ABSTRACT
Time-dependent systems have been developed for colon-targeted delivery utilizing nonbiodegradable polymers that are more frequently employed as excipients in controlled-release systems. The polymers are usually synthetic in nature and undergo dissolution or disintegration in the gastrointestinal tract, without undergoing significant absorption or degradation. They are generally nonspecific with respect to pH-solubility characteristics and the employment of these polymers as carrier matrices for colonic delivery often utilizes a time-dependent mechanism to provide an initial lag phase of low or no release during transit through the upper gastrointestinal tract. In addition, some of the systems described in the patent literature are based on well-established osmotic core technology. Products have been formulated in a variety of compositions, including incorporation of polymers in a drug core, with an application of an enteric polymer coat for preventing drug release in the stomach. This may provide release in the terminal ileum or, if the lag time is sufficient (3-4 h), in the colon. In another variation, the outermost nonenteric layer completely replaces the enteric inner layer resulting in a complete time-dependent drug release mechanism.
