For example, if the Hill slope equals 1, the EC90 equals the EC50 times nine. If you know the EC50 and Hill slope (H), you can easily compute the EC80 or EC10 or any other value you want. (This equation was derived by starting with the equation that defines percent response F, from EC50, H, and concentration, and then rearranging to solve for the concentration (ECF).) If you’ve already obtained an EC 50 value by nonlinear regression in Prism and you don’t need an error estimate, use this equation to determine EC F (where F might be 80 or 90 …) from the EC 50 and Hill Slope (H): Enter the EC50 and Hill Slope and it will calculate whatever EC value you want. One of our free web calculators does the calculation for you.

You can either compute these values from the EC 50 or fit a curve in such a way as to directly fit EC anything.

But in some systems you might be more interested in the EC 80 or the EC 90 or some other value. The potency of a drug is commonly quantified as the EC 50, the concentration that leads to 50% maximal response (or the logarithm of the EC 50).

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