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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/12/05 20:14:50」(JST)

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50%効果濃度（EC₅₀）または半数効果濃度とは、薬物や抗体などが最低値からの最大反応の50%を示す濃度のことを指す^[1]。 EC₅₀は元来英語の"half maximal (50%) effective concentration"の略語であるが、現在ではEC₅₀の表記の方が一般的である。

EC₅₀は特に血中における50%効果濃度を指すこともある。この場合、投与量としてはED₅₀（50%効果用量、半数効果用量）を用いる。

EC₅₀は一般に医薬品の有効度を示すために用いられる。効果の程度が連続的に計測できるような（例えば、心拍数に影響を及ぼすような）薬剤の用量反応曲線のEC₅₀は、最大反応の50％の反応強度を示す化合物の濃度を表している ^[2]。一方、効果が現れるか現れないかでのみ評価できる薬剤（例えば抗てんかん薬）の用量反応曲線のEC₅₀は、試験された母集団のうち50%の個体が反応を示す化合物の濃度を表している ^[3]。 EC₅₀は薬物の阻害能の尺度であるIC₅₀とも関連している。競合結合評価と機能的アンタゴニスト評価のためにはIC₅₀が用量反応曲線の最も一般的な集約尺度であり、アゴニスト/促進剤評価にはEC₅₀が最も一般的である ^[4]。用量反応曲線は通常、少しの濃度の変化に対して効果が急に立ち上がりやがて効果の増加が遅くなってゆく、いわゆるシグモイド曲線の形状を成す。濃度の増加に対して効果の増加が遅くなる点（変曲点）がIC₅₀である。測定値に対して最適な近似曲線を数学的に導びくことでIC₅₀が求められる。しかしながら複雑な計算をするよりもグラフから直接IC₅₀値を読み取る方が容易である^[要出典]。

曲線回帰

EC₅₀を求めるための回帰曲線は薬剤の濃度(X)と効果の度合い(Y)の関数として以下のように表される。

ここでAは測定値の最小値、Bは測定値の最大値、ヒル係数Cは勾配の最大値の絶対値を表す。

脚注

^ Introducing doseresponse curves, Graphpad Software
^ EC50 definition
^ definition of EC₅₀ for quantal dose response curve
^ Assay Operations for SAR SupportNIH Chemical Genomics Center

外部リンク

Online IC50 Calculator
Determination of IC₅₀ values
Neubig et al. International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification. XXXVIII. Update on terms and symbols in quantitative pharmacology. Pharmacol Rev. 2003 Dec;55(4):597-606.

この「EC50」は、薬学に関連した書きかけ項目です。この記事を加筆・訂正などしてくださる協力者を求めています（プロジェクト:薬学／Portal:医学と医療）。

wiki en

[Wiki en表示]

For the UK postcode EC50, see EC postcode area.

The term half maximal effective concentration (EC₅₀) refers to the concentration of a drug, antibody or toxicant which induces a response halfway between the baseline and maximum after a specified exposure time.^[1] It is commonly used as a measure of drug's potency.

The EC₅₀ of a graded dose response curve therefore represents the concentration of a compound where 50% of its maximal effect is observed.^[2] The EC₅₀ of a quantal dose response curve represents the concentration of a compound where 50% of the population exhibit a response,^[3] after a specified exposure duration.

It is also related to IC₅₀ which is a measure of a compound's inhibition (50% inhibition). For competition binding assays and functional antagonist assays IC₅₀ is the most common summary measure of the dose-response curve. For agonist/stimulator assays the most common summary measure is the EC₅₀.^[4]

In biological systems, small changes in ligand concentration typically result in rapid changes in response, following a sigmoidal function.The inflection point at which the increase in response with increasing ligand concentration begins to slow is the EC₅₀. This can be determined mathematically by derivation of the best-fit line. While relying on a graph for estimation is more convenient, this method yields less precise and less accurate results^{[citation needed]}.

Equation

Many different equations can be used to derive an EC₅₀. One possible function is:

where Y is the observed value, Bottom is the lowest observed value, Top is the highest observed value, and the Hill coefficient gives the largest absolute value of the slope of the curve.

Limitations

The effects of a stressor or drug generally depend on the exposure time. Therefore, the EC₅₀ (and similar statistics) will be a function of exposure time. The exact shape of this time function will depend upon the stressor (e.g., the specific toxicant), its mechanism of action, the organism exposed, etc. This time dependency hampers the comparison of potency or toxicity between compounds and between different organisms.

References

^ Introducing dose response curves, Graphpad Software
^ EC50 definition
^ definition of EC₅₀ for quantal dose response curve
^ Assay Operations for SAR Support NIH Chemical Genomics Center

External links

Online IC50 Calculator
Determination of IC₅₀ values
Neubig et al. International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification. XXXVIII. Update on terms and symbols in quantitative pharmacology. Pharmacol Rev. 2003 Dec;55(4):597-606.

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