Controlled release definition

To avoid confusion, several researchers have incorporated therapeutic intention into the definition of controlled release (4—7). Thus, controUed-release pharmaceuticals release dmgs in vivo according to a predictable, therapeutically rational, programmed rate to achieve the optimal dmg concentration in the minimal time (4). Specification by release rate complements specification by quantity jointly considered, they fix the duration of dmg release. Therefore, the dmg s duration of action can become a design property of a controlled release dosage form rather than an inherent pharmacokinetic property of the dmg molecule. 

Acid-catalyzed matrices, kinetics of controlled release, 170-179 Active targeting, definition, 276 Adenosine deaminase, activity of polyethylene glycol modified enzymes, 98-99 Adjuvax... 

Dnring an electron transfer, the acceptor places its LUMO at the electron disposal and the donor releases an electron that is located on its HOMO. These orbitals are frontier orbitals. In the corresponding ion-radicals, the distribution of an unpaired electron proceeds, naturally, under frontier-orbital control. This definitely reflects in the ion-radical reactivity and not always by a self-obvions manner. Let ns concisely trace peculiarities of ion-radical fragmentation reactions that are very important in organic synthesis. 

A general understanding of the definitions of linear and nonlinear will be helpful when discussing drug input into the body, whether that dose or input is delivered by classic delivery means or by novel controlled release delivery systems. Linear and nonlinear pharmacokinetics are differentiated by the relationship between the dose and the resulting drug concentration. A linear pharmacokinetics system exhibits a proportional relationship between dose and Cp for all doses, whereas nonlinear pharmacokinetics systems do not. 

Many controlled release devices are not membranes by the conventional definition, since only transient release of an active agent, without permeation occurring between an upstream and a downstream, is typical. Nevertheless, some controlled release units do operate with a concentration driving force to achieve effectively steady state release from the internal reservoir of the device to the external surrounding. Such processes are included here for completeness. 

Cross-linked versions of water-soluble polymers swollen in aqueous media are broadly referred to as hydrogels (52) and have a growing commercial utility in such applications as oxygen-permeable soft contact lenses (qv) (53) (Table 4) and controlled-release pharmaceutical drug delivery devices (54). Cross-linked PVP and selected copolymers fit this definition and are of interest because of the following structure/performance characteristics ... 

A special kind of RM are standard gaseous mixtures and silica gels or glasses with the surface modified by chemical operations, which during controlled pyrolysis release definite volatile compounds [23]. There are also RMs prepared on the basis of liquids (e.g., natural waters) [24]. 

In this review dealing with recent advances in membrane science, the term membrane" will be used to indicate any medium which acts as a barrier to transport into or out of a region, provides selective transfer of one species over another or regelates the transport of a material to its environment at a controlled rate. In addition to the common usage of the word membrane" to indicate a dense polymer film, the above definition includes a variety of interesting cases such as highly porous ultrafiltration membranes and hydrophobic liquid membranes with selectivity properties which can be tailored by incorporation of materials which selectively complex with one of the species to be processed. The important topics of controlled release of chemicals from polymeric devices and removal of volatile monomers from addition polymers such as poly (vinyl chloride and poly (acrylonitrile are also treated here. 

The ease of migration of small molecules in high polymers has been successfully exploited for gas separations, water purification and controlled release. These topics have been discussed earlier in this review. There is also, however a negative side to the comparative ease of transport in polymers compared with metals and glass. They are obviously not as good gas and vapor barriers and therefore have definite limitations for certain packaging applications. This subject will not be discussed further in this presentation. 

Controlled release implies regulation of the delivery of a drug usually by a device. The control is aimed at delivering the drug at a specific rate for a definite period of time independent of the local environments. The periods of delivery are usually much longer than in case of SR and vary from days to years. Controlled release may also incorporate methods to promote localization of drug at an active site. Site-specific and targeted delivery systems are the descriptive terms used to denote this type of control. 

The lack of definitive studies is due to a mixture of reasons including 1) wide variety of polymers 2) newness of interest in the area 3) wide variety of applications (both potential and actual) of inorganic and organanetallic polymers not requiring thermal stability or thermal analysis (uses as anchored metal catalysis, control release agents, electrical and photochemical applications, speciality adhesives) 4) insufficient description, identification, of the products 5) wider variety of degradation routes and other thermal behavior in comparison to organic polymers and 6) many products were synthesized and briefly characterized before the advent of modern thermal instrumentation. 

Gustafson, J., Greish, K., Frandsen, J. etoL (2009) SUk-elastin-like recombinant polymers for gene therapy of head and neck cancer from molecular definition to controlled gene expression. Journal of Controlled Release, 140,256-261. 

These two definitions of a biomaterial are open to interpretation. The more restrictive interpretation limits the concept of biomaterials to structural materials only, but to the global scientific community, so Umited an interpretation is not generally accepted. A broader interpretation also includes materials, especially polymers, used as components of systems for the controlled release of drugs. 

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