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IC50 calculation: Should you calculate IC50 for each replicate experiment and th - (Aug/21/2013 )

Hi all! I have a question on how to calculate IC50 of drug treatment on cell survival.
For example, I did three independent experiments in 96--well plates using the MTT method. After putting the OD values into Prism one experiment at a time, I can get three different IC50s. From these I can get an averaged IC50. However, when you want to present the fitted survival curve, you can only choose one representative curve from the three, right? 
In order to show a curve which will incorporate all data from the three independent experiments, I did the following and I want to know if this is acceptable. For experiment 1, drug concentration 1, I averaged the OD values from triplicate wells and normalized it to control (100% survival), and got say 10% survival. And I did the same thing for exp. 2 & 3, calculated their survivals at this drug concentration, say 11%, 12%. And similarly calculated survival for all the other drug concentrations. This way, the data input for Prism would be: Drug Conc. 1, 10%, 11%, 12%; (each is the average from one independent exp.) Drug Conc. 2: 20%, 21%, 22%, etc. etc.... Now Prism will only return one fitted curve and one IC50 value. Is this data manipulation acceptable? Thanks!! --Sara


That's pretty normal treatment for data, you could also put one of the graphs and say "representative graph from 3 independent experiments"


I think your method is fine. You can also put 3 lines in the same figure to show that they are almost identical.