Mass Balance: An Old Concept for the New Challenges Proposed by Personalized Medicine

The concept of personalized medicine implies the treatment of each single patient as a unique subject,1 thus overcoming the old idea of the average patient. This strategy, via an optimized dosing, is greatly beneficial for the patient, because it allows the reduction of side effects and the improvement of the effectiveness of the therapeutic treatment. On the other hand, it poses the not negligible problem of patient uniqueness. Indeed, uniqueness requires the definition of a rational approach that can be fitted to each patient. For this purpose, mathematical models, defined as a mathematical metaphor of some aspects of reality,2 can be of great utility.3 Of course, to represent a reliable and effective theoretical tool in the field of personalized medicine, the mathematical model must account for the most important aspects of drug release and the absorption, distribution, metabolism, and excretion (ADME) processes. Moreover, it is mandatory to account for the simultaneous time evolution of drug release and ADME, processes that are not independent but mutually affect each other. This requirement reflects the conviction that the new challenge in the drug delivery field, for what concerns mathematical modeling, resides in the possibility of developing mechanistic theories able to consider together drug release and ADME phenomena within the human body.4