Dissolution-controlled release

The dissolution controlled release matrix systems provide sustained release profiles i.e., the active drugs in these systems are released continuously at a slow rate to provide a long-term therapeutic effect. Unlike diffusion controlled release coated systems, release profiles from dissolution controlled release coated systems do not follow zero-order kinetics but fall within the classification of delayed release systems,4 pulsatile or repeat-action systems,5 and sustained release systems.3... 

Although examples of delivery systems using the parenteral and oral (solid) routes are presented in this chapter, application of dissolution controlled release matrix and coated systems concepts can extended easily (and has been) used for many other delivery routes. 

Theoretical Considerations for Dissolution Controlled Release Matrix and Coated Systems... 

Although Eq. (5.2) seems to be simple, it is actually very complicated because of the preceding factors. However, it does provide some theoretical basis for rational design of dissolution controlled release systems. Therefore, surface area (related to particle size), solubility, and viscosity may be the parameters that could be regulated or modified to suit certain desired release profiles. 

Among the parameters discussed earlier, dissolution controlled release dosage forms can be designed to achieve the desired release profiles by manipulating the parameters related to the coating polymer. 

Delivery systems based on dissolution controlled release solid particles... 

Materials and processing technologies. The polymers discussed previously for nonenteric coatings such as HPMC (the most widely used), PVP, CMC, and carbomer, xanthin gum, and other naturally occurring polysaccharide polymers may be used for dissolution controlled release matrix systems. Furthermore, conventional processing techniques that were discussed for coating systems also can be used for matrix systems. 

Currently, most mature dissolution controlled release systems/ technologies are applicable for water-soluble and low-water-solubility compounds (with low doses). For very poorly water-soluble compounds, dissolution controlled release systems/technologies may not be applicable because these compounds have intrinsically slow dissolution/release rates. Recently, several new technologies such as solid dispersions and self-emulsifying drug delivery systems (SEDDS) have been developed to deliver poorly water-soluble compounds at reasonable doses through enhancement of dissolution rate. These technologies have created new potentials for controlled release of poorly water-soluble compounds, often... 

Equation (6.94) illustrates that zero-order release kinetics are obtained if drug dissolution controls the release kinetics. However, as soon as the last particle in the matrix dissolves, the controlling mechanism of drug release shifts to Fickian diffusion. Figure 6.19 shows the dissolution-controlled release of KC1 at the early stage of release and the diffusion-controlled release at the later stage of release from an ethyl cellulose tablet. 

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