Hi there
What is the difference between IC50 and EC50?
Are they the same? If not, in which cases we should use IC50, and in which cases we should usd EC50?
Thank you in advance.

Thanks for your reply.
IC50 for the case that a complete inhibition was observed.
EC50 for the case that only parcial inhibition was observed.
It this correct?
Thanks.

EC50 is the effective dose of AGONIST that half maximally activates the channel/enzyme. You establish an EC50 by applying increasing amounts of AGONIST to your system and you measure the responses for each dose until you reach saturation - ie the point at which increasing the concentration of agonist dose not increase the magnitude of the response. If you normalize all your responses to the maximum and plot them against AGONIST concentration (plot the concentration on Log scale) you will create a dose-response plot, from which you can determine the dose that gives 50% activation - the EC50

IC50 is the dose of ANTAGONIST that half maximally inhibits the channel -

example - if you establish a dose of AGONIST which gives you maximum activated response and then you coapply a dose of ANTAGONIST with that dose of AGONIST which previously gave the maximum activated response when applied alone and you now see only half the maximum activated response, the dose of ANTAGONIST that you applied is the IC50 dose.

I strongly recommend you go to your library or a bookstore and look at this book

Rang & Dale's Pharmacology: With STUDENT CONSULT Online Access (Paperback)
by Humphrey P. Rang (Author), Maureen M. Dale (Author), James M. Ritter (Author), Rod Flower (Author)

Very interesting information. Might I ask another question, related to whether analysis of EC50 versus IC50 will give the same answer. For example, consider a drug that yields a response of from 0% to 100% - one can analyze EC50. Another way of looking at the same data stems from the fact that the output being measured decreases in the presence of the drug. So, in the absence of the drug, what one measures (the output) is 100%. With increasing drug, this decreases to a value of 0%. One can analyze IC50.
My question is as follows. Can one analyze by either approach, that is by analzing the response data (analysis by EC50) or by analyzing the values as they decrease from 100% to 0% (analysis by IC50)? Will the same answer be obtained by either approach. Thanks very much.

Analyzing the values as they decrease from 100% to 0% still gives you an EC50 because you're still calculating the concentration of agonist at which the response you are measuring is half-maximum. Just because the numbers go from 100% to 0% does not make it an IC50 analysis.

So..

EC50 - Different concentrations of agonist, plot log of [agonist] (x-axis) against % response from maximum (y-axis). Thus the curve rises from 0% to 100%, and you calculate the concentration of agonist that produces a half-maximum response.

IC50 - Different concentrations of antagonist and same concentration of agonist, plot log 10 of [antagonist] (x-axis) against % response from maximum. Thus the curve falls from 100% (no antagonist, maximum response) to 0% (high concentration of antagonist, no response), and you calculate the concentration of antagonist that prouces a half-maximum inhibition.

EC50 describes the effective dose of an agonist

IC50 describes the dose that causes half-maximal inhibition by an antagonist.

Thanks for your reply.

IC50 for the case that a complete inhibition was observed.

EC50 for the case that only parcial inhibition was observed.

It this correct?

Thanks.

No that is not correct

EC50 is the effective dose of AGONIST that half maximally activates the channel/enzyme. You establish an EC50 by applying increasing amounts of AGONIST to your system and you measure the responses for each dose until you reach saturation - ie the point at which increasing the concentration of agonist dose not increase the magnitude of the response. If you normalize all your responses to the maximum and plot them against AGONIST concentration (plot the concentration on Log scale) you will create a dose-response plot, from which you can determine the dose that gives 50% activation - the EC50

Click here for an example of EC50 calculation Agonist-response

IC50 is the dose of ANTAGONIST that half maximally inhibits the channel -

example - if you establish a dose of AGONIST which gives you maximum activated response and then you coapply a dose of ANTAGONIST with that dose of AGONIST which previously gave the maximum activated response when applied alone and you now see only half the maximum activated response, the dose of ANTAGONIST that you applied is the IC50 dose.

Click here for an example of IC50 calculation

innhibitor-response curve

I strongly recommend you go to your library or a bookstore and look at this book

Rang & Dale's Pharmacology: With STUDENT CONSULT Online Access (Paperback)

by Humphrey P. Rang (Author), Maureen M. Dale (Author), James M. Ritter (Author), Rod Flower (Author)

Publisher: Churchill Livingstone; 6 edition (January 25, 2007)

# ISBN-10: 0443069115

# ISBN-13: 978-0443069116

Here is the link to the book on amazon.com

http://www.amazon.com/Rang-Dales-Pharmacology-STUDENT-CONSULT/dp/0443069115/ref=sr_1_1?ie=UTF8&s=books&qid=1205861346&sr=1-1

For a very quick reference, here is the Wikipedia entry for EC50

http://en.wikipedia.org/wiki/Half_maximal_effective_concentration#References

it's ok but only for a staring point of reference - I still recommend you read the text book I told you about in my last post

sir can a dataset contains molecules having both ec50 and ic50 values ...

thanks

Very interesting information. Might I ask another question, related to whether analysis of EC50 versus IC50 will give the same answer. For example, consider a drug that yields a response of from 0% to 100% - one can analyze EC50. Another way of looking at the same data stems from the fact that the output being measured decreases in the presence of the drug. So, in the absence of the drug, what one measures (the output) is 100%. With increasing drug, this decreases to a value of 0%. One can analyze IC50.

My question is as follows. Can one analyze by either approach, that is by analzing the response data (analysis by EC50) or by analyzing the values as they decrease from 100% to 0% (analysis by IC50)? Will the same answer be obtained by either approach. Thanks very much.

Analyzing the values as they decrease from 100% to 0% still gives you an EC50 because you're still calculating the concentration of agonist at which the response you are measuring is half-maximum. Just because the numbers go from 100% to 0% does not make it an IC50 analysis.

So..

EC50 - Different concentrations of agonist, plot log of [agonist] (x-axis) against % response from maximum (y-axis). Thus the curve rises from 0% to 100%, and you calculate the concentration of agonist that produces a half-maximum response.

IC50 - Different concentrations of antagonist and same concentration of agonist, plot log 10 of [antagonist] (x-axis) against % response from maximum. Thus the curve falls from 100% (no antagonist, maximum response) to 0% (high concentration of antagonist, no response), and you calculate the concentration of antagonist that prouces a half-maximum inhibition.