Onychomycosis is a relatively common dermatologic presentation (Table 1). The incidence of the disease varies regionally and with age. Although in most cases the condition poses no significant long-term health risk, treatment is indicated. Affected nails can be cosmetically unsightly and may become painful and cause functional impairment. In some cases, such as among diabetic patients, treatment of onychomycosis is imperative. These patients typically are concurrently using other medications, so treatment must be selected to minimize or anticipate any adverse drug interactions.1 Clinicians may encounter three clinical types of onychomycosis2,3:
Distal lateral subungual onychomycosis develops when the fungus enters via the lateral nail groove and distal subungual area.
Superficial white onychomycosis is the result of infection via the dorsal surface of the nail plate.
Proximal white subungual onychomycosis develops following infection of the undersurface of the proximal nail fold. Although rare in the general population, this presentation may be found in immunocompromised patients. The nail fold remains normal in this presentation. Inflammation may indicate chronic paronychia with secondary nail involvement.
More than 90 percent of cases of onychomycosis are caused by dermatophytes.3 Although dermatology care providers may highly suspect onychomycosis based on the presentation of dystrophic, yellowed nails, many experts now urge the use of diagnostic cultures to confirm the diagnosis and potentially direct treatment. A common mimicker of onychomycosis is psoriatic nail disease, discussed in the sidebar on p. 4.
KOH slide evaluation, using 15-20% KOH in dimethyl sulfoxide, is the easiest method to confirm dermatophyte infection. Chlorazol E stain specific for fungus cell walls is sometimes supportive. If identification of specific causative organisms is desired, culture using one of the commercially available media is possible. 2,3
The quality of the sample evaluated will determine the utility of any analysis or culture. For distal subungual onychomycosis, a small 1ml curette can be used to obtain a specimen from the onychomycotic border, where the highest number of viable hyphae exist.2,3
In the case of proximal white subungual onychomycosis, a No. 15 blade scalpel can be used to remove superficial layers of the nail, after which a curette can be used to remove samples from the infected area.2,3
For superficial white onychomycosis a No. 15 blade scalpel can be used to scrape the nail to obtain sample materials.2,3
Oral Therapy for Onychomycosis
Oral therapy is generally recognized as offering the highest likelihood of cure of onychomycosis, compared to current FDAapproved topical options. Systemic drugs are thought to remain in the nail following discontinuation of therapy, which may allow them to confer continuing antifungal effect. However, there are some practical limitations to oral antifungal therapy. Of greatest interest is the fact that the azole antifungal drugs may affect liver function.4 (Table 2) Although the risk may be relatively low for a given patient, it is actually well known in the public and may cause some patients to refuse oral therapy. There are also important drug interactions to consider when prescribing oral antifungals, as described below. Table 3 reviews oral therapy options.
Itraconazole has the broadest spectrum of effect (active against dermatophytes, Candida, and some nondermatophyte molds). Recommended dosage is usually 200mg BID without food for one week a month. Treatment of toenail onychomycosis will require three to four months of therapy. Fingernails can be treated in one to two months.2,3
Active against Candida and other yeasts, fluconazole will require the longest course of therapy. The option of a 150mg once-weekly pulse dose is attractive for some patients, especially those who may be taking many other medications and appreciate a simplified regimen.2,3
The azoles inhibit certain subtypes of the cytochrome P-450 family, particularly CYP3A4.5,6 Therefore, they may interfere with a range of drugs including oral anticoagulants, calcium channel blockers, statins, most HIV protease inhibitors, certain antineoplastic agents and immunosuppressants, corticosteroids, opiate analgesics, neuro-active substances and others.
Terbinafine has in vivo activity against dermatophytes, some species of Candida, and some molds. Within one to three weeks of therapy, terbinafine is detectable in the nail plate. It persists up to four months following discontinuation of therapy. For toenail infections, a 12-week course of 250mg once daily is effective. Fingernail infections require a six-week course at that dose.2,3
The potential of terbinafine for drug interaction is generally considered low, especially relative to the azoles. Terbinafine is metabolized extensively in the liver, via the action of various P-450 enzymes and requiring less than five percent of the total liver CYP450 capacity. Clinically significant drug interactions are limited to cimetidine and rifampicin; cimetidine decreases the rate of terbinafine plasma clearance and rifampicin increases it.6
Though not commonly used for onychomycosis therapy currently, griseofulvin is an option. Practical limitations of griseofulvin have led to its lower rate of use relative to newer oral antifungal options. Griseofulvin has poor absorption, unless micronized, coated with polyethylene glycol, or given with fatty meals. The drug is also known to interact with phenobarbital and anticoagulants (especially warfarin-type) and may cause contraceptive failure especially of low dose pills.6
For any of these agents, it is important to note that the nail will not appear normal upon completion of the treatment course, even if mycologic cure is obtained. Patients should be educated that it will take time for the affected portion of the nail to grow out. As with most diseases and therapies, incomplete response, non-response, and relapse are all possible with oral antifungal therapy for onychomycosis.
Although conventional topical antifungal therapy does not permit diffusion of the active agent into the nail plate, ciclopirox 8% lacquer nail lacquers demonstrates sufficient penetration. Ciclopirox 8% lacquer produces a polymer film reservoir on the nail. As the solvent within the lacquer evaporates, the concentration of the active antifungal within the film increases. The antifungal diffuses through the nail plate to the nail bed over time. While the lacquer may be used as monotherapy, it may also be used in conjunction with oral agents.2,3
Several novel topical investigational treatments are in various stages of clinical development. The one that is closest to approval is efinaconazole topical solution. Results of a multicenter, randomized, double-blind, vehicle controlled Phase 2 study of efinaconazole solution in mild to moderate toenail distal lateral subungual onychomycosis were recently presented. 7 The multi-arm study investigated efinaconazole 10% semiocclusion, efinaconazole 10%, efinaconazole 5%, and vehicle. At Week 40, complete cure (16-26 percent) was numerically higher in all efinaconazole solution treated groups compared to vehicle (nine percent). Mycologic cure rates with efinaconazole 10% semi-occlusion, efinaconazole 10%, efinaconazole 5%, and vehicle were 83 percent, 87 percent, 87 percent, and 73 percent, respectively.
Phase 3 trial results show that efinaconazole 10% solution was significantly more effective than placebo in providing mycologic and complete cure rates for distal lateral subungual toenail onychomycosis.8 Data come from two identical, multicenter, randomized, double-blind, vehicle-controlled studies in patients with toenail distal lateral subungual onychomycosis (20-50 percent clinical involvement [study 1: N = 870, study 2: N = 785]). Patients were randomized (3:1) to efinaconazole or vehicle, once daily for 48 weeks, with four-week post-treatment follow-up. The primary end point was complete cure rate (0 percent clinical involvement of target toenail, and both negative potassium hydroxide examination and fungal culture) at week 52.
Mycologic cure rates were 55.2 percent and 53.4 percent for efinaconazole—significantly greater than for placebo (16.8 percent and 16.9 percent). Complete cure rates for efinaconazole were 17.8 percent and 15.2 percent, compared to 3.3 percent and 5.5 percent for vehicle. Treatment success as a measure of percent improvement in target toenail ranged from 17.9-44.8 percent for active treatment, compared to 5.6 percent to 16.8 percent for vehicle. Adverse events associated with efinaconazole (local site reactions) occurred in two percent of patients and were clinically similar to vehicle.
Another topical antifungal solution is currently in Phase 3 trials for toenail onychomycosis. Interim Phase 2 data (six of 12 months) have been reported for tavaborole (Anacor), which was compared to placebo for the treatment of toenail onychomycosis.9 After six months of therapy, 50 percent subjects applying tavaborole 7.5% solution once daily had 2mm clear nail growth and negative fungal cultures. Roughly half of these subjects had 5mm clear nail growth. The trial also investigated the efficacy of tavaborole 5% solution; 45 percent of subjects had 2mm clear nail growth and negative fungal cultures.
Finally, an investigational compound was shown noninferior to topical 5% amorolfine nail lacquer, which is used in Europe but not approved in the US. In the study, 1,029 patients with mild to moderate nail fungus were given either topical 10% terbinafine hydrogen chloride (MycoVa, Apricus Bio) or 5% amorolfine nail lacquer for 48 weeks. There was no significant difference in either the primary (complete cure) or secondary endpoints (mycologic cure and cosmetic improvement) between the treatments. Apricus reports that a post-hoc analysis of two Phase 3, randomized, double-blind, vehicle controlled, multicenter, parallel group studies to assess the efficacy, safety, and tolerability of 5% amorolfine nail lacquer demonstrated statistically significant mycological cure rates compared to placebo.10
Conventional topical antifungal creams and ointments may play a role in onychomycosis therapy when and if there is coexistent tinea pedis or tinea manuum. Skin involvement serves as a reservoir for fungi, which enhances the probability of treatment failure for onychomycosis or relapse. Long-term, intermittent use of topical antifungal agents on the plantar surface of the hands and feet and of the toe webs may help prevent tinea pedis or tinea manuum and subsequently limit the likelihood of reinfection of the nail. Patients can also employ strategies to minimize recontamination with dermatophytes by allowing footwear to dry thoroughly, treating footwear with antifungal powders, or if necessary, purchasing new footwear. Proper hot-water laundering11 of towels, socks, or other items can eliminate dermatophyte contamination of these items.
- Cathcart S, Cantrell W, Elewski B. Onychomycosis and diabetes. J Eur Acad Dermatol Venereol. 2009 Oct;23(10):1119-22.
- Aly R. Improve Your Approach to Dermatophyte Infections of the Feet. Practical Dermatology 2006. 3(4):28-35.
- Cutaneous Infection and Therapy, Aly R, Beutner KR, and Maibach H, Eds (Dekker 1997)
- Garcia Rodriguez LA, Duque A, Castellsague J, et al. A cohort study on the risk of acute liver injury among users of ketoconazole and other antifungal drugs. Br J Clin Pharmacol. 1999;48:847–52.
- Traunmüller F, Popovic M, Konz KH, Smolle-Jüttner FM, Joukhadar C. Efficacy and safety of current drug therapies for invasive aspergillosis. Pharmacology. 2011;88(3-4):213-24.
- Elewski B, Tavakkol A. Safety and tolerability of oral antifungal agents in the treatment of fungal nail disease: a proven reality. Ther Clin Risk Manag. 2005 Dec;1(4):299-306.
- Tschen E, Bucko AD, Oizumi C, et al. Efinaconazole solution in the treatment of toenail onychomycosis: a phase 2 multicenter, randomized, double-blind study. Fall Clinical Dermatology Conference. October 2012.
- Elewski BE, Rich P, Pollak R, Pariser DM, Watanabe S, Senda H, Ieda C, Smith K, Pillai R, Ramakrishna T, Olin JT. Efinaconazole 10% solution in the treatment of toenail onychomycosis: Two phase III multicenter, randomized, double-blind studies. J Am Acad Dermatol. 2012; e-pub Nov 20.
- Hammer TR, Mucha H, Hoefer D. Infection risk by dermatophytes during storage and after domestic laundry and their temperature-dependent inactivation. Mycopathologia. 2011 Jan;171(1):43-9.
- Shemer A, Trau H, Davidovici B, Grunwald MH, Amichai B. Onychomycosis in psoriatic patients - rationalization of systemic treatment. Mycoses. 2009 May 29.
- “Step Up Your Approach to Fungal Infections.” Practical Dermatology 2009. 6(7): 41-43.
- Panackal AA, Halpern EF, Watson AJ. Cutaneous fungal infections in the United States: Analysis of the National Ambulatory Medical Care Survey (NAMCS) and National Hospital Ambulatory Medical Care Survey (NHAMCS), 1995-2004. Int J Dermatol. 2009 Jul;48(7):704-12.
TOP 5 ARTICLES FROM DECEMBER 2012
- Management of Onychomycosis: A Review
By Coyle S. Connolly, DO