Membranization, drug release from polymer

Highly water soluble drugs, as they are typical for oral administration, can be released from polymer beads with low (< 10%) water- but high ethanolswelling capacity at controlled rates, for up to 8 hours. The release of oxprenolol-HCl (77% water solubility) and diclofenac Na (2.6% water solubility) from drug loaded monoliths is a function of water content and crosslink density. By partial extraction of the drug loaded beads the release can be further slowed down and, in the case of oxprenolol-HCl, delayed for several hours the delay is dependent on water content of the polymer and is the result of the formation of a hydrophobic surface membrane. 

The following experiment is conducted to And out the pH at which the polymer will precipitate, and induce drug release from the liposomes, once anchored on the membrane. The phase transition pH is determined at 37°C by measuring the turbidity of the polymer solutions at different pHs. As the polymer undergoes coil-to-globule transition and aggregates, the turbidity of the polymer solution increases. 

The insoluble cellulose derivatives utilized for permeation control of various species (e.g. oxygen and water vapor transport in coated pharmaceuticals, contact lenses, packaging, or water and solute transport through semi-permeable membranes in reverse osmosis, as well as drug release from reservoir systems) differ considerably in their permeability characteristics according to the type and extent of substitution, as well as their molar mass. However, very few comparative data are available from the literature on the polymers actually used in biological applications. Recently, new results have been published. Thus, Sprockel et al. [142] determined the water vapor transmission through various CA, CAT, CAB and CAPr films at different relative humidities (Table 22). 

Figure 9.5 Drug release from a cylindrical-reservoir drug delivery system. The cumulative mass of drug released is plotted versus time for cylindrical-reservoir devices with a range of physical characteristics, which are determined principally by the diffusion coefficient for the drug in the polymer and the membrane thickness. In all cases, the overall length of the device, L, and the cross-sectional radius, b, were fixed at 2.7 and 0.5 cm, respectively. In each panel, one of the relevant design parameters was varied (a) hja was varied between 1.2 and 4 with Dj.p = 1x10" and Cl = 20mg/mL (b) Dj.p was varied (for curve A, Dj.p = 5 x 10 cm /s ...

Fang, Y., Cheng, Q., and Lu, X.-B. (1998). Kinetics of in vitro drug release from chitosan/gelatin hybrid membranes, /. Appl. Polym. Sci., 68 1751. 

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