関: Median effective dose

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/02/12 03:47:58」(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くことでIC₅₀が求められる。

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.

この項目は、薬学に関連した書きかけの項目です。この項目を加筆・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）。

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[Wiki en表示]

ED 50 ("European Datum 1950") is a geodetic datum which was defined after World War II for the international connection of geodetic networks.

Some of the important battles of World War II were fought on the borders of Germany, the Netherlands, Belgium and France, and the mapping of these countries had incompatible latitude and longitude positioning. This led to the setting up of ED50 as a consistent mapping datum for much of Western Europe. It was, and still is, used in much of Western Europe apart from Great Britain, Ireland, Sweden and Switzerland, which have their own datums.

It used the International Ellipsoid of 1924 ("Hayford-Ellipsoid" of 1909) (radius of the Earth's equator 6378.388 km, flattening 1/297, both exact). That spheroid was an early attempt to model the whole Earth and was widely used around the world until the 1980s when GRS80 and WGS84 were established.

Many national coordinate systems of Gauss–Krüger are defined by ED50 and oriented by means of geodetic astronomy. Up to now it has been used in data bases of gravity fields, cadastre, small surveying networks in Europe and America, and by some developing countries with no modern baselines. ED50 was also part of the fundamentals of the NATO coordinates (Gauss–Krüger and UTM) up to the 1980s.

The geodetic datum of ED50 was centred at the Helmertturm on the Telegrafenberg in Potsdam, (then East) Germany; the intent was to encourage cooperation with the socialist states during the cold war, which failed. The adjustments for later versions of the datum (ED77, ED79) used the Munich Frauenkirche as starting point.

Datum shift between ED50 and WGS84

The longitude and latitude lines on the two datums are the same in the Archangel region of north-west Russia. As one moves westwards across Europe, the longitude lines on ED50 gradually become further west than their WGS84 equivalents, and are around 100 metres west in Spain and Portugal. Moving southwards, the latitude lines on ED50 gradually become further south than the WGS84 lines, and are around 100 m south in the Mediterranean Sea.

This means that if the lines are further west, the longitude value of any given point becomes more easterly. Similarly, if the lines are south, the values become northerly. This is due to the fact that the International Ellipsoid is larger than the GRS80/WGS84 elipsoid, so a given north-south distance will cover more latitude on the new ellipsoid, and a given east-west distance will cover more longitude.

The datum shift for the Universal Transverse Mercator grid is different. The eastings vary between 0 m in Eastern Europe and 100 m in the far west of the continent, roughly similar to the longitude shift, but the northings are about 200 m different across Europe, with the ED50 UTM northing lines south of the WGS84 UTM northing lines. It should be noted that UTM northings are measured from the Equator; distance from the equator to latitude 50 degrees is 112 m more on the International than on the WGS84 spheroid.

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