Dear Elmira,

for in vitro combination studies I usually use the IC50 values of the two compounds that I want to combine as the highest dose. Base on that concentration, I define 2 or 3 other concentrations which are a dilution of the IC50 value ( IC50/2, IC50/4, IC50/8 and so on).

To define synergism or additivism I usually use compusyn software ( https://www.combosyn.com/) is free and easy to use.

When you have insert all the effects of the two compounds in single agent and the effect of their combinations you can generate a report in which you find different combination index values (CI) for each combo. CI1 antagonism.

You can find also the prediction of the concentration of both compounds you would need to obatin the EC50 value (IC50), but is not very accurate.

Regards

Andrea

Dear Elmira

For in vitro combination study you can go for the median effect principle which determine whether combinations resulted in antagonistic, synergistic or additive effect

You can refer the attached manuscript it might help you

Regards

Naveen Dhingra

Hi every one

I can't install the program for combination index because it's in Java format😭... Any other idea?

Try different ratios between the IC50 values of both compounds, eg.1:5,1:10, 1:100, run the combosyn analysis and report what you get at the different ratios.

BTW, sometimes you have different behaviour ( synergism or antagonism) depending on the ratio used.