EC50
Encyclopedia
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 some specified exposure time. 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. The EC50 of a quantal dose response curve represents the concentration of a compound where 50% of the population exhibit a response, 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.
Concentration measures typically follow a Sigmoid
al curve, increasing rapidly over a relatively small change in concentration. The point at which the effectiveness slows with increasing concentration is the IC50. This can be determined mathematically by derivation of the best-fit line. While relying on a graph for estimation is more convenient, it yields less precise and less accurate results.
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.
or toxicity
between compounds and between different organisms.
The EC50 of a graded dose response curve therefore represents the concentration of a compound where 50% of its maximal effect is observed. The EC50 of a quantal dose response curve represents the concentration of a compound where 50% of the population exhibit a response, after a specified exposure duration.
It is also related to IC50
IC50
The half maximal inhibitory concentration is a measure of the effectiveness of a compound in inhibiting biological or biochemical function. This quantitative measure indicates how much of a particular drug or other substance is needed to inhibit a given biological process by half...
which is a measure of a compound's inhibition (50% inhibition). For competition binding assays and functional antagonist assays IC50
IC50
The half maximal inhibitory concentration is a measure of the effectiveness of a compound in inhibiting biological or biochemical function. This quantitative measure indicates how much of a particular drug or other substance is needed to inhibit a given biological process by half...
is the most common summary measure of the dose-response curve. For agonist/stimulator assays the most common summary measure is the EC50.
Concentration measures typically follow a Sigmoid
Sigmoid function
Many natural processes, including those of complex system learning curves, exhibit a progression from small beginnings that accelerates and approaches a climax over time. When a detailed description is lacking, a sigmoid function is often used. A sigmoid curve is produced by a mathematical...
al curve, increasing rapidly over a relatively small change in concentration. The point at which the effectiveness slows with increasing concentration is the IC50. This can be determined mathematically by derivation of the best-fit line. While relying on a graph for estimation is more convenient, it yields less precise and less accurate results.
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, et cetera. This time dependency hampers the comparison of potencyPotency
Potency may refer to:* Potency , a measure of the activity of a drug in a biological system* Virility* Potency is a measure of the differentiation potential of stem cells...
or toxicity
Toxicity
Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...
between compounds and between different organisms.
See also
- Dose-response relationshipDose-response relationshipThe dose-response relationship, or exposure-response relationship, describes the change in effect on an organism caused by differing levels of exposure to a stressor after a certain exposure time...
- Certain safety factorCertain safety factorThe Certain Safety Factor is the ratio of the lethal dose to 1% of population to the effective dose to 99% of the population . This is a better safety index than the LD50 for materials that have both desirable and undesirable effects, because it factors in the ends of the spectrum where doses may...
- IC50IC50The half maximal inhibitory concentration is a measure of the effectiveness of a compound in inhibiting biological or biochemical function. This quantitative measure indicates how much of a particular drug or other substance is needed to inhibit a given biological process by half...
- LD50LD50In toxicology, the median lethal dose, LD50 , LC50 or LCt50 of a toxin, radiation, or pathogen is the dose required to kill half the members of a tested population after a specified test duration...
- Therapeutic indexTherapeutic indexThe therapeutic index is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes death or toxicity ....