Targeted drug delivery: concepts, approaches, and applications

Targeted drug delivery (TDD) is a relatively novel approach that aims at delivering a drug to a specific site of action or absorption while not releasing it elsewhere in the body. TDD systems provide several benefits over traditional drug administration methods, including greater pharmacological activity, less side effects, and reduced therapeutic regimens. The delivery system is intended to maintain the drug in its original form until the target spot is reached and the cargo is released in situ. The "magic bullet" concept was designed to attain this goal, and, for more than a century, it has fueled scientific research, resulting in the development of many delivery strategies. The primary purpose of a TDD is to focus the pharmacological impact the therapeutic agent to diseased organs while leaving healthy tissues undisturbed, which is exceptionally critical in cancer chemotherapeutics. Active and passive targeting, ligand-mediated targeting, inverse targeting, dual targeting, physical targeting, and double targeting are all examples of TDD mechanisms; yet, almost the totality of these processes requires the help of a carrier to accomplish the ultimate goal. These carriers can be divided in three major classes: lipid-, polymeric-, and monoclonal antibody-based drug delivery systems. Each class, in turn, has several subclasses, which will also be presented and discussed in this chapter.