Transdermal drug delivery types

R. Lipp, H. Laurent, C. Gunther, J. Riedl, P. Esperling, U. Tauber, Prodrugs of Gesto-dene for Matrix-Type Transdermal Drug Delivery Systems , Pharm. Res. 1998,15, 1419 -1424. 

A new generation of transdermal drug delivery (TDD) system was developed to contain one or more skin permeation enhancers in the surface adhesive coating layers. This TDD system has been found, experimentally, to release the enhancers to the surface of stratum corneum to modify the skin s barrier properties, prior to the controlled delivery of the active drug. The extent of enhancement in skin permeability appears to be dependent upon the chemical structure of drug to be delivered transdermally as well as the type and the concentration of enhancer used. The mechanism of skin permeation enhancement have been explored and are analyzed in this report. 

This new type of transdermal drug delivery system is capable of releasing one or a combination of two or more skin permeation enhancers to the stratum corneum surface in order to modify the skin s barrier properties (10), prior to the controlled delivery... 

Because of the large surface area of the skin and its bypass of the liver as a first pass step in metabolism, many drug delivery systems have been developed that control the rate of drug delivery to the skin for subsequent absorption. Effective transdermal drug delivery systems of this type deliver uniform quantities of drug to the skin over a period of time. Technically, transdermal drug delivery systems may be classified into monolithic and membrane-controlled systems (9). 

Lipp R. Selection and use of crystallization inhibitors for matrix-type transdermal drug-delivery systems containing sex steroids. ] Pharm Pharmacol 1998 50 1343—1349. 

Bhattachrya A, Ghosal SK. Effect of hydrophobic permeation enhancers on the release and skin permeation kinetics from matrix type transdermal drug delivery system of ketotifen fumarate. Acta Pol Pharm 2001 58(2) 101-105. 

A transdermal therapeutic system is a rate-controlled drug delivery system which, applied to the surface of the skin, continuously releases the drug at a rate that will provide a desired steady-state plasma concentration for a specified duration. A candidate drug must possess high activity (i.e. be effective at low plasma concentrations) and efficiently penetrate the stratum comeum-, percutaneous absorption must be reliably consistent. Based on technological design there are four types of rate-controlled transdermal drug delivery system (Chien, 1987) ... 

Toddywala, R. D., K. Ulman, P. Walters, and Y. W. Chien. 1991. Effect of physicochemical properties of adhesive on the release, skin permeation and adhesiveness of adhesive-type transdermal drug delivery systems containing silicone-based pressure-sensitive adhesives. Int. J. Pharmaceut. 76 77-89. 

Figure 18.16 The cross-section view of a microreservoir-type transdermal drug delivery system, showing various major structured components [59].

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]. 

Liquid crystalline phases also seem to play an important role in topical and transdermal drug delivery. As discussed above, the protective properties of the stratum corneum seems to depend on the properties of its lipid fraction. More specifically, these have been found to form lamellar structures (169, 170), which could be expected to reduce the transdermal penetration of drugs, as well as water evaporation. On the other hand, the presence of Azone may induce reversed-type phases (172). Thus, the generation of oil and water channels seems to correlate with the commonly observed enhanced transdermal penetration of drugs caused by this penetration enhancer (186). 

The use of pressure-sensitive adhesives(PSAs) for skin-contact applications is discussed and the requirements of these adhesives in various applications are examined. Commercially-available classes of PSAs used for skin-contact applications include acrylics, polyisobutylenes and silicone polymers. Particular attention is paid in this review to transdermal drug delivery. The role of the PSAs in two types of transdermal designs is described and correlations between in-vivo and ex-vivo measurements of adhesion are discussed. Reports in the literature on human studies of various commercially-available transdermal systems are examined critically, with the aim of assessing the relative performance capabilities of each type of transdermal design. A list of currently commercialised transdermals is presented. 32 refs. 

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] ... 

Lipp, R. Laurent, H. Gunther, C. Riedl, J. Esperling, P. Tauber, U. Prodrugs of gestodene for matrix-type transdermal drug delivery systems, Pharm.Res., 1998,15, 1419-1424. 

Adhesive technology for external application is, by contrast, mature and many successful systems are available as the regulatory requirements are fewer. This has not stopped developers working to improve the existing products, and indeed to modify them for use on further dressing types and for other applications, such as for transdermal drug delivery. 

In recent years, drug delivery technologies have grown extensively that go beyond conventional oral dosage forms. For example, intravenous, transdermal, and implant technologies are widely used for sustained drug delivery over increased periods of time. The type of drug, its characteristics, and the intended indication determine the mode of delivery. 

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