Reservoir-membrane drug delivery systems

Figure 9.3 Drug release from a planar membrane-reservoir drug delivery system.

Good, W. R., and Lee, P. I. Membrane-controlled reservoir drug delivery systems, in Medical Applications of Controlled Release, ed. R. S. Langer and D. L. Wise, Vol. I. Boca Raton, CRC Press, 1984, pp. 1-39. 

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 ...

In membrane diffusion systems the polymer membrane with a given pore size or pore size distribution controls the diffusion of the active substance from the drug reservoir. Dosage forms with membrane-controlled drug delivery can be coated tablets, coated granules or pellets, or so-called multiparticulate systems on which various coats are applied. One possibility for transdermal drug administration is the transdermal patch controlled with a membrane [4-7,34-39]. 

One of these types is the membrane-controlled transdermal therapeutic system, which is outlined in Figure 18.12. These systems consist of the following parts i) covering membrane, ii) drug reservoir, iii) micropore membrane controlling drug delivery, and iv) adhesive contact surface. (Further types of transdermal systems are going to be described in Chapter 16.2.4.3.3). The most commonly used membranes are polyethylene vinyl acetate and polyethylene [60-62]. 

Fig. 7. When such device is in contact with a solution or wet environment, the surrounding water molecules will diffuse across the membrane to the osmotic engine, which will increase the pressure inside the osmotic compartment. Then the piston will move forward to induce the gradual release of the dmg inside the drug reservoir through the outlet orifice. The water permeating flux is the most important parameter of such drug delivery system as it ultimately determines drug release rate.

Reservoir-Based MEMS Drug Delivery System, Fig. 4 A magnetically controlled MEMS device for on-demand and controlled drug delivery. Uprai application of a magnetic field ( 250 mT), the membrane... 

FIGURE 10 Membrane-moderated transdermal drug delivery system (not to scale). Drug permeates from the patch reservoir through the protective outer layers of the skin and Is absorbed into the underlying capillaries of the general systemic blood circulation. 

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