Effective Concentration 50 (EC50) and Inhibition Concentration 50 (IC50)

Formal Definition

In in vitro cell and tissue culture, EC50 is the concentration causing a half-maximal response for any measured biological effect of interest, and is equivalent to median effective dose (ED50) and median lethal dose (LD50) used in animal experiments. EC50 is used for read-outs that increase with concentration, whereas IC50 is used in case of an in vitro method where there is a decline in read-out. IC50 is therefore the test item concentration causing a reduction of response/binding etc. by half.