Rate-control drug delivery systems: controlled release vs. sustained release.

Recently, several technical advancements have been made in the development of new generation of drug delivery systems. These systems are capable of controlling the rate of drug delivery, sustaining the duration of therapeutic efficacy, and/or targeting the delivery of drug to a tissue. Depending upon the technical sophistication, these rate-control drug delivery systems can be classified into three major categories: (i) pre-programmed drug delivery, (ii) activation-controlled drug delivery, and (iii) feedback-regulated drug delivery. Various types of drug delivery devices which have been recently marketed or under active development are grouped, on technology basis, under each category. The fundamentals behind the development of each type of the rate-control drug delivery systems with the successful examples of biomedical application are analyzed, aiming to gain a better understanding of the science and technology involved as well as to pave a solid foundation for future development of innovative new drug delivery systems.