Transdermal patches drug reservoir patch

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. 

Other than possibly for the insensible perspiration they absorb, transdermal patches tend to operate as thermodynamically static systems, meaning as com-positionally fixed systems, from the moment they are applied until their removal. Marketed ethanol-driven estradiol and fentanyl patches are exceptions because they meter out ethanol and drive it into the stratum corneum to propel the absorption process. Compositional steadfastness is still the rule, however, and it is this feature that bestows the zero-order delivery attribute on the ordinary transdermal patch. Drug is present within the patches in reservoir amounts whether or not the reservoir compartment is easily distinguished, for there must be enough drug to sustain delivery over the full course of patch wear. 

The most current method of nitroglycerin application is a transdermal device or skin patch. A cross section of such a patch is illustrated in Figure 6. The patch is actually a multi-layered polymer stack. The semipermeable membrane which comes in contact with the skin is usually composed of an ethylene-vinyl acetate copolymer or polypropylene. The reservoir contains the drug in a hydrogel or polymer matrix or solvent (the material must be chosen to insure uniform delivery). Examples of some solvents used include dimethyl sulfoxide (DMSO), sodium lauryl sulfate (SDS - a detergent) and propylene glycol/oleic acid. 

Duragesic is a transdermal patch that delivers the potent opioid analgesic fentanyl. The life span of the patch is three days and it is manufactured in five sizes 12,25, 50, 75, and 100pg/h. Duragesic is a membraned-moderated patch and consists of four patch layers a backing layer of polyester film, a drug reservoir that contains fentanyl, and U.S. Pharmacopeia (USP) alcohol gelled with hydroxyethyl cellulose,... 

Transdermal patches are marketed worldwide with the drug substances glycerole trinitrate, estradiol, testosterone, clonidine, scopolamine, fentanyl and nicotine, respectively. The patch has to remain for up to one week at the appropiate body site. In this case the drug amount in the reservoir is rather high. As liquid crystalline vehicles with lamellar microstructure have... 

Two main types of transdermal patches are commonly used drug reservoir patch and drug-in-adhesive patch. Transdermal patches of early generations are mainly... 

Figure 1.1 A drawing of a typical transdermal patch system to deliver drug into the systemic circulation by way of the skin. Drawn here is the system with (1) a reservoir containing the drug adsorbed to (2) lactose particles in (3) an oil (4) the ratecontrolling membrane, a copolymer whose thickness and composition are altered to achieve the desired rate of transport of the drug and (5) the adhesive layer, also a polymer, although liquid, which attaches the patch to the skin. The basic structure of the skin (6) illustrates the routes of penetration of the drug through this barrier layer into the systemic circulation via the capillary blood supply (7).

In membrane diffusion systems the polymer membrane with a given pore size or pore size distribution controls the diffusion of the active substance from the drug reservoir. Dosage forms with membrane-controlled drug delivery can be coated tablets, coated granules or pellets, or so-called multiparticulate systems on which various coats are applied. One possibility for transdermal drug administration is the transdermal patch controlled with a membrane [4-7,34-39]. 

It is worth noticing that the principles ruling transdermal drug delivery are analogous to those occurring in ophthalmic lenses. Indeed, reservoir patches correspond to sandwich-type lenses [177], while matrix patches correspond to therapeutic lenses where the drng is combined with polymer [178]. 

Controlled release can be achieved by a wide range of techniques a simple example, a transdermal patch, is illustrated in Figure 49. In this device, a drug is held in a reservoir surrounded by a membrane. With such a system, the release rate of drug is constant as long as a constant concentration of drug is maintained within the device. Such a constant concentration is maintained if the reservoir contains a saturated solution and sufficient excess of solid drug. Systems that... 

Transdermal scopolamine is a muscarinic receptor antagonist used for the prevention of post-operative nausea and vomiting. It is supplied as a circular adhesive patch (0.2 mm thick and 2.5 cm ) applied to the post-auricular skin. Each patch contains 1.5 mg of the belladonna alkaloid programmed to continuously release in vivo approximately 1.0 mg over 72 hours. The patch consists of four distinctive layers. Going from visible surface to the surface adherent to the skin, these layers are (1) backing layer (2) drug reservoir of scopolamine (3) microporous polypropylene membrane that controls the rate of scopolamine delivery (4) adhesive contact surface with the skin. 

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] ... 

Yet another newly developed drug is to be used in an externally worn transdermal patch (see Figure 1.15) of no more than 3 cm in diameter. The weighted average diffusivity between the patch reservoir and the target blood capillaries is estimated at 5 x 10" cm /s. The highest saturation capacity attained among a variety of solvents tested was 10 g/L. Is this likely to be sufficient to deliver the desired dose of 1 mg/day Hint Consult Table 2.4.)... 

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