The mean inhibitory concentration (IC50 ) is the concentration of an inhibitor will be referred to, in which a half-maximal inhibition is observed.

In pharmacology, the IC50 is used to specify the potency of an antagonist. This is comparable to the EC50 of agonist.

According to the FDA, the IC50 is the concentration of a substance that is necessary for 50% inhibition in vitro. EC50 indicates the plasma concentration, which is necessary for a 50 % solution of effect in vivo.

Depending on the IC50 or EC50 at competitive inhibitors of the Michaelis constant Km, the dissociation constant of the enzyme - inhibitor complex, Ki, and the substrate concentration [ S]:

Since the IC50 in nanomolar (nM) or micromolar ( uM ) is specified and therefore is a bit unwieldy, also called the pIC50 value is used. It is calculated from the IC50 value by taking the negative logarithm of the numerical value of the concentration in mol / l


Other numerical values ​​, for example, IC95 indicate the concentration needed to inhibit 95%.