7.20 : Model Approaches for Pharmacokinetic Data: Physiological Models

Physiological models in pharmacokinetics are instrumental in understanding the distribution and elimination of drugs within the body. These models describe the drug concentration within target organs, influenced by factors such as drug uptake, tissue volume, and blood flow. Drug uptake is governed by the partition coefficient, which signifies the drug concentration ratio in tissue to that in the blood. The blood flow rate to a specific tissue is expressed as Q_t, and the rate of change in tissue drug concentration can be mathematically expressed, with C_art and C_ven representing the arterial and venous blood drug concentrations, respectively.

Physiological models can be categorized into blood-flow-limited models and diffusion-limited models. In a blood-flow-limited model, drug distribution is primarily regulated by blood flow to the tissue. In contrast, in a diffusion-limited model, the diffusion rate across tissue barriers predominantly controls drug distribution.

The advantages of these models lie in their ability to enhance understanding of complex drug interactions within the body, providing valuable insights for pharmacokinetic studies. Equations such as those expressing the rate of change in tissue drug concentration play a crucial role in quantitatively understanding the dynamics of drug distribution within physiological models. Overall, physiological models in pharmacokinetics serve as powerful tools for understanding the intricate processes involved in drug distribution and elimination within the human body, offering valuable insights for pharmaceutical research and development.