From binding to response

From binding to response

Pharmacodynamics of a drug in practice are usually expressed by the relationship between dose and response. It is obvious that the ligand-receptor binding plays an important role in this dose-response relationship.
The response to a drug is proportional to the concentration of receptors that are bound by the drug.
According to traditional receptor theory, the magnitude of an effect (E) produced when an agonist at a specified concentration ([A]) interacts with a receptor depends upon 4 factors:



Two of these are chemical properties of the agonist

itself unique for each ligand-receptor pair:
KA: the affinity related parameter;
ε: "intrinsic efficacy" (ε describes the capacity of a drug to produce a receptor "stimulus" which is transmitted to the signal transduction components of the cell).

The remaining two parameters are cell or tissue dependent properties:
RT: receptor density;
ƒ: a function that describes the efficiency of signal transduction.