EC50the

EC50the, sometimes written to denote the theoretical EC50, is a term used in pharmacology and quantitative pharmacology to refer to an EC50 value derived from a mathematical dose–response model rather than directly from observed data. It is not a universally standardized term, but it appears in discussions of modeling where researchers distinguish between empirical, data-driven estimates and model-predicted values.

In practice, EC50the is obtained by fitting a dose–response model to experimental data, such as a Hill or four-parameter logistic model, and then reporting the EC50 value that the model parameters imply. In these models, the EC50 is the concentration at which the predicted response reaches 50% of its maximal effect, given the estimated baseline and maximal response. Because EC50the depends on the chosen model, parameterization, and assumptions (for example, the Hill coefficient or baseline E0 and maximum Emax), it can differ from an EC50 calculated directly from raw data.

Applications of EC50the include comparing potency across conditions, drugs, or species within a modeling framework. It is important to specify how EC50the was derived (model form, fitting method, data range) to avoid misinterpretation, as model-dependent values can vary with different assumptions or incomplete saturation in the data.

In summary, EC50the is a model-derived, theoretical version of EC50 used in contexts where a mathematical description of the dose–response is essential, distinct from an experimentally observed EC50.