The effect of an antagonist on the efficacy of an agonist is based on the following equilibrium relationship wherein the empty receptor (R) competes with the antagonist (B) and the receptor can exist in an antagonist bound state (BR) as well:
When applying the law of mass action to these simultaneous equations, we can derive the following relationship: Continue reading
What happens to the log (concentration) vs response curve of a drug in the presence of a competitive antagonist? Assuming that the agonist and the antagonist are in equilibrium with the receptor-binding site, we will observe a parallel shift in the agonist concentration response curve. We can estimate the proportion of agonist and antagonist bound to the receptors by the concentration of the agonist and antagonist and by their affinities for the receptor as follows:
Under the laws of Mass Action, we can derive the following relationship: Continue reading