EC50n

EC50n is a term occasionally used in pharmacology to refer to the EC50 parameter of a dose–response curve modeled with a Hill-type equation, where n denotes the Hill coefficient (the slope or steepness of the curve). The EC50 itself is the concentration of a drug or ligand that produces 50% of the maximal effect (Emax) under chosen assay conditions. The subscript n emphasizes that the curve’s shape is governed by the Hill slope n, which determines how rapidly the response transitions from low to high as concentration increases.

A common representation is the Hill equation: E = E0 + (Emax − E0) * [A]^n / (EC50^n + [A]^n), where E is the observed effect, E0 is the baseline effect, Emax is the maximal effect, [A] is the agonist concentration, and n is the Hill coefficient. In this form, EC50 is the concentration at which the response is halfway between E0 and Emax, and n controls the steepness of the curve.

Estimation and interpretation: EC50n values are obtained by fitting experimental dose–response data to the Hill equation using nonlinear regression. It is common to report both EC50 (or pEC50, which is −log10(EC50)) and the Hill coefficient n, along with E0 and Emax. Note that EC50 can depend on assay conditions and measurement endpoints and does not equal binding affinity; the Hill coefficient reflects cooperative or allosteric effects that shape the response curve.

See also: Hill equation, EC50, dose–response, potency, pEC50.