ABSTRACT
This chapter focuses on a discussion of theories, delivery technologies, examples, and future perspectives regarding design of oral modified-release delivery systems for water-insoluble drugs. The physiological environment of the GI tract plays an important role in determining the solution state and bioavailability of the drug after it is released from the dosage form. Formulation development and optimization requires a step-wise approach by first screening and evaluating various formulations in vitro before one initiates formulations/dosage forms testing in vivo. In vivo evaluations are often conducted in animal models to obtain preliminary information with respect to the in vivo absorption characteristics and PK profile of the dosage form. A diffusion-controlled system is typically based on the drug diffusion through an inert membrane or a drug-carrying matrix. In a typical diffusion-controlled matrix system, drug in the outside layer of the matrix is exposed to the solution medium and dissolved first; it then diffuses out of the matrix.
