"We don't measure the patients metabolism of a drug at all. Individuals bodies process drugs differently and have different side effects. It seems that differences in reactions could be related to different metabolic pathways being used, resulting in more or less toxic byproducts. Could a urine or blood test a few hours after the first dose be an effective mechanism for screening for likelihood of side effects based on the metabolic byproducts detected? Could this test be effective at detecting these byproducts at dosages below what would cause side effects? Could this be incorporated into a "home drug test" style urine dip that patient could do themselves at home without returning to doc?"

Strangely, just the other day I met someone in Cambridge (UK) who is moving forward with a startup solving this EXACT problem.

Let me know if you want me to connect.