Mechanisms of controlled drug release

Silicones are frequently used in transdermal drug delivery. Recently, the use of loosely cross-linked silicone elastomer blends for this application was surveyed.537 The mechanisms of controlled drug release in the silicone-based systems have been studied,538 as silicones are evaluated for relatively new protein drug-delivery systems.5... 

Acharya G, Park K. Mechanisms of controlled drug release from drug-eluting stents. Adv Drug Deliv Rev 2006 58(3) 387—401. 

Yoshida, T., Tasaki, H., Maeda, A., Katsuma, M., Sako, K., Uchida, T. (2008a). Mechanism of controlled drug release from a salting-out taste-masking system. Journal of Controlled Release, 131(1), 47-53. 

The majority of controlled drug delivery systems now being marketed or under development are based on diffusion of the drug through a semipermeable membrane to achieve the requisite release rate. Diffusion control is particularly important to transdermal delivery, where biodegradation and dissolution are not viable mechanisms of controlling the release rate. Provided the process is Fickian, the rate of diffusion through the semipermeable polymer is determined by... 

Tongwen, X., Binghn, H., 1998. Mechanism of sustained drug release in diffusion-controlled polymer matrix-apphcation of percolation theory. International Journal of Pharmaceutics 170, 139-149. 

Since the development of the Spansule brand (Smith Kline Beech am) of coated beads and granules in the late 1960s, various dmg product technologies have been developed and patented to achieve extended durations of therapeutic effects. Each of these does so by various mechanisms of control of dmg release from adrninistered dosage forms. Each method has its advantages and disadvantages, a discussion of which is available in the pharmaceutical hterature (see Drug delivery systems) (21). 

In particular, rotaxane dendrimers capable of reversible binding of ring and rod components, such as Type II, pseudorotaxane-terminated dendrimers, can be reversibly controlled by external stimuli, such as the solvent composition, temperature, and pH, to change their structure and properties. This has profound implications in diverse applications, for instance in the controlled drug release. A trapped guest molecule within a closed dendrimeric host system can be unleashed in a controlled manner by manipulating these external factors. In the type III-B rotaxane dendrimers, external stimuli can result in perturbations of the interlocked mechanical bonds. This behavior can be gainfully exploited to construct controlled molecular machines. 

Regardless of the drug release mechanism, utilizing polymers as a drug delivery vehicle enables controlled and sustained release of the drug. Moreover, for a DES, this has the added benefit of localized delivery to a specific target, that is, the stented artery area. 

It is imperative that the kinetics of drug release are aligned with the kinetics of the restenotic cascade, as well as the pharmacologic mechanism of the drug being released (7,36), Rate-controlling systems, such as polymers, are ideal for this... 

This arbitrary recommendation does not rely on strict theoretical and experimental findings and is based only on the fact that completely different physical conditions have been postulated for the derivation of the equivalent (4.2) and (4.3), while the underlying mechanism in both situations is classical diffusion. In this context, a linear plot of the cumulative amount of drug released q (t) or the fraction of drug released q (f) /f/,Xj (utilizing data up to 60% of the release curve) vs. the square root of time is routinely used in the literature as an indicator for diffusion-controlled drug release from a plethora of delivery systems. 

Following a study of physical properties of these nanoparticles, further research focused on defining stoichiometric coefficients of reactants involved in a batch system. This study was undertaken to gain a better understanding of the assembly process for producing nanoparticles, mechanisms involved in drug release and control of their release. This process is then extensively compared with similar products on the market and reported in the literature. 

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