Reservoir Designed Transdermal Patches

With the exception of the metallic backing layer, manipulation of the physicochemical properties of the other layers repre.scnls opportunities for the engineered control of drug release from these systems. For 

Cross-sectional diagram of the design of a reservoir transdermal therapeutic (patch) system 

The rale of release of therapeutic agents from re.scrvoir transdermal. systems may be conveniently described by the following equation  

and are the diffusion coefficients of the drug in the rale controlling membrane and the adhesive layer, and 

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Rgure 9.27 The four main types of transdermal patch matrix, reservoir, multilaminate and drug-in-adhesive designs. The matrix/reservoir systems are cut away to show the drug. Illustration courtesy of 3M. 

W. Pichayakom, J. Suksaeree, P. Boonme, W. Taweepreda, T. Amnuaikit, G.C. Ritthidej, Deproteinised natural rubber used as a controUing layer membrane in reservoir-type nicotine transdermal patches, Chemical Engineering Research and Design, ISSN 0263-8762 91 (3) (March 2013) 520-529. http //dx.doi.Org/10.1016/j.cherd.2012.09.011. 

Transdermal drug-delivery systems offer several important adventages over more traditional approaches, in addition to the benefits of avoiding the hepatic first-pass effect. Transdermal drug delivery systems (TDDS) are usually in the form of patches incorporating pressure sensitive adhesives. There are two basic designs for transdermal patches matrix or reservoir type. Matrix-type patches include monolithic adhesive and polymer matrices, whereas reservoir-type patches include liquid and solid-state reservoirs [71-73]. For various types of transdermal delivery systems, medical grade adhesive silicones are used as [73,74] ... 

Clonidine is a potent antihypertensive agent which is well absorbed from the GI tract (95%). The dmg has a relatively long half-life (6-20 h) and a modest clearance (13 L h ). The rationale for the development of transdermal clonidine was to reduce side-effects and to improve patient compliance. Catapres-TTS, a reservoir-type patch, reached the market in 1985 in a form designed to remain in place and to deliver dmg for 7 days. Dose titration was possible via the use of systems of different active areas (3.5, 7.0, and 10.5 cm2). The control of dmg delivery over 7 days is impressive, and avoids the peaks and valleys of conventional (twice-a-day) oral administration (Figure 8.7). However, this system has not achieved as wide a success as first seemed likely because of skin sensitization. Clonidine itself, when administered transdermally on a chronic, repetitive basis, induces in a significant fraction of patients a classic immunologic skin reaction, and this has severely attenuated its use. 

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