Drug release

ALAN TALEVI; MARÍA ESPERANZA RUIZ

The ADME Encyclopedia. A Comprehensive Guide on Biopharmacy and Pharmacokinetics

Springer

Lugar: Basel; Año: 2021; p. 1 - 7

The term drug release refers to the processes by which drug molecules are transferred from their initial position in a drug delivery system to the outer surface and, in turn, as solutes, into the release medium [1]. It is (or it can be) a complex phenomenon, which depending on the delivery system can comprise one or (usually) more of the following processes: drug diffusion, drug dissolution, and/or drug partitioning, as well as osmosis, swelling, erosion, disintegration, and/or degradation of the delivery system [1, 2]. Whereas sometimes drug release has been used interchangeably with the term drug dissolution (possibly because drug dissolution is a prerequisite for drug absorption), note that drug dissolution represents only one step in the more intricate process of drug release [3], one that only takes place when the drug is initially in the solid state (as in a tablet or an ointment) or deliberately precipitates once administered (as in intramuscular or subcutaneous depot formulations, e.g., insulin glargine) [4].Depending on their release kinetics, drug delivery systems can be classified diversely. In principle, one can differentiate between immediate- and modified-release drug delivery systems. Classical modified-release systems, in turn, include delayed-release (characterized by a lag time before release starts, e.g., enteric-coated formulations and targeted-release systems), and extended-release (designed to deliver the drug over a prolonged period of time). More sophisticated/complex patterns of drug release are also possible, as observed in pulsatile-release delivery systems, in which the rapid and transient release of a certain amount of drug within short time periods is preceded by predetermined off-release periods, [5] or in systems with bimodal release profiles which alternate fast and slow release of the drug [6]. The kinetics of drug release can follow, depending on the delivery system, zero or first-order kinetics, or intermediate behaviors, and display or not a lag-time before release begins.