Enhanced transdermal delivery of tetracaine by electroporation

The effect of electroporation on the transport of tetracaine through skin in vitro was studied using side-by-side compartment diffusion cells method. After achieving steady state by passive diffusion, fluxes of tetracaine achieved with passive diffusion, electroporative pulse and iontophoresis were compared. Electroporation (square-wave pulse, voltage 130 V, pulse time 0.4 s, pulse frequency 40 pulses min(-1)) or iontophoresis (0.2.mA cm(-2), lasting for 4 h) increased the transport of tetracaine through skin. The flux of tetracaine at 0.25 h after electroporation (pulse number 400) was 54.6+/-6.0 microg.cm(-2).h(-1), that after iontophoresis was 17.4+/-5.8 microg.cm(-2).h(-1) and that after passive diffusion was 8.2+/-0.5 microg.cm(-2).h(-1). In addition, the fluxes of tetracaine increased with the increasing of pulse number. From these results, it is clear that electroporation is effective in enhancing transdermal delivery of tetracaine and its function is better than iontophoresis.     

Lipid and electroosmosis enhanced transdermal delivery of insulin by electroporation

Transdermal transport of insulin and extraction of interstitial glucose under anodal iontophoresis (electroosmosis) following electroporation in the presence of 1,2-dimyristoylphophatidylserine (DMPS) was studied. An earlier study showed that DMPS increased the transport of insulin across porcine epidermis under electroporation by approximately fourfold. It was suggested that DMPS increased the lifetime of electropores in the epidermis resulting in an enhanced transport of permeants. When electroosmosis was applied across the epidermis following electroporation with DMPS, the enhancement of insulin transport was approximately 18-fold over electroporation alone. When the same strategy was applied to extract interstitial glucose, the enhancement was approximately 23-fold over electroporation alone. Real-time transdermal insulin transport kinetics was measured using FITC-labeled insulin and a custom-made vertical diffusion apparatus that had a fluorescence cuvette as the receiver compartment. Insulin transport by electroporation alone showed a nonlinear kinetics that is most likely due to the resealing of the electropores with time. The transport kinetics when electroporation was carried out in the presence of DMPS was more linear, confirming earlier studies that suggested the DMPS stabilizes transport paths formed by electroporation. The data suggests that in vivo, noninvasive insulin delivery to therapeutic levels and glucose extraction may be achieved by combining electroporation with anionic lipids and electroosmosis.     

A practical assessment of transdermal drug delivery by skin electroporation

Transdermal drug delivery has many potential advantages, but the skin's poorly-permeable stratum corneum blocks delivery of most drugs at therapeutic levels. Short high-voltage pulses have been used to electroporate the skin's lipid bilayer barriers and thereby deliver compounds at rates increased by as much as four orders of magnitude. Evidence that the observed flux enhancement is due to physical alteration of the skin by electroporation, as opposed to only providing an iontophoretic driving force, is supported by a number of different transport, electrical and microscopy studies. Practical applications of electroporation's unique effects on skin are motivated by large flux increases for many different compounds, rapidly responsive delivery profiles, and efficient use of skin area and electrical charge. Greater enhancement can be achieved by combining skin electroporation with iontophoresis, ultrasound, and macromolecules. Sensation due to electroporation can be avoided by using appropriate electrical protocols and electrode design. To develop skin electroporation as a successful transdermal drug delivery technology, the strong set of existing in vitro mechanistic studies must be supplemented with studies addressing in vivo/clinical issues and device design.     

Skin permeabilization for transdermal drug delivery: recent advances and future prospects

Introduction: Transdermal delivery has potential advantages over other routes of administration. It could reduce first-pass metabolism associated with oral delivery and is less painful than injections. However, the outermost layer of the skin, the stratum corneum (SC), limits passive diffusion to small lipophilic molecules. Therefore, methods are needed to safely permeabilize the SC so that ionic and larger molecules may be delivered transdermally.

Areas covered: This review focuses on low-frequency sonophoresis, microneedles, electroporation and iontophoresis, and combinations of these methods to permeabilize the SC. The mechanisms of enhancements and developments in the last 5 years are discussed. Potentially high-impact applications, including protein delivery, vaccination and sensing are presented. Finally, commercial interest and clinical trials are discussed.

Expert opinion: Not all permeabilization methods are appropriate for all applications. Focused studies into applications utilizing the advantages of each method are needed. The total dose and kinetics of delivery must be considered. Vaccination is one application where permeabilization methods could make an impact. Protein delivery and analyte sensing are also areas of potential impact, although the amount of material that can be delivered (or extracted) is of critical importance. Additional work on the miniaturization of these technologies will help to increase commercial interest.     

一种葛根素经皮给药系统体外透皮性能的初步考察

目的：制备葛根素经皮给药系统,并对其体外透皮性能进行考察。方法：以月桂氮酮为促透剂,卡波姆980为凝胶基质,制备葛根素经皮给药系统,用RP-HPLC法进行定量,采用改良Franz扩散池测定了32 h葛根素对离体大鼠皮肤累积渗透量。结果：葛根素累积渗透量拟合方程：Q=11.12t-45.18（r=0.9635）,32 h累积渗透量为（335.18±51.45）μg/cm2。结论：葛根素以零级动力学透过皮肤,所研制的葛根素经皮给药系统体外渗透性能良好,质量控制方法简便、快捷、准确。     

The effects of iontophoresis and electroporation on transdermal delivery of buprenorphine from solutions and hydrogels

The in-vitro permeation of buprenorphine across skin was investigated to assess the effects of iontophoresis and electroporation on drug permeation from solutions as well as from hydrogels. Iontophoresis (0.3 mA cm(-2)) increased the buprenorphine permeation from solution by a factor of 14.27 as compared with passive diffusion; the application of electroporation increased the buprenorphine permeation from solutions by a factor of 8.45. The permeation experiments using cellulose membrane and stratum corneum (SC)-stripped skin as permeation barriers suggested that the enhancement with iontophoresis was primarily due to strong electrophoretic drift of buprenorphine molecules, whereas the enhancement seen with electroporation was mainly attributed to the creation of transient aqueous pores in the SC layer. Application of high-voltage pulses followed by iontophoresis resulted in a shorter permeation onset time from both solutions and hydrogels as compared with iontophoresis or electroporation alone. The charge repulsion between buprenorphine and chitosan vehicles as well as the competition effects of counter-ions for carboxymethylcellulose (CMC)-based polymers may account for the different permeation rates under electrical field. This study demonstrates the feasibility of using hydrogels for delivery of buprenorphine under the application of iontophoresis or electroporation, separately or together.     

Investigation into the potential of electroporation facilitated topical delivery of cyclosporin a

Purpose: The potential for electroporation-facilitated topical transport of cyclosporin A (CysA) was investigated using rat skin. Methods: Studies of various electrical factors acting on the deposition of CysA into the stratum corneum and deeper skin of in vitro electroporation were performed. We also tested the synergistic effect of electroporation and other approaches such as chemical enhancers and low-frequency ultrasound on topical drug delivery of CysA. Results: Electroporation increased the amount of CysA retained in the skin by only 3 times that of passive diffusion. We found that the efficacy of electroporation in enhancing topical delivery can be further increased by pretreatment of skin with chemical enhancers, such as Azone and menthol. Meanwhile, only a small amount was seen to transport across the full skin into the receiver compartment. Trimodality treatment comprised of pretreatment with Azone and ultrasound in combination followed by electroporation was not effective in enhancing the topical delivery of CysA. However, this combination strategy increased the penetration of CysA through rat skin by an order of 15. Conclusion: In general, the enhanced skin accumulation of CysA by the combination of electroporation and chemical enhancers could help significantly to optimize the targeting of the drug without a concomitant increase in systemic side effects.     

Novel reverse electrodialysis-driven iontophoretic system for topical and transdermal delivery of poorly permeable therapeutic agents

Topical and transdermal drug delivery has great potential in non-invasive and non-oral administration of poorly bioavailable therapeutic agents. However, due to the barrier function of the stratum corneum, the drugs that can be clinically feasible candidates for topical and transdermal delivery have been limited to small-sized lipophilic molecules. Previously, we fabricated a novel iontophoretic system using reverse electrodialysis (RED) technology (RED system). However, no study has demonstrated its utility in topical and/or transdermal delivery of poorly permeable therapeutic agents. In this study, we report the topical delivery of fluorescein isothiocyanate (FITC)–hyaluronic acid (FITC–HA) and vitamin C and the transdermal delivery of lopinavir using our newly developed RED system in the in vitro hairless mouse skin and in vivo Sprague–Dawley rat models. The RED system significantly enhanced the efficiency of topical HA and vitamin C and transdermal lopinavir delivery. Moreover, the efficiency and safety of transdermal delivery using the RED system were comparable with those of a commercial ketoprofen patch formulation. Thus, the RED system can be a potential topical and transdermal delivery system for various poorly bioavailable pharmaceuticals including HA, vitamin C, and lopinavir.     

Skin targeted DNA vaccine delivery using electroporation in rabbits II. Safety

The Achilles heel of gene-based therapy is gene delivery into the target cells efficiently with minimal toxic effects. Viral vectors for gene/DNA vaccine delivery are limited by the safety and immunological problems. Recently, nonviral gene delivery mediated by electroporation has been shown to be efficient in different tissues including skin. There are no detailed reports about the effects of electroporation on skin tissue, when used for gene/DNA vaccine delivery. In a previous study we demonstrated the efficacy of skin targeted DNA vaccine delivery using electroporation in rabbits [Medi, B.M., Hoselton, S., Marepalli, B.R., Singh, J., 2005. Skin targeted DNA vaccine delivery using electroporation in rabbits. I. Efficacy. Int. J. Pharm. 294, 53-63]. In the present study, we investigated the safety aspects of the electroporation technique in vivo in rabbits. Different electroporation parameters (100-300 V) were tested for their effects on skin viability, macroscopic barrier property, irritation and microscopic changes in the skin. Skin viability was not affected by the electroporation protocols tested. The electroporation pulses induced skin barrier perturbation and irritation as indicated by elevated transepidermal water loss (TEWL) and erythema/edema, respectively. Microscopic studies revealed inflammatory responses in the epidermis following electroporation using 200 and 300 V pulses. However, these changes due to electroporation were reversible within a week. The results suggest that the electroporation does not induce any irreversible changes in the skin and can be a useful technique for skin targeted DNA vaccine delivery.     

Transfersomes for transdermal drug delivery

Transfersomes (Idea AG) are a form of elastic or deformable vesicle, which were first introduced in the early 1990s. Elasticity is generated by incorporation of an edge activator in the lipid bilayer structure. The original composition of these vesicles was soya phosphatidyl choline incorporating sodium cholate and a small concentration of ethanol. Transfersomes are applied in a non-occluded method to the skin and have been shown to permeate through the stratum corneum lipid lamellar regions as a result of the hydration or osmotic force in the skin. They have been used as drug carriers for a range of small molecules, peptides, proteins and vaccines, both in vitro and in vivo. It has been claimed by Idea AG that intact Transfersomes penetrate through the stratum corneum and the underlying viable skin into the blood circulation. However, this has not been substantiated by other research groups who have extensively probed the mechanism of penetration and interaction of elastic vesicles in the skin. Structural changes in the stratum corneum have been identified, and intact elastic vesicles visualised within the stratum corneum lipid lamellar regions, but no intact vesicles have been ascertained in the viable tissues. Using the principle of incorporating an edge-activator agent into a bilayer structure, a number of other elastic vesicle compositions have been evaluated. This review describes the research into the development and evaluation of Transfersomes and elastic vesicles as topical and transdermal delivery systems.     

Microneedles for transdermal drug delivery

The success of transdermal drug delivery has been severely limited by the inability of most drugs to enter the skin at therapeutically useful rates. Recently, the use of micron-scale needles in increasing skin permeability has been proposed and shown to dramatically increase transdermal delivery, especially for macromolecules. Using the tools of the microelectronics industry, microneedles have been fabricated with a range of sizes, shapes and materials. Most drug delivery studies have emphasized solid microneedles, which have been shown to increase skin permeability to a broad range of molecules and nanoparticles in vitro. In vivo studies have demonstrated delivery of oligonucleotides, reduction of blood glucose level by insulin, and induction of immune responses from protein and DNA vaccines. For these studies, needle arrays have been used to pierce holes into skin to increase transport by diffusion or iontophoresis or as drug carriers that release drug into the skin from a microneedle surface coating. Hollow microneedles have also been developed and shown to microinject insulin to diabetic rats. To address practical applications of microneedles, the ratio of microneedle fracture force to skin insertion force (i.e. margin of safety) was found to be optimal for needles with small tip radius and large wall thickness. Microneedles inserted into the skin of human subjects were reported as painless. Together, these results suggest that microneedles represent a promising technology to deliver therapeutic compounds into the skin for a range of possible applications.     

Nanoparticle delivery for transdermal HRT

Nanomedicine is an emerging technology and the first nano-engineered medical products have come to light in the last decade. Transdermal drug delivery has significant advantages compared to other routes of drug administration. Nanoparticles unique physical and chemical properties enable transport of substances directly into the skin. The objective of this paper is to review different aspects of nanoparticle delivery, generally, and discuss its current use for transdermal hormone therapy. Transdermal estrogen therapy remains the most effective treatment for bothersome menopausal symptoms, particularly in those women for whom the potential adverse effects associated with “first pass” hepatic metabolism are to be avoided. Available alternatives for transdermal estrogen delivery include patches, gels, sprays and lotions. Other non-oral therapies which likewise avoid “first pass” hepatic metabolism include: subcutaneous implants and vaginal rings. Some of the transdermal products are associated with mild adverse skin effects such as redness and irritation, but more severe and bothersome consequences include blistering and tattooing. Even the mild adverse skin effects are frequently cited as reasons for discontinuation. Micellar nanoparticle estradiol emulsion (MNPEE) is a lotion-like therapy which constitutes an alternative transdermal delivery system not requiring the permeation enhancers or temporary skin digestion, both of which increase the possibility of irritation. MNPEE's advantages include low fluctuation of plasma estradiol concentrations, infrequent skin related adverse effects, and pleasant cosmetic-like moisturizing properties. The efficacy of MNPEE for management of menopausal vasomotor symptoms has been demonstrated in a randomized placebo controlled trial,¹ and the product is FDA approved for management of moderate to severe vasomotor symptoms. None of the observed adverse effects in the MNPEE group were statistically different from the placebo group.¹ Studies addressing inadvertent transference of estradiol to the male partners of menopausal women using this delivery technology have demonstrated small, but real amounts of transference, which do not exceed the normal physiological male estradiol range. MNPEE is safe and effective for treatment of vasomotor symptoms and represents the commercial validation of nanoparticle technology for transdermal delivery of estrogen therapy (ET) for postmenopausal women with vasomotor symptoms.     

Transfersomes for transdermal drug delivery

Transfersomes^® (Idea AG) are a form of elastic or deformable vesicle, which were first introduced in the early 1990s. Elasticity is generated by incorporation of an edge activator in the lipid bilayer structure. The original composition of these vesicles was soya phosphatidyl choline incorporating sodium cholate and a small concentration of ethanol. Transfersomes are applied in a non-occluded method to the skin and have been shown to permeate through the stratum corneum lipid lamellar regions as a result of the hydration or osmotic force in the skin. They have been used as drug carriers for a range of small molecules, peptides, proteins and vaccines, both in vitro and in vivo. It has been claimed by Idea AG that intact Transfersomes penetrate through the stratum corneum and the underlying viable skin into the blood circulation. However, this has not been substantiated by other research groups who have extensively probed the mechanism of penetration and interaction of elastic vesicles in the skin. Structural changes in the stratum corneum have been identified, and intact elastic vesicles visualised within the stratum corneum lipid lamellar regions, but no intact vesicles have been ascertained in the viable tissues. Using the principle of incorporating an edge-activator agent into a bilayer structure, a number of other elastic vesicle compositions have been evaluated. This review describes the research into the development and evaluation of Transfersomes and elastic vesicles as topical and transdermal delivery systems.     

Skin targeted DNA vaccine delivery using electroporation in rabbits. I: efficacy

Genetic immunization through skin is highly desirable as skin has plenty of antigen presenting cells (APCs) and is easily accessible. The purpose of this study was to investigate the effects of electroporation pulse amplitude, pulse length and number of pulses on cutaneous plasmid DNA vaccine delivery and immune responses, following intradermal injection in vivo in rabbits. Expression of the delivered plasmid was studied using a reporter plasmid, coding for beta-galactosidase. The efficiency of DNA vaccine delivery was investigated using a DNA vaccine against Hepatitis B, coding for Hepatitis B surface antigen (HBsAg). Serum samples and peripheral blood mononuclear cells (PBMC) were analyzed for humoral and cellular immunity, respectively, following immunization. The expression of transgene in the skin was transient and reached its peak in 2 days post-delivery with 200 and 300 V pulses. The expression levels with 200 and 300 V pulses were 48- and 129-fold higher, respectively, compared with the passive on day 2. In situ histochemical staining of skin with X-gal demonstrated the localized expression of beta-galactosidase with electroporation pulses of 200 and 300 V. Electroporation mediated cutaneous DNA vaccine delivery significantly enhanced both humoral and cellular immune responses (p<0.05) to Hepatitis B compared to passive delivery. The present study demonstrates the enhanced DNA vaccine delivery to skin and immune responses by topical electroporation. Hence, electroporation mediated cutaneous DNA vaccine delivery could be developed as a potential alternative for DNA vaccine delivery.     

Testosterone ethosomes for enhanced transdermal delivery

Physiological decrease in testosterone levels in men with age causes various changes with clinical significance. Recent testosterone replacement therapy is based mainly on transdermal nonpatch delivery systems. These products have the drawback of application on extremely large areas to achieve required hormone blood levels. The objective of the present study was to design and test a testosterone nonpatch formulation using ethosomes for enhanced transdermal absorption. The ethosomal formulation was characterized by transmission electron microscopy and dynamic light scattering for structure and size distribution and by ultracentrifugation for entrapment capacity. To evaluate the feasibility of this delivery system to enhance testosterone permeation through the skin, first the systemic absorption in rats was compared with a currently used gel (AndroGel®). Further, theoretical estimation of testosterone blood concentration following ethosomal application in men was made. For this purpose, in vitro permeation experiments through human skin were performed to establish testosterone skin permeation values. In the design of these experiments, testosterone solubility in various solutions was measured and the effect of the receiver medium on the skin barrier function was assessed by confocal laser scanning microscopy. Theoretical estimation shows that testosterone human plasma concentration value in the upper part of the physiological range could be achieved by application of the ethosomal formulation on an area of 40 cm². This area is about 10 times smaller than required with current nonpatch formulations. Our work shows that the ethosomal formulation could enhance testosterone systemic absorption and also be used for designing new products that could solve the weaknesses of the current testosterone replacement therapies.     

Wearable patches for transdermal drug delivery

Transdermal drug delivery systems (TDDs) avoid gastrointestinal degradation and hepatic first-pass metabolism, providing good drug bioavailability and patient compliance. One emerging type of TDDs is the wearable patch worn on the skin surface to deliver medication through the skin. They can generally be grouped into passive and active types, depending on the properties of materials, design principles and integrated devices. This review describes the latest advancement in the development of wearable patches, focusing on the integration of stimulus-responsive materials and electronics. This development is deemed to provide a dosage, temporal, and spatial control of therapeutics delivery.     

A transdermal delivery system for glipizide

Glipizide is one of the most commonly prescribed drugs for treatment of type 2 diabetes. Oral therapy with glipizide comprises problems of bioavailability fluctuations and may be associated with severe hypoglycaemia and gastric disturbances. As a potential for convenient, safe and effective antidiabetic therapy, the rationale of this study was to develop a transdermal delivery system for glipizide. For this purpose, inclusion complexes of the drug in beta-cyclodextrin (beta-CyD), dimethyl-beta-cyclodextrin (DM-beta-CyD), hydroxypropyl-beta-cyclodextrin (HP-beta-CyD), and hydroxypropyl-gamma-cyclodextrin (HP-gamma-CyD) were prepared. Several percutaneous formulations of the drug and the prepared complexes in different bases (o/w emulsion, polyethylene glycol, carboxymethyl cellulose and Carbopol) were developed. Release studies revealed an improved release of the drug from formulations containing glipizide-CyD complexes. Ex vivo permeation studies through full thickness rat abdominal skin were conducted, whereby the effect of several conventional penetration enhancers (propylene glycol [PG], oleic acid, urea, dimethyl sulfoxide, menthol, limonene and cineole) was monitored. Highest flux was obtained from ointments prepared with Carbopol gel base containing a combination of PG and oleic acid as well as ointments prepared in the same base utilizing glipizide-DM-beta-CyD complex and urea. In vivo studies on diabetic male Wistar rats revealed a marked therapeutic efficacy sustained for about 48 hours. In this respect, two formulations showed best biological performance. In the first formulation, the drug was incorporated in Carbopol gel base in the presence of 20% PG together with 15% oleic acid. The second was prepared by incorporating glipizide-DM-beta-CyD complex in Carbopol gel base in presence of 15% urea. The glucose tolerance test showed suppression of hyperglycaemia induced in glucose-loaded rats. The above-mentioned results might shed a strong beam of light on the feasibility of using glipizide in a transdermal delivery system for treatment of type 2 diabetes with the aim of improving both patient compliance and pathophysiology of the disease.