Controlled drug release monolithic devices

Controlled Drug Release—Because the degradation products of Type III bioerosion are small, water soluble molecules, the principal application of polymers undergoing such degradation is for the systemic administration of therapeutic agents from subcutaneous, intramuscular or intraperitoneal implantation sites. Application of Type III bioerosion to controlled drug release was first described in 1970 (32) and has since then been extensively investigated. The various types of devices currently under development can be classified into (a) diffusional and (b) monolithic (7). 

Monolithic Devices—In these systems the drug is homogeneously dispersed within a bioerodible polymer matrix, and release of the drug can be controlled either by diffusion or by polymer erosion. If erosion of the matrix is very much slower than drug diffusion, then release kinetics follow the Higuchi model (37) and drug release rate decreases exponentially with time, following t dependence over a major portion of the release rate. 

In developing such devices, two fundamentally different approaches are possible. In one, mechanism of drug release is by diffusion from a reservoir through a rate-limiting bioerodible pol3nner membrane, and in the other, drug release is controlled by matrix erosion. However, to achieve zero order drug delivery from monolithic erosional devices the erosion process must be confined to the surface of the solid device. ... 

The second type of device is a monolithic system (Fig. 9, middle) incorporating a backing layer, a matrix layer, and an adhesive layer. The matrix layer consists of a polymer material in which the solid drug is dispersed the rate at which the drug is released from the device is controlled by this polymer matrix. With this type of system, the drug release rate falls off with time as the drug in the skin-contacting side of the matrix is depleted. 

The simplest configuration of a controlled release device is where a drug is either dissolved in high concentration or suspended as particles in a monolithic polymer such as a cylindrical polymer fiber. The release of the drug from it may occur via ... 

Rod-shaped monolithic hydrogel devices with progesterine have been studied in the development of controlled release system for contraceptive application. It was found that progesterine release depends on the initial drug load, the degree of cross-linking, and the water content of the hydrogel. The first-order release was observed. 

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