Efficacy. I: A new method for estimating relative efficacy of full agonists via a newly defined efficacy related parameter

Eur J Pharmacol. 1997 Feb 12;320(2-3):223-31. doi: 10.1016/s0014-2999(96)00899-0.


A new method for estimating relative efficacies and relative intrinsic efficacies of agonists is described. Relative efficacy is estimated by employing a newly defined efficacy related parameter (eES) and it may be estimated without prior knowledge of efficacy values or the value of the equilibrium dissociation constants, KA, of agonist-receptor complexes. The parameter eES is directly related to efficacy (e) and is defined as the ratio of maximal stimulus to maximal effect of an agonist. The value of eES indicates whether or not spare receptors are present for a particular agonist-effector system. The eES values of agonists are estimated by utilizing submaximal concentration-effect curves determined with fixed agonist-competitive antagonist concentration combinations and choosing a suitable reference (height of an agonistic concentration-effect curve) to which the height of the stimulus concentration-effect curves of the agonist may be compared. In addition to eES, other new agonist-effector parameters, namely SEm/Sm and phi min, were also defined.

MeSH terms

  • Binding, Competitive
  • Drug Antagonism
  • Kinetics
  • Mathematical Computing
  • Pharmacology / methods*
  • Receptors, Cell Surface / agonists*
  • Receptors, Cell Surface / antagonists & inhibitors


  • Receptors, Cell Surface