Aqueous-based controlled release

Development of an Aqueous-Based Controlled Release Pheromone-Pesticide System... 

Membrane diffusion illustrates the uses of Fick s first and second laws. We discussed steady diffusion across a film, a membrane with and without aqueous diffusion layers, and the skin. We also discussed the unsteady diffusion across a membrane with and without reaction. The solutions to these diffusion problems should be useful in practical situations encountered in pharmaceutical sciences, such as the development of membrane-based controlled-release dosage forms, selection of packaging materials, and experimental evaluation of absorption potential of new compounds. Diffusion in a cylinder and dissolution of a sphere show the solutions of the differential equations describing diffusion in cylindrical and spherical systems. Convection was discussed in the section on intrinsic dissolution. Thus, this chapter covered fundamental mass transfer equations and their applications in practical situations. 

Several other investigators have reported microencapsulation methods based upon polyelectrolyte complexes [289, 343]. For example, oppositely-charged polyelectrolytes (Amberlite IR120-P (cationic) and Amberlite IR-400 (anionic)) were recently used along with acacia and albumin to form complex coacervates for controlled release microcapsule formations [343]. Tsai and Levy [344,345] produced submicron microcapsules by interfacial crosslinking of aqueous polyethylene imine) and an organic solution of poly(2,6 dimethyl... 

We have developed a two-step procedure for the in silico screening of compound libraries based on biopharmaceutical property estimation linked to a mechanistic simulation of GI absorption. The first step involves biopharmaceutical property estimation by application of machine learning procedures to empirical data modeled with a set of molecular descriptors derived from 2D and 3D molecular structures. In silico methods were used to estimate such biopharmaceutical properties as effective human jejunal permeability, cell culture permeability, aqueous solubility, and molecular diffusivity. In the second step, differential equations for the advanced compartmental absorption and transit model were numerically integrated to determine the rate, extent, and approximate GI location of drug liberation (for controlled release), dissolution, and absorption. Figure 17.3 shows the schematic diagram of the ACAT model in which each one of the arrows represents an ordinary differential equation (ODE). 

Kang, S. I. Bae, Y. H. A sulfonamide based glucose-responsive hydrogel with covalently immobilized glucose oxidase and catalase. /. Controlled Release 2003,86,115-121. Gohy, J. F. Lohmeijer, B. G. G. Varshney, S. K. Decamps, B. Leroy, E. BoUeau, S. Schubert, U. S. Stimuli-responsive aqueous micelles from an ABC metaUo-supramolecular triblock copolymer. Macromolecules 2002, 35, 9748-9755. 

Metoclopramide hydrochloride controlled release suppositories were prepared by mixing Witepsol W35 with 30 % lecithin [13]. The metoclopramide is incorporated in this base in a (solid) reversed micellar solution. The diffusion rate of the active substance from the melted suppository in contact with the aqueous rectum fluid was very low. Compared to licensed normal metoclopramide suppositories a five times longer mean residence time was found in vivo for the lecithin suppositories. 

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