Controlled release applications

For many drug delivery applications, the preferred method of delivery of the dosage form is by injection. For controlled release applications, the most frequently used approach to allow this method of administration is to prepare microspheres of the polymer containing the drug to be delivered. Several different techniques have been developed for the preparation of microspheres from polyanhydrides. 

Kohn, J., and Langer, R., A new approach to the development of bioerodible polymers for controlled release applications employing naturally occurring amino acids, in Proceeding of the ACS Division of Polymeric Materials. Science and Engineering. American Chemical Society, 1984, Vol. 51, pp. 119-121. 

The use of polymers for biomedical applications has been widely accepted since the 1960 s (7), and specifically for controlled release applications since the 1970 s (2). The primary goal of this research was to create a controlled release matrix from polymers with pre-existing Food and Drug Administration (FDA) histories, which would be capable of releasing insoluble active agents, and upon exhaustion of the device, leave a stable, inert, removable skeleton. The application of such a matrix would be as an intracervical device which would prevent both conception and ascending infection. 

Inert polymer matrices, studied for use in possible controlled release applications, have used porosimetry to investigate a number of properties [54-56]. The kinetics of liquid capillary penetration into these matrices was explored using a modified Washburn equation [54]. It was shown that water... 

Thurmond, K. B. II and Wooley, K. L. ACS Symposium Series on Materials for Controlled Release Applications, Ch. 13, American Chemical Society, Washington, DC, 1998. 

Kost, J. and Langer, R. Equilibrium swollen hydrogels in controlled release applications, in N. A. Peppas, ed. Hydrogels in Medicine and Pharmacy, pp. 95-107. CRC Press, Boca Raton, FL, 1986. 

Polyelectrolyte complexes have also been studied as tablet matrices for controlled release applications. For example, the interpolymer complexes of chitosan with pectin and acacia were investigated as tablet matrices for release of chlorpromazine HCL [353]. The complex formed in situ by mixing chitosan with either pectin or acacia displayed the most efficient sustained release (compared to either pectin, acacia or a preformed complex). The results were attributed to the swelling and gel-forming capacity of the freshly formed complex in contrast to the preformed version. 

C., Nakache, E., Sanchez, C., Schmitt, C. (2002). Biopolymeric colloidal carriers for encapsulation or controlled release applications. International Journal of Pharmaceutics, 242, 163-166. 

Polylactic acid has been studied extensively for controlled release applications ranging from the oral delivery of simple drugs such as indomethacin9 to the parental administration of complex proteins such as insulin.10 Polylactic acid of different molecular weights has been studied as matrix material for parenteral administration. Seki et al.11 used polylactic acid 6000 and Smith and Hunneyball8 used polylactic acid 100,000 for the controlled delivery of drugs by the parenteral route. Several polylactic acid systems have been studied for the controlled... 

The purpose of this article is to review the use of microgel particles and of core shell particles, primarily in the context of selective uptake and controlled release applications. Most of the examples will be taken from the work of the author and his coworkers in Bristol, carried out over many years of researching this topic. 

A relatively novel class of derivatives is obtained by the covalent incorporation of organometallic moieties into cellulose. For example, cellulose ferro-cenyl derivatives have been prepared by esterification of cellulose with an intermediate derived from ferrocene carboxylic acid and triphenyl phosphite in the presence of pyridine [84]. An enzymatically cleavable cellulose ester has been developed [85], and prodrugs have been coupled to the hydroxyl or carboxyl functions of C-terminal aromatic amino acids of cellulose peptide derivatives for controlled release applications [86]. 

Controlled release applications for a variety of cellulose esters have recently been summarized by Marchessault et al. [86] as well as by Edger [79]. 

Methyl cellulose and hydroxyalky methyl cellulose manufacture involves in part Williamson synthesis with methyl chloride and alkoxylation. The various ethers are used primarily in building materials and in industrial applications (O Table 13). Higher grades with greater purities consist of modified vegetable gums, and they find uses in controlled release applications in pharmaceuticals, and in food products and cosmetics where they serve as emulsifiers and texture agents. 

Beecher, E.D. Carr, M.E. Grille, J.G. Starch compounding on co-rotating twin screw extruder starch as an encapsulation medium for a controlled release application. SPE Antec Proceedings, Boston, MA, May 7-11,1995 2037-2041. 

Only the thermal process is capable of yielding isotropic microporous structures in thick sections. Wet and dry processes tend to become increasingly anisotropic as the thickness of the membrane gel is Increased. This unique property renders thermal process gels ideally suitable for use in controlled release applications. The gels can be cooled, ground up, extracted and filled with volatile insect repellents, for example. 

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