Pharmacotherapy of onychomycosis

Antifungal Selection for the Treatment of Onychomycosis: Patient Considerations and Outcomes

Onychomycosis, a common fungal nail infection, affects >20% of adults over age 60 and >50% of people over age 70. Onychomycosis may cause pain, psychosocial problems, and secondary infections, therefore meriting treatment. This review describes the range of treatment modalities, including FDA-approved systemic drugs and topical therapies. Additionally, new and emerging oral and topical therapies are discussed. We emphasize the importance of tailoring onychomycosis therapy to individual patient characteristics, comorbidities, preferences, extent of nail involvement, and fungal species, such that physicians may optimize treatment outcomes, patient satisfaction, and safety.

UV-curable gels as topical nail medicines:In vivo residence, anti-fungal efficacy and influence of gel components on their properties

UV-curable gels, used as nail cosmetics for their in vivo durability, were reported to be promising as topical nail medicines. Our first aim was thus to investigate whether such durability applies to drug-loaded formulations. This was found to be true. However, ethanol inclusion in the pharmaceutical formulation (to enable drug loading) reduced the in vivo residence. The second aim was therefore to determine any other effects of ethanol, and if ethanol could be avoided by the choice of monomers. Thus, three methacrylate monomers, ethyl methacrylate, isobornyl methacrylate and 2-hydroxyethyl methacrylate (HEMA) were selected, and their influence on the formulation properties were determined. Ethanol and the methacrylate monomer influenced some (but not all) of the formulation properties. The most significant was that HEMA could dissolve drug and enable the preparation of ethanol-free, drug-loaded formulations, which would benefit in vivo residence. The absence of ethanol reduced drug loading, release and ungual flux, but had no negative impact on the in vitro anti-fungal efficacy. Thus, judicious selection of gel components enabled the exclusion of ethanol. The long in vivo residence, little residual monomers, sufficient ungual permeation and in vitro anti-fungal activity of the gels indicates their potential as anti-onychomycotic topical medicines.

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.

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.

Medical devices for the treatment of onychomycosis

Device-based therapies are the most rapidly expanding area of onychomycosis treatment. Traditional pharmacotherapy of onychomycosis has a low to moderate efficacy and is associated with adverse reactions and drug interactions that limit its use in many patients. These new therapies include laser systems, photodynamic therapy, iontophoresis, and ultrasound. Device-based therapies are procedures conducted in the clinic by a trained professional, which mitigates the requirement for long-term patient compliance. In addition, the drug component of these therapies is topical, preventing the adverse events associated with systemic antifungal administration, and potentially allowing for the treatment of individuals who were previously excluded due to drug interactions. Device-based therapy is a nascent field, so clinical data is still in an emergent stage; however, preliminary clinical trials of laser, photodynamic therapy, and iontophoresis suggest that some devices may have a degree of efficacy. More studies are required to better determine their ability to treat onychomycosis.

New therapeutic options for onychomycosis

INTRODUCTION

Onychomycosis is a fungal infection of the nail apparatus that affects 10 - 30% of the global population. Current therapeutic options for onychomycosis have a low to moderate efficacy and result in a 20 - 25% rate of relapse and reinfection. New therapeutic options are needed to broaden the spectrum of treatment options and improve the efficacy of treatment.

AREAS COVERED

This review discusses the emerging pharmacotherapeutics; including topical reformulations of terbinafine, new azole molecules for systemic and topical administration, topical benzoxaboroles and topical polymer barriers. The paper also discusses device-based options, which may be designed to activate a drug or to improve drug delivery, such as photodynamic therapy and iontophoresis; laser device systems have also begun to receive regulatory approval for onychomycosis.

EXPERT OPINION

Device-based therapeutic options for onychomycosis are expanding more rapidly than pharmacotherapy. Systemic azoles are the only class of pharmacotherapy that has shown a comparable efficacy to systemic terbinafine; however terbinafine remains the gold standard. The most notable new topical drugs are tavaborole, efinaconazole and luliconazole, which belong to the benzoxaborole and azole classes of drugs. Photodynamic therapy, iontophoresis and laser therapy have shown positive initial results, but randomized controlled trials are necessary to determine the long-term success of these devices.

Microemulsion-based gel of terbinafine for the treatment of onychomycosis: optimization of formulation using D-optimal design

The aim of the present investigation was to evaluate microemulsion as a vehicle for dermal drug delivery and to develop microemulsion-based gel of terbinafine for the treatment of onychomycosis. D-optimal mixture experimental design was adopted to optimize the amount of oil (X(1)), Smix (mixture of surfactant and cosurfactant; X(2)) and water (X(3)) in the microemulsion. The formulations were assessed for globule size (in nanometers; Y(1)) and solubility of drug in microemulsion (in milligrams per milliliter; Y(2)). The microemulsion containing 5.75% oil, 53.75% surfactant-cosurfactant mixture and 40.5% water was selected as the optimized batch. The globule size and solubility of the optimized batch were 18.14 nm and 43.71 mg/ml, respectively. Transmission electron microscopy showed that globules were spherical in shape. Drug containing microemulsion was converted into gel employing 0.75% w/w carbopol 934P. The optimized gel showed better penetration and retention in the human cadaver skin as compared to the commercial cream. The cumulative amount of terbinafine permeated after 12 h was 244.65 ± 18.43 μg cm(-2) which was three times more than the selected commercial cream. Terbinafine microemulsion in the gel form showed better activity against Candida albicans and Trichophyton rubrum than the commercial cream. It was concluded that drug-loaded gel could be a promising formulation for effective treatment of onychomycosis.

[Antifungal agents for onychomycoses]

Nail fungal infections are considered one of the major dermatological problems due to their high rate of therapeutic failure, management and treatment difficulties. Long-term treatments, inadequate therapies, mycological misdiagnosis and follow-up, secondary alterations of the nail, and resistant microorganisms, are some of the causes of these complications. Although the discovery of new antifungal agents has provided some effective molecules, none of the current available drugs are totally effective. It is important to continue researching in this field to provide new antifungal agents and combined therapies.

Clinicopathologic presentations of dermatomycoses in cancer patients

Many of the skin fungal infections in cancer patients may look similar to those infections in non-cancer patients. However, in some cases, they become more extensive and even life threatening. Prolonged and severe neutropenia is the main risk factor for the dramatic issue of fungal infections. The dermatomycoses in cancer patients can be classified in four broad groups: primary superficial dermatophytoses, primary superficial yeast infections, opportunistic mold infections with distinct potential for dissemination and secondary cutaneous manifestations of fungaemia. Occasionally, more than one fungus are found inside a given skin lesion. A special condition is represented by the mycotic colonization of mucosal squamous cell carcinomas. Angio-invasion by fungi accounts for the frequency of disseminated infections prevailing in immunocompromised cancer patients. In case of skin involvement, the dermatologist may assist by recognizing subtle semiological signs and performing biopsies for swift histological examination, molecular biology and/or culture.

Emerging therapeutic agents for onychomycosis

Onychomycosis is a frequent disorder that represents the most prevalent fungal infection, particularly among older individuals. Diverse fungi of the dermatophyte, non-dermatophyte mold and yeast families have been reported to be responsible for onychomycosis. The output from the pharmaceutical industry of new antifungals to treat onychomycosis has been limited over the last decade. Present treatment options include both oral and topical drugs, with oral therapies giving better outcomes. However, neither of these treatment options provides high cure rates that are durable. At present, azoles and allylamines are keeping the pivotal roles. New derivatives with a favorable risk-benefit ratio and new formulations of older azoles seem to be promising. Thus, ongoing drug development activities have focused on novel delivery technologies to facilitate incorporation of existing antifungal drugs inside the nail plate and the discovery of new active antifungals.

Recent progress on the topical therapy of onychomycosis

Onychomycosis is a fungal infection of the fingernails and toenails that results in thickening, discoloration, splitting of the nails and lifting of the nail from the nail bed. The disease is caused by dermatophytes and has a high incidence within the general population, especially among older individuals. Present treatment options include both oral and topical drugs, with oral therapies giving better outcomes; however, neither of these treatment options provides high cure rates that are durable. The difficulty in treating onychomycosis results from the deep-seated nature of the infection within the nail unit (nail plate, nail bed and surrounding tissue) and the inability of drugs to effectively reach all sites. Ongoing drug development activities have focused on novel delivery technologies to facilitate penetration of existing antifungal drugs through the nail plate and on the discovery of inherently penetrable antifungals. AN-2690 represents an oxaborole antifungal that is designed to penetrate the nail plate and is showing promising results in clinical trials.

Onychomycosis in older patients

Onychomycosis represents the most frequent nail disorder. Its prevalence is influenced by gender, age and several comorbid diseases. Accurate diagnosis relies on laboratory examination, particularly nail histomycology. This method refers to the microscopic examination of histological sections prepared from nail clippings for the purpose of detecting the presence of invading fungi. The pathogens may belong to one or a combination of the groups of dermatophytes, yeasts or nondermatophyte molds. The choice of the diagnostic laboratory method influences the accuracy of the information. Histomycology is recognized to be the most sensitive and specific method. The prevalence of onychomycosis in the elderly population varies according to gender and the nature of the fungal pathogen. Epidemiological figures differ according to the nature of the reference population. In particular, it is of the utmost importance to establish the ratio between the raw numbers of onychomycoses and the total number of individuals in the same age group living in the same geographical area.

Interactions of a fungistatic antibiotic, griseofulvin, with phospholipid monolayers used as models of biological membranes

Griseofulvin (GF) is an oral antibiotic for widely occurring superficial mycosis in man and animals caused by dermaphyte fungi; it is also used in agriculture as a fungicide. The mechanism of the biological activity of GF is poorly understood. Here, the interactions of griseofulvin with lipid membranes were studied using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), and 1,2-myristoyl-sn-glycero-3-phosphoethanolamine (DMPE) monolayers spread at the air/water interface. Surface pressure (Pi), electric surface potential (Delta V), grazing incidence X-ray diffraction (GIXD), and Brewster angle microscopy (BAM) were used for studying pure phospholipid monolayers spread on GF aqueous solutions, as well as mixed phospholipid/GF monolayers spread on pure water subphase. Moreover, phospholipase A2 (PLA2) activity toward DLPC monolayers and molecular modeling of the GF surface and lipophilic properties were used to get more insight into the mechanisms of GF-membrane interactions. The results obtained show that GF has a meaningful impact on the film properties; we propose that nonpolar interactions are by and large responsible for GF retention in the monolayers. The modification of membrane properties can be detected using both physicochemical and enzymatic methods. The results obtained may be relevant for elaborating GF preparations with increased bioavailability.

Antifungal activity of propolis extract against yeasts isolated from onychomycosis lesions

The aim of this study was to determine the in vitro activity of propolis extract against 67 yeasts isolated from onychomycosis in patients attending at the Teaching and Research Laboratory of Clinical Analysis of the State University of Maringá. The method used was an adaptation made from the protocol approved by the National Committee for Clinical Laboratory Standards. The yeasts tested were: Candida parapsilosis 35%, C. tropicalis 23%, C. albicans 13%, and other species 29%. The propolis extract showed excellent performance regarding its antifungal activity: the concentration capable of inhibiting the all of the yeasts was 5 x 10(-2) mg/ml of flavonoids and 2 x 10(-2) mg/ml of flavonoids stimulated their cellular death. Trichosporon sp. were the most sensitive species, showing MIC50 and MIC90 of 1.25 x 10(-2) mg/ml of flavonoids, and C. tropicalis was the most resistant, with CFM50 of 5 x 10(-2) mg/ml of flavonoids and MFC90 of 10 x 10(-2) mg/ml. In view of the fact that propolis is a natural, low cost, nontoxic product with proven antifungal activity, it should be considered as another option in the onychomycosis treatment.

Oral antifungal-exacerbated inflammatory flare-up reactions of dermatomycosis : case reports and review of the literature

Inflammatory flare-up reactions of some dermatomycoses, particularly those caused by zoophilic fungi, are typical and potentially severe adverse effects following the intake of some oral antifungals. However, this condition has not previously been reported with the most frequently used antifungals in dermatology, namely fluconazole, itraconazole, and terbinafine. In this report, we describe five patients, observed over a 10-year period, who presented with inflammatory exacerbations following oral antifungal therapy for dermatomycoses. We also review the literature on inflammatory reactions exacerbated by oral antifungal agents. Details of the patients' age, sex, occupation, and atopic background; the site of the lesion, its clinical and histologic features, and any systemic signs; the identity of the fungal pathogen; the antifungal agent taken by the patient; the time between drug intake and occurrence of the flare-up; the approach to management; and the outcome were documented for each patient. A PubMed literature search was also conducted, focusing on inflammatory exacerbations induced by griseofulvin, ketoconazole, itraconazole, fluconazole, and terbinafine. The patients were four farmers and one veterinarian (all male). All primary lesions were inflammatory dermatophytoses, including one kerion. Inflammatory exacerbation of the skin lesions started 12-24 hours after the intake of oral antifungals. Mild systemic changes, including slight fever and malaise, occurred in two cases. Itraconazole 400 mg/day was implicated as the causative agent in four cases and terbinafine 250 mg/day in one case. Mycologic cultures grew Trichophytonverrucosum in four cases. Antifungal treatment was discontinued in all patients. Oral and topical corticosteroids were administered to the two patients with systemic changes; the other three patients were treated with topical corticosteroids only. Two days after the onset of corticosteroids, lower doses of itraconazole (100 mg/day) and terbinafine (125 mg/day) were reintroduced. All lesions healed after 4-5 weeks. The PubMed search did not identify any articles that described inflammatory exacerbations of dermatomycoses induced by oral antifungals. Inflammatory flare-up of dermatomycoses is a rare but potentially severe cutaneous complication of oral antifungal use. Occupational contact with animals, inflammatory dermatomycoses, and zoophilic fungi represent common features in these patients. Although evidence-based data are not available, clinical experience shows that, in addition to antifungal therapy, topical and/or systemic corticosteroids are helpful to reduce the inflammatory reactions. The cases described in this article represent the first published report of oral antifungal-exacerbated inflammatory flare-up reactions of dermatomycosis in patients taking itraconazole or terbinafine.

Methylene blue in photodynamic therapy: From basic mechanisms to clinical applications

Methylene blue (MB) is a molecule that has been playing important roles in microbiology and pharmacology for some time. It has been widely used to stain living organisms, to treat methemoglobinemia, and lately it has been considered as a drug for photodynamic therapy (PDT). In this review, we start from the fundamental photophysical, photochemical and photobiological characteristics of this molecule and evolved to show in vitro and in vivo applications related to PDT. The clinical cases shown include treatments of basal cell carcinoma, Kaposi's Sarcoma, melanoma, virus and fungal infections. We concluded that used together with a recently developed continuous light source (RL50(®)), MB has the potential to treat a variety of cancerous and non-cancerous diseases, with low toxicity and no side effects.