Chemical method to enhance transungual transport and iontophoresis efficiency

Nail Peeling with Glycolic Acid 50%: A Prospective Study of 20 Cases

Background

Surface abnormalities of the nail may be due to nail diseases or chemical abuse. So, every nail plate change does not require medical treatment. The aim of our study was to support the benefit of glycolic acid (GA) in both pathological conditions and dry, discolored nails due to cosmetics.

Methods

A prospective single open label uncontrolled study is conducted in our department from January until April 2017. We divided our cases into 2 groups: G1 (consequences of cosmetics) and G2 (pathological conditions). In G1, we used 1-2 coat of GA 50% in 1-2 sitting at weekly intervals, but we needed multiple sittings (6-12 weeks) in G2 with 2-4 coats.

Results

We have collected 20 cases: 12 in G1 and 8 in G2. In G1, 8 patients had good response. In G2, 6 had good response. Adverse effects were tolerable.

Conclusion

Good response in G1 was also noted in the Indian report. The improvement in the chemotherapy side effect led us to widen the sample in order to have more credible results. GA 50% peels can offer aesthetically better looking nails. However, larger studies with a longer follow-up are required to validate the results.

Vesicular drug delivery for the treatment of topical disorders: current and future perspectives

OBJECTIVES

Vesicular drug delivery has become a useful approach for therapeutic administration of pharmaceutical compounds. Lipid vesicles have found application in membrane biology, immunology, genetic engineering and theragnostics. This review summarizes topical delivery, specifically dermal/transdermal, ocular and transungual, via these vesicles, including future formulation perspectives.

KEY FINDINGS

Liposomes and their subsequent derivatives, viz. niosomes, transferosomes, pharmacososmes and ethosomes, form a significant part of vesicular systems that have been successfully utilized in treating an array of topical disorders. These vesicles are thought to be a safe and effective mode of improving the delivery of lipophilic and hydrophilic drugs.

SUMMARY

Several drug molecules are available for topical disorders. However, physicochemical properties and undesirable toxicity have limited their efficacy. Vesicular delivery systems have the potential to overcome these shortcomings due to properties such as high biocompatibility, simplicity of surface modification and suitability as controlled delivery vehicles. However, incorporating these systems into environmentally responsive dispersants such as hydrogels, ionic liquids and deep eutectic solvents may further enhance therapeutic prowess of these delivery systems. Consequently, improved vesicular drug delivery can be achieved by considering combining some of these formulation approaches.

Enhanced nail delivery of voriconazole-loaded nanomicelles by thioglycolic acid pretreatment: A study of protein dynamics and disulfide bond rupture

This work aimed to select an effective penetration enhancer (PE) for nail pretreatment, develop voriconazole (VOR)-loaded nanomicelles, and evaluate their ability to deliver VOR to the nail. A complete analysis of nail protein dynamics, bond rupture, and microstructure was performed. Alternative methods as electron paramagnetic resonance (EPR) and the Ellman's reagent (DTNB) assay were also evaluated. Nanomicelles were produced and characterized. The PE hydrated the hooves, following the order: urea ≈ cysteine ≈ glycolic acid < thioglycolic acid (TGA) < NaOH. SEM images and methylene blue assay showed enlarged pores and roughness of porcine hooves after incubation with NaOH and TGA. EPR was demonstrated to be the most sensitive technique. DTNB assay quantified higher thiol groups for samples treated with TGA (p < 0.05). A stratigraphic analysis with Raman spectroscopy demonstrated that hooves treated with TGA presented a higher SH/SS ratio at the edges, affecting protein secondary structure. In vitro permeation studies demonstrated significant VOR permeation (29.44 ± 6.13 µg/cm²), 10-fold higher than previous studies with lipid nanoparticles. After TGA pretreatment, VOR permeation was further enhanced (3-fold). TGA pretreatment followed by VOR-loaded nanomicelles demonstrates a promising approach for onychomycosis treatment. The novel methods for protein analysis were straightforward and helpful.

Onychomycosis: Current Understanding and Strategies for Enhancing Drug Delivery into Human Nail Tissue

BACKGROUND

Onychomycosis is by far the most common finger or toe nail fungal infectious disease caused by dermatophytes, non-dermatophytic molds or yeast. It accounts for 50% of the total nail disorders, and affects patients physically, socially, and psychologically and can seriously influence their quality of life.

OBJECTIVES

Oral antifungals are routinely used to treat the nail fungal disease; however oral therapy is associated with severe side effects and longer treatment times. In recent years, drug delivery directly into the nail or nail bed has gained attention and various topical products have been tested that can cure the disease when applied topically or transungually. Nevertheless, drug penetration into and through the nail is not straightforward and requires chemicals to improve its permeability or by applying physical stress to promote drug penetration into and through the nail. This lucid review presents an overview of various causes of onychomycosis, current therapeutic approaches, and efforts aimed at increasing the permeability of nails through various strategies such as chemical, physical and mechanical methods for permeation enhancement.

CONCLUSION

Various strategies have been proposed for the treatment of onychomycosis, however, much research into a more precise and effective therapy is still required.

Iontophoresis to Overcome the Challenge of Nail Permeation: Considerations and Optimizations for Successful Ungual Drug Delivery

Iontophoresis is a widely used drug delivery technique that has been used clinically to improve permeation through the skin for drugs and other actives in topical formulations. It is however not commonly used for the treatment of nail diseases despite its potential to improve transungual nail delivery. Instead, treatments for nail diseases are limited to relatively ineffective topical passive permeation techniques, which often result in relapses of nail diseases due to the thickness and hardness of the nail barrier resulting in lower permeation of the actives. Oral systemic antifungal agents that are also used are often associated with various undesirable side effects resulting in low patient compliance. This review article discusses what is currently known about the field of transungual iontophoresis, providing evidence of its efficacy and practicality in delivering drug to the entire surface of the nail for extended treatment periods. It also includes relevant details about the nail structure, the mechanisms of iontophoresis, and the associated in vitro and in vivo studies which have been used to investigate the optimal characteristics for a transungual iontophoretic drug delivery system. Iontophoresis is undoubtedly a promising option to treat nail diseases, and the use of this technique for clinical use will likely improve patient outcomes.Graphical abstract.

Co-delivery of terbinafine hydrochloride and urea with an in situ film-forming system for nail targeting treatment

Onychomycosis is a chronic nail disorder consisting of a fungal infection that causes physical and psychosocial discomfort to patients. However, its treatment remains challenging owing to the barrier of the highly keratinized nail plate and the short time that conventional formulations reside on nails. In this work, we developed an in situ film-forming system(IFFS) based on Eudragit® RLPO to co-deliver terbinafine hydrochloride (TBH) and urea, i.e., TBH-urea-RLPO IFFS, with the aim of overcoming the nail barrier, prolonging the residence time, and efficiently treating onychomycosis. The IFFS formulation formed a thin film with good appearance and adhesion upon application in situ. The physical states of TBH and urea in the film were evaluated with polarization microscopy and powder X-ray diffraction. TBH and urea were both amorphousmiscible components within the RLPO film. TBH release from TBH-urea-RLPO IFFS fitted to the Korsmeyer-Pappas model, and the cumulative release at 72 h was significantly higher than that from commercial preparations (Lamisil Pedisan® once). In vitro permeation of TBH from TBH-urea-RLPO IFFS through bovine hoof membranes was evaluated in comparison with the film containing TBH alone (TBH-RLPO) and commercial preparations. The retention and cumulative permeated amount of TBH were significantly enhanced for the TBH-urea-RLPO IFFS (170.80 ± 44.63 μg/cm²vs 75.49 ± 21.50 μg/cm²vs 60.25 ± 27.38 μg/cm²; 61.81 ± 16.09 μg/cm²vs 21.80 ± 11.56 μg/cm²vs 7.91 ± 1.03 μg/cm², respectively), and the membranes treated with different formulations were observed with SEM and FTIR to identify the denaturing effect of urea on bovine hoof keratin. In vitro antifungal tests against Trichophyton rubrum,Microsporum canis, Fusarium, and Aspergillus fumigatus were cultured on Muller-Hinton agar; the findings indicated that TBH-urea-RLPO IFFS enhanced TBH antifungal activity. Overall, the results support that TBH-urea-RLPO IFFS is an efficient and promising approach for onychomycosis targeting treatment.

Potential of Naftifine Application for Transungual Delivery

Naftifine is used to treat fungal skin infections as it inhibits dermatophytes, which are the cause of onychomycosis. However, naftifine's ability to permeate the human nail barrier has not been investigated, thus, the antimycotic potential is not clearly established. This work aims to evaluate the effect of penetration enhancing factors on the accumulation of naftifine hydrochloride through human nail clippings. Naftifine polymeric nail lacquers with Eudragit RL100 were developed as a suitable delivery system. Low penetration of naftifine into nail has been determined as less than 10% of applied drug dose accumulated in the nail layers. Incorporation of thioglycolic acid into formulations resulted in increased accumulation of antifungal agent in the nail layers by 100% compared with a control group. Salicylic acid did not effect naftifine accumulation in the human nail. The permeation of naftifine through the nail increased by threefold when the thioglycolic acid-containing formulation was applied and the nail was pretreated with a fractional CO2 laser. Structural changes of the nail barrier, induced by fractional CO2 laser, were visualized by microscopy. The results suggest, that naftifine nail penetration could be significantly increased when physical and chemical enhancing factors are applied.

Treatment and management strategies of onychomycosis

Onychomycosis is one of the most prevalent and severe nail fungal infections, which is affecting a wide population across the globe. It leads to variations like nail thickening, disintegration and hardening. Oral and topical drug delivery systems are the most desirable in treating onychomycosis, but the efficacy of the results is low, resulting in a relapse rate of 25-30%. Due to systemic toxicity and various other disadvantages associated with oral therapy like gastrointestinal, hepatotoxicity, topical therapy is commonly used. Topical therapy improves patient compliance and reduces the cost of treatment. However, due to poor penetration of topical therapy across the nail plate, research is focused on different chemical, mechanical and physical methods to improve drug delivery. Penetration enhancers like Thioglycolic acid, Hydroxypropyl-β-cyclodextrin (HP-β-CD), Sodium lauryl sulfate (SLS), carbocysteine, N-acetylcysteine etc. have shown results enhancing the drug penetration across the nail plate. Results with physical techniques such as iontophoresis, laser and Photodynamic therapy are quite promising, but the long-term suitability of these devices is in need to be determined. In this article, a brief analysis of the treatment procedures, factors affecting drug permeation across nail plate, chemical, mechanical and physical devices used to increase the drug delivery through nails for the onychomycosis management has been achieved.

Potential of Chemical and Physical Enhancers for Transungual Delivery of Amorolfine Hydrochloride

Topical monotherapy of nail infection is limited by poor drug permeability into the human nail plate. Numerous substances and methods are applied to improve the antifungal agent delivery across the nail plate. This work aimed to evaluate the effect of chemical and physical enhancers on the accumulation and permeation of amorolfine hydrochloride through human nail clippings. Polymeric nail lacquers with Eudragit E100 were developed as a potentially suitable delivery system for amorolfine hydrochloride. Incorporating thioglycolic acid and urea into formulations provided increased accumulation of antifungal agent in nail layers of up to 100% and 57%, respectively. Structural changes of nail barrier, induced by fractional CO₂ laser, were visualized by microscopy. The permeation of amorolfine hydrochloride through the nail increased twofold when thioglycolic acid-containing formulation was applied and the nail was pretreated with a fractional CO₂ laser. The results suggest that this novel combination of enhancers has the potential to be an effective option for topical drug delivery through the nail, and increased the efficacy of treatment.

Chemical and physical strategies in onychomycosis topical treatment: A review

Onychomycosis is a fungal infection of the fingernails or toenails caused by dermatophytes, nondermatophytes, moulds, and yeasts. This condition affects around 10-30% people worldwide, negatively influencing patients' quality of life, with severe outcomes in some cases. Since the nail unit acts as a barrier to exogenous substances, its physiological features hampers drug penetration, turning the onychomycosis treatment a challenge. Currently, there are several oral and topical therapies available; nevertheless, cure rates are still low and relapse rates achieves 10-53%. Also, serious side effects may be developed due to long-term treatment. In light of these facts, researchers have focused on improving topical treatments, either by modifying the vehicle or by using some physical technique to improve drug delivery trough the nail plate, hence increasing therapy effectiveness. Therefore, the aim of this paper is to explain these novel alternative approaches. First, the challenges for drug ungual penetration are presented. Then, the chemical and physical strategies developed for overcoming the barriers for drug penetration are discussed. We hope that the information gathered may be useful for the development of safer and more effective treatments for onychomycosis.

Voriconazole-loaded nanostructured lipid carriers (NLC) for drug delivery in deeper regions of the nail plate

Voriconazole-loaded nanostructured lipid carriers (VOR-NLC) were developed and drug penetration evaluated in porcine hooves in vitro. Synergistic effect of urea (Ur), selected among other known chemical enhancers according to hoof hydration potential, was also evaluated. VOR-NLC presented a high encapsulation efficiency (74.52±2.13%), approximate mean diameter of 230nm and were positively charged (+27.32±2.74mV). Stability studies indicated they were stable under refrigeration (4±2°C) for up to 150days. SEM images revealed hooves treated with VOR-NLC and VOR-NLC-Ur suffered a disturbance on the surface depicting high roughness and porosity. Permeation data showed a substantial VOR amount retained in superficial hooves sections independent of the formulation used (2.42±0.26; 2.52±0.36 and 2.41±0.60μg/cm² for unloaded VOR, VOR-NLC and VOR-NLC-Ur, respectively, p>0.05). Still, successive extractions, revealed the amount of VOR retained in deeper regions was significantly higher when VOR-NLC or VOR-NLC-Ur was used (0.17±0.04, 0.47±0.14 and 0.36±0.07μg/cm² for unloaded VOR, VOR-NLC and VOR-NLC-Ur, respectively, p<0.05). Such results indicate NLC are promising formulations for the management of onychomycosis. Further studies in diseased nail plates are necessary.

Understanding the formidable nail barrier: A review of the nail microstructure, composition and diseases

The topical treatment of nail fungal infections has been a focal point of nail research in the past few decades as it offers a much safer and focused alternative to conventional oral therapy. Although the current focus remains on exploring the ways of enhancing permeation through the formidable nail barrier, the understanding of the nail microstructure and composition is far from complete. This article reviews our current understanding of the nail microstructure, composition and diseases. A few of the parameters affecting the nail permeability and potential causes of the recurrence of fungal nail infection are also discussed.

Size and Charge Dependence of Ion Transport in Human Nail Plate

The electrical properties of human nail plate are poorly characterized yet are a key determinate of the potential to treat nail diseases, such as onychomycosis, using iontophoresis. To address this deficiency, molar conductivities of 17 electrolytes comprising 12 ionic species were determined in hydrated human nail plate in vitro. Cation transport numbers across the nail for 11 of these electrolytes were determined by the electromotive force method. Effective ionic mobilities and diffusivities at infinite dilution for all ionic species were determined by regression analysis. The ratios of diffusivities in nail to those in solution were found to correlate inversely with the hydrodynamic radii of the ions according to a power law relationship having an exponent of -1.75 ± 0.27, a substantially steeper size dependence than observed for similar experiments in skin. Effective diffusivities of cations in nail were 3-fold higher than those of comparably sized anions. These results reflect the strong size and charge selectivity of the nail plate for ionic conduction and diffusion. The analysis implies that efficient transungual iontophoretic delivery of ionized drugs having radii upward of 5 Å (molecular weight, ca. ≥ 340 Da) will require chemical or mechanical alteration of the nail plate.

Glycolic Acid peels for nail rejuvenation

Background:

With the increasing use of nail paints, nail art, acetone, repeated manicures, cosmetic nail procedures and detergents, the nail plate undergoes regular damage resulting in rough, lusterless and pigmented nails. Besides that onychomycosis, nail lichen planus, nail pitting and ridging due to various diseases also cause cosmetically disfiguring nails.

Objective:

The study is directed toward use of 70% glycolic acid for controlled keratolysis of the nail-plate, resulting that could result in shinier, smoother and brighter nails.

Materials and Methods:

A prospective single-center open-label uncontrolled study of 31 patients, 22 with dry, rough, discolored nails and 9 with hyperkeratotic nails were included in the study group. After examination and ruling out any infection, petroleum jelly was applied on the cuticle margins of the nails for protection and 70% glycolic acid was applied over the nail plate for 45 minutes. In dry rough discolored nails, only a single sitting was done while in hyper-keratotic nail conditions multiple weekly sittings were done.

Results:

In 22 patients with dry rough nails, 80% showed good improvement, 10% showed average improvement, whereas 10% were non-responsive. Nine patients with thickened nail plate showed good improvement in 60% average improvement in 25% improvement and 15% were non-responsive, after multiple sessions.

Conclusion:

Controlled keratolysis of the nail plate with application of 70% glycolic acid can be a promising treatment for modality for thick, uneven, rough and pigmented nail-plate conditions with cosmetically pleasing results.

Diffusion of uncharged solutes through human nail plate

Passive diffusion data for uncharged solutes in hydrated human nail plate are collected and compared to the predictions of two theories for diffusion of uncharged solutes in dense keratin matrices. Quantitative agreement between the experimental data and the theories examined is poor. Concerns with both the experiments and the theories are identified and discussed. It is evident from the analysis that magnitude of the experimental nail permeability data may be questioned, as may the extrapolation procedures used to estimate the properties of dense fiber arrays from more dilute systems. Despite these caveats, it can be inferred that the microstructure of the nail plate is more complex than that assumed in the described models. The influence of residual lipids is implicated. More rigorous experiments and theoretical analysis of mass transport in the nail plate system are warranted. Successful completion of these tasks could lead not only to better predictions of transungual drug delivery, but also to better models of skin permeability, if hydrated nail plate can indeed serve as a model for the corneocyte phase of (partially hydrated) stratum corneum.

Development of topical therapeutics for management of onychomycosis and other nail disorders: a pharmaceutical perspective

The human nail plate is a formidable barrier to drug permeation. Development of therapeutics for management of nail diseases thus remains a challenge. This article reviews the current knowledge and recent advances in the field of transungual drug delivery and provides guidance on development of topical/ungual therapeutics for management of nail diseases, with special emphasis on management of onychomycosis, the most common nail disease. Selection of drug candidates, drug delivery approaches, and evaluation of formulations are among the topics discussed. A comprehensive mathematical description for transungual permeation is also introduced.

Lateral drug diffusion in human nails

The main objective of the current work is to demonstrate the process of passive lateral diffusion in the human nail plate and its effect on the passive transungual permeation of antifungal drug ciclopirox olamine (CPO). A water soluble dye, methyl red sodium salt (MR) was used to visualize the process of lateral diffusion using a novel suspended nail experiment. The decline in concentration of CPO correlates with that of concentration of MR from the proximal to the distal end of the nail in suspended nail study. Three toenails each were trimmed to 5 mm × 5 mm (25 mm(2)), 7 mm × 7 mm (49 mm(2)), and 9 mm × 9 mm (81 mm(2)) to study the extent and effect of lateral diffusion of the CPO on its in vitro transungual permeation. The permeation flux of CPO decreased as the surface area of the toenail increased. There was a positive correlation between the concentrations of CPO and MR in the area of application and in the peripheral area of the toenails of the three surface areas, confirming the findings in the suspended nail experiment. Profound lateral diffusion of CPO was demonstrated and shown to reduce the in vitro passive transungual drug permeation and prolong the lag-time in human toenails. The study data implies that during passive in vitro transungual permeation experiments, the peripheral nail around the area of drug application has to be kept to a minimum, in order to get reliable data which mimics the in vivo situation.

Hydroxypropyl- β -cyclodextrin: A Novel Transungual Permeation Enhancer for Development of Topical Drug Delivery System for Onychomycosis

The treatment of onychomycosis is a challenging task because of unique barrier properties of the nail plate which hampers the passage of antifungal drugs in a concentration required to eradicate the deeply seated causative fungi in the nail bed. In present investigation, application of hydroxypropyl-β-cyclodextrin (HP-β-CD) was established as an effective and nail friendly transungual drug permeation enhancer especially for poorly water soluble drugs using terbinafine hydrochloride as a poorly soluble drug. HP-β-CD significantly improves hydration of nail plates and increases solubility of terbinafine hydrochloride in the aqueous environment available therein, which leads to uninterrupted drug permeation through water filled pores of hydrogel-like structure of hydrated nail plates. A nail lacquer formulation was designed with an objective to deliver the drug in an effective concentration across nail plates, using HP-β-CD as a permeation enhancer. The formulations containing HP-β-CD showed higher flux than the control formulation in in vitro drug permeation study. The formulation containing 10% w/v of HP-β-CD showed maximum flux of 4.586 ± 0.08 μg/mL/cm² as compared to the control flux of 0.868 ± 0.06 μg/mL/cm². This finding supports application of HP-β-CD as an effective permeation enhancer for transungual delivery of terbinafine hydrochloride and possibly other poorly water soluble drugs where HP-β-CD can act as a solubilizer.

Insights into drug delivery across the nail plate barrier

Topical therapy is at the forefront in treating nail ailments (especially onychomycosis and nail psoriasis) due to its local effects, which circumvents systemic adverse events, improves patient compliance and reduces treatment cost. However, the success of topical therapy has been hindered due to poor penetration of topical therapeutics across densely keratinized nail plate barrier. For effective topical therapy across nail plate, ungual drug permeation must be enhanced. Present review is designed to provide an insight into prime aspects of transungual drug delivery viz. nail structure and physiology, various onychopathies, techniques of nail permeation enhancement and in vitro models for trans-nail drug permeation studies. Updated list of drug molecules studied across the nail plate and key commercial products have been furnished with sufficient depth. Patents pertinent to, and current clinical status of transungual drug delivery have also been comprehensively reviewed. This is the first systematic critique encompassing the detailed aspects of transungual drug delivery. In our opinion, transungual drug delivery is a promising avenue for researchers to develop novel formulations, augmenting pharmaceutical industries to commercialize the products for nail disorders.

Hydration of nail plate: a novel screening model for transungual drug permeation enhancers

Drug delivery by topical route for the treatment of onychomycosis, a nail fungal infection, is challenging due to the unique barrier properties of the nail plate which imparts high resistance to the passage of antifungal drugs. Permeation enhancers are used in transungual formulations to improve the drug flux across the nail plate. Selection of the effective permeation enhancer among the available large pool of permeation enhancers is a difficult task. Screening the large number of permeation enhancers using conventional Franz diffusion cells is laborious and expensive. The objective of present study was to evolve a simple, accurate and rapid method for screening of transungual drug permeation enhancers based on the principle of hydration of nail plate. The permeation enhancer which affects the structural or physicochemical properties of nail plate would also affect their hydration capacity. Two screening procedures namely primary and secondary screenings were evolved wherein hydration and uptake of ciclopirox olamine by nail plates were measured. Hydration enhancement factor, HEF(24) and drug uptake enhancement factor, UEF(24) were determined for screening of 23 typical permeation enhancers. The Pearson's correlation coefficient between HEF(24) and UEF(24) was determined. A good agreement between the HEF(24) and UEF(24) data proved the validity of the proposed nail plate hydration model as a screening technique for permeation enhancers.

The human nail--barrier characterisation and permeation enhancement

The human nail remains one of the most challenging membranes for formulation scientists to target and for clinicians to heal. Its formidable barrier properties are the primary reason that oral therapy remains the primary approach to manage ungual infections. This article considers the major structural properties underlying the excellent barrier function of the nail, with particular emphasis on the role of biophysical methods in advancing our knowledge of this appendage. Formulations currently available for management of ungual disease are discussed and their therapeutic efficacy is assessed. Finally, experimental strategies to enhance ungual permeation are reviewed and prospects for future developments in the field are considered.

Iontophoretic drug delivery across the nail

INTRODUCTION

Topical drug delivery to treat nail diseases such as onychomycosis and psoriasis is receiving increasing attention. Topical nail delivery is challenged by the complicated structure of the nail and the low permeability of most drugs across the nail plate. Considerable effort has been directed at developing methods to promote drug permeation across the nail plate. Iontophoresis efficiently enhances molecular transport across the skin and the eye and is now being tested for its potential in ungual delivery.

AREAS COVERED

This review covers the basic mechanisms of transport (electro-osmosis and -migration) and their relative contribution to nail iontophoresis as well as the key factors governing nail permselectivity and ionic transport numbers. Methodological issues concerning research in this area are summarized. The data available in vivo on nail iontophoresis of terbinafine specifically are reviewed in separate sections.

EXPERT OPINION

Our understanding of nail iontophoresis has improved considerably since 2007; most decisively, the feasibility of nail iontophoresis in vivo has been clearly demonstrated. Future work is required to establish the adequate implementation of the technique so that its clinical efficacy to treat onychomycosis and nail psoriasis can be unequivocally determined.

Effects of organic solvents on the barrier properties of human nail

The effects of organic solvent systems on nail hydration and permeability have not been well studied. The objectives of the present study were to investigate the effects of binary aqueous organic solvent systems of ethanol (EtOH), propylene glycol (PPG), and polyethylene glycol 400 (PEG) on the barrier properties of nail plates. (3) H-water, (14) C-urea, and (14) C-tetraethylammonium ions were the probes in the nail uptake and transport experiments to study the effect(s) of organic solvents on nail hydration and permeability. Gravimetric studies were also performed as a secondary method to study nail hydration and the reversibility of the nail after organic solvent treatments. Both ungual uptake and transport were directly related to the concentration of the organic solvent in the binary systems. Partitioning of the probes into and transport across the nail decreased with an increase in the organic solvent concentration. These changes corresponded to the changes in solution viscosity and the barrier properties of the nail. In general, the effects for PPG and PEG were more pronounced than those for EtOH. Practically, these results suggest that organic solvents in formulations can increase nail barrier resistivity.

Time-dependent electrical properties of human nail upon hydration in vivo

The objectives of this study were to investigate the effects of hydration and solution ion concentration on the electrical properties of human nail in vivo and compare these in vivo results with those in vitro. In vivo electrical resistance measurements on the nail were conducted with a three-electrode system in phosphate buffered saline of 0.01-0.6 M. The effect of electric current on nail resistance and possible adverse effects were studied under 1.5- and 9-V iontophoresis in vivo. The electrical resistance of the nail plate was measured in vitro in side-by-side diffusion cells under the same conditions and compared with those in vivo. The in vivo electrical resistance decreased significantly upon 2-h nail hydration and then slowly decreased to a constant value, showing the same pattern as that in vitro. No significant effect of the applied voltage upon the nail electrical resistance was observed. Higher current densities caused moderate sensation and slight changes in nail appearance after iontophoresis. The observed decrease in nail resistance demonstrates the significance of nail hydration in transungual iontophoresis. The in vitro and in vivo correlation suggests that the in vitro nail plate can be a model in the research and development of transungual iontophoretic delivery.

Influence of pH on transungual passive and iontophoretic transport

The present study investigated the effects of pH on nail permeability and the transport of ions such as sodium (Na) and chloride (Cl) ions endogenous to nail and hydronium and hydroxide ions present at low and high pH, which might compete with drug transport across hydrated nail plate during iontophoresis. Nail hydration and passive transport of water across the nail at pH 1-13 were assessed. Subsequently, passive and iontophoretic transport experiments were conducted using (22)Na and (36)Cl ions under various pH conditions. Nail hydration was independent of pH under moderate pH conditions and increased significantly under extreme pH conditions (pH >11). Likewise, nail permeability for water was pH independent at pH 1-10 and an order of magnitude higher at pH 13. The results of passive and iontophoretic transport of Na and Cl ions are consistent with the permselective property of nail. Interestingly, extremely acidic conditions (e.g., pH 1) altered nail permselectivity with the effect lasting several days at the higher pH conditions. Hydronium and hydroxide ion competition in iontophoretic transport was generally negligible at pH 3-11 was significant at the extreme pH conditions studied.

Ungual and trans-ungual iontophoretic delivery of terbinafine for the treatment of onychomycosis

The application of iontophoresis was demonstrated in the nail drug delivery of terbinafine (TH) recently. This study explored a systematic assessment of this approach to enhance the drug delivery using a novel topical formulation, and the subsequent release of TH from the drug loaded nails. For the first time, a nail on-agar plate model was used to study the release of drug from the iontophoresis (0.5 mA/cm(2)) loaded nails. In addition, the activity of the drug released from the drug loaded nail plate was studied against Trichophyton rubrum. An increase in applied current density and current duration enhanced the transport of TH into and through the nail plate. In vitro release of drug from the iontophoretic loaded nails into agar plates exhibited 2-phase release pattern. The amount of drug released in both of the in vitro models was comparable, and the nails loaded using iontophoresis continued to release levels of TH > 2 orders of magnitude above the minimum inhibitory concentration over at least 52 days. Results indicate that iontophoresis enhances the delivery of terbinafine into and through the nail plate and suggest that the use of this treatment approach could result in a safe and more efficacious outcome with less frequent treatments.

A study on the effect of inorganic salts in transungual drug delivery of terbinafine

Objectives

The poor success rate of topical therapy in nail disorders is mainly because of the low permeability of keratinized nail plates. This can be overcome by utilizing potent perungual drug penetration enhancers that facilitate the drug permeation across the nail plate. This study evaluated the efficacy of inorganic salts in enhancing the trans-nail permeation using a model potent antifungal agent, terbinafine hydrochloride.

Methods

Permeation studies were carried out across human cadaver nail in a Franz diffusion cell using terbinafine solution (1 mg/ml; pH 3). Preliminary studies were carried out to assess the effect of salts (0.5 m) on the terbinafine permeation into and through the nail. Further, the influence of salt concentration (0.25–3 m) on permeation, the mechanism for the enhancement and the suitability of developing a formulation were also studied.

Key findings

Terbinafine permeation (3–5 fold) through the nail and drug load (4–7 fold) in the nail were enhanced significantly when salts were used at 0.5 m concentration. Increase in salt concentration up to 1 m increased the permeation, which decreased with further increase in salt concentration (&gt;1 m). Mechanistic studies revealed that the enhanced permeation by salts was mainly due to their ability to increase the nail hydration and also to increase the thermodynamic activity of the drug. The cumulative amount of terbinafine permeated at 24 h from the formulated gel (9.70 ± 0.93 μg/cm2) was comparable with that of a solution (11.45 ± 1.62 μg/cm2).

Conclusions

Given the promising results from the permeation and drug load studies, it was concluded that inorganic salts could be used as potent transungual permeation enhancers.

Iontophoretically enhanced ciclopirox delivery into and across human nail plate

Transungual delivery of antifungal drugs is hindered by the low permeability of human nail plates, and as such, repeated dosing over a long period of time is necessary for effective treatment. The objectives of this study were to explore the possibilities of (a) enhancing the delivery of ciclopirox (CIC) across human nail plates and (b) sustaining CIC delivery from the larger resultant drug depot in the nail plates with constant voltage iontophoresis. In vitro passive and 9 V cathodal iontophoretic transport experiments of CIC across human nails were performed. Transungual CIC delivery with Penlac was the control. The amounts of CIC released from and deposited in the nails were determined in drug release and extraction experiments, respectively. Iontophoresis increased the flux of CIC permeated across the nail approximately 10 times compared to passive delivery from the same formulation or from Penlac. A significant amount of CIC was loaded into and released from the nails; the CIC concentrations were estimated to be above the minimum inhibitory concentrations of CIC for dermatophytic molds. The apparent transport lag time decreased in iontophoretic transport. The results demonstrate that iontophoresis was able to deliver an effective amount of CIC into and across the nails, and this suggests the feasibility of a constant voltage battery-powered transungual iontophoretic device.

An ex vivo toe model used to assess applicators for the iontophoretic ungual delivery of terbinafine

PURPOSE

An ex vivo intact toe model was developed to assess two different applicator designs for iontophoretic delivery of terbinafine into the nail only or the nail and surrounding skin.

METHODS

Iontophoretic permeation studies were carried out on intact cadaver toes using nail-only and nail/skin applicators with a current dose of 10 mA*min (0.5 mA for 20 min).

RESULTS

Iontophoresis enhanced drug permeation and tissue loading with both applicators tested. Greater drug delivery was observed with the nail/skin applicator due to the additional terbinafine being delivered directly through the lower impedance skin area surrounding the nail. The concentration of drug loaded into the contact area of the nail with the nail-only and nail/skin applicator was ~13 and ~7 fold higher than their respective passive delivery levels but equivalent from each other in total drug mass delivered over the whole nail plate. In vitro release of drug from the iontophoretically loaded nails into agar suggests that a single treatment could have a prolonged effect (>50 days).

CONCLUSIONS

This study demonstrates that the ex vivo toe model was useful in assessing the functionality of the different applicator designs. These results suggest that iontophoresis can significantly enhance the delivery of drugs to both the hard and soft tissues of the toe for the treatment of onychomycosis and other nail disorders.

Alteration of the diffusional barrier property of the nail leads to greater terbinafine drug loading and permeation

The diffusional barrier property of biological systems varies with ultrastructural organization of the tissues and/or cells, and often plays an important role in drug delivery. The nail plate is a thick, hard and impermeable membrane which makes topical nail drug delivery challenging. The current study investigated the effect of physical and chemical alteration of the nail on the trans-ungual drug delivery of terbinafine hydrochloride (TH) under both passive and iontophoretic conditions. Physical alterations were carried out by dorsal or ventral nail layer abrasion, while chemical alterations were performed by defatting or keratolysis or ionto-keratolysis of the nails. Terbinafine permeation into and across the nail plate following various nail treatments showed similar trends in both passive and iontophoretic delivery, although the extent of drug delivery varied with treatment. Application of iontophoresis to the abraded nails significantly improved (P<0.05) TH permeation and loading compared to abraded nails without iontophoresis or normal nails with iontophoresis. Drug permeation was not enhanced when the nail plate was defatted. Keratolysis moderately enhanced the permeation but not the drug load. Ionto-keratolysis enhanced TH permeation and drug load significantly (P<0.05) during passive and iontophoretic delivery as compared to untreated nails. Ionto-keratolysis may be more efficient in permeabilization of nail plates than long term exposure to keratolysing agents.

Effects of ionic strength on passive and iontophoretic transport of cationic permeant across human nail

PURPOSE

Transport across the human nail under hydration can be modeled as hindered transport across aqueous pore pathways. As such, nail permselectivity to charged species can be manipulated by changing the ionic strength of the system in transungual delivery to treat nail diseases. The present study investigated the effects of ionic strength upon transungual passive and iontophoretic transport.

METHODS

Transungual passive and anodal iontophoretic transport experiments of tetraethylammonium ion (TEA) were conducted under symmetric conditions in which the donor and receiver had the same ionic strength in vitro. Experiments under asymmetric conditions were performed to mimic the in vivo conditions. Prior to the transport studies, TEA uptake studies were performed to assess the partitioning of TEA into the nail.

RESULTS

Permselectivity towards TEA was inversely related to ionic strength in both passive and iontophoretic transport. The permeability and transference number of TEA were higher at lower ionic strengths under the symmetric conditions due to increased partitioning of TEA into the nail. Transference numbers were smaller under the asymmetric conditions compared with their symmetric counterparts.

CONCLUSIONS

The results demonstrate significant ionic strength effects upon the partitioning and transport of a cationic permeant in transungual transport, which may be instrumental in the development of transungual delivery systems.