# How to calc. IC50? - (Jun/12/2009 )

Hi all,

I calculated the cell viability percentage follwing promega Cell-titre glo, but I don't know how to convert this into an IC50 number? for example I have increasing concentrations of the drug I'm using, and viability % for each dose,, I tried using GraphPad Prism program but didn't know how to use the program? can someone please give me step by step how to use that.. where to put the data and all... I tried searching the net,, but the info is too complicated for me... I need someone who used it and can guide me step by step... pleeeeeeeeeeeeease...

jazmenia on Jun 12 2009, 04:42 PM said:

I calculated the cell viability percentage follwing promega Cell-titre glo, but I don't know how to convert this into an IC50 number? for example I have increasing concentrations of the drug I'm using, and viability % for each dose,, I tried using GraphPad Prism program but didn't know how to use the program? can someone please give me step by step how to use that.. where to put the data and all... I tried searching the net,, but the info is too complicated for me... I need someone who used it and can guide me step by step... pleeeeeeeeeeeeease...

GraphPad Prism got a video step by step introduction, perhaps you should try to watch it. It's not that long so I hope it'll help.

Hi,

Here is a step-by-step manual for GrafPad Prism. You can also download it directly from the software.

A.

Hi all,

I have never tried to calculate ic50 with grafpad prism. I have calculated ic50 simply using excel. According to the technique I use I created an excel template which plot a graph for the data of 3 (I perform cytotoxicity tests in triplicates) 96-well plates. From the equation of the trendline I can calculate IC50. There is no need for a software

jazmenia on Jun 12 2009, 09:42 AM said:

I calculated the cell viability percentage follwing promega Cell-titre glo, but I don't know how to convert this into an IC50 number? for example I have increasing concentrations of the drug I'm using, and viability % for each dose,, I tried using GraphPad Prism program but didn't know how to use the program? can someone please give me step by step how to use that.. where to put the data and all... I tried searching the net,, but the info is too complicated for me... I need someone who used it and can guide me step by step... pleeeeeeeeeeeeease...

I routinely use Grafit:

Grafit

been into the same problem of calculating IC50 but now using excel to determine IC50 same as **genom38** because using graph pad prism somehow quite confusing.

I've also using excel for my analysis... Dont be upset...

Hi,

From my experience using Graphpad Prism, it gives somewhat arbitary results. After you done the analysis, it will show the curve fitting graph. Most of the time the log IC50 value in the table is different from the graph. For example, when you looking at the graph, the log value for 50% inhibition was 2.1, but in the table it showed 3.0, it is a value for 70% inhibition, not 50%... I rather use microsoft excel. It gives reliable results.

Hi,

I tried GraphPad Prism to calculate ic50, however it gives different results from the results of excel. These results drastically change fold changes. I can't understand why. Results are below. I am waiting for your comments.

GraphPad Prism

ic50 1 = 4,66 Fold Change(FC) = 1

ic50 2 = 83,82 FC = 17.99

ic50 3 = 124,3 FC = 26.67

Excel

ic50 1 = 43,5 FC = 1

ic50 2 = 60,4 FC = 1.4

ic50 3 = 178,79 FC = 4.1

genom38 on Fri Aug 13 09:50:30 2010 said:

Hi,

I tried GraphPad Prism to calculate ic50, however it gives different results from the results of excel. These results drastically change fold changes. I can't understand why. Results are below. I am waiting for your comments.

GraphPad Prism

ic50 1 = 4,66 Fold Change(FC) = 1

ic50 2 = 83,82 FC = 17.99

ic50 3 = 124,3 FC = 26.67

Excel

ic50 1 = 43,5 FC = 1

ic50 2 = 60,4 FC = 1.4

ic50 3 = 178,79 FC = 4.1

The problem with calculating IC50 values in Prism is that you must have proper dose response curves for it to work properly as in calculates based on a formula (hope I am making sense ) i.e if you viability curve does reach 0% it can cause problems.

If I am comparing IC50 values for viability honestly I do it manually by reading of the IC50 value for each individual experiment (not replicate just the average for each experiment).

The IC50 is the concentaion of your drug that reduces the viabilty of you cells by 50% (I just add this as in reply what was in the initial post )

I then enter this data into Prism to do my statistics this way the error can be calculated the type of analysis will depend on the number of conditions you are comparing.