Tissue Drug Concentration.

Area of Science:

• Pharmacokinetics and Drug Distribution
• Physiology
• Biochemistry

Background:

• Blood flow is crucial for delivering oxygen, nutrients, and drugs to tissues.
• Drug concentrations within tissues are heterogeneous and influenced by blood flow, transporters, and metabolism.
• Tissue drug concentrations, not just blood concentrations, dictate pharmacodynamics.

Purpose of the Study:

• To develop a theoretical concept for solute partitioning between blood and tissues.
• To explore the relationship between in vitro metabolism and in vivo drug elimination.
• To enhance the prediction of drug behavior within the body.

Main Methods:

• Theoretical modeling of solute partition between intravascular and extravascular spaces.
• Review of experimental studies on aqueous/non-aqueous solute partitioning.
• Analysis of clinical microdialysis research.
• Formulation of hypotheses linking in vitro metabolism to in vivo elimination.

Main Results:

• Drug concentrations in tissues are influenced by blood flow, membrane transporters, and metabolic enzymes, leading to heterogeneity.
• Systemic drug elimination is driven by elimination rates rather than solely free drug concentration.
• Tissue drug concentration is a dynamic balance between input and output rates.

Conclusions:

• A theoretical framework for understanding solute distribution in tissues was developed.
• In vitro metabolism data can potentially predict in vivo drug elimination rates.
• Accurate prediction of drug elimination requires considering tissue-specific factors beyond blood concentration.