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Types of mean residence times
1College of Pharmacy, Department of Pharmacology, University of Michigan, Ann Arbor 48109.
Biopharmaceutics & Drug Disposition
|January 1, 1988
Summary
This study clarifies mean residence times (MRTs), distinguishing between system moment MRT and system matrix MRT. It highlights their differences in specific pharmacokinetic models, crucial for understanding drug disposition.
Area of Science:
- Pharmacokinetics and Drug Metabolism
- Mathematical Modeling in Biology
- Systems Pharmacology
Background:
- Mean Residence Times (MRTs) are critical pharmacokinetic parameters, but literature often lacks clarity on specific types used.
- Existing classifications of MRTs, including system moment MRT [MRT(S,MO)] and system matrix MRT [MRT(S,MA)], require precise definition.
- Understanding different MRTs is essential for accurate modeling of drug disposition and behavior within biological systems.
Purpose of the Study:
- To differentiate and clarify the definitions and applications of system moment MRT [MRT(S,MO)] and system matrix MRT [MRT(S,MA)].
- To analyze the conditions under which MRT(S,MO) equals or differs from MRT(S,MA) in various pharmacokinetic models.
- To review methods for estimating MRTs and discuss their utility in drug concentration and amount analysis.
Main Methods:
- Review and analysis of existing literature on Mean Residence Times (MRTs) in pharmacokinetic modeling.
- Comparison of system moment MRT [MRT(S,MO)] and system matrix MRT [MRT(S,MA)] under different model assumptions, including compartment-specific elimination.
- Derivation and presentation of mathematical relationships between MRT(S,MO) and MRT(S,MA) for specific two-compartment open models.
Main Results:
- MRT(S,MO) and MRT(S,MA) are equal in classical two-compartment open models with central compartment input, sampling, and elimination.
- When elimination occurs from a non-central compartment, MRT(S,MO) is not equal to MRT(S,MA).
- For the Rowland two-compartment model with peripheral elimination, MRT(S,MA) - MRT(S,MO) = 1/(k20 + k21), indicating MRT(S,MA) is larger.
Conclusions:
- Clear distinction between system moment MRT and system matrix MRT is vital for accurate pharmacokinetic interpretation.
- The relationship between MRT(S,MO) and MRT(S,MA) depends on the model structure, particularly the site of elimination.
- Accurate MRT estimation and differentiation are crucial for understanding drug behavior, especially for 'first-pass' drugs.