Onychomycosis is a fungal nail infection either caused by a dermatophyte (tinea unguium) or by other non-dermatophyte filamentous fungi or Candida spp [1]. Onychomycosis is a common condition accounting for about 50% of all nail problems [2, 3] with a worldwide prevalence of 5.5% (based on a weighted average of 6 epidemiologic studies published in 2016) [4-9]. The prevalence increases with age [10]. Onychomycosis is a cosmetically disfiguring and debilitating disease adversely affecting the self-esteem of patients and sometimes leading to depression. Apart from the pain and difficulty in walking, it carries the risk of cellulitis in the elderly and diabetic patients [11].

Treating onychomycosis is problematic for a variety of reasons. Oral therapy is more effective than topical therapy, but it is expensive, requires monitoring for toxicity, and can result in multiple drug interactions. Topical therapy is a long process that often requires nail debridement and multiple return visits and still delivers a relatively poor success rate. The very nature of the hard, protective nail plate itself makes it difficult for topical drugs to reach the fungal pathogens beneath it [12, 13]. Surgical nail avulsion for the treatment of onychomycosis should be avoided as potential side effects include post-operative pain, narrowing of the nail bed, distal paronychia, and infection [14]. It is contraindicated for patients with diabetes mellitus, peripheral and collagen vascular diseases, autoimmune disorders, disorders of hemostasis, and paronychia. Moreover, recurrences and reinfection are not uncommon (up to 20% of cured patients) [10]. Long-term negative effects on quality of life, difficult management associated with a high prevalence of onychomycosis show the need for new treatment modalities.

Recently, there has been a growing interest in the laser industry following a series of scientific trials that have introduced various laser systems as a therapeutic alternative for this condition. Lasers are potential therapeutic modalities for onychomycosis because they have very few contraindications, minimal adverse effects, short treatment regimens, and good patient compliance [15]. The CO₂ laser system was the first laser device studied for onychomycosis. Tissue heating from laser machines can produce direct damage or induce an immune reaction against pathogens [16-18]. Furthermore, they have been studied as adjuvants to topical therapies for onychomycosis, as they can facilitate drug delivery through the nail plate by increasing permeability [19]. Ablative standard CO₂ in combination with a topical antifungal drug, proved to be efficacious [20, 21]. However, patients experienced pain for weeks after treatment [22]. Yang et al. [23] used the ablative fractional CO₂ laser for onychomycosis patients for 12 weeks with 8 sessions. The results showed clinical efficacy in 52%. Moreover, two other studies used fractional CO₂ laser plus a topical medication (amorolfine and terbinafine, respectively) for onychomycosis treatment. The clinical efficacy was 71% and 73%, respectively [24, 25]. These results suggested that a combination of ablative fractional CO₂ with topical antifungals could be more effective than fractional CO₂ therapy alone. However, no randomized trial comparing this treatment approach to standard systemic antifungal therapy.

Therefore, we designed a randomized, controlled study to compare the safety and efficacy of carbon dioxide laser-assisted delivery of topical clotrimazole with systemic itraconazole plus topical clotrimazole in the treatment of onychomycosis.

Up-to-date oral and topical antifungal agents (used alone or in combination) are considered the mainstay of therapy against onychomycosis. Even in the most experienced hands, these approved and widely used drugs may offer only disappointing results with high rates of relapse. Laser treatments are the most rapidly expanding area of onychomycosis therapy. Laser devices can be used to enhance drug delivery, activate topically applied drugs, or photothermally kill fungi. Laser treatments have a number of advantages over traditional therapy as they are primarily conducted in the clinic by trained professionals, reducing the need for patient compliance. They also have the potential to reduce adverse events and systemic interactions. To our knowledge, this study is the first controlled trial that compares the efficacy and safety of carbon dioxide laser-assisted delivery of topical clotrimazole to systemic itraconazole for onychomycosis treatment.

In the present study, there was more female than male patients (60% versus 40%). Similar results were found by previous studies [7, 9, 27, 28]. The difference might result from daily habits such as nail cosmetics, frequent water contact, detergents, raw food, cleaning materials, hydrocarbons, and trauma. The habit of sharing nail care equipment such as scissors, clippers, and emery boards in nail salons also contributes to the spread of infection [29-32]

In our study, onychomycosis involving toenails is about two times more common than that of fingernails. These findings are comparable to the results of a multicenter survey of 15,000 patients in Canada [3]. The warm, moist, confined environment provided by our occlusive footwear, combined with slower toenail than fingernail growth and less blood flow to the area, all combine to make the feet and toes specifically vulnerable.

Distal and lateral subungual onychomycosis was the most common pattern of onychomycosis in our study, followed by total dystrophic onychomycosis. A similar result was found in the studies of Gupta et al. [3], the largest epidemiology survey has reported.

We found no significant differences between laser and itraconazole group in the mycological clearance rate defined by negative KOH examination at the end of the study (73.3% vs. 79.1%).

However, the laser group showed a significantly higher clinical improvement defined as a reduction in the mean SCIO at the end of the study compared with the itraconazole group (P<0.001).

A few uncontrolled studies with a combination of fractional CO₂ laser and a topical antifungal drug have been done. Lim et al. [24] was the first group using the combination of fractional CO₂ laser and a topical antifungal agent for the management of onychomycosis. They treated 119 nails in 24 patients with fractional CO₂ laser and topical amorolfine. The fluence used was at 24 J/cm². The laser treatment consisted of three sessions at four-week intervals. Ninety-two percent of the patients showed a clinical response and 50% showed a complete response with a negative KOH. Similarly, Bhatta et al. [25] used fractional CO₂ laser (also three sessions at four-week intervals) combined with daily 1% terbinafine cream for the treatment of onychomycosis. The authors reported 95% negative KOH and 92% negative culture at the end of the study. Most laser-treated nails (98%) showed improvement: the mean SCIO was significantly decreased.

To date, the exact mechanism of action of laser devices against fungal pathogens is still under investigation. Fungal inactivation through unselective tissue heating is the most prevailing hypothesis. It has been reported that temperatures of 55°C are the lowest capable of destroying dermatophytes [16], whereas temperatures of less than 45°C can stimulate germination with Trichophyton spp.-specific optimal values [17]. Tissue heating can produce direct damage or induce an immune reaction against pathogens. The optimal temperature and duration of heating tolerated by human tissue have not been elucidated yet. Nevertheless, heating should be done cautiously as temperatures above 60°C, which lead to protein denaturation and coagulation of healthy surrounding tissue. Carney et al. [18] showed that heat produced a fungicidal effect for T. rubrum at 50°C with exposure times of 15 min, for Epidermophyton floccosum at 50°C with exposure times of 10 min, and limited growth of Scytalidium spp. was seen at 55°C with exposure times of 5 min. Additionally, the fractional CO₂ laser can create multiple tiny columns that facilitate drug delivery through the nail plate by increasing permeability [24]. Furthermore, during the laser procedure, nail plates, the environment for fungal growth, are partially vaporized [33].

In total, 11 adverse events related to itraconazole were experienced by 8 patients. The most frequently reported itraconazole-related adverse events were gastrointestinal disorders. Patients treated by fractional CO₂ laser only experienced slight pain. This correlates with most published studies [24, 25, 34, 35].

Fractional CO₂ laser combined with topical clotrimazole 1% is a safe and effective treatment option for onychomycosis. It achieved a greater clinical improvement with a similar mycotic cure rate rather than oral itraconazole in combination with topical clotrimazole 1%. Candidates for this method are patients who have failed previous therapies or those in whom systemic therapies are contraindicated, fearing polypharmacy, or drug interactions. Patients with certain non-dermatophyte molds, such as N. dimidiatum infections, in whom there is no good alternative therapy, may also be considered ideal candidates.