Controlled drug delivery types

Figure 4.1 Released amount Qt versus square-root-time -Jt plots. Illustration of loading less than or equal to saturation (dispersed, A < Cs) and greater than saturation (dissolved, A > Cs) in a matrix-type diffusion-controlled drug delivery system.

Fatty acid based biodegradable polymers have many biomedical applications. This short review focuses on controlled drug delivery using two classes of the polymers polyanhydrides and polyesters based on fatty acids as drug carriers. Different polymer types and compositions are summarized showing the potential of these polymers as drug carriers. 

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).

A transdermal therapeutic system is a rate-controlled drug delivery system which, applied to the surface of the skin, continuously releases the drug at a rate that will provide a desired steady-state plasma concentration for a specified duration. A candidate drug must possess high activity (i.e. be effective at low plasma concentrations) and efficiently penetrate the stratum comeum-, percutaneous absorption must be reliably consistent. Based on technological design there are four types of rate-controlled transdermal drug delivery system (Chien, 1987) ... 

Site-specific controlled release following delivery to a target organ Release in response to requirements or feedback Receptor-mediated targeted drug delivery Type of drug delivery device... 

Time-controlled drug delivery systems can be classified according to different principles, for example, with respect to the route of administration, field of application, and/or underlying drug-release mechanisms. In this chapter, the various types of devices that have been described so far in literature have been classified based on the major... 

Figure 2 Classification scheme for predominantly diffusion-controlled drug delivery systems. Only spherical dosage forms are illustrated, but the scheme is applicable to any type of geometry. Stars represent dissolved (individual) drug molecules, whereas black circles represent undissolved drug excess (e.g., crystals and/or amorphous aggregates).

OTHER TYPES OF CONTROLLED DRUG DELIVERY SYSTEMS... 

Figure 9.6 Schematic of matrix-type systems for controlled drug delivery. Matrix delivery systems can be constructed with drug dissolved in the matrix material (a) or particles of drug dispersed to form a composite material (b and c). For dispersed drug particles, the overall loading is an important determinant of the dynamics of release.

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]. 

The Genesis and General Types of Controlled Drug Delivery Systems... 

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