ABSTRACT
A number of oral controlled release systems have been developed to improve the delivery of drugs to the systemic circulation. Although such systems can control precisely and predictably the drug release rate for extended periods of time, even over a number of days, they do not al ways perform satisfactorily if they pass through the drug absorption site, e.g., the small intes tine, before the release of loaded drug is complete. Thus, attention must be given to prolong ing the residence time of the system to achieve complete drug release in the gastrointestinal (GI) tract (stomach or small intestine) as well as to modulating the drug release rate as pre dicted by the system in order to obtain an ideal oral controlled release system. Several ap proaches to extend the gastric residence time have been developed including an intragastric floating system; a high-density system; a mucoadhesive system; a magnetic system; unfoldable, extendible, or swellable systems; and a superporous hydrogel system (1). An important issue in the development of these systems is how to avoid interunit and intersubject variations in GI residence time. Another problem is how to improve the absorption of a poorly absorbed drug by using such systems.
