4.8 : Dose-Response Relationship: Overview

Agonists can bind with and activate receptors, resulting in the formation of drug-receptor complexes. Once formed, these complexes catalyze many biochemical processes at the cellular level and subsequently induce a pharmacologic response. The degree of response is directly proportional to the fraction of activated receptors, which in turn, depends on the concentration of the drug at the receptor site as well as the sensitivity of the receptor. An increase in the administered dose contributes to increased drug concentration at the receptor site, enhancing the strength of the biological response. The graded dose-response curve is a graphical representation that showcases the correlation between the drug's concentration and the extent of the resultant response. The hyperbolic curve demonstrates that the magnitude of the response gradually increases with the increase in drug dose. The maximum effect of the drug is observed once the receptors attain complete saturation. Sigmoidal curves emerge upon the semi-logarithmic plotting of hyperbolic curves, and these curves are used for depicting drug efficacy and potency. Potency is gauged by evaluating the drug concentration required to reach half of the maximum effect, represented by the EC₅₀ value. Conversely, efficacy is a measure of the drug's ability to produce a maximal therapeutic effect, which is determined by the E_max value.