Kindly, for calculating IC50 from the linear equation; Y=MX+C, what would be the value for Y; 50 or 0.5(taking the % of 50).
Regards.
First, linear interpolation is not the best practice for the measurement of IC50. You can search RG or elsewhere for more information about the method of calculating this parameter from a set of inhibitor concentrations and resulting % inhibitions using nonlinear regression.
Now, to answer your question. If your inhibition results are expressed as % inhibition (on a scale of 0 to 100), then Y = 50. If the results are expressed as fraction inhibition (on a scale of 0 to 1), then Y = 0.5.
Dear colleague,
The percentage (inhibition or mortality) as function the dose (expressed as log dose) do not follow a linear equation. You must convert the percenatge as probit and doses as their logarithm in order to linearize your data. Then, it is easy for you to determine the IC50 (Y= 5 in probit scale). See the probit analysis (Finney, 1971).
Best regards N. Soltani
I see this explication that:
1. After putting your x-and y-axis values in graphpad go to analysis-->transform
2. Convert x-axis values (conc.) to their log values
3. Then again go to analysis and go for "Nonlinear regression (curve fit)" under XY analysis
4. Then select what you want to calculate the inhibition IC50 or induction IC50
5. Then press ok and all the things will be done.
How can I calculate IC50 value from percent inhibition graph for antioxidant activity?. Available from: https://www.researchgate.net/post/How_can_I_calculate_IC50_value_from_percent_inhibition_graph_for_antioxidant_activity4 [accessed Apr 23, 2017].
Dear Labran,
The colleagues answered your question satisfactory. However, i would like to remember only a concept, you determine the quantities as you define them.
Concerning the biological effects of the medicine dose, one measures the concentration of the biological substance as a function of the dose. Conceptually the effect of the dose on the biological substance can be ranged from 0 to 100 percent. Where zero means no effect to 100 percent means 100 percent effect. I50 is the dose required to inhibit the biological function by 50 percent. So, the matter is to get the measurement curve of the biological substance concentration as a function of the dose and then process the data as described to get out the dose at I50.
The problem with determining this point is the scattering in the test results. One can increase the test point and then build an average curve.
Best wishes
Dear Labaran Ibrahim
Linear regression is inaccurate to measure IC50 , because IC50 can be calculated from sigmoidal curve (s shape curve) and there are many programs to calculate IC50 value such as ( graphpad prism , origin, etc.).. but if you don't have a program you can take log concentration on (x axis) and inhibition % on (Y axis), in this case the midpoint will be 50 not 0.5... however i can help you with the program send me your data and I wills end you the rsults,, good luck
Dear colleagues,
IC50 can be estimated from linear regression (probit analysis) and also from sigmoidal curve using Prism v 6.01 for Windows (GraphPad Software Inc., www.graphpad.com) according to your possibilites.
Best regards N. Soltani
the Y will be probit value of 50% M = 5.00
wile x will be the concentration logarithm
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