Pharmacodynamics
Pharmacodynamics (PD) is the study of the progression of pharmacological effects that result from the administration of a drug. PD effects can be either therapeutic or adverse (toxic). The values for the observed PD effect can represent the actual effect, or they can be surrogate biomarkers that provide an indication of the true PD effect.
Most PD models relate an observed PD effect, for example, the suppression of pain sensation, with an easily observable or measurable quantity such as the total or unbound concentration of the drug in the plasma or in tissue, or the drug dose. PD models can be divided into two main categories: direct response and indirect response, where:
In the direct response category, the PD response is directly proportional to the concentration of the drug in the plasma or if you are using PBPK, to the concentration of the drug in a given tissue.
In the indirect response category, the drug concentration in an “effect” compartment that is connected to either the central compartment or PBPK tissue determines the PD effect.
This section details the scientific principles behind the implementation of the optional PBPKPlus module that Simulations Plus developed for modeling multiple PD effects for any drug record in a database.
This section covers the following topics:
For details about the internal standards that were used to define the equations in this section, see Equation Standards.
The PD effect can also be referred to as the pharmacological response, or just the response, and is abbreviated as E or R, respectively. These terms and abbreviations are used interchangeably in this chapter.