Skin deep.

Over the past 30 or so years there has been a considerable advance in our knowledge of the mechanisms of skin permeation. This has largely been brought about by the development of sophisticated biophysical techniques and increased computing powers. The advanced technology has clearly provided indications, at a molecular level, about routes of permeation and how the barrier function can be modulated by excipients with which actives are formulated. This publication reviews some of the advances that have been made and mathematical models that have been constructed to predict percutaneous penetration and transdermal delivery. The models also indicate the various enhancement strategies that can be used in dermal penetration. In the past, it has been difficult to identify precise mechanisms of action of the different classes of enhancer but a combination of appropriate biophysical techniques, mathematical modelling and chemometric analysis can help identify the contributing processes. The models can also be used to indicate rate control in transdermal delivery, whether it is in the applied delivery device or in the skin.     

皮肤给药的经皮吸收与测量技术研究进展

经皮给药系统（TDDS）可避免首关效应、胃肠道破坏，为新型皮肤给药系统，可通过控制释放而延长治疗效果，成为药物制剂开发研究的热点之一。但是，药物的理化性质以及皮肤屏障影响药物的经皮吸收。综述了TDDS常用的促渗透技术，包括化学、物理、纳米、天然促渗透技术；介绍了促渗透能力的测定方法，包括体外、离体和体内评估皮肤渗透性的方法。通过对经皮药物递送系统和经皮吸收能力测定方法的归纳与总结，以期为TDDS的合理使用和快速发展提供参考。     

Delivery of hormones: some new concepts

Some new concepts in the delivery of hormones are described. Transmucosal or transdermal penetration of hormones can be facilitated, often by the use of absorption enhancers. Studies of nasal insulin delivery are described. Recently developed iontophoretic delivery devices can be useful for pulsatile transdermal administration of peptide hormones. A self-regulating delivery system releasing insulin in response to glucose levels is described. A vaginal ring relasing ethinylestradiol and 3-ketodesogestrel is a new concept in long-acting contraception. A nasal estradiol formulation, containing the absorption enhancer dimethyl-β-cyclodextrin, is an interesting alternative to oral and transdermal delivery of female sex hormones.     

Transdermal delivery of some anti-emetics

One group of drugs that could be usefully delivered by the transdermal route are the anti-emetics. Representative examples of this class of drugs have been examined and their potential for transdermal delivery assessed. This has been achieved by an examination of their physicochemical properties from which skin permeability can be predicted using a range of mathematical models. The results have been compared with data in the literature for the penetration of the drugs across rat skin. The predicted permeabilities have then been equated with the known clearance kinetics of the drugs to calculate probable plasma levels. In this way the feasibility of delivering these drugs transdermally can be assessed.     

Deep percutaneous penetration into muscles and joints

The transdermal absorption of drugs and its subsequent deep tissue delivery is a complex process, with many factors influencing the penetration mechanisms. Nonsteroidal antiinflammatory drugs (NSAIDs) are widely used in the treatment of joint and muscle diseases. However, the dangers associated with oral medications highlight the need for alternative methods of targeting and retaining drugs; one such means is through topical delivery. The drug's lipophilicity, permeability, and fraction unbound found in the viable skin are some physiochemical factors influencing the delivery mechanism after transdermal absorption. These and other variables play a role in determining whether the drug reaches the deep tissues via direct penetration or from systemic redistribution. Pharmacokinetic models have been developed to help elucidate the penetration routes and efficacy for various drugs. While there are still uncertainties regarding the deep tissue penetration kinetics, improvements to current research methodologies may bring about a greater understanding of percutaneous absorption into the deep muscle and joints.     

微针与新型经皮给药载体结合的研究进展

经皮给药系统具有给药方便、血药浓度稳定、无首过效应等优点,但皮肤的屏障作用使得药物难以透过皮肤。近年来,出现了很多新型经皮给药的药物载体,如脂质体、醇质体、囊泡等,这些能通过化学方法促进药物的经皮渗透。而微针能穿透皮肤角质层形成微孔通道,通过物理方法促进药物的渗透,将微针与新型经皮给药载体结合能显著提高药物的经皮吸收的速率。本文对微针与新型经皮给药载体结合的最新研究进行了综述,并展望了微针辅助新型药物载体经皮给药的发展前景。     

Transdermal skin delivery: predictions for humans from in vivo, ex vivo and animal models

The assessment of percutaneous permeation of molecules is one of the main steps in the initial design and later in the evaluation of dermal or transdermal drug delivery systems. The literature reports numerous ex vivo, in vitro and in vivo models used to determine drug skin permeation profiles and kinetic parameters, some studies focusing on the correlation of the data obtained using these models with the dermal/transdermal absorption in humans. This paper reviews work from in vitro permeation studies to clinical performance, presenting various experimental models used in dermal/transdermal research, including the use of excised human or animal skin, cultured skin equivalents and animals. Studies focusing on transdermal absorption of a series of drug molecules and various delivery systems as well as mathematical models for skin absorption are reviewed.     

Prodrugs for transdermal drug delivery – trends and challenges

Prodrugs continue to attract significant interest in the transdermal drug delivery field. These moieties can confer favorable physicochemical properties on transdermal drug delivery candidates. Alkyl chain lengthening, pegylation are some of the strategies used for prodrug synthesis. It is usually important to optimize partition coefficient, water and oil solubilities of drugs. In this review, progress made in the field of prodrugs for percutaneous penetration is highlighted and the challenges discussed.     

Iontophoresis and electroporation: comparisons and contrasts

The techniques of iontophoresis and electroporation can be used to enhance topical and transdermal drug delivery. Iontophoresis applies a small low voltage (typically 10 V or less) continuous constant current (typically 0.5 mA/cm2 or less) to push a charged drug into skin or other tissue. In contrast, electroporation applies a high voltage (typically, ?100 V) pulse for a very short (micros-ms) duration to permeabilize the skin. This electric assistance of drug delivery across skin will expand the scope of transdermal delivery to hydrophilic macromolecules such as the drugs of biotechnology. These two techniques differ in several aspects such as the mode of application and pathways of transport but can be used together for effective drug delivery. Iontophoresis is already used clinically in physical therapy clinics and is close to commercialization for development of a systemic delivery patch with miniaturized circuits and similar in overall size to a passive patch. The use of electroporation for drug delivery is relatively new and is being actively researched.     

Veterinary drug delivery: potential for skin penetration enhancement

A range of topical products are used in veterinary medicine. The efficacy of many of these products has been enhanced by the addition of penetration enhancers. Evolution has led to not only a highly specialized skin in animals and humans, but also one whose anatomical structure and skin permeability differ between the various species. The skin provides an excellent barrier against the ingress of environmental contaminants, toxins, and microorganisms while performing a homeostatic role to permit terrestrial life. Over the past few years, major advances have been made in the field of transdermal drug delivery. An increasing number of drugs are being added to the list of therapeutic agents that can be delivered via the skin to the systemic circulation where clinically effective concentrations are reached. The therapeutic benefits of topically applied veterinary products is achieved in spite of the inherent protective functions of the stratum corneum (SC), one of which is to exclude foreign substances from entering the body. Much of the recent success in this field is attributable to the rapidly expanding knowledge of the SC barrier structure and function. The bilayer domains of the intercellular lipid matrices within the SC form an excellent penetration barrier, which must be breached if poorly penetrating drugs are to be administered at an appropriate rate. One generalized approach to overcoming the barrier properties of the skin for drugs and biomolecules is the incorporation of suitable vehicles or other chemical compounds into a transdermal delivery system. Indeed, the incorporation of such compounds has become more prevalent and is a growing trend in transdermal drug delivery. Substances that help promote drug diffusion through the SC and epidermis are referred to as penetration enhancers, accelerants, adjuvants, or sorption promoters. It is interesting to note that many pour-on and spot-on formulations used in veterinary medicine contain inert ingredients (e.g., alcohols, amides, ethers, glycols, and hydrocarbon oils) that will act as penetration enhancers. These substances have the potential to reduce the capacity for drug binding and interact with some components of the skin, thereby improving drug transport. However, their inclusion in veterinary products with a high-absorbed dose may result in adverse dermatological reactions (e.g., toxicological irritations) and concerns about tissue residues. These are important considerations when formulating a veterinary transdermal product when such compounds are added, either intentionally or otherwise, for their penetration enhancement ability.     

Physicochemical, physiological, and mathematical considerations in optimizing percutaneous absorption of drugs

The percutaneous absorption or transdermal permeation of drugs has gained considerable prominence in recent years through the development of transdermal systemic delivery systems and the related interest in the design and use of topical products. The present review discusses the phenomenon of percutaneous absorption in drug delivery and its importance in regard to the anatomy of skin, its physiological function, and biomechanical properties, as well as the physicochemical properties of the skin and the drug. The mathematical relationships and models used to describe the phenomenon of percutaneous absorption are also reported. The importance of these factors in optimizing percutaneous absorption or transdermal permeation of drugs for local or systemic effect is also discussed.     

Antihistamine effects of triprolidine from the transdermal administration of the TPX matrix in rats

The antihistamine effects of the triprolidine were studied in rats to determine the feasibility of their enhanced transdermal delivery from the poly (4-methyl-1-pentene) (TPX) matrix system containing penetration enhancer and plasticizer. The antihistamine effects were determined by the Evans blue dye procedure by comparing the changes in vascular permeability increase following the transdermal administration. The vascular permeability increase was significantly reduced by transdermal administration of the triprolidine-TPX system containing triethyl citrate (TEC) and polyoxyethylene-2-oleyl ether (POE). Both the plasticizer and penetration enhancer played an important role in the skin permeation of triprolidine and increased the antihistamine effects. These results showed that the triprolidine-TPX matrix system containing plasticizer and penetration enhancer could be a transdermal delivery system providing the increased antihistamine effects.     

Transdermal delivery of levosimendan

The aim of this study was to determine if transdermal penetration of levosimendan, a novel positive inotropic drug, could be enhanced and controlled by formulation modifications. Penetration of levosimendan across human epidermis in vitro was determined using abdominal excised skin and diffusion cells. Predicted steady-state plasma concentrations of levosimendan were estimated using permeabilities and pharmacokinetic parameters of levosimendan. For penetration enhancement we used different pH values, co-solvents, cyclodextrins, surfactants, penetration enhancers, liposomes, and iontophoresis. Sodium lauryl sulfate, ethanol, oleic acid, and soya phosphatidylcholine or their combinations clearly increased levosimendan permeation across the skin in vitro. Iontophoresis was also an efficient method to increase transdermal permeation of levosimendan. A hydrophilic co-solvent/penetration enhancer is needed to achieve better permeability of levosimendan across the skin. In conclusion, transdermal delivery of levosimendan can be significantly increased by formulation modification. Based on kinetic calculations, therapeutic plasma concentrations may be achievable transdermally.     

Investigation of the carbopol gel of solid lipid nanoparticles for the transdermal iontophoretic delivery of triamcinolone acetonide acetate

The purpose of this study was to investigate solid lipid nanoparticles (SLN) hydrogel for transdermal iontophoretic drug delivery. Triamcinolone acetonide acetate (TAA), a glucocorticoids compound, was employed as the model drug. SLN containing the drug triamcinolone acetonide acetate (TAA-SLN) and their carbopol gel with stable physicochemical properties were prepared. The use of TAA-SLN carbopol gel as a vehicle for the transdermal iontophoretic delivery of TAA was evaluated in vitro using horizontal diffusion cells fitted with porcine ear skin. We found that the TAA-SLN gel possessed good stability, rheological properties, and high electric conductance. Transdermal penetration of TAA from TAA-SLN gel cross the skin tissue was significantly enhanced by iontophoresis. The enhancement of the cumulative penetration amount and the steady-state penetration flux of the penetrated drug were related to the particle size of TAA-SLN and the characteristics of the applied pulse electric current, such as density, frequency, and on/off interval ratio. These results indicated that SLN carbopol gel could be used as a vehicle for transdermal iontophoretic drug delivery under suitable electric conditions.     

Enhanced transdermal delivery of atenolol from the ethylene-vinyl acetate matrix

To enhance transdermal delivery of atenolol, ethylene-vinyl acetate (EVA) matrix of drug containing penetration enhancer was fabricated. Effect of penetration enhancer on the permeation of atenolol through the excised rat skin was studied. Penetrating enhancers showed the increased flux probably due to the enhancing effect on the skin barrier, the stratum corneum. Among enhancers used such as glycols, fatty acids and non-ionic surfactants, polyoxyethylene 2-oleyl ether showed the best enhancement. For the controlling transdermal delivery of atenolol, the application of EVA matrix containing permeation enhancer could be useful in the development of transdermal drug delivery system.     

聚合物胶束在经皮给药系统中的应用

摘 要 目的：综述聚合物胶束作为药物载体在经皮传递系统中的应用进展。方法: 根据国内外发表的最新文献,对聚合物胶束的制备方法、促进皮肤渗透的机制、释药过程及其在经皮给药系统中的应用进行分析与讨论。结果: 聚合物胶束具有增加难溶性药物的溶解度,促进药物的经皮吸收等作用,作为药物载体在经皮传递系统的应用越来越广泛。结论:聚合物胶束可作为药物载体被广泛用于经皮给药系统的研究中,具有较好的发展前景。     

Biomaterials as novel penetration enhancers for transdermal and dermal drug delivery systems

Abstract

The highly organized structure of the stratum corneum provides an effective barrier to the drug delivery into or across the skin. To overcome this barrier function, penetration enhancers are always used in the transdermal and dermal drug delivery systems. However, the conventional chemical enhancers are often limited by their inability to delivery large and hydrophilic molecules, and few to date have been routinely incorporated into the transdermal formulations due to their incompatibility and local irritation issues. Therefore, there has been a search for the compounds that exhibit broad enhancing activity for more drugs without producing much irritation. More recently, the use of biomaterials has emerged as a novel method to increase the skin permeability. In this paper, we present an overview of the investigations on the feasibility and application of biomaterials as penetration enhancers for transdermal or dermal drug delivery systems.     

空心微针透皮给药技术的研究进展

空心微针类似于微米级的注射针,具有注射给药和透皮给药的双重特点.作为一种新型的透皮给药技术,空心微针近年来在疫苗和胰岛素等生物大分子药物的递送方面显示出极大的潜力.笔者根据近年来国内外相关的研究报道,对空心微针的促透机制、常用制备材料及工艺和在透皮给药中的应用等进行归纳总结,以期为空心微针技术的研究和发展提供参考借鉴.     

Enhanced skin penetration of P20 phosphopeptide using protein transduction domains.

Protein transduction domains (PTDs) were recently demonstrated to increase the penetration of the model peptide P20 when the PTD and P20 were covalently attached. Here, we evaluated whether non-covalently linked PTDs were capable of increasing the skin penetration of P20. Two different PTDs were studied: YARA and WLR. Porcine ear skin mounted in a Franz diffusion cell was used to assess the penetration of P20 in the stratum corneum (SC) and viable skin (VS); VS consists of dermis and epidermis without SC. The transdermal delivery of P20 was also assessed. At 1mM, YARA promoted a 2.33-fold increase in the retention of P20 in the SC but did not significantly increase the amount of P20 that reached VS. WLR significantly increased (2.88-fold) the penetration of P20 in VS. Compared to the non-attached form, the covalently linked WLR fragment was two times more effective in promoting the penetration of P20 into VS. None of the PTDs promoted transdermal delivery of P20 at 4h post-application. It was concluded that selected non-covalently linked PTDs can be used as a penetration enhancer, but greater skin penetration efficiency can be achieved by covalently binding the PTD to the therapeutic agent.     

柔性脂质体的促渗作用研究

本文以水杨酸钠为模型药，系统研究了不同柔性脂质体的经皮促渗能力，实验结果表明掺有强亲水性表面活性剂的脂质体具有很好的促渗作用，是一类新的透皮促进剂。