Calculating the EC10 or IC90 values for a dose response curve is not as simple as the EC50 or IC50 values when using the 4PL or 5PL model equations.

The equation for calculating any EC value given a 4PL curve fit is the following:

EC_F = (F/(100-F))^(1/H) * EC₅₀

0 < F < 100 (This is the EC value you are interested in. For example, F=10 for EC₁₀.)
H = Hill Slope for the 4PL curve fit

Luckily, our latest release of MasterPlex ReaderFit 2010 makes this easy. Yes, even with the 5PL curve-fit!

Here’s how:

1. Copy & paste your data into ReaderFit

   Copy your response values from the source and paste it into ReaderFit via CTRL+V -> Paste Response Values.

2. Mark data as Sample Curve type (part 1)

   Select all of the data points that will be used to fit one entire dose response curve including all replicates. In the example given below, there are 7 groups each done in duplicate.
   

3. Mark data as Sample Curve type (part 2)

   Click on the blue Mark Sample Curve button. (The Auto Fill dialog may pop up. Click the Close button if you see it.)
   

4. Indicate known dose concentration values (part 1)

   Select Independent Values(X-axis) from the data pull-down menu. This will show the corresponding data in the plate view. By default, all of the Independent Values(X-axis) will be 0.
   

5. Indicate known dose concentration values (part 2)

   Select the sample of interest and double-click the lower-cell to enter edit mode. Once in edit mode, type in the concentration value. Make sure all values have the same unit. We will edit that later.
   

6. Fitting the curve (part 1)

   Select the Fit Curves tab.
   

7. Fitting the curve (part 2)

   Select either the Four Parameter Logistic (4PL) or Five Parameter Logistic (5PL) from the Curve Fitting section and press the Calculate button.
   

8. Edit dose response curve axes

   Right-click on the dose response curve chart and edit the x and y axes. You also have the option to add a chart title.
   

9. Calculate EC or IC(Anything) value (part 1)

   Press the Statistics Toolbar button.

10. Calculate EC or IC(Anything) value (part 2)

    By default the EC50 and the log EC50 values are calculated for you. If you have an inhibition curve, press the ICxx radio button to switch to IC50 and log IC50 values.
    

11. Calculate EC or IC(Anything) value (part 3)

    If you have an inhibition curve and you are interested in the IC90 calculation, simply select the ICxx radio button and enter “90” into the Percentages section and press the Add button.
    

If you have not done so yet, I would like to invite you to try the free 14-day trial of MasterPlex ReaderFit.