According to an aspect of the present invention, polymeric release regions are provided, which contain one or more partially biodegradable progenitor polymers and which control the release of one or more therapeutic agents disposed beneath or within the same. The progenitor polymers within the release regions are composed of a plurality of biostable polymer portions (which may be the same or different from one another) linked via one or more biodegradable linkages. Upon implantation or insertion into the body, the linkages degrade, cleaving the progenitor polymers into two or more biostable polymers of reduced molecular weight (relative to the molecular weight of the progenitor polymers). As a consequence of this reduction in molecular weight, the release characteristics of the release regions change over time.