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:


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.