# Ic50 equation

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By continuing to use this site, you consent to the use of cookies. We value your privacy. Asked 1st Jan, Aysegul Bildik. How can IC 50 calculate using excel? Most recent answer. Ramesh Mani. For IC50 calculation my all time user friednly software is Graphpad prism. Popular Answers 1. Dudley J Benton. McHale Performance. If you have the data and want to calculate the IC50, then it's just like calculating a half-life. Select the data, insert a "scatter plot," and set the Y-axis to "logarithmic.

Select "add trend line" and pick "exponential. I attached an example.

Confidence and Prediction Limits for EC50 and IC50

All Answers Wayne Schmedel. Grays Harbor Community Hospital. I found that using the Add-On features can be helpful:. Excel add-in. Input your data in the left columns, and your results will be shown in the right half of the Excel table. Four-Parameter Logistic Function.The concept of an absolute IC50 is not standard, and many find it not to be useful. But if you do, it is not hard to fit a curve to determine it. This EPA documentgive the needed equation which I have generalized a bit, so not require that the data already be normalized.

Note the distinction between the parameter Bottom and Baseline. Bottom is the Y value of the bottom plateau of the curve itself. You'll definitely want to constrain Baseline to be a constant value based on controls. You may also want to constrain Top. Download the Prism file that fits that equation to make the graph shown above.

When fitting data to that equation, don't forget to constrain Baseline and Top to appropriate values determined by controls. These data are fit to a simpler equation where Baseline is set to equal zero, and Top is set to equal These are hard wired into the equation, so you don't have to remember to constrain those two parameters to constant values.

Here is an alternative approach you can use if your data are normalized. It does not require entering a user-defined equation. Make sure that your data are normalized to some controls. At the bottom of the data table, add a new row of data.

Enter 50 into each Y column. Leave X blank for this row. Use nonlinear regression to fit the data to the log inhibitor vs. On the first fit tab of the nonlinear regression dialog, check the option: " Interpolate unknowns from standard curve.

On the Constrain tab, consider constraining Top to have a constant value of The IC50 reported as part of the main results table will be the relative IC This is the absolute IC All rights reserved.

This guide is for an old version of Prism. Browse the latest version or update Prism. Fitting a dose-response curve to find the absolute IC50 The concept of an absolute IC50 is not standard, and many find it not to be useful. An alternative approach for normalized data Here is an alternative approach you can use if your data are normalized.

Scroll Prev Top Next More.A new web-server tool estimates K i values from experimentally determined IC 50 values for inhibitors of enzymes and of binding reactions between macromolecules e.

This converter was developed to enable end users to help gauge the quality of the underlying assumptions used in these calculations which depend on the type of mechanism of inhibitor action and the concentrations of the interacting molecular species. Additional calculations are performed for nonclassical, tightly bound inhibitors of enzyme-substrate or of macromolecule-ligand systems in which free, rather than total concentrations of the reacting species are required.

Required user-defined input values include the total enzyme or another target molecule and substrate or ligand concentrations, the K m of the enzyme-substrate or the K d of the target-ligand reaction, and the IC 50 value. Assumptions and caveats for these calculations are discussed along with examples taken from the literature.

Some analyses of networks, pathways and metagenomics focus on identifying key proteins or polynucleic acids as targets for inhibitory compounds. Typically, high-throughput screening assays are initially used to compare and down-select potential inhibitors of enzymatic activity or macromolecule-ligand binding. However, the IC 50 value depends on concentrations of the enzyme or target moleculethe inhibitor, and the substrate or ligand along with other experimental conditions.

What is required is an accurate determination of the K i value, an intrinsic, thermo-dynamic quantity that is independent of the substrate ligand but depends on the enzyme target and inhibitor. Thus, comparisons can be more readily made among different laboratories to characterize the inhibitors.

While these more time-consuming assays are usually done with the most promising candidates, accurate, initial estimates of K i values for more of the candidates would be beneficial. A much discussed problem in the literature 1—8 is converting IC 50 to K i values because even the simplest types of inhibitory mechanisms e.

Additional calculations are performed for tightly bound inhibitors of enzyme-substrate reactions in which free, rather than total, concentrations of the molecular species are calculated for nonclassic Michaelis—Menten kinetics.

## How can IC 50 calculate using excel?

Similar calculations can be performed for target molecule-ligand systems. User-defined input values include total concentrations of the enzyme or target molecule and substrate or ligandthe K m of the enzyme-substrate or the K d of the target-ligand reaction and the IC 50 value.

The outputs include tabulations of the K i values under different kinetic schemes, extensive tabulations of the results, summary histograms and the corresponding equations. Help buttons are available for Background, Assumptions, Literature, Links and Equations along with examples taken from the host database-server that contains kinetic information on neurotoxin inhibitors.

An example calculation is included here for a tight-binding inhibitor of an enzyme—substrate reaction, while other enzyme inhibitor and protein—ligand—inhibitor examples are also provided. Our rationale for creating this converter is to enable end users to judge the quality of the underlying assumptions for these calculations and to help facilitate research and the development of potential therapeutic products.

## IC50 Calculator

The website cited in 9 served as an initial design template for our IC 50 -to- K i converter. Equations 1—4 were adapted from refs. The analytic expressions for K i that are shown below were verified numerically by methods used in a previous kinetic analysis The derivations for converting IC 50 to K i values published by Brandt et al.

For tightly bound inhibitors, the equation for K i by Copeland et al. These equations are also relevant for protein—ligand—inhibitor P—L—I interactions that also adhere to the above assumptions. For noncompetitive inhibition 2. For total concentrations, E is replaced by P and S is replaced by L. Additional reaction schemes are located at this tool's website. As in classic enzyme—substrate systems the relation of K i and IC 50 in competitive inhibition is:.

For protein—ligand experiments with tight-binding inhibitors, the free rather than the total concentrations of the reactants need to be used as modified from ref. The concentration of the free inhibitor species is given by. For this study, we derived a corresponding value of K i for uncompetitive inhibition. Although in this study we use the term K d to quantify an antagonist's effect, the pharmacology-derived EC 50 value is more appropriate when functional experiments are performed It is assumed that all of the substrate- and inhibitor-binding reactions are reversible and that they all have a one-to-one stoichiometry, i.

It is also assumed that in the enzymatic reactions enzyme autocleavage did not occur and that when substrates for fluorescence resonance energy transfer were used, appropriate corrections for inner filter effects were performed. Comparison of K m or IC 50 values for a set of inhibitor candidates is only assumed to be valid when they are evaluated under identical experimental conditions.The concentration of an inhibitor that is required for percent inhibition of an enzyme in vitro.

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.

In other words, it is the half maximal inhibitory concentration of a substance. It is commonly used as a measure of antagonist drug potency in pharmacological research. It is comparable to an EC50 for agonist drugs. The smaller the IC 50, more potent the drug is. Drugs having large IC50 can be toxic and can have side effects.

Word in Definition. Wiktionary 5. Freebase 4.

### 50% of what? How exactly are IC50 and EC50 defined?

Editors Contribution 3. IC50 is given to patients only in critical conditions. Submitted by anonymous on March 15, How to pronounce IC50? Alex US English. Daniel British. Karen Australian. Veena Indian. How to say IC50 in sign language? Select another language:. Powered by CITE.

Are we missing a good definition for IC50? Don't keep it to yourself Submit Definition. The ASL fingerspelling provided here is most commonly used for proper names of people and places; it is also used in some languages for concepts for which no sign is available at that moment. There are obviously specific signs for many words available in sign language that are more appropriate for daily usage.

We're doing our best to make sure our content is useful, accurate and safe. If by any chance you spot an offensive image within your image search results please use this form to let us know, and we'll take care of it shortly.Half maximal effective concentration EC 50 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.

For competition binding assays and functional antagonist assays IC 50 is the most common summary measure of the dose-response curve. Biological responses to ligand concentrations typically following a sigmoidal function.

The inflection point at which the increase in response with increasing ligand concentration begins to slow is the EC 50which can be mathematically determined by derivation of the best-fit line. While relying on a graph for estimation is more convenient, this typical method yields less accurate results and less precise. The response or effect, E, is dependent on both the binding of the drug and the drug-bound receptor.

The agonist that binds to the receptor and initiates the response is usually abbreviated A or D. At low agonist concentrations, [A], the response, E is immeasurably low but at higher [A], E becomes measurable. E increases with [A] until at sufficiently high [A], when E plateaus towards an asymptotic maximum attainable response, E max. The term "potency" refers to the EC 50 value. There is a wide range of EC 50 values of drugs; they are typically anywhere from nM to mM.

Hence, it is often more practical to refer to the logarithmically transformed p EC 50 values instead of EC 50where. A drug's potency is dependent on the drug's affinity and efficacy. Affinity describes how well a drug can bind to a receptor. Faster or stronger binding is represented by a higher affinity, or equivalently a lower dissociation constant.

The EC 50 should not be confused with the affinity constant, K d. While the former reflects the drug concentration needed for a level of tissue response, the latter reflects the drug concentration needed for an amount of receptor binding.

Efficacy is the relationship between receptor occupancy and the ability to initiate a response at the molecular, cellular, tissue or system level. The EC 50 relates to the Hill equationwhich is a function of the agonist concentration, [A]:. The EC 50 represents the point of inflection of the Hill equation, beyond which increases of [A] have less impact on E. In dose response curvesthe logarithm of [A] is often taken, turning the Hill equation into a sigmoidal logistic function.

In this case, the EC 50 represents the rising section of the sigmoid curve. The effects of a stressor or drug generally depend on the exposure time. Therefore, the EC 50 and similar statistics will be a function of exposure time.

The exact shape of this time function will depend upon the stressor e. This time dependency hampers the comparison of potency or toxicity between compounds and between different organisms.

A drug will not have a single value of EC 50 due to different tissues having different sensitivities to the drug in part due to tissue specific receptor expression. From Wikipedia, the free encyclopedia. Pharmacological Reviews. Retrieved Archived from the original on Antagonist Competitive antagonist Irreversible antagonist Physiological antagonist Inverse agonist Enzyme inhibitor. Drug Neurotransmitter Agonist-antagonist Pharmacophore.

Mechanism of action Mode of action Binding Receptor biochemistry Desensitization pharmacology. Loading dose Volume of distribution Initial Rate of infusion Onset of action Biological half-life Plasma protein binding Bioavailability. Compartment Bioequivalence.

Neuropsychopharmacology Neuropharmacology Psychopharmacology Electrophysiology. Clinical pharmacology Pharmacy Medicinal chemistry Pharmacoepidemiology. Pharmacoinformatics Pharmacogenetics Pharmacogenomics.The half maximal inhibitory concentration IC 50 is a measure of the potency of a substance in inhibiting a specific biological or biochemical function. IC 50 is a quantitative measure that indicates how much of a particular inhibitory substance e.

IC 50 values are typically expressed as molar concentration. IC 50 is commonly used as a measure of antagonist drug potency in pharmacological research. IC 50 is comparable to other measures of potency, such as EC 50 for excitatory drugs.

IC 50 can be determined with functional assays or with competition binding assays. Sometimes, IC 50 values are converted to the pIC 50 scale. Due to the minus sign, higher values of pIC 50 indicate exponentially more potent inhibitors.

The IC 50 terminology is also used for some behavioral measures in vivo, such as a two bottle fluid consumption test. The IC 50 of a drug can be determined by constructing a dose-response curve and examining the effect of different concentrations of antagonist on reversing agonist activity. IC 50 values can be calculated for a given antagonist by determining the concentration needed to inhibit half of the maximum biological response of the agonist. IC 50 values are very dependent on conditions under which they are measured.

In general, the higher the concentration of inhibitor, the more agonist activity will be lowered.

IC 50 value increases as agonist concentration increases. Furthermore, depending on the type of inhibition other factors may influence IC 50 value; for ATP dependent enzymes IC 50 value has an interdependency with concentration of ATP, especially so if inhibition is all of it competitive. 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 K d 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 antagonistsin 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. IC 50 is not a direct indicator of affinity although the two can be related at least for competitive agonists and antagonists by the Cheng-Prusoff equation. Alternatively, for inhibition constants at cellular receptors: [7]. Whereas the IC 50 value for a compound may vary between experiments depending on experimental conditions, e.

The Cheng-Prusoff equation produces good estimates at high agonist concentrations, but over- or under-estimates K i at low agonist concentrations. In these conditions, other analyses have been recommended. An agonist is a chemical that binds to a receptor and activates the receptor to produce a biological response. Whereas an agonist causes an action, an antagonist blocks the action of the agonist, and an inverse agonist causes an action opposite to that of the agonist.Statistical analysis.

The PowerPoint presentations provided below are annotated with notes. The first provides guidance on interpretation of raw data for NA activity and IC 50 assays. It covers the following topics: determining standard virus dose; validation and interpretation of NA activity and IC 50 analysis; how to calculate IC 50 values, and examples of fluorescence and chemiluminescence data. Interpretation of raw data. The second addresses a number of the issues encountered when undertaking statistical analysis of IC 50 data.

It covers the impact of using different methods for determining IC 50 values; how to identify outlying results above the seasonal normand how to monitor trends in IC 50 data:. Statistical analysis of IC 50 s. Examples of both correct and incorrect curve fitting and point-to-point graphs for both sensitive and resistant isolates are provided below. The files contain graphical examples and accompanying explanatory notes to aid interpretation.

Frequently asked questions on IC 50 data analysis. Susceptibility to NI drugs is not absolute.

There are typical ranges of IC 50 values that differ between influenza subtypes and between oseltamivir and zanamivir for each subtype. Therefore this subtype and drug specific data should not be compared. Influenza B viruses tend to have IC 50 values fold higher than influenza A viruses. This is normal for influenza B and this lower susceptibility does not appear to have a significant clinical impact.

IC 50 values for influenza B viruses tend to be higher for oseltamivir than zanamivir. IC 50 values for H1N1 viruses tend to be higher for zanamivir than oseltamivir and IC 50 values for H3N2 viruses tend to be higher for oseltamivir than zanamivir. Also, values generated by fluorescence and chemiluminescence methods should not be compared. Typically, values generated by chemiluminescence are lower than those for the same virus and drug in the fluorescence test.

IC 50 values generated from the different assay methods should not be directly compared. Raw data relative fluorescence or luminescence units are plotted against the drug concentration. IC 50 values can be determined in two ways; using curve fitting software, or by a point to point analysis.

CDC have developed a curve fitting software which is available from them directly. Point to Point: This method uses in house excel templates.

Guidance on how to undertake point-to-point analysis is provided above in the IC 50 analysis section. Is this normal? There is no firm definition of a resistant IC Commonly used criteria to identify isolates that outside the normal range are either:.

A value greater than 3SD from the mean or median value for the given subtype and drug. A value fold or greater than the mean or median value for the given subtype and drug.

True resistant isolates with one of the currently known and characterised mutations tend to have IC 50 valuestimes higher than the normal range for that subtype and therefore are instantly recognisable. Confirmation of a resistant phenotype should be carried out by sequencing of the NA gene where possible. Intermediate results are those which fall over the minor cut off whether using box and whisker or SMAD to monitor IC 50 s and under the major outlier cut off and therefore are not strictly termed as resistant.

These viruses could potentially be mixtures, containing quasi-species of sensitive and resistant virus or may have reduced susceptibility to drug.

The IC 50 test for such isolates should be repeated to confirm the result, and further characterised where possible, for example, sequencing of the NA gene. This can be done in two ways: Box Plot Analysis and robust statistics using the standard deviation of the median absolute deviation of the median SMAD.

It is important to note that all calculations for box plot and robust statistics are performed on log data. Only after all calculations have been completed are the data back-transformed by taking the antilog. How should I monitor trends?