Polymeric drug targeting

Figure 12.1 Schematic design of polymeric drug targeting carrier.

Polymeric microparticles have been studied and developed for several years. Their contribution in the pharmacy field is of utmost importance in order to improve the efficiency of oral delivery of drugs. As drug carriers, polymer-based microparticles may avoid the early degradation of active molecules in undesirable sites of the gastrointestinal tract, mask unpleasant taste of drugs, reduce doses and side effects and improve bioavailability. Also, they allow the production of site-specific drug targeting, which consists of a suitable approach for the delivery of active molecules into desired tissues or cells in order to increase their efficiency. 

In the area of drug targeting, there needs to be continuing emphasis on understanding the interaction between polymeric particles and biological systems such as blood components, cell types (e.g., phagocytes), and cell receptors. 

Probably the most promising polymeric drug carrier system involves polysaccharide molecules. These are natural polymers and are often biodegradable to products that are useful to the host or easily eliminated by the host. Dextrans have been the most extensively used polysaccharide for macromolecular prodrug preparations (79). These materials are biocompatible and the in vivo fate is directly related to their molecular weight. Moreover these macromolecules can be easily targetted to the hepatocytes with D-mannose or L-fucose (20). 

The polymeric nature may inhibit premature drug deactivation. Thus, cisplatin (structure 19.20), the most widely used anticancer drug, is converted into numerous inactive, but more toxic, platinum-containing compounds before it arrives at the targeted cancer cells. Placement of the active platinum-containing moiety into a polymer (structure 19.21) decreases this tendency to hydrolyze into these unwanted cisplatin compounds because of the greater hydrophobic character of the polymeric drug. 

Polymeric Drug Type of Bond Targeting Type of Bond Activity in vitro Activity in vivo Ref. 

Fig. 10a. Structure of a targetable polymeric drug based on HPMA copolymer carrier.

Another beneLt of polymeric surfactants over traditional surfactants is the potential for much lower CMCs. Amphiphiles with a high CMC may not be suitable as drug-targeting devices since they are unstable in an aqueous environment and easily dissociate upon dilution (Jones and Ler-oux, 1999). It must be noted that while some polymers exhibit very low CMCs, for instance, the CMC of poly -benzyl-L-aspartate) (PEO-PBLA), poly(N-isopropylacrylamide-polystyrene (PNIPA-PST), and poly(caprolactone) (PEO-PCL) are between 0.00005% and 0.002% (La etal.,... 

Nishiyama N, Amida JWD et al (2006) Photochemical enhancement of transgene expression by polymeric micelles incorporating plasmid DNA and dendrimer-based photosensitizer. J Drug Target 14 413 124... 

Maeda H, Bharate GY, Daruwalla J (2009) Polymeric drugs for efficient tumor-targeted drug delivery based on EPR-effect. Eur J Pharm Biopharm 71 409 -19... 

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