What is the best approach to valuing a drug in development, during clinical trials?
This is an active area of research, so expect more soon on this topic. R&D projects can be viewed as investments that create options. The value of a drug in the R&D stage can be obtained through a nested options valuation model. See Chapter 11 of Amram and Kulatilaka for an overview, and their Guide to the Literature for some pointers to other papers.