ABSTRACT
The rate, extent and duration of drug release from a controlled release device depend on a number of design variables and upon the physicochemical properties of the drug. Controlled-release devices are designed to limit or slow the rate of drug release relative to fast release systems containing the same drug. Drugs are combined with these polymers in a variety of methods to produce controlled-release devices. The method of fabrication affects both duration and mechanism of release. In general, devices that release drug at constant or zero-order rates are desirable so that the associated plasma concentrations are invariant with time. The most straightforward method to achieve constant-release-rate devices is to provide a constant activity source of drug such as a concentrated drug suspension in a suitable solvent placed within a polymeric capsule. Monolithic or matrix devices are preferred for their relative ease of manufacture, in spite of their release rates which decrease over time.
