Drug delivery systems direct

Adherence of a drug delivery system directly to any mucosal membrane can occur if the mucus layer is disturbed or the bioadhesive penetrates the mucin. Disruption of the mucus layer can be by abrasion, cell sloughing, chemical alterations by mucolytic agents, or disease state of the tissue [15]. If such an interruption occurs, bioadhesives can serve (1) to maintain continuity of the mucus layer and minimize the exposed area, (2) replace the mucus layer and provide a protective covering for the underlying cell layers from physical and chemical injury, and (3) act as a platform for drug delivery to local tissues and facilitate recovery of the damaged or diseased cell layers. 

Polysaccharides for drug delivery systems have been prepared by a variety of routes. They will be discussed only briefly in this chapter and the reader is directed to publications on the subject, which appear as references. 

If one were to imagine the ideal drug-delivery system, two prerequisites would be required. First, it would be a single dose for the duration of treatment, whether it be for days or weeks, as with infection, or for the lifetime of the patient, as in hypertension or diabetes. Second, it should deliver the active entity directly to the site of action, thereby minimizing or eliminating side effects. This may necessitate delivery to specific receptors, or to localization to cells or to specific areas of the body. 

For osmotic drug delivery systems, Eq. (2) is of critical importance. This equation demonstrates that the quantity of water that can pass a semipermeable film is directly proportional to the pressure differential across the film as measured by the difference between the hydrostatic and osmotic pressures. Osmotic delivery systems are generally composed of a solid core formulation coated with a semipermeable film. Included in the core formulation is a quantity of material capable of generating an osmotic pressure differential across the film. When placed in an aqueous environment, water is transported across the film. This transported water in turn builds up a hydrostatic pressure within the device which leads to expulsion of the core material through a suitably placed exit port. 

In addition to solvent uses, esters of lactic acid can be used to recover pure lactic acid via hydrolysis, which in-tum is used to make optically active dilactide and subsequently polylactic acid used for drag delivery system.5 This method of recovery for certain lactic acid applications is critical in synthesis of medicinal grade polymer because only optically active polymers with low Tg are useful for drug delivery systems. Lactic acid esters themselves can also be directly converted into polymers, (Figure 1), although the commercial route proceeds via ring-opening polymerization of dilactide. 

H. Sezaki, M. Hashida, Macromolecules as Drug Delivery Systems , in Directed Drug Delivery - A Multidisciplinary Approach , Eds. R. T. Borchardt, A. J. Repta, V. J Stella, Humana Press, Chfton, N. J., 1985, p. 189-208. 

The failure in increasing residence time of mucoadhesive systems in the human intestinal tract has led scientists to the evaluation of multifunctional mucoadhesive polymers. Research in the area of mucoadhesive drug delivery systems has shed light on other properties of some of the mucoadhesive polymers. One important class of mucoadhesive polymers, poly(acrylic acid) derivatives, has been identified as potent inhibitors of proteolytic enzymes [72-74]. The interaction between various types of mucoadhesive polymers and epithelial cells has a direct influence on the permeability of mucosal epithelia by means of changing the gating properties of the tight jrmctions. More than being only adhesives, some mucoadhesive polymers can therefore be considered as a novel class of multifunctional macromolecules with a number of desirable properties for their use as delivery adjuvants [72,75]. 

Many interactions will directly influence the efficacy of the product, and thus potentially the health and/or treatment of the patient. However, it must be reemphasized that excipient interactions are not always detrimental. Sometimes they can be used to our advantage, particularly in the areas of product manufacture and drug delivery systems (see below). 

Applications being developed for responsive gels include drug delivery systems, novel separation systems, artificial muscles and the like, switches and sensors. The rate of response to the environmental changes may directly influence the system performance, as in switches and sensors, or indirectly, as in the cases of recyclable absorbents, where cycling times must be minimized to ensure the economic feasibility of the application. Much of the research on responsive gels... 

Oth, M., Franz, M., Timmermans, J., and Moes, A. The bilayer floating capsule A stomach-directed drug delivery system for misoprostol. Pharm. Res. 9(3) 298—302, 1992. 

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