EC50

From Wikipedia, the free encyclopedia

The term EC₅₀ is the concentration of a drug which induces a response halfway between the baseline and maximum.^[1] It is commonly used as a measure of drug potency.

The EC₅₀ of a graded dose response curve therefore represents the concentration of a compound where 50% of its maximal effect is observed^[2]. The EC₅₀ or a quantal dose response curve represents the concentration of a compound where 50% of the population exhibit a response^[3].

It is also related to IC₅₀ which is a measure of a compound's inhibition (50% inhibition).

According to the FDA, IC₅₀ represents the concentration of a drug that is required for 50% inhibition in vitro whereas EC₅₀ represents the plasma concentration required for obtaining 50% of a maximum effect in vivo.^[4]

Concentration measures typically follow an S-shaped curve, increasing rapidly over a relatively small change in concentration. The point at which the effectiveness slows with increasing concentration is the IC₅₀. This can be determined mathematically by derivation of the best-fit line. However, it is more easily observed from a graph and estimated rather than through complex calculus equations.