scope:

PREFACE

Paul Ehrlich's image of a "magic bullet" is one answer to the problem of drug action specificity. Though perhaps an idealistic image, it is true that the concept of drug targeting is gaining more and more interest in the medical community. The rationale behind the concept is to bring molecules into intimate contact with an elusive target in a controlled way. Beside specificity, other advantages may be protection against potential premature inactivation and decreased toxicity by using reduced doses.

Historically, the basic philosophy behind the development of drug therapies was to push drug action as much as possible. Indeed, the pharmacological response to a drug is directly related to drug concentration at the required site. Because the body distribution of a molecule is essentially based on physicochemical properties, not necessarily fitting the characteristics of the diseased area, large amounts of drug have to be given. Toxicity comes then from massive drug penetration into healthy organs and tissues. Until now, changing chemical structure of the drug has been the only way to improve the selectivity of an active molecule.

An alternative philosophy is to start at the zero drug level and find the amount which is required by the affected area only. Novel approaches to drug delivery concern the association of an active molecule with a carrier system. Liposomes are certainly the most developed carrier system and have been extensively described in publications, reviews, and books. There has been great interest generated in the use of liposomes for membrane model studies, but, they do present some disadvantages, particularly related to their in vivo instability and to difficulties in their preparation at an industrial level.

Another type of carrier system is solid polymeric nano- or microparticles. These new pharmaceutical formulations are generally able to carry a wide variety of drugs in a more stable and reproducible way. Considering the number of newly published papers dealing with polymeric nanoparticles or microspheres, it is clear that interest in the development of such drug delivery systems is increasing. Nevertheless, as far as we know, there is no general book covering the subject. The aim of this work is to partially fill this lack and we hope it will act as a great stimulus for developing new polymeric drug delivery systems.

Contributors were asked to emphasize their own experience with nanoparticles or microspheres. They were also encouraged to provide aspects normally not stipulated in specialized reviews. The objective was to produce a book which although written by specialists, presented a subject which could be easily understood by people in different fields of life sciences. Another goal was to set up a condensed work covering many aspects of nanoparticles and microspheres. That is the reason why, although mainly dealing with synthetic drug carriers, the first chapter is related to preparation and physicochemical properties of nanoparticles constructed from natural polymers. This is followed by two chapters involving the application of polymeric drug carriers in cancer therapy. The second chapter extensively describes in vitro and in vivo behavior of purely synthetic nanoparticles. As in the case of liposomes, a problem can be that some particles are preferentially taken up by the reticuloendothelial system. Magnetic drug carriers provide a partial answer to this problem since their tropism can be managed by an external magnet. The third chapter is entirely devoted to this aspect. A brief but original application of nanoparticles is given in the fourth chapter by reviewing their use in ocular therapy. Finally, two general applications of polymeric microspheres are discussed in Chapters 5 and 6 . These micrometer-sized spherules are of tremendous interest either for embolization or for diagnostics.

The editors thank all contributors for their valuable work and CRC Press Inc. for their professional cooperation

Authors: P. Couvreur, P. Guiot