Membrane controlled drug delivery systems

Figure 18.6 Schematic drawing illustrating drug release from membrane controlled drug delivery systems (membrane diffusion systems and osmeotic systems).

The majority of controlled drug delivery systems now being marketed or under development are based on diffusion of the drug through a semipermeable membrane to achieve the requisite release rate. Diffusion control is particularly important to transdermal delivery, where biodegradation and dissolution are not viable mechanisms of controlling the release rate. Provided the process is Fickian, the rate of diffusion through the semipermeable polymer is determined by... 

Giannos, S., Dinh, S., and Berner, B., Temporally controlled drug delivery systems Coupling of pH oscillators with membrane diffusion, Journal of Pharmaceutical Sciences, Vol. 84, No. 5, 1995, pp. 539-543. 

Polymer membrane permeation-controlled drug delivery systems. 

Polymer Membrane Permeation-Controlled Drug Delivery Systems... 

Fig. 3 Release of drug from various shapes of pol5mer membrane permeation-controlled drug-delivery systems (A) sphere-type, (B) cylinder-type, and (C) sheet-type. In (D), the drug concentration gradients across the rate-controlling polymeric membrane and hydrodynamic diffusion layer exist in series. Both the polymer membrane, which is either porous or non-porous, and the diffusion layer have a controlled thickness and h, respectively).

Polymers and biopolymers have been used in medicine for centuries. These important materials partly have their own therapeutic effect (active substances), and partly ensure the formulation, stability, and applicability of the dosage form (additives). The discovery of controlled drug delivery systems was a major result of research-development in pharmaceutical technology. In these so-called therapeutic systems, polymers ensuring a predetermined rate of membrane or matrix diffusion are used. Mucoadhesion (adhesion to biological surfaces) and the group of stimuli sensitive (environment sensitive) polymers play an important role in controlling the therapeutic effect. 

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]. 

PLA is a non-toxic and biodegradable material that is extensively used in coating membranes [10] and as carrier compounds [11-18]. The application of PLA in controlled drug-delivery systems is often limited due to its poor wettability. It has... 

MAJOR APPLICATIONS Produced for many years in developmental quantities for evaluation in research and limited use in commercial tests and military applications nonflammable fibers and films. Under evaluation for controlled drug delivery systems, hydrogels, implants, and membranes. 

Today polymeric membranes are widely used to produce potable water from seawater, treat industrial effluents, for controlled drug delivery systems, separate common gases, pesticide release systems, and in prosthetic devices for humans, among others (76). Most of these methods require the separation of two or more components. Membrane-based separation processes are environmentally green, economic, and frequently more efficient than conventional methods. 

Controlled-release drug delivery systems mimic nature. Molecules called lipids are found in fats and also form the membranes of living cells. A lipid molecule is similar in struc-... 

K Tojo, Y Sun, M Ghannam, Y Chien. Characterization of a membrane permeation system for controlled drug delivery studies. AIChE J 31 741, 1985. 

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