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[[File:IC50 determination illustration.png|thumb|Graphical representation of the IC50 determination of the inhibition of an enzyme's activity by a small molecule ("drug"). Four different concentrations of the small molecule (ranging from 30 to 300 μM) were tested.]]'''Half maximal inhibitory concentration (IC<sub>50</sub>)''' is a measure of the potency of a substance in inhibiting a specific biological or biochemical function. IC<sub>50</sub> is a quantitative measure that indicates how much of a particular inhibitory substance (e.g. drug) is needed to inhibit, ''in vitro'', a given biological process or biological component by 50%.<ref name="FDA">{{cite web | vauthors = Hoetelmans RM | location = Amsterdam | publisher = Slotervaart Hospital | via = U.S. Food and Drug Administration | url = https://www.fda.gov/ohrms/dockets/ac/00/slides/3621s1d/sld036.htm | title = IC50 versus EC50 | series = PK-PD relationships for anti-retroviral drugs | archive-url = https://web.archive.org/web/20170528053210/https://www.fda.gov/ohrms/dockets/ac/00/slides/3621s1d/sld036.htm |archive-date=2017-05-28 }}</ref> The biological component could be an enzyme, cell, cell receptor or microorganism. IC<sub>50</sub> values are typically expressed as [[molar concentration]].
[[File:IC50 determination illustration.png|thumb|Graphical representation of the IC50 determination of the inhibition of an enzyme's activity by a small molecule ("drug"). Four different concentrations of the small molecule (ranging from 30 to 300 μM) were tested.]]'''Half maximal inhibitory concentration (IC<sub>50</sub>)''' is a measure of the potency of a substance in inhibiting a specific biological or biochemical function. IC<sub>50</sub> is a quantitative measure that indicates how much of a particular inhibitory substance (e.g. drug) is needed to inhibit, ''in vitro'', a given biological process or biological component by 50%. The biological component could be an enzyme, cell, cell receptor or microorganism. IC<sub>50</sub> values are typically expressed as [[molar concentration]].


IC<sub>50</sub> is commonly used as a measure of antagonist drug potency in pharmacological research. IC<sub>50</sub> is comparable to other measures of potency, such as [[half maximal effective concentration|EC<sub>50</sub>]] for [[agonist|excitatory drugs]]. EC<sub>50</sub> represents the dose or plasma concentration required for obtaining 50% of a maximum effect ''in vivo''.<ref name="FDA" />
IC<sub>50</sub> is commonly used as a measure of antagonist drug potency in pharmacological research. IC<sub>50</sub> is comparable to other measures of potency, such as [[half maximal effective concentration|EC<sub>50</sub>]] for [[agonist|excitatory drugs]]. EC<sub>50</sub> represents the dose or plasma concentration required for obtaining 50% of a maximum effect ''in vivo''.


IC<sub>50</sub> can be determined with functional assays or with competition binding assays.
IC<sub>50</sub> can be determined with functional assays or with competition binding assays.
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Sometimes, IC<sub>50</sub> values are converted to the '''pIC<sub>50</sub>''' scale.
Sometimes, IC<sub>50</sub> values are converted to the '''pIC<sub>50</sub>''' scale.
:<math chem="">\ce{pIC_{50}} = -\log_{10} \ce{(IC_{50})}</math>
:<math chem="">\ce{pIC_{50}} = -\log_{10} \ce{(IC_{50})}</math>
Due to the minus sign, higher values of pIC<sub>50</sub> indicate exponentially more potent inhibitors. pIC<sub>50</sub> is usually given in terms of molar concentration (mol/L, or M), thus requiring IC<sub>50</sub> in units of M.<ref name="stewart">{{cite journal | vauthors = Stewart MJ, Watson ID | title = Standard units for expressing drug concentrations in biological fluids | journal = British Journal of Clinical Pharmacology | volume = 16 | issue = 1 | pages = 3–7 | date = July 1983 | pmid = 6882621 | pmc = 1427960 | doi = 10.1111/j.1365-2125.1983.tb02136.x }}</ref>
Due to the minus sign, higher values of pIC<sub>50</sub> indicate exponentially more potent inhibitors. pIC<sub>50</sub> is usually given in terms of molar concentration (mol/L, or M), thus requiring IC<sub>50</sub> in units of M.{{pmid|6882621}}


== See Also ==
== See Also ==
* [[EC50|EC<sub>50</sub>]]
* [[EC50|EC<sub>50</sub>]]
* {{SeeWikipedia|IC50}}
* {{SeeWikipedia|IC50}}
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