Although the idea of drug targeting to a specific site in the body was first introduced almost a century ago by Paul Ehrlich (1), the field has emerged as an important area of research only in the past 40 years or so. The advent of recombinant deoxyribonucleic acid (DNA) technology and progress in biochemical pharmacology and molecular biology have not only provided a clearer elucidation of pathogenesis of many diseases and identification of various types of surface cell receptors but also enabled the production of several new classes of highly potent protein and peptide drugs (e.g., homo- and heterologous peptidergic mediators and sequence-specific oligonucleotides) (2). For these new drugs, and for some conventional drugs (e.g., antineoplastic agents) that have narrow therapeutic windows and require localization to a particular site in the body, it is essential that they be delivered to their target sites intact, in adequate concentrations, and in an efficient, safe, convenient, and cost-effective manner. Most drug therapies currently available provide little, if any, target specificity. The selective delivery of drugs to their pharmacological receptors should not only increase the therapeutic effectiveness but also limit side effects and increase safety.

In this chapter, various target-specific drug delivery systems and biological events/ processes that influence drug targeting are discussed.

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