I am not a biologist but I imagine someday soon a scenario like this will be possible: You have a model of the sites and interactions the drug targets, and optimum biology - metabolism, target cells' proteomes etc. Measure these in the patient and you can predict ahead of time the efficacy of the drug and then optimize the drug's chemistry to be more effective for this individual. With a better understanding of protein modelling and such you could do a search for similar structures and compute the expected interactions and optimize for personalized effectiveness.