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.
