IC50 is the inhibitory concentration. It is the concentration which inhibits growth of 50% of the test organisms. Therefore, you will need to draw a graph of concentration on X-axis vs. percentage inhibition on Y-axis, as the Pushpinder Kaur suggested. The slope of this graph will give you the IC50 value.

https://www.researchgate.net/post/How_do_we_calculate_the_IC_50_value_in_antioxidant_assays

Check the answers given in the above link. This should give you a clear idea of how to find the IC50 value. Hope this helps.

I think you would like to find the EC50 value in your case. The EC50 value is the concentration of compound decreasing the absorbance of a DPPH solution by 50%. Calculation is similar to that of IC50. You can refer to this for further information on how to calculate both IC50 and EC50.

http://www.ncbi.nlm.nih.gov/pubmed/22328315

Regards,

Subramaniyam

Yes Thangaraj, u can have only one ic50 per compound per assay condition. You can get it by using regression analysis from grapgpad prism software or even in excel.. and the equation for antioxidant assay is usually not in the form of a straight line.. its a curcilnear increase

There are different methods to estimate IC50, LD50 and LC50. All of them have the same concept.. Estimate 50% of  their effect.  Usually the concentration or dose transformed to log. Many non linear equations can be used and also many programs such as sas spss graphpad prism medcalc and calcsyn.

HI to everyone !!  I have set of compounds and their % of inhibition value.i want to find IC50 value from inhibition value.

I put plot but i did't get it.pls help me.i attached one paper,in that paper has 20 compounds and their percentage of inhibition value(TABLE 1,2,3).i want ic50 value of those compounds.pls help me..thank you

http://www.ncbi.nlm.nih.gov/pubmed/21189020

I would like to convert DPPH radical scavenging activity

% to Ic50 e.g. 46.6 ± 2.5% equal ??? ic50, please help me

To estimate IC50 you need the different levels of concentrations and percentages of inhibition or death or response. Then you must convert proportions to probit unit

and then to construct the prediction equation.

I have a book published in Arabic. This book included many methods to estimate LD50 by 5 programs. (SAS, SPSS, Minitab, STATGRAPH ، STATISTICA).Anyhow, The common method is Probit. Below an example you can apply by SAS:

data conc;

input dose r n;

cards;

0.02 0 30

0.04 2 30

0.06 3 30

0.08 5 30

0.10 8 30

0.20 12 30

0.30 20 30

0.40 26 30

0.50 27 30

0.60 30 30

proc probit data=conc lackfit log10 inversecl;

model r/N = Dose;

run;

many thanks dr. Firas Rashad Al-Samara

There are many ways. Most efficient if you have a single measurement is using the relation IC50 = Conc. * (50/ %NH). where Conc = the concentration of agent tested & %INH is per cent inhibition.

Hi Samra,

1. After putting your x-and y-axis values in graphpad go to analysis-->transform

2. Convert x-axis values (conc.) to their log values

3. Then again go to analysis and go for "Nonlinear regression (curve fit)" under XY analysis

4. Then select what you want to calculate the inhibition IC50 or induction IC50

5. Then press ok and all the things will be done.

I believe if someone has clear understanding of what IC50 ( half maximal inhibitory concentration) basically infers: the concentration of extract which hunt 50 of under investigation radicals either of DPPH or ABTS. So, it does not matter which software you are using, you have plot a scatter plot of various extract concentration (normally from 2-2000ug/ml), add a trend line, see the equation of line, like Y=2.358X+4.69;. Now substitute y=0.5 in this equation to calculate the x (IC 50)

Dear Sir,

I have a book published in Arabic which included several methods and programs to estimate LC50. Anyhow if you know the SAS program, below the code of estimation and hope to be useful.

data conc;

input dose r n;

cards;

0.02 0 30

0.04 2 30

0.06 3 30

0.08 5 30

0.10 8 30

0.20 12 30

0.30 20 30

0.40 26 30

0.50 27 30

0.60 30 30

proc probit data=conc lackfit log10 inversecl;

model r/N = Dose;

run;

Dear Dr. Al-Samarai

thanks for your complete answer, but would you please tell me how i can calculate IC50 using minitab or SPSS? I really need that right now. I appreciate you beforehand.

The logit and Probit method is very easy using Excel.

All you need is Excel program, and the probit table

Some hint to follow the sample calculation:

** Probit serves as y-axis while *log 10 values serves as x-axis. The Linest excel function can be used to determine the slope and the intercept. †Since IC50 was to be determined, the value 50 need be probited which gives 5 i.e. the Y (see the probit table). This method of IC50 determination is called non-linear regression method.

Dear Mr. Egbuna

Thanks for detailful answer you shared , but what abou linear regression? and also if i'm gonna compare the results with trolox or BHT what further steps should I take into consideration?

Dear Dr. Shagayegh thanks for your kind comments ok. The linear regression is very simple but comes with some limitations. I recommend the non-linear regression method. This non-linear method is what is programmed into some of these recommended softwares where you just enter the values and get your IC50. Even the probit table can be generated by yourself through the configuration of excel statistical functions.

Thank you.

With regards,

Egbuna, C.

Should the graph be a linear one or a sigmoidal? I believe the data fits better to a sigmoidal curve.

A discussion on which mathematical model provides the best fit to the data for all the concentration range, is interesting but differences are likely to be least near to 50% inhibition.

For most application scientist, you want a quick & robust comparison between samples . Pls. use linear regression as a simple tool.

Plot your data

Y = mx +B,

where Y = % inhibtiion and X = concentration/ or quantity of sample added (whatever the conc. units) and B = graph Y-intercept value.

Find the equation for the line, i.e. determine slope (m) and intercept B

Next:

50% = m (IC50) + B

IC50 = (50% - B)/m

Use any software/ and or platform to perform linear regression. Good luck.

Thank you for your response Sir. Can you tell me what should be the ideal R square value for this?

Hello. Sir. This is a very astute question. The answer will seem surprising. Pls. after plotting %Inh vs. conc the graph may be non-linear. For example, at very high concentrations % Inh will be always 100%. Pls. proceed thus. Delete highest concentration data from you graph. Check if R increaess, delete the next highest point, check if R increases and so on: delete highest points untll R does not rise. Thne stop. You have found the "linear dynamic range" for your data. Fit equation of the straight line (Y= m x + B) and calculate IC50 value as advised.

Thank you Sir.