When a dose-response curve is incomplete, then the determination of a value on the curve is not accurate. What if the dose-response curve is incomplete? If you actually want the concentration that brings the curve down by 80%, to 20%, then you'd need to set F equal to 20. Then the ECf for inhibitory data would be the concentration (X value) required to bring the curve down to 80%. In situations where the response goes down as you increase dose, you may think of this as the 'IC90' since it gives 90% of the maximum inhibition.Īnother example. Let's say you set F=80. If your response goes down with increasing dose (so the Hill slope is negative), watch out for the terminology. The EC10 (for example) is defined as the concentration that gives you a response 10% of the way between the Bottom and Top plateaus. The needed equation is built in to Prism starting with version 5. The advantage of this approach is that Prism will report the 95% confidence value for ECF. You can fit data directly to an equation written in terms of the ECF, where F=fraction of maximal response (example: for EC90, F=90). If H equals 0.5, the curve is shallower and the EC90 equals the EC50 times 81.įitting the ECanything directly using Prism 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. 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).

Calculate ic50 in prism