Drug delivery systems limitations

Aguzzi, C., Cerezo, P., Viseras, C. and Caramella, C. 2007. Use of clays as drug delivery systems Possibilities and limitations. Applied Clay Science 36 22-36. 

A pharmacotectonics concept was illustrated by researchers, in which drug-delivery systems were arranged spatially in tissues to shape concentration fields for potent agents. NGF-releasing implants placed within 1-2 mm of the treatment site enhanced the biological function of cellular targets, whereas identical implants placed mm from the target site of treatment produced no beneficial effect (Mahoney and Saltzman, 1999). Because of some limitations with controlled delivery systems, alternatives such as encapsulation of cells that secrete these factors are discussed in the next section. 

NeubergerT, Schopf B, Hofmann H, Hofmann M, von Rechenberg B (2005) Superparamagnetic nanoparticles for biomedical applications possibilities and limitations of a new drug delivery system. Journal of Magnetism and Magnetic Materials 293 483 196. 

Drug-delivery systems are essentially specialized dosage forms developed to overcome the limitations of conventional dosage forms, such as simple tablets, capsules, injectable solutions, etc. Some of the reasons behind the development of oral DDSs are listed below ... 

A buccal drug delivery system is applied to a specific area on the buccal membrane. Moreover, the delivery system ean be designed to be unidirectional in drug release so that it can be protected from the loeal environment of the oral cavity. It also permits the inclusion of a permeation enhancer/protease inhibitor or pH modifier in the formulation to modulate the membrane or the tablet-mucosal environment at that particular application site. While the irritation is limited to the well-defined area, the systemic toxicity of these enhancers/inhibitors and modifiers can be reduced. The buccal mucosa is well suited for this type of modification as it is less prone to irreversible damage [9]. In the event of drug toxicity, delivery can be terminated promptly by removal of the dosage form. 

The use of albumin microparticles as a drug delivery system was first suggested by Kramer (1974) and several methods for their production were subsequently developed (Gupta and Haung 1989). Most methods involved the application of emulsification methodology and factors involved in this process have been evaluated by a number of authors. However, studies of the in vitro disintegration process of protein microspheres, induced by the presence of protease enzymes in the environment, are limited (El-Samaligy and Rohdewald 1983). 

In many cases in drug development, the solubility of some leads is extremely low. Fast dissolution rate of many drug delivery systems, for example, particle size reduction, may not be translated into good Gl absorption. The oral absorption of these molecules is usually limited by solubility (VWIImann et al., 2004). In the case of solubility limited absorption, creating supersaturation in the Gl Luids for this type of insoluble drugs is very critical as supersaturation may provide great improvement of oral absorption (Tanno et al., 2004 Shanker, 2005). The techniques to create the so-called supersaturation in the Gl Luids may include microemulsions, emulsions, liposomes, complexations, polymeric micelles, and conventional micelles, which can be found in some chapters in the book. 

Self-Emulsifying Systems Emulsion systems have the disadvantage of being physically unstable, and over time a separation between the oil and water phases of the emulsion will occur. The use of conventional emulsions is also less attractive due to poor precision of the taken dose and the relatively large volume that has to be administered. To overcome these limitations, self-emulsifying drug delivery systems (SEDDS) have been developed. The... 

This chapter discusses the GI physiology that defines the limits of gastric retentive technology and a more detailed analysis of the different approaches to design gastric retentive drug delivery systems. 

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