Pulsatile drug-delivery systems.

Delivery systems with a pulsatile-release pattern are receiving increasing interest for the development of drugs for which conventional controlled drug-release systems with a continuous release are not ideal. These drugs often have a high first-pass effect or special chronopharmacological needs. A pulsatile-release profile is characterized by a time period of no release (lag time) followed by a rapid and complete drug release. Pulsatile drug-delivery 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 colon), or time-controlled devices in which the drug is released after a well-defined time period. Site-controlled release is usually controlled by environmental factors, like the pH or enzymes present in the intestinal tract, whereas the drug release from time-controlled systems is controlled primarily by the delivery system and, ideally, not by the environment. This review covers various single- and multiple-unit oral pulsatile drug-delivery systems with an emphasis on time-controlled drug-release systems.