Abstract

Modern therapeutic system has often been criticized for the toxicity associated with the drugs. To minimize this drawback, many researchers have focussed attention towards developing modulated drug delivery systems capable of releasing therapeutic agents in response to physiological requirements. Another class of modulated drug delivery systems are those in which pulsatile release of drugs is triggered by external signals. The former is known as self-regulated or responsive systems while the latter is known as externally regulated or pulsatile delivery systems. This article briefly describes the fundamental principles of various types of pulsatile as well as responsive drug delivery systems. Recent developments in the field of pulsatile systems based on external triggers such as electrical, ultrasound, magnetic and massages have been reported. This article also traces recent research in the field of polymer based temperature-sensitive, pH-responsive, inflammation-responsive and glucose-and other saccharide-sensitive systems; enzymebased urea-responsive, glucose-responsive and morphine-triggered systems; systems based on antibody interactions, and systems utilizing chelation.