the literature.  The flow model for the transit of soluble and insoluble drug is based on an approximation of dispersed plug  flow, ex., Ho, N.F.H., et Al., Advancing Quantitative Approaches in Interfacing Gastrointestinal Drug Absorption Studies in Animals and Humans.  In "Animal Models for Oral Drug Delivery in Man", W. Crouthamel, et. Al., APHA, 1973.

The model accounts for the forward and retrograde movement of the solid and dissolved dosage form, accounts for dissolution of solid dosage form, adjusts solubility according to regional pH, and calculates the compound flux in each region of the intestine.  The correlation of in vitro solubility and permeability to human absorption was achieved by optimizing the values of a series of proprietary parameters against measured absorption data obtained through pharmacokinetics analysis of the in vivo training set.


Characteristics of the Absorption Model Training Set



Caco-2 Permeability




Extent of Absorption


Min Value

5.87 x 10-8

5.0 x 10-8


Max Value

1.18 x 10-4

> 5 x 102



7.70 x 10-5




3.79 x 10-6








Data Set (%)

Passive -Transcellular 41
Passive - Paracellular 3
Carrier -Mediated 12
Apically Recycled 16
Mixed Mechanism 13