EC50

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Half maximal effective concentration (EC50) 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.[1] It is commonly used as a measure of a drug's potency. EC50 is expressed in molar units (M), where 1 M is equivalent to 1 mol/L.

The EC50 of a graded dose response curve therefore represents the concentration of a compound where 50% of its maximal effect is observed.[2] The EC50 of a quantal dose response curve represents the concentration of a compound where 50% of the population exhibit a response,[3] after a specified exposure duration.

It is also related to IC50 which is a measure of a compound's inhibition (50% inhibition). For competition binding assays and functional antagonist assays IC50 is the most common summary measure of the dose-response curve. For agonist/stimulator assays the most common summary measure is the EC50.[4] The half maximal effective concentration is sometimes also expressed as pEC50 instead of EC50, where:

A small change in ligand concentration typically result in rapid changes in response in the biological system, following a sigmoidal function.The inflection point at which the increase in response with increasing ligand concentration begins to slow is the EC50, 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.[5]

Equation[edit]

Many different equations can be used to derive an EC50. One possible function is:

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.[6]

Limitations[edit]

The effects of a stressor or drug generally depend on the exposure time. Therefore, the EC50 (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 or toxicity between compounds and between different organisms.

See also[edit]

References[edit]

  1. ^ Introducing dose response curves Archived 2007-02-19 at the Wayback Machine., Graphpad Software
  2. ^ EC50 definition
  3. ^ definition of EC50 for quantal dose response curve
  4. ^ Assay Operations for SAR Support Archived 2006-11-29 at the Wayback Machine. NIH Chemical Genomics Center
  5. ^ Assay Operations for SAR Support Archived 2006-11-29 at the Wayback Machine. NIH Chemical Genomics Center
  6. ^ EC50 equation Archived 2012-04-17 at the Wayback Machine. - see page 5

External links[edit]