Main Body

6. Characteristics of Drug-Receptor Interactions:

  1. Follow Mass-Action Law: rate of reaction is DIRECTLY proportional to the concentration of the reactants, however, there is a limit. This limit is called the point of saturation
    • There are only so many receptors on each cell to which a drug can bind. Point of saturation refers to the point at which every receptor is bound.
  2. Selectivity: every drug has a preferred receptor; however, it may bind to others with the same or lesser affinity than its preferred receptor. Side effects of drugs are a direct result of low selectivity because one drug can bind multiple receptors producing undesired biological responses.
    • Not to be confused with “specificity” meaning drug can only bind to one type of receptor, regardless of the drug dose: drugs that are “specific” are unheard of at this point
  3. Response is Proportional to Drug Dose [Concentration] up to the point of saturation
  4. Binding Changes the Receptor: when a drug binds a receptor it results in one of two changes as outlined below:
    • AGONIST: results in an active receptor conformation to produce desired biological effect, i.e. intracellular signaling or changes in organ function
  5. ANTAGONIST: a simple occupancy by the antagonist of the receptor to hinder access of an agonist to its binding site on the receptor, therefore, obliterating the response to the agonist.


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Principles of Pharmacology - Study Guide by Edited by Dr. Esam El-Fakahany and Becky Merkey, MEd is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.