EC50、IC5、LC50、LD50

LC50 ：（Lethal Concentration 50，致死中浓度/半致死浓度/半数致死浓度）表示杀死 50% 防治对象的药剂浓度，单位为PPm 。

IC50 :(英文全称half maximal (50%) inhibitory concentration (IC) of a substance (50% IC, or IC50))半数抑制浓度

IC50, the half maximal inhibitory concentration, represents the concentration of an inhibitor that is required for 50% inhibition of things like an enzyme, a cell, a cell receptor or a microorganism.

It's commonly used as a measure of drug effectiveness. Another measure of drug efficacy is EC50 which represents the concentration of a compound that is required to obtain 50% of the maximum effect. (Ex. EC100 would be the minimum concentration of a compound to obtain 100% of its effect).

是指“反应”被抑制一半时抑制剂的浓度，这里的反应可以是酶催化反应、抗原抗体反应等。在凋亡方面，可以理解为一定浓度的某种药物诱导肿瘤细胞凋亡50%，该浓度称为50%抑制浓度，即凋亡细胞与全部细胞数之比等于50%时所对应的浓度，IC50值可以用来衡量药物诱导凋亡的能力，即诱导能力越强，该数值越低,当然也可以反向说明某种细胞对药物的耐受程度。

EC50 半数有效浓度 越低越好

LD50 半数致死量 越高越好，毒理学常用参数

IC50 半数抑制浓度 越低越好，多用于抗菌抗病毒

LD为Lethal dose(致死剂量)的缩写

LD50是半数致死计量，指使实验动物一次染毒后，在14天内有半数实验动物死亡所使用的毒物计量。

LC是致死浓度，单位为mg/L或mg/m3

LD是致死剂量，单位为mg/kg体重。

LD50——经口、经皮半数致死剂量。较为简单的定义是指引起一群受试对象50%个体死亡所需的剂量。精确的定义指统计学上获得的，预计引起动物半数死亡的单一剂量。LD50的单位为mg/kg体重，LD50的数值越小，表示毒物的毒性越强；反之，LD50数值越大，毒物的毒性越低。

LC50——呼吸道吸入半数致死浓度。LC50 是指能引起一群受试对象50%个体死亡所需的浓度。如受试物在液体中时，单位为mg/L。LC50也用于表示空气中化学物的浓度，以mg/m3为表示单位。

LD100——绝对致死剂量。指某实验总体中引起一组受试动物全部死亡的最低剂量。实验总体中一组受试动物的数量视不同实验设计而定，少则10个，多则50～100个以上。

LD50 535mg/kg(大鼠经口); 一只1KG的大鼠染毒535m

g,14天内，一半数量死亡。

LC50 102235mg/m3(大鼠吸入)：如果空气中化学物的浓度 达到102235mg/m3，一半的大鼠在14天内死亡。

IC50

The IC50 is a measure of the effectiveness of a compound in inhibiting biological or biochemical function. Often, the compound in question is a drug candidate. This quantitative measure indicates how much of a particular drug or other substance (inhibitor) is needed to inhibit a given biological process (or component of a process, i.e. an enzyme, cell, cell receptor or microorganism) by half. In other words, it is the half maximal (50%) inhibitory concentration (IC) of a substance (50% IC, or IC50). It is commonly used as a measure of antagonist drug potency in pharmacological research. Sometimes, it is also converted to the pIC50 scale (-log IC50), in which higher values indicate exponentially greater potency. According to the FDA, IC50 represents the concentration of a drug that is required for 50% inhibition in vitro. It is comparable to an EC50 for agonist drugs. EC50 also represents the plasma concentration required for obtaining 50% of a maximum effect in vivo.

Determination IC50 of a drug

Functional antagonist assay:

The IC50 of a drug can be determined constructing a dose-response curve and examining the effect of different concentrations of antagonist on reversing agonist activity. IC50 values can be calculated for a given antagonist by determining the concentration needed to inhibit half of the maximum biological response of the agonist.

IC50 values are dependent on conditions under which they are measured. In general, the higher the concentration of inhibitor, the more will agonist activity be lowered. IC50 value increases as enzyme concentration increases. Furthermore depending on the type of inhibition other factors may influence IC50 value; for ATP dependent enzymes IC50 value has an interdependency with concentration of ATP, especially so if inhibition is all of it competitive. IC50 values can be used to compare the potency of two antagonists.

Competition binding assays:

In this type of assay, a single concentration of radioligand (usually an agonist) is used in every assay tube. The ligand is used at a low concentration, usually at or below its KD value. The level of specific binding of the radioligand is then determined in the presence of a range of concentrations of other competing non-radioactive compounds (usually antagonists), in order to measure the potency with which they compete for the binding of the radioligand. Competition curves may also be computer-fitted to a logistic function as described under direct fit.

In this situation the IC50 is the concentration of competing ligand which displaces 50% of the specific binding of the radioligand. The IC50 value is converted to an absolute inhibition constant Ki) using the Cheng-Prusoff equation (see Ki).

IC50 and affinity:

IC50 is not a direct indicator of affinity although the two can be related at

least for competitive agonists and antagonists by the Cheng-Prusoff eqtn.

where Ki is the binding affinity of the inhibitor, IC50 is the functional strength of the inhibitor, [S] is substrate concentration and Km is the affinity of the substrate for the enzyme.Whereas the IC50 value for a compound may vary between experiments depending on radioligand concentration, the Ki is an absolute value. Ki is the inhibition constant for a drug; the concentration of competing ligand in a competition assay which would occupy 50% of the receptors if no radioligand were present.

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ECx Concentration having an effect on x% of the population compared to control

EC50 " Effect Concentration 50% " or concentration having 50% of effect compared to control

LCx concentration having caused the death of X% of the population tested compared to control

IC50 " Inhibition Concentration 50% " or concentration inhibiting of 50% a parameter like the growth or luminescence compared to control

LC50 concentration having caused the death of 50% of the population tested compared to control

LD50 " Lethal Proportions 50% " or proportions having caused the death of 50% of the population tested.

ED50 “50%median effective dose”(半数有效剂量)

LOEC " Lowest Observed Effect Concentration "（最低观察效应浓度） or concentration with a very weak observable effect. It is about the lowest concentration for which the effect is different from that of controls. It is the first concentration tested after the NOEC.

NOEC " No Observed Effect Concentration " （无观察效应浓度）or concentration without observable effect. It is about the highest concentration tested for which the effect is significantly not different from controls

IC50(EC50)计算软件开发成功

IC50（EC50）表示半抑制浓度或半效应浓度值的大小，是衡量不同物质同一性能大小的重要数据。但IC50和EC50的计算一般需要测定5个以上的点，再通过曲线拟合得到函数计算而得，或者假设IC50（EC50）附近的点连成直线计算而得等，但这都存在较大的误差。因为拟合的函数曲线并不能保证都通过所测定的点，其次IC50（EC50）附近的点并不都连成直线，所以计算误差较大。IC50（EC50）计算软件解决了以上问题。本软件输入可以为多组试验数据，软件将自动取最靠近IC50（EC50）处的三个点进行二次曲线拟合，所建立的函数能完全通过IC50（EC50）附近的3个点，决定系数R2=1.00，并自动生成曲线图、曲线方程和IC50（EC50）值。支持曲线图的复制、粘贴及图上上文字的编辑。在保证试验数据精度的前提下可以确保在IC50（EC50）周围的曲线的高精度，由此算得的IC50（EC50）可以保证是高精度的，使用效果优于SPSS、SAS和DPS等软件。

IC50（EC50）计算软件使用语言为C++（MFC），可正常运行

于Windows 2000、NT、XP 或更高版本的Windows操作系统，内存要求256M以上。

IC50（EC50）计算软件已于2009年9月30日通过国家版权局的登记和审批，登记号为2009SR044013。西北农林科技大学校内有需要者请与设计者李志成副教授等联系，可以免费使用。校外计划每所大学或研究院所赠送2-3人。