Physiological substance models

Physiologically Based Pharmacodynamic (PBPD) Model—A type of physiologically-based dose-response model which quantitatively describes the relationship between target tissue dose and toxic end points. These models advance the importance of physiologically based models in that they clearly describe the biological effect (response) produced by the system following exposure to an exogenous substance. 

Physiological Models for chemical bioaccumulation in fish are based on the same mass balance equations as the kinetic models for bioaccumulation, but the rate constants and chemical fluxes that quantify the rates of uptake and elimination of the substance are derived from Kow and a set of physiological parameters. The most well known model in this category is the FGETS (Food and Gill Exchange of Toxic Substances) model Barber et al. (1988, 1991) developed. This is a FORTRAN simulation model that predicts dynamics of a fish s whole body concentration of non-ionic, nonmetabolized, organic chemicals absorbed from the water only, or from water and food jointly. 

FIGURE 20.9 The pattern and time course of response to treatment is crucially dependent on the dose. This shows the same model as that illustrated in Figure 20.8, without treatment (thick line) and with three different dose rates of a drug that reduces the rate of loss of physiological substance (dotted line, dose rate of 10 dashed line, dose rate of 100 thin line, dose rate of 1000). 

Conceptual Representation of a Physiologically Based Pharmacokinetic (PBPK) Model for a Hypothetical Chemical Substance... 

Note This is a conceptual representation of a physiologically based pharmacokinetic (PBPK) model for a hypothetical chemical substance. The chemical substance is shown to be absorbed via the skin, by inhalation, or by ingestion, metabolized in the liver, and excreted in the urine or by exhalation. 

---