Current Technologies To Increase The Transdermal Delivery Of Drugs

The skin is the largest organ of the body and its main function is to protect the organism against undesirable effects of the environment. The skin is composed of three different laye rs: epidermis, dermis and hypodermis. The epidermis contains the stratum corneum, the uppermost layer of the epidermis, that acts as the barrier function of the skin due to its very high density and its low hydration. The dermis is an extensive vascular network providing skin nutrition, repair, thermal regulation and immune response. The hypodermis acts as a heat insulator, a shock absorber, and an energy storage region. There are also several appendages in the skin: hair follicles, sebaceous, sweat glands and nails. The skin prope rties play an important role to allow penetration of topically applied drugs or substanc es into the skin. Drug permeation through the skin include the diffusion through the intact epidermis and the skin appendages. In this chapter we reviewed structure, immunological and electrical properties, penetration routes of drugs throughout skin, types of skin and the most common skin disorders that affect humans.

The transdermal administration of drugs is an effe ctive alternative to conve ntional methods such as oral or subcutaneous injections, as it overcomes the difficulties associated with these routes. Several methodologies have been developed in order to enhance drug transdermal absorption. Chemical percutaneous enhancers have long been used to incr ease the range of drugs that can be effectively delivered through the skin. To date, a vast array of chemicals has been evaluated as enhancers. This chapter reviews the principal chemical percutaneous enhancers and their mechanisms of acti on. The techniques to determine permeation enhancement and their uses in topical/transdermal formulations are also discussed.

Among the different methods of incrementing the transdermal absorption of drugs, iontophoresis has been the focus of considerable research. The fundamental s of iontophoresis are presented in this chapter along with the factors that need to be considered in order to apply this technique effectively (i.e. current density, ionic strength, and pH). The main applications of iontophoresis for the topical and systemic delivery of drugs are also discussed. Finally, the usefulness of reverse iontophoresis is addressed.

Transdermal drug delivery offers an attractive alternative to the conve ntional drug delivery methods of oral administration and injection. However, the stratum corneum acts as a barrier that limits the penetration of substances through the skin. Application of ultrasound to the skin increases its permeability (sonophoresis) and enables the delivery of various substances into and through the skin.

Ultrasound has been used extensively for medical diagnostics and to a cer tain extent in medical therapy (physiotherapy, ultrasonic surgery, and hyperthermia). Nevertheless, it has only recently become popular as a technique to enhance drug release from drug delivery system s. A number of studies suggest the use of ultrasound as an external mean of delivering drugs at increased rates and at desired times.

This chapter presents the main findings in the field of sonophoresis, namely transdermal drug delivery and transdermal monitoring. Particular attention is paid to proposed enhancement mechanisms and future trends in the field of cutaneous vaccination and gene delivery.

Transdermal drug delivery offers an attractive alternative to the conve ntional drug delivery methods of oral administration and injection. However, the stratum corneum acts as a barrier that limits the penetration of substances through the skin. Applic ation of high voltage pulses to th e skin increases its permeability (electroporation) and enables the delivery of va rious substances into and through the skin.

The application of electroporation to the skin has been shown to increase transdermal drug delivery. Moreover, electroporation, used alone or in combination with other enhancement methods, expands the range of drugs (small to macromolecules, lipophilic or hydrophilic, charged or neutra l molecules) which can be delivered transdermally.

The efficacy of transport depends on the electrical parameters and the physicochemical properties of drugs. The in vivo application of high voltage pulses is well tolerated but muscle cont ractions are usually induced. The electrode and patch design is an important issue to reduce the discomfort of the electrical treatment in humans.

This chapter presents the main findings in the field of electroporation. Par ticular attention is paid to proposed enhancement mechanisms and trends in the field of topical and transdermal delivery.

Microneedles have been introduced as a measure to solve the shortcoming of normal transdermal patches and hypodermic injections as they are able to pierce through th e stratum corneum, the top sub-layer of skin, in a simple and almost painless manner. Previous studies have shown microneedles to enhance drug delivery through the skin by significant amount as compared to the conventional drug delivery methods using transdermal patches. A number of designs have b een proposed using both solid and hollow microneedles of different types of materials. These studies show the effects of a number of factors that affect the drug delivery efficiency using these microneedles. Mathematical models have also been proposed to represent transport of drug through the skin and blood concentration in the blood using microneedles. These models provide the relationships between parameters such as needle length and skin thickness, a nd factors such as permeability of the drug through the skin and the force to insert the microneedle into the skin. Di fferent applications of microneedles in transdermal drug delivery have been proposed in different publications, which may include, e.g., delivery of vaccines for immunization, insulin delivery for cont rolling glucose level in diabetic pati ents, and others. The results from the existing studies have shown microneedle s to have promising prospects in transdermal drug delivery applications. This chapter aims to review various aspects of transdermal drug delivery by microneedle arrays.

This chapter aims to show state-of-the-art transd ermal drug-delivery nanocarriers. The advances in this field are very important at present because the skin offe rs many advantages over othe r organs due to its size. Depending on the location, we can deliver drugs very close to the target area. The skin provides protection against microorganisms, temperature, mechanical factors, etc. [1-3]. The development of submicron particles and other nanostructures in the pharmaceutical and cosmetic fields has been employed for the design of formulations for application through the skin [4-7]. The mechanism by which submicron particles traverse the skin is interesting and important as well as size and composition. The nature of drugs that can be applied through the skin offers many possibilities for future therapies. Both lipophilic and hydrophilic compounds can be used for this purpose, depending on the chosen nanocarrier. Finally, rega rding the specific applications of nanocarriers, it is worth mentioning that scientists have used nanocarriers for several applicat ions, including delivery of local and systemic therapies.