Daily Application of an Aqueous, Acidifying, Peelable Nail Polish versus Weekly Amorolfine for Topical Onychomycosis Treatment: A Prospective, Randomized, Blinded Trial

Onychomycosis is a common nail infection with a worldwide prevalence of 5%, but this value may vary according to the studied area. Most common pathogens are dermatophytes, but also yeasts (e.g. Candida albicans) and non-dermatophyte moulds [1]. Depending on the location and the route of pathogen penetration, the following types of onychomycosis have been characterized: (1) disto-lateral onychomycosis, (2) white superficial onychomycosis, (3) proximal subungual onychomycosis, (4) total onychodystrophy, and (5) endonyx onychomycosis [2]. Disto-lateral subungual onychomycosis is the most common form and is usually caused by Trichophyton rubrum, which invades the nail bed and underside of the nail plate [3‐5].

Onychomycosis gradually destroys the nail by affecting the nail plate, nail bed, and periungual tissue. Depending on the degree of infection, nail discolouration, thickening, dystrophy, brittleness, and loosening (onycholysis) are observed [6]. Although the disease is not life-threatening, its morbidity may negatively impact patients' quality of life [7].

Efficient treatment is challenging because of the inherent slow growth of the nail and its composition as well as patient compliance. Also, comorbidity in risk groups (e.g. elderly, diabetic, immunosuppressed, or psoriasis patients) will further hamper treatment [8].

Oral medication has been shown to be rather ineffective against specific forms of onychomycosis (e.g. endonyx forms). Manufacturers have focused on the development of topical products that affect dermatophytes through a physical, non-specific, or pharmacological mode of action, respectively [9]. Topical treatments are the best choice for the treatment of lateral onychomycosis. Most of the topical products are lacquers that need to be removed with solvents on a weekly basis, a fact that stands in the way of patient compliance.

A randomized, controlled, multicentre, open-label trial was performed to assess the clinical efficacy against onychomycosis of an aqueous, acetic acid-based, peelable nail polish (daily application) versus a medicated nail lacquer (5% amorolfine; Loceryl^®; weekly application), serving as reference. After penetration, acetic acid acidifies the nail and consequently blocks fungal spreading, thereby allowing the infected part of the nail to grow out [10, 11]. The amorolfine nail lacquer elicits its action by destroying the fungal cell membrane [12].

The primary objective of the present study was to assess variation in the percentage of healthy surface of the great toenail after a treatment period of 180 days with both products in combination with changes in microbiological findings at baseline and at the end of the treatment (assessed via KOH staining and fungal culture). Clinical diagnosis was performed by blinded investigators using digital image analysis (contour tracing). Secondary objectives included evaluation of clinical efficacy against onychomycosis of the great toenail at distinct time points (days 30, 60, 120, and 180), microbiological efficacy of both products, product safety, impact on quality of life (QoL), and finally product efficacy, tolerance, and acceptability by subject’s self-assessment and medical examination.

Fungal infections are responsible for 23% of foot diseases and 50% of nail conditions in patients seen by dermatologists. However, they are less common in the general population (3% to 5%) [17]. Prevalence varies among populations, which may be related to different screening techniques. In one large European project, including 13,695 people with a range of foot conditions, a fungal infection (diagnosed by microscopy and culture) was present in 35% of the patients [18]. One prospective study in Spain (1000 adults, aged > 20 years) reported a prevalence of fungal toenail infection of 2.7% (infection defined as clinically abnormal nails with positive microscopy and culture) [19]. In Denmark, a study (5755 adults, aged > 18 years) reported a prevalence of fungal toenail infection of 4.0% (determined by positive fungal cultures) [20]. The incidence of mycotic nail infections may have increased over the past few years. This may be explained by the increasing use of systemic antibiotics, immunosuppressive treatment, more advanced surgical techniques, and the increasing incidence of HIV infection [21].

During recent years, different topical products have been put on the market for the treatment of onychomycosis. They are used either alone or in combination with systemic treatments, resulting in higher cure rates. For topical treatment, both medicated nail solutions and medical devices with a physical mode of action are commercially available. In the present study, an aqueous, acetic acid-based, peelable nail polish, which inhibits fungal growth by acidification of the nail environment, was compared with Loceryl^®, a nail lacquer containing 5% amorolfine [22, 23]. Amorolfine is a morpholine antifungal drug that disrupts the fungal cell membrane [12].

All subjects were diagnosed with either superficial onychomycosis or light-to-moderate disto-lateral onychomycosis on at least one great toenail. Fungal infection was further confirmed using the KOH staining method [13] and fungal culture, respectively.

Both females and males were included, with a higher proportion of females. Average age was 54.3 ± 11.8 years and 52.3 ± 14.2 years in the test product and reference group, respectively. At baseline (D0), both treatment arms were homogeneous for all studied parameters.

At the end of the study (D180), three subjects (n = 2, test product; n = 1, reference) did not complete the trial (lost to follow-up). For this reason, these subjects were excluded from the data analyses, resulting in a final number of 99 patients.

The primary objective of this study implied the evolution in  % healthy surface between baseline and D180 following treatment with both products. For the test product, an increase of 11.8% (n = 48) was observed, whereas treatment with the reference product resulted in an increase of 13.2% (n = 46). The difference between the two treatments was not significantly different. At the end of the study, application of both products resulted in a significant (p < 0.001) improvement compared with baseline.

With both treatments, other onychomycosis-related parameters showed a significant improvement compared with baseline, being more pronounced (but not significantly different) for nail dystrophy, discolouration, nail thickening, and healthy aspect of the nail, respectively. The more pronounced effects may be explained by differences in nail penetration (polarity of the active substance), different modes of action, the condition of the nail, inter- and intra-individual variations, and so on. All these factors may contribute to a different but not necessarily significant outcome.

Clinical efficacy was further reflected by the improvement in patient’s quality of life, as evaluated using the NailQoL questionnaire [16]. This was observed in both treatment arms. Finally, both treatments were well tolerated, thereby confirming product safety.

The mode of action of the test product, which contains acetic acid, relies on acidification of the nail. Following application, acid penetration and the consequent pH decrease of the nail environment will inhibit acid-sensitive keratolytic enzymes, which are essential for dermatophyte nail penetration [10, 24‐26]. In turn, fungal growth inhibition allows the infected part to grow out in vivo, without further fungal spreading.

Susceptibility of dermatophytes to acids has been demonstrated in independent experiments and literature reports. Results of a “minimum inhibitory concentration” (MIC) assay confirmed fungal growth inhibition following exposure to different organic acids, including acetic acid. We established MIC values varying between 0.0976% W/W (T. rubrum) and 0.195% (T. mentagrophytes), respectively (unpublished data). For amorolfine, MIC values varying between 4 and 16 µg/ml were reported, depending on the tested dermatophyte species [27]. Although the higher MIC value was for acetic acid, Trichophyton mentagrophytes growth was clearly inhibited following nail penetration, as shown in a validated bovine hoof assay [10]. As the nail behaves like a hydrogel [28], the low molecular weight and polarity of acetic acid allow quick penetration (within 20 min, in-house results). These data clearly contradict the results reported by Ghannoum et al. [29]. In their set-up, no activity was observed with three acid-based medical devices. However, these observations must be put in perspective. First, only a very small volume of product was applied once, which does not correspond with the instructions for use (twice daily application for the acetic acid-based product). Furthermore, the authors do not provide information regarding the hydration status of the nail, type of agar (buffered or not), or condition of the nails. For this reason, their results are inconclusive. Indeed, in a validated bovine hoof assay, both an acetic acid-based solution and amorolfine were able to penetrate the nail and inhibit Trichophyton mentagrophytes growth [10]. These in vitro data are further confirmed by the results of the present clinical study and previous clinical data with an equivalent medical device, showing a comparable outcome for product performance and safety [30]. The latter product also relies on acidification of the nail environment via penetration of acetic acid but must be applied twice-daily compared with the investigational product (once daily). Besides being water-based, the test product offers additional advantages because the film can be easily removed after 24 h.

Finally, product usability and safety were clearly confirmed by the subjective questionnaire data. Indeed, product application and removal were highly appreciated by the patients. Furthermore, the water- and physical-stress-resistant film can cover the affected nail, which is clearly a cosmetic advantage.

Limitations of the present trial include a relatively low number of patients. However, sample size was calculated using data of earlier clinical trials with acetic acid-based and medicated topical treatments, confirming a comparable outcome in view of product performance and safety. Another limitation implies a treatment period of 180 days. Depending on the degree of infection, a treatment period of at least 6 months may be required for full recovery of the infected nail.

In conclusion, the test product is an efficient and safe treatment for mild-to-moderate cases of onychomycosis. At study end, the increase in  % of healthy surface of the nail was comparable to the medicated nail lacquer Loceryl^®. Clinical performance of the test product was further confirmed by: (1) the high number of patients with onychomycosis improvement or success (96.0% vs. 79.6% for reference), (2) the more pronounced positive evolution of different onychomycosis-related parameters in function of time, (3) the positive impact on quality of life of the patients, and (4) confirmed safety.