IC50

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 (IC50) is a measure of the potency of a substance in inhibiting a specific biological or biochemical function. IC50 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%.[1] The biological component could be an enzyme, cell, cell receptor or microbe. IC50 values are typically expressed as molar concentration.

IC50 is commonly used as a measure of antagonist drug potency in pharmacological research. IC50 is comparable to other measures of potency, such as EC50 for excitatory drugs. EC50 represents the dose or plasma concentration required for obtaining 50% of a maximum effect in vivo.[1]

IC50 can be determined with functional assays or with competition binding assays.

Sometimes, IC50 values are converted to the pIC50 scale.

Due to the minus sign, higher values of pIC50 indicate exponentially more potent inhibitors. pIC50 is usually given in terms of molar concentration (mol/L, or M), thus requiring IC50 in units of M.[2]

The IC50 terminology is also used for some behavioral measures in vivo, such as the two bottle fluid consumption test. When animals decrease consumption from the drug-laced water bottle, the concentration of the drug that results in a 50% decrease in consumption is considered the IC50 for fluid consumption of that drug.[3]

  1. ^ a b Hoetelmans RM. "IC50 versus EC50". PK-PD relationships for anti-retroviral drugs. Amsterdam: Slotervaart Hospital. Archived from the original on 2017-05-28 – via U.S. Food and Drug Administration.
  2. ^ Stewart MJ, Watson ID (July 1983). "Standard units for expressing drug concentrations in biological fluids". British Journal of Clinical Pharmacology. 16 (1): 3–7. doi:10.1111/j.1365-2125.1983.tb02136.x. PMC 1427960. PMID 6882621.
  3. ^ Robinson SF, Marks MJ, Collins AC (April 1996). "Inbred mouse strains vary in oral self-selection of nicotine". Psychopharmacology. 124 (4): 332–9. doi:10.1007/bf02247438. PMID 8739548. S2CID 19172675.