Fate of nanoparticles used as drugs in the body

Medicines used in human health today not only have their main pharmacological activity, but also so-called undesirable side effects. Improving a drug's performance by limiting its potential toxic effects is tantamount to improving its benefit/risk balance. Nanotechnologies provide the means to increase the benefit/risk balance by changing the drug's fate in the body. This is particularly important in the field of cancer treatment, where the aim is to target tumor cells rather than healthy cells. The idea behind this therapeutic strategy is to associate the active molecule with a vector that possesses physico-chemical properties (size, electrostatic surface charges, hydrophilicity, etc.) that will determine where it diffuses in the body and how it is eliminated. In this way, the fate of the active drug molecule in the body no longer depends on its own chemical properties, but on those of the vector. This concept is known as vectorization. Successful vectorization involves targeting molecules to the body tissues in which they are intended to be active, while limiting their diffusion to tissues in which they could be toxic, by extending their residence time in the tissues of interest to prolong their pharmacological effect and obtain more effective drugs. The development of an effective, low-toxicity vector relies on mastery of the manufacturing and characterization processes, which are sometimes difficult at the nanometric scale, but also on knowledge of the physiological, histological, biological and biochemical structures of the body's tissues. The fate in the body of the vector we wish to control, in order to control the action of the drug, will depend on the interaction between the vector and the living environment. So, depending on the route of drug administration, the vector will come into contact with different tissues, and its path through the body may be different. The discipline that studies the behavior of a drug in relation to the biological structures it encounters is called biopharmacy. The aim of this article is to describe the particular concepts of biopharmacy when applied to drug carriers, also known as nanomedicines. An analysis of the fate of nanomedicines by route of administration will be proposed in this article to enlighten the formulator on the cellular and tissue structures to be taken into account for a rational and efficient design of nanomedicines.