When are the relative and absolute IC50s the same? If the inhibitor only brings the response down to (say) 60%, then the curve never crosses the Y=50% line, so the absolute IC50 is undefined. The absolute IC50 requires that the inhibitor brings the binding or response down to less than 50%. It doesn't use the terms relative and absolute. That document uses the term IC50 to refer to the absolute IC50, and the term EC50 to refer to the relative IC50. It is also used by the Environmental Protection Agency (EPA) in evaluating endocrine disrupters (Appendix A).
It is the concentration that results in inhibiting cell growth by 50%. The abbreviation GI50 is used for what we call here the absolute IC50. The concept (but not the term "absolute IC50") is used to quantify drugs that slow cell growth. This term is not very standard, and is a bit misleading as there is nothing absolute about an "absolute EC50". Since this value does not quantify the potency of a drug, the authors of the International Union of Pharmacology Committee on Receptor Nomenclature think that the concept of absolute IC50 (and that term) is not useful in most situations (R. The concentration that provokes a response halfway between the Blank and the NS value is sometimes called the absolute IC50, The horizontal dotted lines show how 100% and 0% are defined, which then defines 50%. Unless the data are normalized to run from 0 to 100, the relative IC50 is not the value that corresponds to 50% on the right Y axis. With appropriate consideration of the biological system and concentrations of interacting ligands, estimated Kd values can often be derived from the IC50 value defined this way. This definition is the one upon which classical pharmacological analysis of agonist and antagonist interactions is based.
It is the concentration required to bring the curve down to point halfway between the top and bottom plateaus of the curve. This is by far the most common definition, and is usually what people mean by "the IC50". The middle of the curve, the IC50, can be ambiguous as is sometimes defined in two alternative ways: You'd need at least two values, one to quantify the middle of the curve (the drug's potency) and one to quantify how low it gets (the drug's maximum effect). This figure (from a longer article on IC50 values) shows a situation where the IC50 can be defined two ways.Ĭlearly, a single value cannot summarize such a curve. The difference between the relative and absolute IC50
0 kommentar(er)
