Method

ICEstimator carries out a nonlinear regression on the relative effect - concentration points. The relative effects in % are used; they are derived from the raw effects entered by the user. The raw effect(s) for null concentration are used to derive the 100% relative effect. The raw effect(s) for the maximal concentrations are used to derive the 0% relative effect.
The resulting curve depicts an inhibitory sigmoid Emax model that shows a decrease in the relative effect of the parasite from 100% at the null concentration towards zero when the drug concentration increases to infinity.

The model

ICEstimator applies the following model:

Estimated parameters: IC50, γ

IC90 and IC99 are the concentrations leading to relative effects of 10% and 1%, respectively. IC90, IC99 an their standard errors are computed as follow:
IC90 = 91/γ x IC50          and       SE(IC90)= 91/γ x SE(IC50);
IC99 = 991/γ x IC50        and       SE(IC99) = 991/γ x SE(IC50).

« RE » is the relative effect of the parasite in %. It defines the Y-axis.
« C » is the concentration of the tested drug. It defines the X-axis.
« IC50 »: drug concentration inhibiting 50% of parasite’s activity.
« IC90 »: drug concentration inhibiting 90% of parasite’s activity.
« IC99 »: drug concentration inhibiting 99% of parasite’s activity.
« γ »: sigmoidicity factor which expresses the steepness of the curve.

NB: The definition of the model is such as ICEstimator applies only to activity that decreases versus concentration with a sigmoid form.