Iontophoretically enhanced ciclopirox delivery into and across human nail plate

Utility of devices for onychomycosis: a review

Onychomycosis is difficult to treat due to long treatment durations, poor efficacy rates of treatments, high relapse rates, and safety issues when using systemic antifungal agents. Device-based treatments are targeted to specific regions of the nail, have favorable safely profiles, and do not interfere with systemic agents. They may be an effective alternative therapy for onychomycosis especially with increasing reports of squalene epoxidase gene mutations and potential resistance to terbinafine therapy. In this review, we discuss four devices used as antifungal treatments and three devices used as penetration enhancers for topical agents. Lasers, photodynamic therapy, microwaves, and non-thermal plasma have the capacity to inactivate fungal pathogens demonstrated through in vivo studies. Efficacy rates for these devices, however, remain relatively low pointing toward the need to further optimize device or usage parameters. Ultrasound, nail drilling, and iontophoresis aid in improving the permeability of topical agents through the nail and have been investigated as adjunctive therapies. Due to the paucity in clinical data, their efficacy in treating onychomycosis has not yet been established. While the results of clinical studies point toward the potential utility of devices for onychomycosis, further large-scale randomized clinical trials following regulatory guidelines are required to confirm current results.

Design, Development, and Evaluation of Constant Voltage Iontophoresis for the Transungual Delivery of Efinaconazole

The efficacy of topical antifungal therapy in onychomycosis has been hindered by the failure of the antimycotic to permeate the nail plate. This research aims to design and develop a transungual system for the effective delivery of efinaconazole utilizing constant voltage iontophoresis. Seven prototype drug-loaded hydrogel formulations (E1-E7) were prepared to assess the influence of solvent (ethanol) and cosolvent (Labrasol^®) on transungual delivery. Optimization was performed to evaluate the effect of three independent variables; voltage, solvent-to-cosolvent ratio, and penetration enhancer (PEG 400) concentration on critical quality attributes (CQAs), such as drug permeation and loading into the nail. The selected hydrogel product was characterized for pharmaceutical properties, efinaconazole release from the nail, and antifungal activity. Preliminary data indicates ethanol, Labrasol^®, and voltage influence the transungual delivery of efinaconazole. Optimization design indicates a significant impact by applied voltage (p-0.0001) and enhancer concentration (p-0.0004) on the CQAs. Excellent correlation between selected independent variables and CQAs was confirmed by the high desirability value (0.9427). A significant (p < 0.0001) enhancement in the permeation (~78.59 µg/cm²) and drug loading (3.24 µg/mg) was noticed in the optimized transungual delivery with 10.5 V. FTIR spectral data indicates no interaction between the drug and excipients, while the DSC thermograms confirmed the amorphous state of the drug in the formulation. Iontophoresis produces a drug depot in the nail that releases above the minimum inhibitory concentration level for an extended period, potentially reducing the need for frequent topical treatment. Antifungal studies further substantiate the release data and have shown remarkable inhibition of Trichophyton mentagrophyte. Overall, the promising results obtained here demonstrate the prospective of this non-invasive method for the effective transungual delivery of efinaconazole, which could improve the treatment of onychomycosis.

Iontophoresis application for drug delivery in high resistivity membranes: nails and teeth

Iontophoresis has been vastly explored to improve drug permeation, mainly for transdermal delivery. Despite the skin's electrical resistance and barrier properties, it has a relatively high aqueous content and is permeable to many drugs. In contrast, nails and teeth are accessible structures for target drug delivery but possess low water content compared to the skin and impose significant barriers to drug permeation. Common diseases of these sites, such as nail onychomycosis and endodontic microbial infections that reach inaccessible regions for mechanical removal, often depend on time-consuming and ineffective treatments relying on drug's passive permeation. Iontophoresis application in nail and teeth structures may be a safe and effective way to improve drug transport across the nail and drug distribution through dental structures, making treatments more effective and comfortable for patients. Here, we provide an overview of iontophoresis applications in these "hard tissues," considering specificities such as their high electrical resistivity. Iontophoresis presents a promising option to enhance drug permeation through the nail and dental tissues, and further developments in these areas could lead to widespread clinical use.

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.

Influence of a Combination of Chemical Enhancers and Iontophoresis on In Vitro Transungual Permeation of Nystatin

To promote transungual permeation of nystatin (NYST), molecule with high molecular weight, no water-soluble, amphoteric by iontophoresis. The synergic effect of the combination of cetylpyridinium chloride, CPC, or polyoxyethylene (20) sorbitan monooleate, TW80, and iontophoresis was investigated. In vitro permeation experiments were carried out through bovine hoof slices using vertical diffusion cells. A low current density (0.2 mA/cm²) was applied by introducing Ag/AgCl electrodes in the donor (anode) and receptor (cathode) chambers. The donor phase consisted of a solution, a suspension, or gel-type vehicles containing NYST and surfactants in pH 5.6 HEPES buffer. The addition of CPC to NYST suspension (SOSP) produced a fivefold increase on the permeability of the bovine hoof membrane to the drug. The application of anodal iontophoresis further improved NYST flux. Conversely, NYST transungual permeation was not influenced by TW80 either in the passive diffusion or iontophoretic flux. Furthermore, the iontophoretic treatment does not appear to induce irreversible alterations to the hoof bovine membranes. The present work demonstrated the efficacy of iontophoresis as a treatment for different nail pathologies with large molecules very slightly soluble in water without irreversibly affecting the nail structure. A synergistic effect between CPC and iontophoresis was observed.

Microstructural alterations in the onychomycotic and psoriatic nail: Relevance in drug delivery

Despite the important nail alterations caused by onychomycosis and psoriasis few studies have characterized the microstructure of the diseased nail plate and the diffusion and penetration of drugs through this altered structure. This work aimed to characterize the microstructure of the healthy, onychomycotic and psoriatic human nail using Raman spectroscopy, scanning electron microscopy, optical microscope profilometry and mercury intrusion porosimetry followed by analysis of the structure with PoreCor® software. The results showed that onychomycotic nails have higher porosity and lower amounts of disulphide bonds compared to healthy nails. This suggests that the presence and action of fungi on the nail plate makes this structure more permeable to water and drugs. Psoriatic nails had increased porosity compared to healthy nails but lower than fungal infected specimens. In vitro permeation studies showed that diseased nails were more permeable to ciclopirox (onychomycosis) and clobetasol (psoriasis) although drug permeation was highly variable and likely to be influenced by the degree of alteration of the nail structure. On the whole, this work provides new and valuable information about the microstructure and porosity of diseased nails and a plausible explanation of the increased drug permeability observed in this work and elsewhere.

Trans-ungual Delivery of AR-12, a Novel Antifungal Drug

AR-12 is a novel small molecule with broad spectrum antifungal activity. Recently, AR-12 was found to be highly active against Trichophyton rubrum, one of the predominantly responsible organisms that cause onychomycosis. The primary objective of this project was to investigate the ability of AR-12 to penetrate into and across the human nail plate followed by improving its trans-ungual permeation using different penetration enhancers. TranScreen-N™, a high throughput screening method was utilized to explore the potential nail penetration enhancers to facilitate the drug delivery through the nail. This screen demonstrated that dexpanthenol and PEG 400 were the most efficient enhancers. The in vitro permeation studies were performed across the human cadaver nail plates for 7 days with three AR-12 (5% w/v) formulations containing 10% w/v dexpanthenol (Formulation A), 10% w/v PEG 400 (Formulation B), and a combination of 10% w/v dexpanthenol + 10% w/v PEG 400 (Formulation C). The in vitro studies concluded that dexpanthenol and PEG 400 were able to deliver a significant amount of AR-12 into and across the nail plate that was found to be more than MIC 50 level of the drug.

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.

Improving Cure Rates in Onychomycosis

Background:

Onychomycosis is a persistent fungal nail infection that is notoriously hard to treat. Approximately 20% to 25% of patients with onychomycosis do not respond to treatment, and 10% to 53% of patients relapse. As such, successful treatment is imperative for long-term disease management.

Objective:

To identify ways to improve cure rates for onychomycosis.

Method:

The literature on onychomycosis treatment and recurrence was reviewed to summarize treatment approaches and suggest strategies to increase cure rates.

Results and Conclusion:

To improve treatment success in onychomycosis, we suggest the following measures be followed: (1) onychomycosis must be correctly diagnosed, (2) the treatment regimen should be tailored to the individual patient, (3) the efficacy of antifungals must be maximized, and (4) recurrence must be prevented.

Iontophoresis for drug delivery into the nail apparatus: exploring hyponychium as the site of delivery

In present studies, a hyponychium pathway (from ventral side of the nail plate) was investigated as a potential route of drug delivery into the nail apparatus using iontophoresis as an active physical method. In vitro transport studies were performed across the human nail plate using sodium fluorescein as a marker substrate for 24 h. After transport studies, the amount of sodium fluorescein extracted from an active diffusion area of the nail plate in case of iontophoresis was found to be ∼54-folds more to that of passive. The amount of sodium fluorescein retained in the peripheral area of the nail plate after application of iontophoresis was found to be ∼30-folds more relative to passive. Ex vivo transport studies were performed on excised human cadaver toe using terbinafine hydrochloride as a model drug for three days (8 h/day). The amount of terbinafine retained in the nail plate after application of iontophoresis (3.43 ± 1.34 µg/mg) was ∼20-folds more when compared with passive (0.17 ± 0.10 µg/mg). The amount of drug extracted from the nail bed and nail matrix was 1.73 ± 0.12 µg/mg and 0.55 ± 0.22 µg/mg, respectively. On the other hand, there was no detectable amount of terbinafine found in the nail bed and nail matrix in case of control (passive delivery). These studies show that the iontophoretic drug delivery through hyponychium region to other parts of the nail apparatus could be a potential way of onychomycosis treatment.

Transungual permeation: current insights

Nail disorders are beyond cosmetic concern; besides discomfort in the performance of daily chores, they disturb patients psychologically and affect their quality of life. Fungal nail infection (onychomycosis) is the most prevalent nail-related disorder affecting a major population worldwide. Overcoming the impenetrable nail barrier is the toughest challenge for the development of efficacious topical ungual formulation. Sophisticated techniques such as iontophoresis and photodynamic therapy have been proven to improve transungual permeation. This article provides an updated and concise discussion regarding the conventional approach and upcoming novel approaches focused to alter the nail barrier. A comprehensive description regarding preformulation screening techniques for the identification of potential ungual enhancers is also described in this review while highlighting the current pitfalls for the development of ungual delivery.

Progressive development in experimental models of transungual drug delivery of anti-fungal agents

Pre-clinical development comprises of different procedures that relate drug discovery in the laboratory for commencement of human clinical trials. Pre-clinical studies can be designed to recognize a lead candidate from a list to develop the procedure for scale-up, to choose the unsurpassed formulation, to determine the frequency, and duration of exposure; and eventually make the foundation of the anticipated clinical trial design. The foremost aim in the pharmaceutical research and industry is the claim of drug product quality throughout a drug's life cycle. The particulars of the pre-clinical development process for different candidates may vary; however, all have some common features. Typically in vitro, in vivo or ex vivo studies are elements of pre-clinical studies. Human pharmacokinetic in vivo studies are often supposed to serve as the 'gold standard' to assess product performance. On the other hand, when this general assumption is revisited, it appears that in vitro studies are occasionally better than in vivo studies in assessing dosage forms. The present review is compendious of different such models or approaches that can be used for designing and evaluation of formulations for nail delivery with special reference to anti-fungal agents.

Microemulsion-based antifungal gel delivery to nail for the treatment of onychomycosis: formulation, optimization, and efficacy studies

Onychomycosis is the most common nail disease affecting nail plate and nail bed. Onychomycosis causes onycholysis which creates cavity between the nail plate and nail bed, where drug formulations could be applied, providing a direct contact of drug with the nail bed facilitating drug delivery on the infected area. The purpose of the present study was to design and evaluate the potential of microemulsion-based gel as colloidal carrier for itraconazole for delivery into onycholytic nails for effective treatment of onychomycosis. Itraconazole-loaded microemulsions were prepared and optimized using D-optimal design. The microemulsion containing 6.24 % oil, 36 % Smix, and 57.76 % water was selected as the optimized batch (MEI). The globule size and drug loading of the optimized batch were 48.2 nm and 12.13 mg/ml, respectively. Diffused reflectance FTIR studies were performed to study drug-excipient incompatibility. Ex vivo permeation studies were carried out using bovine hoof and human cadaver skin as models for nail plate and nail bed, respectively. Microemulsion-based itraconazole gel (MBGI) showed better penetration and retention in human skin as well as bovine hoof as compared to commercial preparation (market formulation, MFI). The cumulative amount of itraconazole permeated from the MBGI after 12 h was 73.39 ± 3.55 μg cm(-2) which was 1.8 times more than MF. MBGI showed significantly higher ex vivo antifungal activity (P < 0.05) against Candida albicans and Trichophyton rubrum when compared to MFI. Stability studies showed that MBGI was stable at refrigeration and room temperature for 3 months. It was concluded that drug-loaded gel could be a promising formulation for effective treatment of onychomycosis.

Trans-ungual delivery of itraconazole hydrochloride by iontophoresis

Itraconazole (ITR) is a potent antifungal drug. However, poor aqueous solubility limits its permeation ability across the human nail plate. Therefore, in this project, ITR was converted to hydrochloride salt (ITR-HCl) to improve its solubility and to render it amenable to iontophoresis. ITR-HCl was characterized by spectroscopic methods and antifungal efficacy was evaluated in comparison to the base. In vitro and ex vivo transport studies (passive and iontophoresis) were carried out across the porcine hoof membrane and excised human cadaver toe using two different protocols; continuous delivery of drug for 24 h and pulsed delivery of drug for 3 days (8 h/day). The antifungal efficacy of ITR-HCL was comparable to ITR. Iontophoresis was found to be more effective than passive mode of delivery of ITR-HCL. In both iontophoresis as well as passive mode of delivery, the pulsed protocol resulted in more ungual and trans-ungual delivery of drug than continuous protocol. ITR-HCL could be delivered into and across the nail plate by iontophoresis. Human cadaver toe appears to be a good model to investigate the ungual delivery of drugs.

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.

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.

A comprehensive study to evaluate the effect of constant low voltage iontophoresis on transungual delivery

Treatment of nail diseases by topical drug delivery continues to draw much attention in the recent days. This study aims to systematically investigate the effect of constant voltage iontophoresis in the transungual drug delivery, using ciclopirox as a model drug. Preliminary permeation studies were carried out by applying constant voltage (6 V for 24 h) using a gel formulation across the human nail plate in a Franz diffusion cell. Different protocols have been studied to authenticate the potential of the proposed technique. Antifungal studies were carried out to assess the pharmacodynamic effect of drug depot formed in the nail plate. Initial studies revealed that application of constant voltage iontophoresis enhanced the permeation by an order of magnitude (p = 0.019) and delivered significant amount of drug into the deeper nail layers. Noticeably higher permeation was observed during the active phase in on-off studies. Excellent correlation was observed in permeation (r(2) = 0.98) and drug load (r(2) = 0.97) with the increase in applied voltage (3-12 V), indicating that the current technique is predictable. The data observed suggest that any further increase in voltage could eventually lead to increase in the permeation and drug load, as the saturation level is very distant. Furthermore, the enhancement in permeation with the applied voltage (3-12 V) was found to be 6-20 folds, compared to the passive process. Results of step up and step down studies substantiated the viability of the current technique. Zone of inhibition measured during the antifungal studies demonstrated that the drug molecules loaded into the nail plate by low voltage iontophoresis is active and releases over an extended period of time (~32 days). Given the excellent results, the current technique could be used as an effective approach for the delivery of antimycotics, which would localize the drug at the infection site and potentially offer higher patient compliance.

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.

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.

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.