Review of recent research on hepatitis C therapy for 54th annual meeting of the American association for the study of liver diseases

/pdf/degradable-controlled-release-polymers-and-polymeric-1y322ha58z.pdf

Degradable Controlled-Release Polymers and Polymeric Nanoparticles: Mechanisms of Controlling Drug Release

Novel crosslinking methods to design hydrogels

Hydrogels in controlled release formulations: network design and mathematical modeling

Pharmaceutical dosage forms contain both pharmacologically active compounds and excipients added to aid the formulation and manufacture of the subsequent dosage form for administration to patients. Indeed, the properties of the final dosage form (i.e. its bioavailability and stability) are, for the most part, highly dependent on the excipients chosen, their concentration and interaction with both the active compound and each other. No longer can excipients be regarded simply as inert or inactive ingredients, and a detailed knowledge not only of the physical and chemical properties but also of the safety, handling and regulatory status of these materials is essential for formulators throughout the world. In addition, the growth of novel forms of delivery has resulted in an increase in the number of the excipients being used and suppliers of excipients have developed novel coprocessed excipient mixtures and new physical forms to improve their properties. The Handbook of Pharmaceutical Excipients has been conceived as a systematic, comprehensive resource of information ​ on all of these topics. URI http://repositorio.ub.edu.ar/handle/123456789/5143 Collections Libros Farmacia www.ub.edu.ar | biblioteca.ub.edu.ar Contact Us | Send Feedback Handbook of pharmaceutical excipients 

Handbook of Pharmaceutical Excipients

This paper deals with the physical and mathematical modelling description of drug release from matrix systems. In the introduction, matrix systems are considered in the wide frame of the controlled release systems and the concept of mathematical model is briefly discussed. Then, matrix structure and topology are matched, analysing the characteristics of the three-dimensional network constituting them. In this context, drug release mechanisms are considered with particular emphasis on the key factors ruling the release kinetics, such as matrix swelling, erosion, drug dissolution (re-crystallisation), drug diffusion, drug - polymer interaction, initial drug distribution and particle size distribution (for powdered matrix systems). The mathematical modelling section firstly considers the empirical and semi-empirical models that have the great advantage of showing analytical solutions. Then, the attention is focused on theoretical approaches regarding matrix swelling equilibrium and kinetics, drug dissolution, drug diffusion, drug - polymer interaction, initial drug distribution and matrix erosion. Finally, release kinetics from polydispersed spherical particles is studied. This review points out the fact that the comprehension of the phenomena ruling drug release from matrix systems is appropriate from both the physical and modelling point of view, although further improvements are always possible and desirable.

Mathematical modelling and controlled drug delivery: matrix systems.

Drug mechanochemical activation

Demand for better reliability from drug delivery systems has caused designers and researchers to move away from trial-and-error approaches and toward model-based methods of product development. Developing such models requires cross-disciplinary physical, mathematical, and physiological knowledge. Combining these areas under a single cover, Under

Understanding Drug Release and Absorption Mechanisms : A Physical and Mathematical Approach

Many industrial products often include in their formulation more than one polysaccharide to achieve the desired properties during and after processing. Many such mixed systems behave as would be expected from the known properties of the individual polymers. In others, however, their properties are superior to those of either component alone, or may be qualitatively different. In many polysaccharide systems, the combination of a gelling polymer with a nongelling one gives rise to strong synergistic effects, as a consequence of interaction among different chain polymers and formation of mixed junction zones. Probably, the most exploited mixed gels, especially by the food industry, are those involving the microbial polysaccharide xanthan gum (XG) and the plant galactomannans, like locust bean gum (LBG). Concentrated aqueous systems of LBG and XG display quite different rheological properties: the former show the behaviour typical of hyperentangled macromolecular solutions, whereas the flow and viscoelastic properties of XG systems correspond to those of tenuous, weak-gel networks. Interestingly, when mixed together these macromolecules interact to form a firm, thermoreversible gel with synergistic effects. In the present paper we report the results of a thorough investigation of both polymer concentration and temperature effects on the rheological properties of mixed LBG-XG systems in 20 mM KCl under continuous and oscillatory flow conditions. Under continuous shear at 25 degrees C, pure LBG shows the flow properties of a macromolecular solution, with a shear-thinning behaviour and a Newtonian region at low shear rates, whereas the rheological behaviour of XG and all LX mixed systems is that typical of weak-gels. Furthermore, in the mixed systems the viscosity values do not increase monotonically with increasing xanthan concentration, but the synergistic effect has a maximum in accordance with the XG:LBG ratio 1:1. As the temperature is increased from 25 degrees C to 85 degrees C, whilst the LBG system do not show any qualitative change but there is only a parallel, downward shift of viscosity values, in the case of xanthan there is a dramatic change in the corresponding curve profiles, due to the thermally induced helix-coil conformational transition. The differences in the rheological behaviour of the systems examined can be better shown through dynamic tests at 25 degrees C. The strain sweeps performed at constant frequency of oscillation reveal that the mixed systems show higher sensitivity to strain amplitude, and lower strain values must be attained to ensure linear viscoelastic properties. The mechanical spectra clearly show the influence of composition on the viscoelastic properties of these biopolymer systems. All LX systems show the mechanical spectra typical of polysaccharide gels: G' is always much greater than G" and is nearly independent of the applied frequency over a wide frequency range. In addition, the marked gap between the elastic responses of the pure LBG and the LX 1:3 systems demonstrates the strong effect of the initial addition of xanthan to the pure LBG, especially in the low frequency range, whereas the highest synergistic effect is attained for the LX 1:1 system. A comprehensive description of the frequency dependence of both moduli can be suitably obtained through the four-parameter Friedrich model, which belongs to the class of fractional derivative approaches viscoelasticity. The same thermal effect is observed for the XG and all LX mixed systems considered, indicating a progressive change from the behaviour of a typical gel to that of a quasi-solution state, when temperature is increased from 25 degrees C to 85 degrees C. Among all mixed systems, the LX 1:1 has the highest values of the moduli at any temperature considered, and is characterized by the highest gel-sol transition temperature. (ABSTRACT TRUNCATED)

Mario Grassi

Papers

Mathematical modelling and controlled drug delivery: matrix systems.

Drug mechanochemical activation

Understanding Drug Release and Absorption Mechanisms : A Physical and Mathematical Approach

Synergistic gelation of xanthan gum with locust bean gum: a rheological investigation.

Chirality Effects on Peptide Self-Assembly Unraveled from Molecules to Materials