Pulsatile drug-delivery systems

Delivery systems with a pulsatile-release pattern are receiving increasing interest for the development of drugs for which conventional controlled dru g-release systems with a continuous release are not ideal. These drugs ofte n have a high first-pass effect or special chronopharmacological needs. A p ulsatile-release profile is characterized by a time period of no release (l ag time) followed by a rapid and complete drug release. Pulsatile drug-deli very systems can be classified into site-specific systems in which the drug is released at the desired site within the intestinal tract (e.g., the col on), or time-controlled devices in which the drug is released after a well- defined time period. Site-controlled release is usually controlled by envir onmental factors, Eke the pH or enzymes present in the intestinal tract, wh ereas the drug release from time-controlled systems is controlled primarily by the delivery system and, ideally, not by the environment. This review c overs various single- and multiple-unit oral pulsatile drug-delivery system s with an emphasis on time-controlled drug-release systems.