Time-Controlled Drug Delivery Systems

The relatively constant transit time in the small intestine of approximately 3-4 h is another physiological characteristic which can be exploited to achieve colon specificity (time-controlled drug release). After gastric empt5ung, a time-controlled drug delivery system is intended to release the drug after a predetermined lag phase. 

Figure 6.4. Swelling-induced time-controlled drug delivery systems.

The use of time-controlled drug delivery systems can provide tremendous advantages for a pharmaco-treatment including the following ... 

Time-controlled drug delivery systems can be classified according to different principles, for example, with respect to the route of administration, field of application, and/or underlying drug-release mechanisms. In this chapter, the various types of devices that have been described so far in literature have been classified based on the major... 

Siepmann J, Siepmann F (2009) Time-controlled drug delivery systems. In Florence AT, Siepmann J (eds) Modem pharmaceutics, volume 2 Applications and... 

In the case of controlled drug-delivery systems, the goal is to have the drug released at a relatively constant rate (zero-order kinetics) at a concentration within the therapeutic range. It is obviously important to minimize the amount of time the concentration is in... 

Figure 4.1 Released amount Qt versus square-root-time -Jt plots. Illustration of loading less than or equal to saturation (dispersed, A < Cs) and greater than saturation (dissolved, A > Cs) in a matrix-type diffusion-controlled drug delivery system.

Comparative pharmacokinetic profiles of nifedipine delivered from Procardia XL, an osmotic pressure-controlled drug delivery system, once-a-day versus that from Procardia, an immediate-release dosage form, taken on time 0, 8 and 16 in human volunteers. Modified from Y.W. Chien. Oral drug delivery and delivery systems. Y.W.Chien (ed.) (1992) Novel Drug Delivery Systems. Marcel Dekker, Inc. New York, pp. 139-196... 

A supercritical C02-based technique was applied to produce a biocompatible polymer in form of microspheres. With the SAS process carried out in a batch mode, micronic particles of polymer were obtained with a narrow particle size distribution. Co-precipitation of pharmaceuticals for the production of controlled drug delivery systems has been proposed as a preliminary result, since further analyses are under development. The experimental apparatus is easy-to-use and the purification of the precipitated solid from the solvent can be achieved by suitably increasing the time for solvent removing. 

Anal, A. K. (2007),Time-controlled pulsatile delivery systems for bioactive compounds, Recent Patents Drug Deliv. Formulate 1, 73-79. 

Swelling is one of the functional properties used to characterize biopolymers required for modified or controlled drug delivery systems. The biopolymers employed for modified drug delivery applications are hydrogels that form three-dimensional polymeric networks when they come into contact with water, they absorb many times their weight of water but they do not dissolve. Swelling of the ceUulosics in different biorelevant media must be established. 

Especially in controlled drug delivery systems, that materials are considered to be suited and potentially useful, because at least some of the essential requirements of a controlled dmg delivery system, which is supposed to assure an improved drug treatment (outcome) through rate- and time-programmed and site-specific drug delivery (Breimer 1999 Yang et al. 2005) could be met in inorganic materials too. 

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