ABSTRACT
I. INTRODUCTION Following parenteral administration of drugs, an active substance distributes throughout the body as a function of its physico-chemical properties and molecular structure. The amount of drug reaching the site of action is often only a small fraction of the administered dose. Accumulation at nontarget sites may lead to adverse reactions and undesirable side effects [1]. A way of modifying the original biodistribution of substances is to entrap them in submicroscopic drug carriers. Among such carriers, liposomes (see chapter 2 on liposomes in this volume), polymeric nanoparticles [2], solid lipid nanoparticles [3], and pharmacosomes [4] have been studied. Twenty-five years ago, liposomal formulations were facing stability problems as well as poor drug loading capacities. Therefore, nanoparticles were at that time seen as a promising alternative for targeting substances. Nanoparticles are solid or semisolid colloidal particles ranging in size from 10 to 1000 run [5]. They consist of macromolecular materials and can be used as drug carriers. Polymeric nanoparticles is a collective name for nanospheres and nanocapsules [2] (Fig. 1). Nanospheres have a matrix-type structure. Drugs may be adsorbed at their surface, entrapped in the particle or dissolved in it. Nanocapsules have a polymeric shell and an inner liquid core. In this case, the active substances are usually dissolved in the inner core, but may also be adsorbed at their surface. Nanoparticles can be prepared by polymerization techniques or by dispersion of preformed polymers. For example, preparation of nanoparticles by polymerization of cyanoacrylates has been extensively studied (see chapter 3 in this volume).
