The low keratin affinity of efinaconazole contributes to its nail penetration and fungicidal activity in topical onychomycosis treatment

Efficacy Coefficients Determined Using Nail Permeability and Antifungal Activity in Keratin-Containing Media Are Useful for Predicting Clinical Efficacies of Topical Drugs for Onychomycosis

Onychomycosis is difficult to treat topically due to the deep location of the infection under the densely keratinized nail plate. In order to obtain an in vitro index that is relevant to the clinical efficacy of topical anti-onychomycosis drugs, we profiled five topical drugs: amorolfine, ciclopirox, efinaconazole, luliconazole, and terbinafine, for their nail permeabilities, keratin affinities, and anti-dermatophytic activities in the presence of keratin. Efinaconazole and ciclopirox permeated full-thickness human nails more deeply than luliconazole. Amorolfine and terbinafine did not show any detectable permeation. The free-drug concentration of efinaconazole in a 5% human nail keratin suspension was 24.9%, which was significantly higher than those of the other drugs (1.1-3.9%). Additionally, efinaconazole was released from human nail keratin at a greater proportion than the other drugs. The MICs of the five drugs for Trichophyton rubrum were determined at various concentrations of keratin (0-20%) in RPMI 1640 medium. The MICs of ciclopirox were not affected by keratin, whereas those of efinaconazole were slightly increased and those of luliconazole and terbinafine were markedly increased in the presence of 20% keratin. Efficacy coefficients were calculated using the nail permeation flux and MIC in media without or with keratin. Efinaconazole showed the highest efficacy coefficient, which was determined using MIC in media with keratin. The order of efficacy coefficients determined using MIC in keratin-containing media rather than keratin-free media was consistent with that of complete cure rates in previously reported clinical trials. The present study revealed that efficacy coefficients determined using MIC in keratin-containing media are useful for predicting the clinical efficacies of topical drugs. In order to be more effective, topical drugs have to possess higher efficacy coefficients.

Application of Hansen Solubility Parameters to predict drug-nail interactions, which can assist the design of nail medicines

We hypothesised that Hansen Solubility Parameters (HSPs) can be used to predict drug-nail affinities. Our aims were to: (i) determine the HSPs (δD, δP, δH) of the nail plate, the hoof membrane (a model for the nail plate), and of the drugs terbinafine HCl, amorolfine HCl, ciclopirox olamine and efinaconazole, by measuring their swelling/solubility in organic liquids, (ii) predict nail-drug interactions by comparing drug and nail HSPs, and (iii) evaluate the accuracy of these predictions using literature reports of experimentally-determined affinities of these drugs for keratin, the main constituent of the nail plate and hoof. Many solvents caused no change in the mass of nail plates, a few solvents deswelled the nail, while others swelled the nail to varying extents. Fingernail and toenail HSPs were almost the same, while hoof HSPs were similar, except for a slightly lower δP. High nail-terbinafine HCl, nail-amorolfine HCl and nail-ciclopirox olamine affinities, and low nail-efinaconazole affinities were then predicted, and found to accurately match experimental reports of these drugs' affinities to keratin. We therefore propose that drug and nail Hansen Solubility Parameters may be used to predict drug-nail interactions, and that these results can assist in the design of drugs for the treatment of nail diseases, such as onychomycosis and psoriasis. To our knowledge, this is the first report of the application of HSPs in ungual research.

Characterization of Antifungal Activity and Nail Penetration of ME1111, a New Antifungal Agent for Topical Treatment of Onychomycosis

Fungal nail infection (onychomycosis) is a prevalent disease in many areas of the world, with a high incidence approaching 23%. Available antifungals to treat the disease suffer from a number of disadvantages, necessitating the discovery of new efficacious and safe antifungals. Here, we evaluate the in vitro antifungal activity and nail penetration ability of ME1111, a novel antifungal agent, along with comparator drugs, including ciclopirox, amorolfine, terbinafine, and itraconazole. ME1111 showed potent antifungal activity against Trichophyton rubrum and Trichophyton mentagrophytes (the major etiologic agents of onychomycosis) strains isolated in Japan and reference fungal strains with an MIC range of 0.12 to 0.5 mg/liter and an MIC50 and MIC90 of 0.5 mg/liter for both. Importantly, none of the tested isolates showed an elevated ME1111 MIC. Moreover, the antifungal activity of ME1111 was minimally affected by 5% wool keratin powder in comparison to the other antifungals tested. The ME1111 solution was able to penetrate human nails and inhibit fungal growth in a dose-dependent manner according to the TurChub assay. In contrast, 8% ciclopirox and 5% amorolfine nail lacquers showed no activity under the same conditions. ME1111 demonstrated approximately 60-fold-greater selectivity in inhibition of Trichophyton spp. than of human cell lines. Our findings demonstrate that ME1111 possesses potent antidermatophyte activity, maintains this activity in the presence of keratin, and possesses excellent human nail permeability. These results suggest that ME1111 is a promising topical medication for the treatment of onychomycosis and therefore warrants further clinical evaluation.

Efinaconazole 10% topical solution for the topical treatment of onychomycosis of the toenail

Efinaconazole 10% topical solution is a new antifungal therapy for the topical treatment of mild to moderate toenail onychomycosis. In vitro and in vivo data have shown significant antifungal activity against dermatophytes, Candida spp. and nondermatophyte molds, and its mechanism of action is through inhibition of fungal lanosterol 14α-demethylase. In two parallel, double-blind, randomized, controlled, Phase III trials, complete cure rates were 17.8 and 15.2%, respectively, and mycological cure rates were 55.2 and 53.4%, respectively, for efinaconazole 10% topical solution, which were superior to vehicle, with minimal adverse events. This drug profile reviews the most recent basic science and clinical data for efinaconazole in the treatment of toenail onychomycosis.

Efinaconazole Topical Solution, 10%: Factors Contributing to Onychomycosis Success

To provide an adequate therapeutic effect against onychomycosis, it has been suggested that topical drugs should have two properties: drug permeability through the nail plate and into the nail bed, and retention of their antifungal activity in the disease-affected areas. Only recently has the importance of other delivery routes (such as subungual) been discussed. Efinaconazole has been shown to have a more potent antifungal activity in vitro than the most commonly used onychomycosis treatments. The low keratin affinity of efinaconazole contributes to its effective delivery through the nail plate and retention of its antifungal activity. Its unique low surface tension formulation provides good wetting properties affording drug delivery both through and under the nail. High antifungal drug concentrations have been demonstrated in the nail of onychomycosis patients, and effectiveness of efinaconazole topical solution, 10% confirmed in two large well-controlled multicenter Phase 3 clinical studies in patients with mild-to-moderate disease.

Efinaconazole in the treatment of onychomycosis

Efinaconazole 10% topical solution is a new triazole recently approved for the treatment of onychomycosis. It inhibits fungal lanosterol 14α-demethylase in the ergosterol biosynthesis pathway, has potent antifungal activity against dermatophytes, as well as activity against Candida spp. and non-dermatophyte molds, and showed promising results in clinical trials. This review summarizes the mechanism of action, in vitro and in vivo data, clinical trials, safety, and quality-of-life data of efinaconazole as it applies to the treatment of onychomycosis.

Efinaconazole topical solution, 10%: formulation development program of a new topical treatment of toenail onychomycosis

Transungual drug delivery of antifungals is considered highly desirable to treat common nail disorders such as onychomycosis, due to localized effects, and improved adherence resulting from minimal systemic adverse events. However, the development of effective topical therapies has been hampered by poor nail penetration. An effective topical antifungal must permeate through, and under the dense keratinized nail plate to the site of infection in the nail bed and nail matrix. We present here the formulation development program to provide effective transungual and subungual delivery of efinaconazole, the first topical broad spectrum triazole specifically developed for onychomycosis treatment. We discuss the important aspects encompassing the formulation development program for efinaconazole topical solution, 10%, focusing on its solubility in a number of solvents, in vitro penetration through the nail, and in vivo efficacy. Efinaconazole topical solution, 10% is a stable, non-lacquer, antifungal with a unique combination of ingredients added to an alcohol-based formulation to provide low surface tension and good wetting properties. This low surface tension is believed to affect effective transungual delivery of efinaconazole and believed to provide a dual mode of delivery by accessing the nail bed by wicking into the space between the nail and nail plate.

Patient considerations in the management of toe onychomycosis - role of efinaconazole

Onychomycosis is a difficult diagnosis to manage and treatment is sometimes avoided, as this diagnosis is often wrongly perceived as a cosmetic problem. However, onychomycosis has a negative impact on patients' quality of life, affecting social interaction, psychological well-being, and physical activities. Onychomycosis is also a risk factor for patients with diabetes, with proven increased rates of cellulitis, gangrene, and foot ulcers. Treatments are only mild to moderately effective, and rates of relapse and reinfection are high. Oral treatments require laboratory monitoring due to risk of hepatotoxicity and may be contraindicated in some patients due to risk of drug-drug interactions. Topical treatments require prolonged application and are not very effective. Efinaconazole 10% solution is a new topical triazole treatment for mild to moderate distal subungual onychomycosis, with good efficacy and without the need for debridement of nails. In onychomycosis of the toenails, efinaconazole 10% solution is documented to have a statistically significant, positive impact on patient satisfaction and quality of life.

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.

Efinaconazole topical solution, 10%: the development of a new topical treatment for toenail onychomycosis

BACKGROUND

Toenail onychomycosis is a common disease with limited treatment options; treatment failure and relapse are frequently encountered. Many patients experience long-standing disease affecting multiple toenails, with substantial discomfort and pain. Although some patients might prefer a topical therapy, efficacy with ciclopirox nail lacquer has been disappointing.

METHODS

Efinaconazole topical solution, 10% is the first topical triazole antifungal agent specifically developed for the treatment of onychomycosis. This paper reviews the preclinical and clinical data on efinaconazole topical solution, 10%.

RESULTS

Efinaconazole has a broad spectrum of antifungal activity in vitro and is more potent than ciclopirox against common onychomycosis pathogens. It has a more optimal keratin affinity than ciclopirox, and it exhibits significantly greater in vivo activity owing to its superior nail penetration. Mycologic cure rates at week 52 were 55.2% (study 1) and 53.4% (study 2) with efinaconazole topical solution, 10% compared with 16.8% and 16.9%, respectively, with vehicle (P<.001 for both). In addition, efinaconazole is well tolerated.

CONCLUSIONS

Efinaconazole topical solution, 10% may likely become a preferred topical agent for the management of mild-to-moderate onychomycosis.