MTT: for 5 days - (Dec/05/2012 )

I'm doing MTT to check the effect of a drug on the proliferation of a cancer cell line. I've seeded about 2,000 cells / 100ul in each well. The medium won't be enough to sustain the cells for 5 days. In such a case, do I replace the medium (with the drug) with fresh medium containg the drug, after about 3 days?

Thank you.

That should be OK, though this would be equivalent to giving two doses of the drug. Do you know much about the physiology/pharmacology of the drug and how it is broken down/metabolized and the effects of the metabolites?