How can we calculate ic50

Be sure you select the correct equation when performing nonlinear regression! If you'd like to convert concentration values to log concentration values - or vice versa - you can use Prism's Transform analysis to convert the X values. Also note that this sample data set includes unknown values.

These are Y values without corresponding X values. Prism can interpolate these X values. Click Analyze and then Nonlinear regression. Or click the Nonlinear Regression shortcut button just above the Analyze button.

It is the concentration required to bring the curve down to a point halfway between the "Top" and "Bottom" plateaus of the curve. The concentration that provokes a response halfway between the blank no antagonist, maximum measured response and some positive control to represent a fully inhibited response is sometimes called the Absolute IC In many cases, the positive control used may be a different, standard drug known to elicit a maximal inhibitory effect on the measured response.

Often, the response measured for this standard positive control is lower than the "Bottom" of the dose-response curve. In some cases, an Absolute IC50 simply cannot be calculated. Be sure to know which IC50 you want to report, and what your values mean. Read more about Absolute IC50 here.

Create an XY data table. Enter the logarithm of the concentration of the agonist into X. Enter response into Y in any convenient units. From the data table, click Analyze, choose nonlinear regression, and choose the panel of equations: Dose-Response -- Special, X is log concentration. Then choose " Absolute IC50, X is log concentration ".

You must enter a value for the parameter "Baseline" on the Constrain tab of the analysis parameters dialog. 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. Q: A fold difference is seen when the same virus is re-tested. 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 values , times 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.