World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0003742950
Reproduction Date:

Title: Ec50  
Author: World Heritage Encyclopedia
Language: English
Subject: Spironolactone, Progesterone, Lipophilic efficiency, NIAID ChemDB, BitterDB
Collection: Pharmacodynamics, Pharmacology, Toxicology
Publisher: World Heritage Encyclopedia


The term 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 drug's potency.

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] Sometimes it is also expressed as pEC50 = - LOG(EC50) (with EC50 in M/l).

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 1
  • Limitations 2
  • See also 3
  • References 4
  • External links 5


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

Y = Bottom + \frac{Top - Bottom}{1 + (\frac{X}{EC_{50}})^{\mathrm{-Hill coefficient}} }

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]


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


  1. ^ Introducing dose response curves, Graphpad Software
  2. ^ EC50 definition
  3. ^ for quantal dose response curve50definition of EC
  4. ^ Assay Operations for SAR Support NIH Chemical Genomics Center
  5. ^ Assay Operations for SAR Support NIH Chemical Genomics Center
  6. ^ EC50 equation - see page 5

External links

  • Online IC50 Calculator
  • values50Determination of IC
  • 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.
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.