5. Local action

Nanodrug routes of administration vary widely. Although most formulations on the market have been designed for the parenteral route (particularly intravenous), they can also be administered via the ocular, nasal, oral, cutaneous, digestive or pulmonary routes. For these routes, nanomedicines can be retained locally, releasing the active substance in situ. However, epithelial or skin barriers are not always impenetrable. A certain quantity of nanoparticles may be absorbed through these barriers (figure 4 ). The drug's action then changes from a local to a systemic effect, as the particles enter the bloodstream and are then transported to the tissues in what is known as the distribution phase (figure