Drug release polymeric matrix influence

The purpose of this chapter is to provide a description of the different types of polymeric matrices existing in the market and how the properties of the principal polymers employed in their manufacture affect the drug release. Furthermore, the main concepts of percolation theory are exposed in order to explain the critical points influencing the drug release from matrix systems. 

Figure 2.3 IgG levels after administration of drug delivery systems in rats. Controlled-delivery systems for antibody class IgG. The insert figures show the release of antibody from the delivery system during incubation in buffered saline. The panel (a) inset shows release from poly(lactic acid) microspheres these spherical particles were 10-100/rm in diameter. The panel (b) inset shows release from a poly[ethylene-co-(vinyl acetate)] matrix these disk-shaped matrices were 1 cm in diameter and 1 mm thick. In both cases, molecules of IgG were dispersed throughout the solid polymer phase. Although the amount of IgG released during the initial 1-2 days is greater for the matrix, the delivery systems have released comparable amounts after day 5. (a) Comparison of plasma IgG levels after direct injection of IgG (open circles) or subcutaneous injection of the IgG-releasing polymeric microspheres characterized in the inset (filled circles). The delivery system produces sustained IgG concentrations in the blood [3]. (b) Comparison of plasma IgG levels after direct intracranial injection of IgG (open squares) or implantation of an IgG-releasing matrix (filled squares) [4]. The influence of the delivery is less dramatic in this situation, probably because the rate of IgG movement from the brain into the plasma controls the kinetics of the overall process.

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