Current status and future potential of transdermal drug delivery

Applications of ultrasonic skin permeation in transdermal drug delivery

Transdermal ultrasound-mediated drug delivery has been studied as a method for needle-less, non-invasive drug administration. Potential obstacles include the stratum corneum, which is not sufficiently passively permeable to allow effective transfer of many medications into the bloodstream without active methods. A general review of the transdermal ultrasound drug delivery literature has shown that this technology offers promising potential for non-invasive drug administration. Included in this review are the reported acoustic parameters used for achieving delivery, along with the known intensities and exposure times. Ultrasound mechanisms are discussed as well as spatial field characteristics. Accurate and precise quantification of the acoustic field used in drug delivery experiments is essential to ensure safety versus efficacy and to avoid potentially harmful bioeffects.

Transdermal drug delivery

Transdermal drug delivery has made an important contribution to medical practice, but has yet to fully achieve its potential as an alternative to oral delivery and hypodermic injections. First-generation transdermal delivery systems have continued their steady increase in clinical use for delivery of small, lipophilic, low-dose drugs. Second-generation delivery systems using chemical enhancers, noncavitational ultrasound and iontophoresis have also resulted in clinical products; the ability of iontophoresis to control delivery rates in real time provides added functionality. Third-generation delivery systems target their effects to skin's barrier layer of stratum corneum using microneedles, thermal ablation, microdermabrasion, electroporation and cavitational ultrasound. Microneedles and thermal ablation are currently progressing through clinical trials for delivery of macromolecules and vaccines, such as insulin, parathyroid hormone and influenza vaccine. Using these novel second- and third-generation enhancement strategies, transdermal delivery is poised to significantly increase its impact on medicine.

Transdermal drug delivery

Transdermal drug delivery has made an important contribution to medical practice, but has yet to fully achieve its potential as an alternative to oral delivery and hypodermic injections. First-generation transdermal delivery systems have continued their steady increase in clinical use for delivery of small, lipophilic, low-dose drugs. Second-generation delivery systems using chemical enhancers, noncavitational ultrasound and iontophoresis have also resulted in clinical products; the ability of iontophoresis to control delivery rates in real time provides added functionality. Third-generation delivery systems target their effects to skin's barrier layer of stratum corneum using microneedles, thermal ablation, microdermabrasion, electroporation and cavitational ultrasound. Microneedles and thermal ablation are currently progressing through clinical trials for delivery of macromolecules and vaccines, such as insulin, parathyroid hormone and influenza vaccine. Using these novel second- and third-generation enhancement strategies, transdermal delivery is poised to significantly increase its impact on medicine.

Microbubble Generation in Phase-Shift Nanoemulsions used as Anticancer Drug Carriers

The paper describes droplet-to-bubble transition in block copolymer stabilized perfluoropentane nanoemulsions. Three physical factors that trigger droplet-to-bubble transition in liquid emulsions and gels were evaluated, namely heat, ultrasound, and injections through fine-gauge needles. Among those listed, ultrasound irradiation was found the most efficient factor. Possible mechanisms of bubble generation and growth discussed in the paper include liquid-to-gas transition inside the individual bubble; bubble coalescence; and diffusion of dissolved air and/or perfluoropentane from small bubbles into larger bubbles (i.e., Oswald ripening). The last two factors result in irreversibility of the droplet-to-bubble transition. In gel matrices, ultrasound-induced droplet-to-bubble transition was substantially inhibited but was catalyzed by large (hundred micron) pre-existing bubbles irradiated by low frequency (hundred kilohertz) ultrasound. The dependence of the droplet-to-bubble transition on initial bubble size is theoretically treated and the role of increase of surface area in promoting bubble coalescence is discussed. Therapeutic implications of observed effects are discussed.

Dose comparison of ultrasonic transdermal insulin delivery to subcutaneous insulin injection

Prior studies have demonstrated the effectiveness of noninvasive transdermal insulin delivery using a cymbal transducer array. In this study the physiologic response to ultrasound mediated transdermal insulin delivery is compared to that of subcutaneously administered insulin. Anesthetized rats (350–550 g) were divided into four groups of four animals; one group representing ultrasound mediated insulin delivery and three representing subcutaneously administered insulin (0.15, 0.20, and 0.25 U/kg). The cymbal array was operated for 60 minutes at 20 kHz with 100 mW/cm² spatial-peak temporal-peak intensity and a 20% duty cycle. The blood glucose level was determined at the beginning of the experiment and, following insulin administration, every 15 minutes for 90 minutes for both the ultrasound and injection groups. The change in blood glucose from baseline was compared between groups. When administered by subcutaneous injection at insulin doses of 0.15 and 0.20 U/kg, there was little change in the blood glucose levels over the 90 minute experiment. Following subcutaneous administration of insulin at a dose of 0.25 U/kg, blood glucose decreased by 190 ± 96 mg/dl (mean ± SD) at 90 minutes. The change in blood glucose following ultrasound mediated insulin delivery was −262 ± 40 mg/dl at 90 minutes. As expected, the magnitude of change in blood glucose between the three injection groups was dependant on the dose of insulin administered. The change in blood glucose in the ultrasound group was greater than that observed in the injection groups suggesting that a higher effective dose of insulin was delivered.

Micro-scale devices for transdermal drug delivery

Skin makes an excellent site for drug and vaccine delivery due to easy accessibility, immuno-surveillance functions, avoidance of macromolecular degradation in the gastrointestinal tract and possibility of self-administration. However, macromolecular drug delivery across the skin is primarily accomplished using hypodermic needles, which have several disadvantages including accidental needle-sticks, pain and needle phobia. These limitations have led to extensive research and development of alternative methods for drug and vaccine delivery across the skin. This review focuses on the recent trends and developments in this field of micro-scale devices for transdermal macromolecular delivery. These include liquid jet injectors, powder injectors, microneedles and thermal microablation. The historical perspective, mechanisms of action, important design parameters, applications and challenges are discussed for each method.

Application of attenuated total reflection Fourier transform infrared imaging and tape-stripping to investigate the three-dimensional distribution of exogenous chemicals and the molecular organization in Stratum corneum

Attenuated total reflection Fourier transform infrared spectroscopic imaging combined with tape-stripping is an advantageous approach to map the depth penetration and lateral distribution of topically applied chemicals in Stratum corneum (SC) and the conformational order of SC lipids. Tape-stripping progressively removes layers of SC, and chemical imaging provides spatially resolved information on the chemical composition of both the newly exposed SC surface and of the tapes used for stripping. The procedure is rapid, minimally invasive, and does not necessitate cross-sectioning of the skin. This approach offers a simple and direct way to determine the distribution of exogenous volatile and non-volatile chemicals in SC as a function of the chemical composition of the formulation and time, and the conformational order of SC lipids in native and topically treated skin. The procedure described here is well suited to address questions of relevance for the areas of drug delivery, dermatology, and skin care.

Evaluation of the Transdermal Permeation Behavior of Proterguride from Drug in Adhesive Matrix Patches Through Hairless Mouse Skin

The transdermal in vitro permeation behavior of the highly potent dopamine agonist Proterguride was investigated using hairless mouse skin as a model membrane. Drug in adhesive matrix formulations based on different types of pressure-sensitive adhesives (Eudragit E 100 and Gelva7883 as acrylates, Oppanol B 15 SFN as polyisobutylene, and BioPSA 7-4202 as silicone) with a drug load of 3% by weight were manufactured. All patches were examined for drug crystallization by polarized microscopy immediately after the manufacturing process and after storage for 30 days in sealed aluminium laminate bags at ambient temperature and at 40 degrees C, respectively. Furthermore, the influence of the drug load in acrylate-based formulations onto the steady-state flux of Proterguride was examined. The Eudragit E 100 system delivered a significantly higher steady-state flux than the systems based on Oppanol B 15 SFN and also a somewhat higher steady-state flux than the Gelva-based patch. An addition of 10% by weight of the crystallization inhibitor povidone 25 did not significantly influence the steady-state flux of Proterguride from acrylate matrices. The lipophilic silicone and polyisobutylene adhesives facilitated drug crystallization within the short storage periods at both conditions, probably due to the absence of povidone 25, which was incompatible with these polymers. Varying the drug load in acrylate-based formulations led to a linear increase of the steady-state flux until the steady-state flux of Proterguride leveled off and the patches tended to drug crystallization. It was found that Gelva-based patches show good physical stability, good skin adhesion, and moderate flux values and, thus, can be evaluated as a basis for a suitable formulation for the transdermal administration of Proterguride.

[New substances and applications for postoperative pain therapy]

The onset of postoperative pain is the result of various pathophysiological mechanisms and depends on the type of surgery performed. Therefore, any adequate postoperative pain treatment requires multimodal and procedure-specific analgesia. In addition to reducing perioperative complications and improving patient comfort, optimal postoperative pain management also represents an important quality characteristic which can influence the patient in their choice of hospital. In the past 1-2 years, known groups of substances have been rediscovered for postoperative pain therapy (e.g., Gabapentin and Pregabalin, i.v. Lidocaine, Ketamine or glucocorticoids), while new substances (coxibe, oral oxycodone+naloxone) and applications have been developed. The present overview article discusses the advantages and disadvantages of these substances and analgesic methods, as well as their specific areas of application.

Effect of Nerodilol and Carvone on in vitro Permeation of Nicorandil Across Rat Epidermal Membrane

The objective of the study was to investigate the effect of nerodilol and carvone on the in vitro transdermal delivery of nicorandil so as to fabricate a membrane-moderated transdermal therapeutic system. The in vitro permeation studies were carried across the rat epidermal membrane from the hydroxypropyl methylcellulose (HPMC) gels (prepared with 70:30 v/v ethanol-water) containing selected concentrations of a terpene such as nerodilol (0%w/w, 4%w/w, 8%w/w, 10%w/w, or 12%w/w) or carvone (0%w/w, 4%w/w, 8%w/w, 12%w/w, or 16%w/w). The amount of nicorandil permeated (Q(24)) from HPMC gel drug reservoir without a terpene was 3424.6+/-51.4 microg/cm(2), and the corresponding flux of the drug was 145.5+/-2.2 microg/cm(2). h. The flux of nicorandil increased with an increase in terpene concentration in HPMC gel. It was increased ranging from 254.9+/-3.1 to 375.7+/-3.2 microg/cm(2).h or 207.6+/-4.7 to 356.7+/-15.3 microg/cm(2). h from HPMC gels containing nerodilol (4%w/w to 12%w/w) or carvone (4%w/w to 16%w/w), respectively. Nerodilol increased the flux of nicorandil by about 2.62-folds whereas carvone increased the flux of the drug by about 2.49-folds across the rat epidermal membrane. The results of the Fourier Transform Infrared (FT-IR) study indicated that the enhanced in vitro transdermal delivery of nicorandil might be due to the partial extraction of stratum corneum lipids by nerodilol or carvone. It was concluded that the terpenes, nerodilol and carvone, produced a marked penetration enhancing effect on the transdermal delivery of nicorandil that could be used in the fabrication of membrane-moderated transdermal therapeutic systems.

Effect of microneedle design on pain in human volunteers

OBJECTIVES

To design microneedles that minimize pain, this study tested the hypothesis that microneedles cause significantly less pain than a 26-gauge hypodermic needle, and that decreasing microneedle length and the number of microneedles reduces pain in normal human volunteers.

METHODS

Single microneedles with lengths ranging from 480 to 1450 microm, widths from 160 to 465 microm, thicknesses from 30 to 100 microm, and tip angles from 20 to 90 degrees; and arrays containing 5 or 50 microneedles were inserted into the volar forearms of 10 healthy, human volunteers in a double-blinded, randomized study. Visual analog scale pain scores were recorded and compared with each other and to the pain from a 26-gauge hypodermic needle.

RESULTS

All microneedles investigated were significantly less painful than the hypodermic needle with microneedle pain scores varying from 5% to 40% of the hypodermic needle. Microneedle length had the strongest effect on pain, where a 3-fold increase in length increased the pain score by 7-fold. The number of microneedles also affected the pain score, where a 10-fold increase in the number of microneedles increased pain just over 2-fold. Microneedle tip angle, thickness, and width did not significantly influence pain.

DISCUSSION

Microneedles are significantly less painful than a 26-gauge hypodermic needle over the range of dimensions investigated. Decreasing microneedle length and number of microneedles reduces pain.

Pig skin structure and transdermal delivery of liposomes: a two photon microscopy study

In this work we have characterized the architecture and physical properties of pig skin epidermis including its permeability to different liposome formulations. Autofluorescence images show that cells in the epidermis, from the basal layer to the stratum corneum, are organized in clusters that are in turn separated by particular structures we named "canyons". These canyons start in the surface as a wrinkle, eventually closing and going all the way inside the epidermis as a distinct structure that reaches the stratum basale. This structure, described previously in the epidermis of mouse skin as "intercluster pathway", was suggested to be filled with an unknown material and offer low resistance to vesicle penetration. Analysis of LAURDAN Generalized Polarization images of pig skin show that the canyons are filled with a non-polar poorly hydrated material, similar to that observed in pig skin stratum corneum. These results together with the data obtained from skin autofluorescence images suggest that these canyons are invaginations/extension of SC material. Fluorescently labeled lipids incorporated into very flexible liposomes are able to penetrate into the skin, eventually reaching the basal layer and the dermis plane. The presence of charged lipids in the liposomes enhances size stability and thus the efficiency of penetration.

Optimizing transdermal drug therapy

PURPOSE

The pharmacokinetics, benefits, risks, and future of transdermal drug products are reviewed.

SUMMARY

Transdermal drug delivery capitalizes on an attractive route of drug delivery, as it avoids the need for painful i.v. drug administration, i.v. site access, and syringe disposal and is an option for drug delivery to patients who are unable to swallow oral medications. Specific transdermal drug designs have advantages and disadvantages, including the ability to alter the patch size or readily manipulate the products. Transdermal drug delivery systems currently available include drug reservoir and microreservoir membrane-modulated systems, drug-in-adhesive layer designs, and matrix patches. Maximizing patient response to transdermal drug formulations may also rely on a number of other practical concerns, including patient dexterity, dose reproducibility, storage and stability of the remaining portion, and decreased adhesive efficacy. Adhesives in transdermal precuts may be locally irritating, and prolonged use and high dosages have resulted in dermatological reactions to some patches. Patients may also develop contact sensitization or systemic sensitization to the transdermal formulation itself. When a transdermal product regimen is initiated, caregivers should be mindful of the product's primary features and educate patients accordingly, specifically addressing where and how to apply the patch, duration of patch use, and procedures for properly changing and storing patches.

CONCLUSION

The increasing complexity of transdermal drug products, the growing number of medications available in such dosage forms, and reports of potential safety concerns contribute to the need for clinicians to understand the principles of transdermal drug delivery, safe usage techniques, and proper patient counseling points.

In vitro percutaneous permeation and skin accumulation of finasteride using vesicular ethosomal carriers

In order to develop a novel transdermal drug delivery system that facilitates the skin permeation of finasteride encapsulated in novel lipid-based vesicular carriers (ethosomes)finasteride ethosomes were constructed and the morphological characteristics were studied by transmission electron microscopy. The particle size, zeta potential and the entrapment capacity of ethosome were also determined. In contrast to liposomes ethosomes were of more condensed vesicular structure and they were found to be oppositely charged. Ethosomes were found to be more efficient delivery carriers with high encapsulation capacities. In vitro percutaneous permeation experiments demonstrated that the permeation of finasteride through human cadaver skin was significantly increased when ethosomes were used. The finasteride transdermal fluxes from ethosomes containing formulation (1.34 +/- 0.11 microg/cm(2)/h) were 7.4, 3.2 and 2.6 times higher than that of finasteride from aqueous solution, conventional liposomes and hydroethanolic solution respectively (P < 0.01).Furthermore, ethosomes produced a significant (P < 0.01) finasteride accumulation in the skin, especially in deeper layers, for instance in dermis it reached to 18.2 +/- 1.8 microg/cm(2). In contrast, the accumulation of finasteride in the dermis was only 2.8 +/- 1.3 microg/cm(2) with liposome formulation. The study demonstrated that ethosomes are promising vesicular carriers for enhancing percutaneous absorption of finasteride.

Low-frequency sonophoresis: current status and future prospects

Application of ultrasound enhances skin permeability to drugs, a phenomenon referred to as sonophoresis. Significant strides have been made in sonophoresis research in recent years, especially under low-frequency conditions (20 kHz<f<100 kHz). This article reviews the mechanistic principles and current status of sonophoresis under low-frequency conditions. Several therapeutic macromolecules including insulin, low-molecular weight heparin, and vaccines have been delivered using low-frequency sonophoresis in vivo. Clinical trials have been performed with several drugs including lidocaine and cyclosporin. Novel theoretical and experimental approaches have provided insights into the mechanisms of low-frequency sonophoresis. Current understanding of these mechanisms is presented.

Flux across [corrected] microneedle-treated skin is increased by increasing charge of naltrexone and naltrexol in vitro

PURPOSE

The purpose of this investigation was to evaluate the in vitro microneedle (MN) enhanced percutaneous absorption of naltrexone hydrochloride salt (NTX x HCl) compared to naltrexone base (NTX) in hairless guinea pig skin (GP) and human abdominal skin. In a second set of experiments, permeability of the major active metabolite 6-beta-naltrexol base (NTXOL) in the primarily unionized (unprotonated) form at pH 8.5 was compared to the ionized form (pH 4.5).

METHODS

In vitro fluxes of NTX, NTX.HCl and ionized and unionized NTXOL were measured through microneedle treated or intact full thickness human and GP skin using a flow through diffusion apparatus. Solubility and diffusion samples were analyzed by HPLC.

RESULTS

Both GP and human skin show significant increases in flux when treated with 100 MN insertions as compared to intact full thickness skin when treated with NTX.HCl or ionized NTXOL (pH 4.5; p < 0.05). MN increased GP skin permeability for the hydrophilic HCL salt of NTX by tenfold and decreased lag time by tenfold too. Similar results were found using human skin, such that skin permeability to NTX.HCl was elevated to 7.0 x 10(-5) cm/h. Permeability of the primarily unionized (unprotonated) form of NTXOL at pH 8.5 was increased by MN only threefold and lag time was only modestly reduced. However, MN treatment with the primarily ionized (protonated) form of NTXOL at pH 4.5 increased skin permeability fivefold and decreased lag time fourfold.

CONCLUSION

Enhancement was observed in vitro in both GP and human skin treated with MN compared to intact skin with the salt form of NTX and the ionized form of NTXOL. We conclude that transdermal flux can be optimized by using MN in combination with charged (protonated) drugs that have increased solubility in an aqueous patch reservoir and increased permeability through aqueous pathways created by MN in the skin.

Pocketed Microneedles for Drug Delivery to the Skin

Drug delivery to the skin is limited by the strong barrier properties of skin's outer layer of stratum corneum. Micron-scale needles have been developed to deliver drugs across this barrier layer and into the skin in a minimally invasive manner. One method of delivery involves coating these microneedles with a drug that rapidly dissolves off within the skin. As a variation on this approach, this study examines microneedles with holes cut through their shafts to form "pockets" that can be filled with drug formulations using a dip-coating method. Our results (i) demonstrated the filling of microneedle pockets having a variety of different sizes and shapes, (ii) quantified the amount of drug that can be filled into pockets and coated onto microneedle surfaces, (iii) developed composite microneedle structures that sequester one model drug within the microneedle pocket and coat another model drug on the microneedle surface and (iv) showed that pocketed microneedles can deliver a model drug to a targeted depth within the skin. We conclude that pocketed microneedles offer unique capabilities for controlled drug delivery to the skin.

Optimization of transdermal delivery using magainin pore-forming peptide

The skin's outer layer of stratum corneum, which is a thin tissue containing multilamellar lipid bilayers, is the main barrier to drug delivery to the skin. To increase skin permeability, our previous work has shown large enhancement of transdermal permeation using a pore-forming peptide, magainin, which was formulated with N-lauroyl sarcosine (NLS) in 50% ethanol-in-PBS. Mechanistic analysis suggested that magainin and NLS can increase skin permeability by disrupting stratum corneum lipid structure. In this study, our goal was to improve conditions that increase skin permeability by magainin by further optimizing the pretreatment time and concentration of magainin exposure. We found that skin permeability increased with increasing pretreatment time. Skin permeability also increased with increasing magainin concentration up to 1 mM, but was reduced at a magainin concentration of 2 mM. Enhancement of skin permeability to fluorescein (323 Da) up to 35-fold was observed. In contrast, this formulation did not enhance skin permeability to larger molecules, such as calcein (623 Da) and dextran (3,000 Da).

The effect of heat on skin permeability

Although the effects of long exposure (>>1s) to moderate temperatures (< or =100 degrees C) have been well characterized, recent studies suggest that shorter exposure (<1s) to higher temperatures (>100 degrees C) can dramatically increase skin permeability. Previous studies suggest that by keeping exposures short, thermal damage can be localized to the stratum corneum without damaging deeper tissue. Initial clinical trials have progressed to Phase II (see http://clinicaltrials.gov), which indicates the procedure can be safe. Because the effect of heating under these conditions has received little systematic or mechanistic study, we heated full-thickness skin, epidermis and stratum corneum samples from human and porcine cadavers to temperatures ranging from 100 to 315 degrees C for times ranging from 100ms to 5s. Tissue samples were analyzed using skin permeability measurements, differential scanning calorimetry, thermomechanical analysis, thermal gravimetric analysis, brightfield and confocal microscopy, and histology. Skin permeability was shown to be a very strong function of temperature and a less strong function of the duration of heating. At optimal conditions used in this study, transdermal delivery of calcein was increased up to 760-fold by rapidly heating the skin at high temperature. More specifically, skin permeability was increased (I) by a few fold after heating to approximately 100-150 degrees C, (II) by one to two orders of magnitude after heating to approximately 150-250 degrees C and (III) by three orders of magnitude after heating above 300 degrees C. These permeability changes were attributed to (I) disordering of stratum corneum lipid structure, (II) disruption of stratum corneum keratin network structure and (III) decomposition and vaporization of keratin to create micron-scale holes in the stratum corneum, respectively. We conclude that heating the skin with short, high temperature pulses can increase skin permeability by orders of magnitude due to structural disruption and removal of stratum corneum.

Microneedles permit transdermal delivery of a skin-impermeant medication to humans

Drugs with poor oral bioavailability usually are administered by hypodermic injection, which causes pain, poor patient compliance, the need for trained personnel, and risk of infectious disease transmission. Transdermal (TD) delivery provides an excellent alternative, but the barrier of skin's outer stratum corneum (SC) prevents delivery of most drugs. Micrometer-scale microneedles (MNs) have been used to pierce animal and human cadaver skin and thereby enable TD delivery of small molecules, proteins, DNA, and vaccines for systemic action. Here, we present a clinical study of MN-enhanced delivery of a medication to humans. Naltrexone (NTX) is a potent mu-opioid receptor antagonist used to treat opiate and alcohol dependence. This hydrophilic and skin-impermeant molecule was delivered from a TD patch to healthy human subjects with and without pretreatment of the skin with MNs. Whereas delivery from a standard NTX TD patch over a 72-h period yielded undetectable drug plasma levels, pretreatment of skin with MNs achieved steady-state plasma concentrations within 2 h of patch application and were maintained for at least 48 h. The MNs and NTX patch were well tolerated with mild systemic and application site side effects. The MN arrays were painless upon administration and not damaged during skin insertion, and no MNs were broken off into the skin. This human proof-of-concept study demonstrates systemic administration of a hydrophilic medication by MN-enhanced TD delivery. These findings set the stage for future human studies of skin-impermeant medications and biopharmaceuticals for clinical applications.

Safety, efficacy and patient acceptability of the combined estrogen and progestin transdermal contraceptive patch: a review

The worldwide introduction of the first, unique patch for hormonal contraception (ethinyl estradiol/norelgestromin, EE/NGMN patch) was widely recognized as a significant event in the development of drug delivery systems. This innovation offers a number of advantages over the oral route, and extensive clinical trials have proved its safety, efficacy, effectiveness, and tolerability. The weekly administration and ease of use/simplicity of the EE/NGMN patch contribute to its acceptability, and help to resolve the two main problems of non-adherence, namely early discontinuation and inconsistent use. The patch offers additional benefits to adolescents (improvement of dysmenorrhea and acne), adults (improvement in emotional and physical well-being, premenstrual syndrome, and menstrual irregularities), and perimenopausal women (correction of hormonal imbalance, modulation of premenopausal symptoms), thus providing high satisfaction rates (in nearly 90% of users). Since its introduction, the transdermal contraceptive patch has proved to be a useful choice for women who seek a convenient formulation which is easy to use, with additional, non-contraceptive tailored benefits for all the ages.

Effect of permeation enhancers and organic acids on the skin permeation of indapamide

The aim of present study was to investigate the transdermal properties of indapamide and to explore the efficacy of various permeation enhancers and organic acids with regard to the percutaneous absorption of indapamide. Permeation experiments were performed in vitro, using rat abdominal skin as a barrier. In the permeation studies, 2-chamber diffusion cells were used. The results obtained indicate that N-dodecylazepan-2-one, N-methyl-2-pyrrolidone, menthol and oleic acid had a strong enhancing effect on the permeation of indapamide and N-dodecylazepan-2-one exhibited the most potent enhancing effect. All eight of the organic acids chosen had a potent enhancing effect on the permeation of indapamide across rat abdominal skin. Among the organic acids examined, lactic acid had the greatest enhancing effect. The formation of an ion-pair between indapamide and organic acids may be responsible for the enhanced skin permeation of indapamide. Although the exact reason remains unknown, it is worth carrying out further investigations.

An evaluation of mathematical models for predicting skin permeability

A number of mathematical models have been proposed for predicting skin permeability, mostly empirical and very few are deterministic. Early empirical models use simple lipophilicity parameters. The recent trend is to use more complicated molecular structure descriptors. There has been much debate on which models best predict skin permeability. This article evaluates various mathematical models using a comprehensive experimental dataset of skin permeability for 124 chemical compounds compiled from various sources. Of the seven models compared, the deterministic model of Mitragotri gives the best prediction. The simple quantitative structure permeability relationships (QSPR) model of Potts and Guy gives the second best prediction. The two models have many features in common. Both assume the lipid matrix as the pathway of transdermal permeation. Both use octanol-water partition coefficient and molecular size. Even the mathematical formulae are similar. All other empirical QSPR models that use more complicated molecular structure descriptors fail to provide satisfactory prediction. The molecular structure descriptors in the more complicated QSPR models are empirically related to skin permeation. The mechanism on how these descriptors affect transdermal permeation is not clear. Mathematically it is an ill-defined approach to use many colinearly related parameters rather than fewer independent parameters in multi-linear regression.

Dermal Peptide Delivery Using Colloidal Carrier Systems

The advancement in synthetic and molecular biology techniques over the past years has resulted in the application of peptides or peptide-like drugs becoming a growing field in therapeutics. Because of the unfavorable chemical properties of peptides, it poses a challenge to find an optimized way of drug administration. The transdermal route has attracted interest as a promising way to advance the delivery of these drugs. The objective of this review is to summarize the level of research of microemulsions as colloidal carrier for dermal peptide drug delivery. The presented studies resulted in enhanced drug delivery or superior penetration profiles of peptides incorporated in microemulsions in comparison to conventional vehicles. Due to their benefits like high solubilization capacity, enhanced drug delivery, noninvasive administration or easy preparation, microemulsions offer a suitable vehicle for dermal and transdermal drug delivery.

Current challenges in non-invasive insulin delivery systems: a comparative review

The quest to eliminate the needle from insulin delivery and to replace it with non- or less-invasive alternative routes has driven rigorous pharmaceutical research to replace the injectable forms of insulin. Recently, various approaches have been studied involving many strategies using various technologies that have shown success in delivering insulin, which are designed to overcome the inherent barriers for insulin uptake across the gastrointestinal tract, mucosal membranes and skin. This review examines some of the many attempts made to develop alternative, more convenient routes for insulin delivery to avoid existing long-term dependence on multiple subcutaneous injections and to improve the pharmacodynamic properties of insulin. In addition, this article concentrates on the successes in this new millennium in developing potential non-invasive technologies and devices, and on major new milestones in modern insulin delivery for the effective treatment of diabetes.

Feasibility of an electrode-reservoir device for transdermal drug delivery by noninvasive skin electroporation

Electrical creation of aqueous pathways across the skin's outer layer [stratum corneum (SC)] provides an approach to transdermal delivery of medium-size water-soluble compounds. However, nerve stimulation should be avoided. Here, we show that a microstructured electrode array can significantly confine the electric field to the nerve-free SC. The prototype electrode-reservoir device (ERD) contains field-confining electrodes and a fluorescent drug surrogate [sulphorhodamine (SR)]. In vivo human experiments at the forearm with approximately rectangular voltage pulses up to 500 V and 1-ms duration cause electroporation as measured by skin resistance change but only rarely caused sensation. Human skin in vitro experiments with such pulses up to 300 V transported SR across the SC. Our results are supported by a model's prediction of the field in the ERD and nearby tissue.

Modelling transdermal delivery of high molecular weight drugs from microneedle systems

In the past few years, a number of microneedle designs have been proposed for transdermal drug delivery of high molecular weight drugs. However, most of them do not increase the drug permeability in skin significantly. In other cases, designs developed based on certain criteria (e.g. strength of the microneedles) have failed to meet other criteria (e.g. drug permeability in skin, throughputs of the drugs, etc.). It is obvious therefore that in order to determine the 'optimum' design of these microneedles, the effect of different factors (e.g. length of the microneedle, surface area of the patch, etc.) along with various transport properties of drug transport behaviour using microneedles should be determined accurately. Appropriate mathematical models for drug transport from these systems into skin have the potential to resolve some of these issues. To address this, a parametric analysis for transdermal delivery of a high molecular weight drug from a microneedle is presented in this paper. The simulations have allowed us to identify the significance of various factors that influence the drug delivery while designing microneedle arrays. A scaling analysis is also done which shows the functional dependence of drug concentration on other variables of skin and microneedle arrays.

Piezoelectric control of needle-free transdermal drug delivery

Transdermal drug delivery occurs primarily through hypodermic needle injections, which cause pain, require a trained administrator, and may contribute to the spread of disease. With the growing number of pharmaceutical therapies requiring transdermal delivery, an effective, safe, and simple needle-free alternative is needed. We present and characterize a needle-free jet injector that employs a piezoelectric actuator to accelerate a micron-scale stream of fluid (40-130 microm diameter) to velocities sufficient for skin penetration and drug delivery (50-160 m/s). Existing jet injectors, powered by compressed springs and gases, are not widely used due to painful injections and poor reliability in skin penetration depth and dose. In contrast, our device offers electronic control of the actuator expansion rate, resulting in direct control of jet velocity and thus the potential for more precise injections. We apply a simple fluid-dynamic model to predict the device response to actuator expansion. Further, we demonstrate that injection parameters including expelled volume, jet pressure, and penetration depth in soft materials vary with actuator expansion rate, but are highly coupled. Finally, we discuss how electronically-controlled jet injectors may enable the decoupling of injection parameters such as penetration depth and dose, improving the reliability of needle-free transdermal drug delivery.