IC 50
The mean inhibitory concentration ( IC 50 ) is the concentration of an inhibitor (synonym inhibitor ) at which half-maximal inhibition ( half-maximal inhibition ) is observed. The dose-effect curve is sigmoidal , which is why a concentration with maximum effect only occurs at comparatively high concentrations. Therefore, the value is taken near the turning point . For example, if an inhibitor at 100 nanomol / l has 50% of the maximum inhibitory effect , that would be the IC 50 .
In pharmacology , the IC 50 is used to indicate the strength of an antagonist . This is comparable to the EC 50 of an agonist .
According to the FDA , the IC 50 is the concentration of a substance that is necessary for 50% inhibition in vitro . The EC 50 also indicates the plasma concentration that is necessary for a 50% effect in vivo .
The IC 50 or EC 50 for competitive inhibitors depends on the Michaelis constant K m , the dissociation constant of the enzyme-inhibitor complex K i and the substrate concentration [S], shown in the Cheng-Prusoff equation :
![{{\ text {IC}} _ {{50}}} = \ left (1 + {\ frac {[{\ text {S}}]} {K_ {m}}} \ right) \ cdot K_ {i }](https://wikimedia.org/api/rest_v1/media/math/render/svg/63c9751a894826d8852ddc2e70b82c1c1f251217)
Since the IC 50 value is given in nanomolar (nM) or micromolar (µM) and is therefore somewhat unwieldy, the so-called pIC 50 value is also used. It is calculated from the IC 50 value by forming the negative decadic logarithm from the numerical value of the concentration in mol / l.
Example:
Other numerical values, for example IC 95, indicate the concentration that is necessary to inhibit 95%.
swell
- ↑ a b FDA: IC50 versus EC50
literature
- JM Berg, JL Tymoczko, Gregory J. Gatto jr., L. Stryer: Stryer Biochemie , Springer Spectrum 2018