Lumping of whole-body physiologically based pharmacokinetic models

Area of Science:

• Pharmacokinetics and Systems Biology
• Computational Modeling and Simulation

Background:

• Physiologically based pharmacokinetic (PBPK) models are crucial for understanding drug disposition.
• Model complexity and dimensionality reduction are often necessary for practical implementation.
• Incorrect lumping in PBPK models leads to misspecification and unreliable predictions.

Purpose of the Study:

• To develop formal principles and standard procedures for lumping in PBPK modeling.
• To ensure that lumping reduces complexity without losing critical kinetic information.
• To provide a systematic approach for accurate PBPK model reduction.

Main Methods:

• Examined the lumping process using a system theory framework.
• Defined lumping principles based on tissue specification and structural position.
• Outlined a multi-stage lumping procedure including classification, parameter calculation, simulation, data lumping, and verification.
• Applied the principles to a whole-body PBPK model for barbiturate pharmacokinetics in rats.

Main Results:

• Established a formal lumping principle: group tissues with identical specifications and positions.
• Identified criteria for lumping parallel (similar time constants) and serial (rapid equilibration) tissues.
• Demonstrated the lumping procedure with a practical example, validating its applicability.

Conclusions:

• A system theory-based approach provides a formal foundation for PBPK model lumping.
• Adherence to defined principles and procedures ensures accurate and reliable model reduction.
• The proposed methodology enhances the utility of PBPK models by managing complexity effectively.