These are hard wired into the equation, so you don't have to remember to constrain those two parameters to constant values. These data are fit to a simpler equation where Baseline is set to equal zero, and Top is set to equal 100. Additionally, this file contains another graph where the data are already normalized to run from 0 to 100%. When fitting data to that equation, don't forget to constrain Baseline and Top to appropriate values determined by controls.

ĭownload the Prism file that fits that equation to make the graph shown above. You'll definitely want to constrain Baseline to be a constant value based on controls. Baseline is the Y value that defines 0% - maximal inhibition by a standard drug. Bottom is the Y value of the bottom plateau of the curve itself. Note the distinction between the parameter Bottom and Baseline. This EPA document gives the needed equation (which I have generalized a bit, so does not require that the data already be normalized). But if you do, it is not hard to fit a curve to determine it.

The concept of an absolute IC50 is not standard, and many find it not to be useful. Where F is the percentage of response.Fitting a dose-response curve to find the absolute IC50 How about EC20? Since EC20 is the concentration where 20% response, we can deduce the formula from DoseResp function that:įor more general cases, you can always calculate the EC/IC-anything by derived parameters using this equation: When fitting this function, the X values are supposed to be the logarithm of dose, and LOGx0 is the center of the curve, that is, the concentration for half response. At the bottom of the page, the derived parameters are defined as:įrom the formula tab, we can know the DoseResp function is: Open the Fitting Function Organizer (press F9) and select the DoseResp function under the Growth/Sigmoidal Category. The information provided below show how the formulas for EC20, EC50, and EC80 were derived:įirst, let's look into how Origin defines the Dose Response fitting function. This computation is performed post-fit, using the Derived Parameters feature for fitting functions. Origin automatically computes and reports EC20, EC50, and EC80 values in the output Report Sheet when fitting with Dose Response function in the nonlinear fitter dialog. 3.23 FAQ-251 How to compute EC50/IC50 in Dose Response fitting

Calculate ic50 in prism