Nanoparticles As Drug Delivery Systems

The challenge of modern drug therapy is the optimization of the pharmacological action of the drugs coupled with the reduction of their toxic effects in vivo. The prime objectives in the design of drug delivery systems are the controlled delivery of the drug to its site of action at a therapeutically optimal rate and dosage to avoid toxicity and improve the drug effectiveness and therapeutic index.

Among the most promising systems to achieve this goal are the colloidal drug delivery systems, which include liposomes, niosomes, microemulsions, and nanoparticles. Nanoparticles are considered promising colloidal drug carriers, as they overcome the technological limitations and stability problems associated with liposomes, niosomes, and microemulsions. For instance, camptothecin-based drugs, because of their poor solubility and labile lactone ring, pose challenges for drug delivery. Williams et al.3 developed a nanoparticle delivery system for a camptotheca alkaloid (SN-38) that is stable in human serum albumin; high lactone concentrations were observed even after 3 h and showed prolonged in vivo half-life of the active (lactone) form.

Nanoparticles are solid colloidal particles ranging in size from 10 to 1000 nm. Depending on the process used for their preparation, two types of nanoparticles are obtained: nanospheres and nanocapsules (Figure 15.1). Nanospheres possess a rigid matrix structure that incorporates the drug, whereas the nanocapsule contains an oily core incorporating the drug surrounded by a membrane structure.4 These are prepared from either synthetic or natural macromolecules in which the drug is dissolved, entrapped, encapsulated, or adsorbed on the surface. Generally, the definition of nano-particles includes not only the particles described by Birrenbach and Speiser5 by the term "Nanopellets," but also nanocapsules and polymer lattices such as the "molecular scale drug entrapment" products described by Rhodes et al.6 and Boylan and Banker.7 Nanoparticles possess a matrix structure that incorporates the pharmacologically active substance and facilitates the controlled release of the active agent.

Polymeric matrix containing drug

Polymeric membrane

Nanosphere Nanocapsule

FIGURE 15.1 Representation of nanosphere and nanocapsule.

Nanosphere Nanocapsule

FIGURE 15.1 Representation of nanosphere and nanocapsule.

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