The effects of a stressor or drug generally depend on the exposure time. In this case, the EC 50 represents the rising section of the sigmoid curve. In dose response curves, the logarithm of is often taken, turning the Hill equation into a sigmoidal logistic function. The EC 50 represents the point of inflection of the Hill equation, beyond which increases of have less impact on E. Where E is the observed response or effect above baseline, and nH, the Hill coefficient reflects the slope of the curve. Hence, it is often more practical to refer to the logarithmically transformed pEC 50 values instead of EC 50, where There is a wide range of EC 50 values of drugs they are typically anywhere from nM to mM. The EC 10 and EC 90 concentrations to induce 10% and 90% maximal responses are defined similarly. The lower the EC 50, the less the concentration of a drug is required to produce 50% of maximum effect and the higher the potency. The term "potency" refers to the EC 50 value. The at which E is 50% of E max is termed the half maximal effective concentration and is abbreviated EC 50, or rarely 50. E increases with until at sufficiently high, when E plateaus towards an asymptotic maximum attainable response, E max. At low agonist concentrations,, the response, E is immeasurably low but at higher, E becomes measurable. The agonist that binds to the receptor and initiates the response is usually abbreviated A or D. The response or effect, E, is dependent on both the binding of the drug and the drug-bound receptor. While relying on a graph for estimation is more convenient, this typical method yields less accurate results and less precise. The inflection point at which the increase in response with increasing ligand concentration begins to slow is the EC 50, which can be mathematically determined by derivation of the best-fit line. The EC 50 is also related to IC 50 which is a measure of a compound's inhibition (50% inhibition).īiological responses to ligand concentrations typically follow a sigmoidal function. For agonist/stimulator assays the most common summary measure is the EC 50. A quantal dose response curve shows the percentage of subjects where a response is noted in an all-or-none manner (y axis) over the dose of the drug (x axis).įor competition binding assays and functional antagonist assays IC 50 is the most common summary measure of the dose-response curve. The EC 50 of a quantal dose response curve represents the concentration of a compound where 50% of the population exhibit a response, after a specified exposure duration.įor clarification, a graded dose response curve shows the graded effect of the drug (y axis) over the dose of the drug (x axis) in one or an average of subjects. The EC 50 of a graded dose response curve therefore represents the concentration of a compound where 50% of its maximal effect is observed.
EC 50 is a measure of concentration, expressed in molar units (M), where 1 M is equivalent to 1 mol/ L. It is commonly used as a measure of a drug's potency, and the use of EC 50 is preferred over that of 'potency', which has been criticised for its vagueness. More simply, EC 50 can be defined as the concentration required to obtain a 50% effect and may be also written as 50. Half maximal effective concentration (EC 50) refers to the concentration of a drug, antibody or toxicant which induces a response halfway between the baseline and maximum after a specified exposure time. The EC 50 of the agonist is represented by the x co-ordinate that corresponds with the half-maximum of the leftmost curve.
The tissue response (y-axis) to an agonist, in log concentration (x-axis), in the presence of different antagonist concentrations.
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