Hello

The time point for IC50 depends on the drug candidate and the cell line used in the assay. For instance, Doxorubicin treatment gives a good response curve for most cell lines at 24 to 48 hrs.

I would suggest you try getting more information on your candidate drug and go for 24hr or 48hr time point for the IC50.

Using 72hr time point for IC50 would not be advisable because it is too long a time for cells in culture in 96-well plate. The cells may die due to overcrowding and in turn will give you an erroneous IC50 value.

So, it is up to you to decide the right time point for IC50 because there are many factors involved like drug action, type of cell line used and culture conditions. I have just given a rough idea which time point you need to select, but the final decision will be yours.

Good Luck.

24 hour time would be most appropriate for cultures in 96 well plated

If 24 hours cell viability its there continue to 48 hours. after that you can calculate the IC50 value.

If 24 hours only cell viabilty decreases, calculate the IC50 value.