Step by step IC50 determination using GraphPad

GraphPad  is very useful software for measuring enzyme kinetics and  for determination of IC50. This time I will show you how to use that software for determination of IC50 of a drug candidate. Let's say that name of the drug is brangin, you isolate it from a tree which has abililty to stop activity of  SDH, an important enzyme of a parasite.

First this is the data you need.

brangin (uM)   SDH (umol/min/mg)
2 147
5 147
10 146
20 145
50 144
100 125
200 96
500 55
1000 17
5000 7
10000 2

copy and paste above data (number only) to your GraphPad. First, open that software, then click
File > New > New Project File , the pop up will come as follow :

Please make sure that you tick the red circle above. The it will show you an empty sheets. Paste the data above under X as showed below. The press Analyse to change your data to logarithmic form.

Then, a window will pop up as follow, and find Transform Number , select Transform, then click OK. If you don't do this step, you will not get IC50 value !. So, this step is important to do. 

Then   tick the option transform X value using X=log(X). There are lots of choices there, you should select X=log(X), the click OK

The the window will automatically change as follow. Look at X value, your X data already change to log form. Then click the icon which I sign with red circle below. If your mouse pointer on that icon, it will show a sentence fit curve with non linear regression.

Then next window will come and find Dose-response - Inhibition, then select log(inhibitor) vs. response (three parameters), then press OK.

And next, you will see the IC50 value as follow:

Then, you can see the graph of IC50 too. Look at left side of display, you will find last file Transform of Data 1 under folder Graph. Click it and you will see a graph as follow:

But you maybe will feel strange with the number below X axes. Don't worry, you can change that number to power 10 by this way. First right click X axes.  Then select Format axes ,

Then, select Number format : Power 10 and click OK

then you will get as you want.

If you want to change label for X and Y axes, just click XTitle and YTitle and title Transform of Data 1, you can change with your own label. GraphPad also has a complete text editor including Greek letter and Wingding symbols too.

Finish. Save that data if you need that.

Please don't care so much about my English, as far as you understand what I write and you can immediately do  IC50 determination. :).