When ı want to calculate the ıc50 value of my drug in graphpad. It is said that ı must write 1 instead of concentration zero because of logarithm. But ı am confused that what will ı do if use 1 micromolar drug for inhibition studies? Because its logarithm is 0 too.
Instead of using the logarithms of the concentrations, use the actual concentrations.
or
Use percent inhibition instead of the original measurement. That way, you don't need to include the zero concentration data in the curve fitting.
The inhibitor concentration against the percent activity is plotted ([I]-Activity % graph). Using the linear (y=mx+n) or parabolic (y=ax2+bx+c) equation on this graph for y=50 value x point becomes IC50 value.
https://www.researchgate.net/post/How_can_IC_50_calculate_using_excel#:~:text=Techno%20India-,To%20calculate%20the%20IC50%20value%3A%20The%20inhibitor%20concentration%20against%20the,x%20point%20becomes%20IC50%20value.
To be mathematically correct, the inhibition data should be fitted to the Hill equation, or some variation of it (see below), by nonlinear regression. The logistic equation is related to the Hill equation, but using logarithms of the substrate concentrations.
% inhibition = 100[I]n/(IC50n + [I]n)
where [I] is the inhibitor concentration and n is the Hill coefficient of cooperativity.
The factor 100 represent the highest % inhibition. For systems having partial inhibition, this can be a fit parameter instead of a constant.
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