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Human intestinal absorption--neutral molecules and ionic species.

Michael H Abraham¹

¹Department of Chemistry, University College London, London WC1H OAJ, UK.

Journal of Pharmaceutical Sciences

|June 7, 2014

Summary

This summary is machine-generated.

Human intestinal absorption (%HIA) for 280 drugs is accurately predicted using three descriptors for neutral molecules. The study concludes that diffusion through the unstirred mucosal layer is the primary rate-limiting step for drug absorption.

Keywords:

absorption diffusion intestinal absorption ionic descriptors partition passive diffusion/transport perfusion permeability

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Area of Science:

Pharmacokinetics
Drug Discovery
Computational Chemistry

Background:

Understanding human intestinal absorption (%HIA) is crucial for predicting oral drug bioavailability.
Previous models often involve complex descriptors and do not fully elucidate the rate-determining steps.
The physicochemical properties of drug molecules significantly influence their absorption across the intestinal barrier.

Purpose of the Study:

To develop a predictive model for %HIA using minimal molecular descriptors.
To investigate the relationship between %HIA and other transport processes like diffusion and bilayer permeation.
To identify the rate-determining step in the process of human intestinal absorption.

Main Methods:

Quantitative Structure-Property Relationship (QSPR) analysis was performed on a dataset of 280 drugs.
Three molecular descriptors were identified to accurately predict %HIA for neutral molecules.
Comparison of model coefficients with those for diffusion and membrane permeation.
Analysis of substituent effects on %HIA and permeation.
Calculation of permeation rates through the unstirred mucosal layer.

Main Results:

An excellent fit (SD of 13.9%) for %HIA was achieved using only three descriptors for neutral molecules.
Descriptors for ionized species did not improve the goodness-of-fit.
Human intestinal absorption (HIA) kinetics resemble diffusion in water more than permeation through biological bilayers.
Substituent effects on HIA align with diffusion principles, not bilayer permeation.
Calculated permeation rates through the unstirred mucosal layer matched experimental HIA rates.

Conclusions:

For the studied set of 280 compounds, diffusion through the unstirred mucosal layer is the rate-determining step for %HIA.
The model provides a simplified yet accurate approach for predicting drug absorption.
Findings suggest that HIA is primarily governed by diffusion rather than lipid bilayer partitioning.