The inhibition curve plateaus well above the control values (NS) established by a high concentration of a standard drug in this illustration. There are two ways to describe IC50 in this case. A case where IC50 is described in two ways There’s no misunderstanding on what IC50 stands for. Similarly, dealing with the bottom plateau can be done in three ways: Fit only the data, with Bottom set to the average of the NS controls and the NS controls treated as if they were a very high concentration of inhibitor in the fit. The third approach is my favorite because it analyses all of the data, but it is not a strongly preferred. Since the data shape a full dose-response curve with a simple top plateau that is indistinguishable from the null, the results would be quite similar with either of these approaches. You can’t enter zero, because zero is not defined on a log scale. Simply put, start with a low dose, such as 10-10 or 10-11.

As if the blank values were part of the dose-response curve, enter them.

Set the parameter Top to be a constant value equal to the mean of the blanks, and average the Blank control values.

Ignore the Blank control values and just fit the data.

There are three options available to you: When fitting this curve, you must determine how to fit the curve’s top plateau. The experimental dose-response curve’s data (red dots) span the entire range between the two control values. The ones on the right are in the presence of a standard inhibitor at its maximum concentration, so describe “0 percent “. Since the ones on the left (Blank) do not have an inhibitor, describe “100% “.

Measurements taken with controls are indicated by the green symbols. All the concepts can be used to stimulatory curves and EC50 (E for effective) also.

We are considering IC50 in this post (I for inhibition, for downward sloping dose-response curves). The IC50 is the concentration of an inhibitor at which the response (or binding) is decreased by half.Īlthough the concept is simple, there are a few challenges when try to fit data to find these values. The EC50 is the drug concentration that produces a half-maximal response. In pharmacology, the principles of IC50 and EC50 are central.

Calculate ic50 in prism