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| The term '''half maximal effective concentration''' ('''EC<sub>50</sub>''') 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.<ref>[http://www.graphpad.com/curvefit/introduction89.htm Introducing dose response curves], Graphpad Software</ref> It is commonly used as a measure of drug's potency.
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| The EC<sub>50</sub> of a ''graded'' [[dose response curve]] therefore represents the concentration of a compound where 50% of its maximal effect is observed.<ref>[http://www.biochem.northwestern.edu/holmgren/Glossary/Definitions/Def-E/EC50.html EC50 definition]</ref>
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| The EC<sub>50</sub> of a ''quantal'' dose response curve represents the concentration of a compound where 50% of the population exhibit a response,<ref>[http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/190116.htm definition of EC<sub>50</sub> for quantal dose response curve]</ref> after a specified exposure duration.
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| It is also related to [[IC50|IC<sub>50</sub>]] which is a measure of a compound's inhibition (50% inhibition). For competition binding assays and functional antagonist assays [[IC50|IC<sub>50</sub>]] is the most common summary measure of the dose-response curve. For agonist/stimulator assays the most common summary measure is the EC<sub>50</sub>.<ref>[http://www.ncgc.nih.gov/guidance/section3.html Assay Operations for SAR Support] NIH Chemical Genomics Center</ref>
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| A small changes in [[ligand]] concentration typically result in rapid changes in response in the biological system, following a [[Sigmoid function|sigmoid]]al function.The [[inflection point]] at which the increase in response with increasing ligand concentration begins to slow is the EC<sub>50</sub>. Which can be mathematically determined by derivation of the best-fit line. While relying on a graph for estimation is more convenient, this typical method yields less accurate results and less precise.<ref>[http://www.ncgc.nih.gov/guidance/section3.html Assay Operations for SAR Support] NIH Chemical Genomics Center</ref>
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| == Equation ==
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| Many different equations can be used to derive an EC<sub>50</sub>. One possible function is:
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| <math>Y = Bottom + \frac{Top - Bottom}{1 + (\frac{X}{EC_{50}})^{\mathrm{-Hill coefficient}} }</math>
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| where Y is the observed value, Bottom is the lowest observed value, Top is the highest observed value, and the [[Hill coefficient]] gives the largest absolute value of the slope of the curve.<ref>[http://www.sigmaplot.com/products/sigmaplot/Standard_Curves_Analysis.pdf EC50 equation] - see page 5</ref>
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| == Limitations ==
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| The effects of a stressor or drug generally depend on the exposure time. Therefore, the EC<sub>50</sub> (and similar statistics) will be a function of exposure time. The exact shape of this time function will depend upon the stressor (e.g., the specific toxicant), its mechanism of action, the organism exposed, etc. This time dependency hampers the comparison of [[Potency (pharmacology)|potency]] or [[toxicity]] between compounds and between different organisms.
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| == See also ==
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| * [[Measures of pollutant concentration]]
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| * [[Dose-response relationship]]
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| * [[Certain safety factor]]
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| * [[IC50|IC<sub>50</sub>]] (half maximal inhibitory concentration)
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| * [[LD50|LD<sub>50</sub>]] (median lethal dose)
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| * [[Therapeutic index]]
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| == References ==
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| <references/>
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| == External links ==
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| * [http://www.changbioscience.com/stat/ec50.html Online IC50 Calculator]
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| * [http://www.unmc.edu/Pharmacology/receptortutorial/competition/IC50.htm Determination of IC<sub>50</sub> values]
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| * [http://pharmrev.aspetjournals.org/cgi/content/full/55/4/597 Neubig et al. International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification. XXXVIII. Update on terms and symbols in quantitative pharmacology. Pharmacol Rev. 2003 Dec;55(4):597-606.]
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| {{DEFAULTSORT:Ec50}}
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| [[Category:Pharmacology]]
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| [[Category:Toxicology]]
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Hi there. My title is Sophia Meagher although it is not the name on my birth certification. Distributing production has been his profession for some time. Ohio is exactly where her home is. To climb is something I really appreciate doing.
Feel free to visit my web site; psychic love readings; myoceancounty.net,