Mechanistic Insights of Formulation Approaches for the Treatment of Nail Infection: Conventional and Novel Drug Delivery Approaches

Contemporary Techniques and Potential Transungual Drug Delivery Nanosystems for The Treatment of Onychomycosis

The humanoid nail is considered an exceptional protective barrier that is formed mainly from keratin. Onychomycosis is the cause of 50% of nail infections that is generally caused by dermatophytes. Firstly, the infection was regarded as a cosmetic problem but because of the tenacious nature of onychomycosis and its relapses, these infections have attracted medical attention. The first line of therapy was the oral antifungal agents which were proven to be effective; nevertheless, they exhibited hepato-toxic side effects, alongside drug interactions. Following, the opportunity was shifted to the topical remedies, as onychomycosis is rather superficial, yet this route is hindered by the keratinized layers in the nail plate. A potential alternative to overcome the obstacle was applying different mechanical, physical, and chemical methods to boost the penetration of drugs through the nail plate. Unfortunately, these methods might be expensive, require an expert to be completed, or even be followed by pain or more serious side effects. Furthermore, topical formulations such as nail lacquers and patches do not provide enough sustaining effects. Recently, newer therapies such as nanovesicles, nanoparticles, and nanoemulsions have emerged for the treatment of onychomycosis that provided effective treatment with possibly no side effects. This review states the treatment strategies such as mechanical, physical, and chemical methods, and highlights various innovative dosage forms and nanosystems developed in the last 10 years with a focus on advanced findings regarding formulation systems. Furthermore, it demonstrates the natural bioactives and their formulation as nanosystems, and the most relevant clinical outcomes.

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.

Updated Perspectives on the Diagnosis and Management of Onychomycosis

Onychomycosis is the most common nail disease encountered in clinical practice and can cause pain, difficulty with ambulation, and psycho-social problems. A thorough history and physical examination, including dermoscopy, should be performed for each patient presenting with nail findings suggestive of onychomycosis. Several approaches are available for definitive diagnostic testing, including potassium hydroxide and microscopy, fungal culture, histopathology, polymerase chain reaction, or a combination of techniques. Confirmatory testing should be performed for each patient prior to initiating any antifungal therapies. There are several different therapeutic options available, including oral and topical medications as well as device-based treatments. Oral antifungals are generally recommended for moderate to severe onychomycosis and have higher cure rates, while topical antifungals are recommended for mild to moderate disease and have more favorable safety profiles. Oral terbinafine, itraconazole, and griseofulvin and topical ciclopirox 8% nail lacquer, efinaconazole 10% solution, and tavaborole 5% solution are approved by the Food and Drug Administration for treatment of onychomycosis in the United States and amorolfine 5% nail lacquer is approved in Europe. Laser treatment is approved in the United States for temporary increases in clear nail, but clinical results are suboptimal. Oral fluconazole is not approved in the United States for onychomycosis treatment, but is frequently used off-label with good efficacy. Several novel oral, topical, and over-the-counter therapies are currently under investigation. Physicians should consider the disease severity, infecting pathogen, medication safety, efficacy and cost, and patient age, comorbidities, medication history, and likelihood of compliance when determining management plans. Onychomycosis is a chronic disease with high recurrence rates and patients should be counseled on an appropriate plan to minimize recurrence risk following effective antifungal therapy.

Printing Drugs onto Nails for Effective Treatment of Onychomycosis

Inkjet printing (IJP) is an emerging technology for the precision dosing of medicines. We report, for the first time, the printing of the antifungal drug terbinafine hydrochloride directly onto nails for the treatment of onychomycosis. A commercial cosmetic nail printer was modified by removing the ink from the cartridge and replacing it with an in-house prepared drug-loaded ink. The drug-loaded ink was designed so that it was comparable to the commercial ink for key printability properties. Linear drug dosing was shown by changing the lightness of the colour selected for printing (R² = 0.977) and by printing multiple times (R² = 0.989). The drug loads were measured for heart (271 µg), world (205 µg) and football (133 µg) shapes. A disc diffusion assay against Trpytophan rubrum showed inhibition of fungal growth with printed-on discs. In vitro testing with human nails showed substantial inhibition with printed-on nails. Hence, this is the first study to demonstrate the ability of a nail printer for drug delivery, thereby confirming its potential for onychomycosis treatment.

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.

Aloe-emodin-mediated antimicrobial photodynamic therapy against dermatophytosis caused by Trichophyton rubrum

Trichophyton rubrum is responsible for the majority of dermatophytosis. Current systemic and topical antifungals against dermatophytosis are often tedious and sometimes unsatisfactory. Antimicrobial photodynamic therapy (aPDT) is a non‐invasive alternative suitable for the treatment of superficial fungal infections. This work investigated the photodynamic inactivation efficacy and effects of aloe‐emodin (AE), a natural photosensitizer (PS) against T. rubrum microconidia in vitro, and evaluated the treatment effects of AE‐mediated aPDT for T. rubrum‐caused tinea corporis in vivo and tinea unguium ex vivo. The photodynamic antimicrobial efficacy of AE on T. rubrum microconidia was evaluated by MTT assay. The inhibition effect of AE‐mediated aPDT on growth of T. rubrum was studied. Intracellular location of AE, damage induced by AE‐mediated aPDT on cellular structure and surface of microconidia and generation of intracellular ROS were investigated by microscopy and flow cytometry. The therapeutic effects of AE‐mediated aPDT against dermatophytosis were assessed in T. rubrum‐caused tinea corporis guinea pig model and tinea unguium ex vivo model. AE‐mediated aPDT effectively inactivated T. rubrum microconidia in a light energy dose‐dependent manner and exhibited strong inhibitory effect on growth of T. rubrum. Microscope images indicated that AE is mainly targeted to the organelles and caused damage to the cytoplasm of microconidia after irradiation through generation of abundant intracellular ROS. AE‐mediated aPDT demonstrated effective therapeutic effects for T. rubrum‐caused tinea corporis on guinea pig model and tinea unguium in ex vivo model. The results obtained suggest that AE is a potential PS for the photodynamic treatment of dermatophytosis caused by T. rubrum, but its permeability in skin and nails needs to be improved.

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.

Design and evaluation of microemulsion-based efinaconazole formulations for targeted treatment of onychomycosis through transungual route: Ex vivo and nail clipping studies

The onychomycosis treatment remains a big challenge for onychologist due to the shorter nail residence time of topical formulations and the lack of availability of novel formulations in markets for new generation antifungal drugs. The objective of this work was to design, develop, optimize, and evaluate microemulsion formulations for effective delivery of efinaconazole through transungual route in onychomycosis treatment. Capmul® MCM (Glyceryl Caprylate/Caprate) as oil, Labrasol® (caprylocaproyl polyoxyl-8 glycerides) as a surfactant, and Transcutol® P (diethylene glycol monoethyl ether) as co-surfactant exhibited higher solubility of efinaconazole and surfactant-cosurfactant mixture (Smix) in a ratio of 1:1 rendered higher microemulsion region in the pseudo-ternary phase diagram. The optimized microemulsion formulation containing 6%w/w oil phase, 22.5%w/w surfactant, 22.5%w/w co-surfactant, and 49%w/w demineralized water was converted into gel formulation using 1.0%w/w Carbopol® 934 P gelling agent and evaluated for stability of 6 months. The optimized microemulsion formulation globule size was less than 100 nm. The ex vivo permeation confirmed improved permeation of efinaconazole from microemulsion formulations (346.36±12.90μgcm^-2) in comparison to reference formulation without observing any lag in drug permeation through the nail plate. The in vitro antifungal study data indicated increased antifungal efficacy relative to efinaconazole topical solution against Trichophyton rubrum, Trichophyton mentagrophytes, and Candida albicans species. Further, an in vitro cell cytotoxicity study exhibited no toxic effect for any excipients used in the formulation while applied on nail cells. Hence, the efinaconazole loaded microemulsion formulations could be considered as an effective therapy in the treatment of onychomycosis.

Effect of Penetration Enhancers on Toenail Delivery of Efinaconazole from Hydroalcoholic Preparations

The incorporation of permeation enhancers in topical preparations has been recognized as a simple and valuable approach to improve the penetration of antifungal agents into toenails. In this study, to improve the toenail delivery of efinaconazole (EFN), a triazole derivative for onychomycosis treatment, topical solutions containing different penetration enhancers were designed, and the permeation profiles were evaluated using bovine hoof models. In an in vitro permeation study in a Franz diffusion cell, hydroalcoholic solutions (HSs) containing lipophilic enhancers, particularly prepared with propylene glycol dicaprylocaprate (Labrafac PG), had 41% higher penetration than the HS base. Moreover, the combination of hydroxypropyl-β-cyclodextrin with Labrafac PG further facilitated the penetration of EFN across the hoof membrane. In addition, this novel topical solution prepared with both lipophilic and hydrophilic enhancers was physicochemically stable, with no drug degradation under ambient conditions (25 °C, for 10 months). Therefore, this HS system can be a promising tool for enhancing the toenail permeability and therapeutic efficacy of EFN.