I produced some data during an experiment but I am not sure which statistical test I should use. I hope that you could help me with this.

Globally, I expose a defined number of cells to different drugs formulations in order to assay their toxicity (it's an MTT assay for whom is familiar with it).

So the cells are exposed to different formulations at various concentrations for 2 timepoint (24h and 48h). Consequently, I assume that my experiment count 3 predictor variables (formulation, concentration and time of exposure) and one outcome variable (the percentage of surviving cells compared to a control condition).

For the precision, they are not repeated measures and i fit a non-linear curve describing the surviving fraction at the various concentrations for each drug and exposure time.

The questions I would like to answer are:

- Treating apart the results for 24h and 48h, is there a formulation which induces a significant toxicity among the considered interval of concentration (the aim is not to assay if one formulation is more toxic than another but to assay if a significant toxicity is detected compared to the control condition). For this part, I assume to use 2 distinct 2-way anova (one for each timepoint) combined with Dunnett's multiple comparison test to compare the surviving fraction of the different concentrations inside each formulation compared to a control condition.
- Once I would have determined which formulations show a significant toxicity along the considered interval of concentration, I would like to know if there is a significant difference between the same formulations at the 2 timepoint. But I am not sure about the test to select, may be a multiregression analysis?

Feel free to ask any questions and thank you in advance for your help .