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IC50 is the concentration of agonist that gives a response half way between Bottom and Top.
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If you have subtracted off any basal response, consider constraining Bottom to a constant value of 0. If you prefer to enter concentrations, rather than the logarithm of concentrations, use Prism to transform the X values to logs.įrom the data table, click Analyze, choose nonlinear regression, choose the panel of equations "Dose-response curves - Inhibition" and then choose the equation " log(inhibitor) vs. Enter one data set into column A, and use columns B, C. Enter response into Y in any convenient units. Enter the logarithm of the concentration of the inhibitor into X. It is also called a four-parameter dose-response curve, or four-parameter logistic curve, abbreviated 4PL. This is preferable when you have plenty of data points. This model does not assume a standard slope but rather fits the Hill Slope from the data, and so is called a Variable slope model. Many inhibitory dose-response curves have a standard slope of -1.0. The goal is to determine the IC50 of the inhibitor - the concentration that provokes a response half way between the maximal (Top) response and the maximally inhibited (Bottom) response. response curves follow the familiar symmetrical sigmoidal shape. Use a related equation when X values are concentrations or doses. This equation is used when X values are logarithms of doses or concentrations.