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

Therapeutic treatment strategies for the management of onychomycosis: a patent perspective

INTRODUCTION

Onychomycosis, a multifactorial fungal infection of the nails, shows a global prevalence of about 5.5% and is responsible for 50% of all nail infections. To develop effective management strategies, it is necessary to understand the etiology, pathophysiology, and risk factors of onychomycosis. Oral route of drug delivery is one of the routes utilized to deliver anti-fungal agents, but, has its own limitations like longer duration of treatment, increased adverse effects, and potential for drug interaction. The ungual route has received greater attention due to its localized, non- invasive action and improved patient compliance.

AREAS COVERED

This review comprehensively discusses conventional onychomycosis therapies and patented novel drug delivery systems for the management of onychomycosis including chemical permeation enhancers, non-particulate drug delivery systems, penetration enhancing devices etc., Databases such as PubMed, ResearchGate, and Google Patents were searched by using the keywords onychomycosis and trans-ungual drug delivery.

EXPERT OPINION

Enormous research has been conducted and is still ongoing to find the best possible novel drug delivery system for onychomycosis management. Approaches like incorporation of herbal constituents in nano-formulations, inkjet printing, laser devices, iontophoretic techniques, etc. can be employed to make safe and effective drug delivery systems which are regulatory compliant.

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.

Quality by Design Guided Development of Polymeric Nanospheres of Terbinafine Hydrochloride for Topical Treatment of Onychomycosis Using a Nano-Gel Formulation

Superficial fungal diseases of the skin and nails are an increasingly common occurrence globally, requiring effective topical treatment to avoid systemic adverse effects. Polymeric nanoparticles have demonstrated sustained and effective drug delivery in a variety of topical formulations. The aim of this project was to develop polymeric antifungal nanospheres containing terbinafine hydrochloride (TBH) to be loaded into a hydrogel formulation for topical nail drug delivery. A quality by design (QbD) approach was used to achieve optimized particles with the desired quality target product profile (QTPP). Polyvinyl alcohol (PVA) at 2% w/v and a drug to polymer ratio of 1:4, together with a robust set of processes and material attributes, resulted in nanoparticles of 108.7 nm with a polydispersity index (PDI) of 0.63, 57.43% recovery, and other desirable characteristics such as zeta potential (ZP), particle shape, aggregation, etc. The nanospheres were incorporated into a carbomer-based gel, and the delivery of TBH through this formulation was evaluated by means of in vitro drug release testing (IVRT) and ex vivo nail permeation study. The gel containing the TBH nanospheres demonstrated a slower and controlled drug release profile compared with the control gel, in addition to a more efficient delivery into the nail. These antifungal nanospheres can be utilized for topical therapy of a multitude of superficial fungal infections.

Fractional CO2 laser ablation leads to enhanced permeation of a fluorescent dye in healthy and mycotic nails-An imaging investigation of laser-tissue effects and their impact on ungual drug delivery

Purpose

Conventional oral antifungal therapies for onychomycosis (OM) often do not achieve complete cure and may be associated with adverse effects, medical interactions, and compliance issues restricting their use in a large group of patients. Topical treatment can bypass the systemic side effects but is limited by the physical barrier of the nail plate. Ablative fractional laser (AFL) treatment can be used to improve the penetration of topical drugs into the nail. This study visualized the effects of laser ablation of nail tissue and assessed their impact on the biodistribution of a fluorescent dye in healthy and fungal nail tissue.

Methods

For the qualitative assessment of CO₂ AFL effects on healthy nail tissue, scanning electron microscopy (SEM), coherent anti‐Stokes Raman scattering microscopy (CARS‐M), and widefield fluorescence microscopy (WFM) were used. To quantitate the effect of laser‐pretreatment on the delivery of a fluorescent dye, ATTO‐647N, into healthy and fungal nail tissue, ablation depth, nail plate thickness, and ATTO‐647N fluorescence intensity in three nail plate layers were measured using WFM. A total of 30 nail clippings (healthy n = 18, fungal n = 12) were collected. An aqueous ATTO‐647N solution was directly applied to the dorsal surface of 24 nail samples (healthy n = 12, fungal n = 12) and incubated for 4 hours, of which half (healthy n = 6, fungal n = 6) had been pretreated with AFL (30 mJ/mb, 15% density, 300 Hz, pulse duration <1 ms).

Results

Imaging revealed a three‐layered nail structure, an AFL‐induced porous ablation crater, and changes in autofluorescence. While intact fungal samples showed a 106% higher ATTO‐647N signal intensity than healthy controls, microporation led to a significantly increased fluorophore permeation in all samples (p < 0.0001). AFL processing of nail tissue enhanced topical delivery of ATTO‐647N in all layers, (average increase: healthy +108%, fungal +33%), most pronounced in the top nail layer (healthy +122%, fungal +68%). While proportionally deeper ablation craters correlated moderately with higher fluorescence intensities in healthy nail tissue, fungal samples showed no significant relationship.

Conclusion

Fractional CO₂ laser microporation is a simple way of enhancing the passive delivery of topically applied ATTO‐647N. Although the impaired nail plate barrier in OM leads to greater diffusion of the aqueous solution, AFL can increase the permeability of both structurally deficient and intact nails.

Improving Transungual Permeation Study Design by Increased Bovine Hoof Membrane Thickness and Subsequent Infection

Ungual formulations are regularly tested using human nails or animal surrogates in Franz diffusion cell experiments. Membranes sometimes less than 100 µm thick are used, disregarding the higher physiological thickness of human nails and possible fungal infection. In this study, bovine hoof membranes, healthy or infected with Trichophyton rubrum, underwent different imaging techniques highlighting that continuous pores traversed the entire membrane and infection resulted in fungal growth, both superficial, as well as in the membrane’s matrix. These membrane characteristics resulted in substantial differences in the permeation of the antifungal model substance bifonazole, depending on the dosage forms. Increasing the thickness of healthy membranes from 100 µm to 400 µm disproportionally reduced the permeated amount of bifonazole from the liquid and semisolid forms and allowed for a more pronounced assessment of the effects by excipients, such as urea as the permeation enhancer. Similarly, an infection of 400-µm membranes drastically increased the permeated amount. Therefore, the thickness and infection statuses of the membranes in the permeation experiments were essential for a differential readout, and standardized formulation-dependent experimental setups would be highly beneficial.

In Silico Drug Screening Based Development of Novel Formulations for Onychomycosis Management

Onychomycosis is a prominent fungal infection that causes discoloration, thickening, and mutilation leading to the separation of the nail from the nail bed. Treatment modalities for onychomycosis may include oral, topical, or combination therapy with antifungals and at times may require chemical or surgical intervention. The burden of side effects of antifungals is enormous, and therefore using molecular docking-based drug selection in context with the target keratin protein would ensure better disease management. Ciclopirox, Amorolfine HCl, Efinaconazole, Tioconazole, and Tavaborole were submitted for assessment, revealing that Amorolfine HCl is the best fit. Consequently, two formulations (Nail lacquer and nanoemulgel) were developed from Amorolfine HCl to validate the in silico screening outcomes. The formulations were further fortified with over-the-counter ingredients vis-a-vis with vitamin E in nail lacquer and undecylenic acid in nanoemulgel for their prominent roles in improving nail health. Both the formulations were systematically designed, optimized, and characterized. Amorolfine HCl containing nanoemulgel (NEG) was developed using undecylenic acid as an oil phase and thioglycolic acid as a penetration enhancer. The quality parameters evaluated were particle size, the zeta potential for nanoemulsion (NE) (78.04 ± 4.724 nm and −0.7mV, respectively), in vitro cumulative drug release (96.74% for NE and 88.54% for NEG), and transungual permeation (about 73.49% for NEG and 54.81% for NE). Nail lacquer was evaluated for the drying time, non-volatile content, and blush test. In vitro cumulative drug release of the developed nail lacquer and comparator marketed formulations were around 81.5% and 75%, respectively. Similarly, the transungual drug permeation was 6.32 μg/cm² and 5.89 μg/cm², respectively, in 24 h. The in silico guided preparation of both formulations containing Amorolfine HCl and over the counter ingredients is amenable for therapeutic use against onychomycosis and will be evaluated in the in vivo model.

Constant Voltage Iontophoresis Technique to Deliver Terbinafine via Transungual Delivery System: Formulation Optimization Using Box-Behnken Design and In Vitro Evaluation

Topical therapy of antifungals is primarily restricted due to the low innate transport of drugs through the thick multi-layered keratinized nail plate. The objective of this investigation was to develop a gel formulation, and to optimize and evaluate the transungual delivery of terbinafine using the constant voltage iontophoresis technique. Statistical analysis was performed using Box–Behnken design to optimize the transungual delivery of terbinafine by examining crucial variables namely concentration of polyethylene glycol, voltage, and duration of application (2–6 h). Optimization data in batches (F1–F17) demonstrated that chemical enhancer, applied voltage, and application time have influenced terbinafine nail delivery. Higher ex vivo permeation and drug accumulation into the nail tissue were noticed in the optimized batch (F8) when compared with other batches (F1–F17). A greater amount of terbinafine was released across the nails when the drug was accumulated by iontophoresis than the passive counterpart. A remarkably higher zone of inhibition was observed in nails with greater drug accumulation due to iontophoresis, as compared to the passive process. The results here demonstrate that the optimized formulation with low voltage iontophoresis could be a viable and alternative tool in the transungual delivery of terbinafine, which in turn could improve the success rate of topical nail therapy in onychomycosis.

The effects of CO2 laser and topical agent combination therapy for onychomycosis: A meta-analysis

The routine options for onychomycosis are oral, topical, and device-based therapies which are often limited in terms of efficacy and unsatisfactory side effects. Topical agents such as luliconazole, tioconazole, terbinafine, and tazarotene can be more effective when combined with laser therapies. Our aim was to compare the efficacy and satisfaction rates of CO₂ laser therapy with topical agents in patients with onychomycosis. PubMed, the Cochrane Library, Embase, and Ovid databases were searched to identify randomized controlled trials (RCTs) evaluating the effects of combined therapies. Selected study data were analyzed for differences expressed as odds ratio (OR) and relative ratio (RR) with 95% confidence intervals (CI) for dichotomous outcomes. Efficacy and satisfaction outcomes were assessed using quantitative methods. Our investigations showed that combined CO₂ laser and topical treatments significantly increased efficacy 5.38-fold when compared with topical agents alone (OR 5.38; 95% CI; 3.20-9.04; p < 0.00001), with low heterogeneity observed among studies (I²  = 38%). Mycological clearance comparison rates were also improved by combined treatments. The higher satisfaction of the combined group was assessed by pooled effect (OR 4.56; 95% CI; 2.78-7.49; p < 0.00001). Our evidence suggests combined therapy may exert positive effects and satisfactory safety for patients with moderate to severe onychomycosis, however, optimal combination options and appropriate dosages require more comprehensive RCTs.

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.

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.

Effect of monoterpenes on ex vivo transungual delivery of itraconazole for the management of onychomycosis

BACKGROUND

Onychomycosis, a fungal nail infection, is an important problem as it may cause local pain, paresthesia, difficulties in performing activities of daily life, and impair social interactions. Systemic treatment of onychomycosis presents safety issues due to possible drug-drug interactions and severe side effects. Although topical therapy of onychomycosis is advantageous due to its localized effect, the efficacy of such therapy depends on achieving effective concentrations of antifungal agents at the infection site. An approach to reach to this end would be driving benefit from synergic activity of antifungal agents for example itraconazole and monoterpenes. However, because of low transungual penetration of itraconazole, a molecule with high molecular weight and very low water-solubility, the effect of the latter compounds on itraconazole nail delivery should be investigated, which was the aim of this study.

METHODS

Ex vivo permeation experiments were carried out through soaking the nail clippings of ten healthy volunteers in control and working solutions containing itraconazole (1 mg mL^-1 ) and itraconazole (1 mg mL^-1 ) plus 6% of each monoterpene including camphor, eucalyptol, menthol, and thymol, respectively, for 36 hours. The amount of itraconazole in nail clippings was quantified hereafter using a validated HPLC method.

RESULTS

Statistical analysis showed that itraconazole transungual permeation was not influenced by the studied monoterpenes (P value > .05).

CONCLUSION

These results provided a new perspective for designing topical dosage forms for the treatment of onychomycosis.