A compartmental absorption and transit model for estimating oral drug absorption

Area of Science:

• Pharmacokinetics
• Drug Absorption Modeling
• Physiologically Based Pharmacokinetic (PBPK) Modeling

Background:

• Estimating drug absorption is crucial for immediate-release products.
• Passive drug transport is influenced by intestinal transit and absorption dynamics.

Purpose of the Study:

• To develop a compartmental absorption and transit model.
• To estimate the fraction of dose absorbed and absorption rate for passively transported drugs.

Main Methods:

• Developed a model incorporating simultaneous small intestinal transit flow and drug absorption.
• Employed analytical and numerical methods to solve model equations.
• Validated the model using data from ten drugs with varying absorption characteristics.

Main Results:

• Derived an equation: Fraction Absorbed (F(a)) = 1-(1+0.54 P(eff))(-7), where P(eff) is human effective permeability.
• Demonstrated a strong correlation between fraction absorbed and effective permeability.
• Successfully explained oral plasma concentration profiles of atenolol using the model.

Conclusions:

• The developed model accurately estimates drug absorption fractions based on effective permeability.
• This model provides a valuable tool for predicting oral drug bioavailability in immediate-release formulations.
• Effective permeability is a key determinant of drug absorption for passively transported compounds.