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Clinical Trial Designs for Topical Antifungal Treatments of Onychomycosis and Implications on Clinical Practice
Onychomycosis is a fungal nail infection primarily caused by dermatophytes.1 If left untreated, the infection can cause nail destruction and deformities,1 resulting in pain and discomfort,2 impaired foot mobility,3 and an overall reduced quality of life.1 Onychomycosis is a chronic condition that requires long treatment periods due to the slow growth rates of toenails.1 To successfully cure the condition, fungal eradication must be achieved.
Prior to the US Food and Drug Administration (FDA) approval of tavaborole and efinaconazole, ciclopirox was the only approved topical treatment for onychomycosis.4 The recent approval of tavaborole and efinaconazole has increased treatment options available to patients and has started to pave the way for future topical treatments. This article discusses the 3 approved topical treatments for onychomycosis and focuses on the design of the phase 3 clinical trials that led to their approval.
Topical Agents Used to Treat Onychomycosis
Tavaborole, efinaconazole, and ciclopirox have undergone extensive clinical investigation to receive FDA approval. Results from pivotal phase 3 studies establishing the efficacy and safety of each agent formed the basis for regulatory submission. Although it may seem intuitive to compare the relative performance of these agents based on their respective phase 3 clinical trial data, there are important differences in study methodology, conduct, and populations that prevent direct comparisons. The FDA provides limited guidance to the pharmaceutical industry on how to conduct clinical trials for potential onychomycosis treatments. Comparative efficacy and safety claims are limited based on cross-study comparisons. The details of the phase 3 trial designs are summarized in the Table.
Tavaborole
Tavaborole is a boron-based treatment with a novel mechanism of action.5 Tavaborole binds to the editing domain of leucyl–transfer ribonucleic acid synthetase via an integrated boron atom and inhibits fungal protein synthesis.6 Two identical randomized, double-blind, vehicle-controlled, parallel-group, phase 3 clinical trials evaluating tavaborole were performed.5 The first study (registered at www.clinicaltrials.gov with the identifier NCT01270971) included 594 participants from27 sites in the United States and Mexico and was conducted between December 2010 and November 2012. The second study (NCT01302119) included 604 participants from 32 sites in the United States and Canada and was conducted between February 2011 and January 2013.
Eligible participants 18 years and older had distal subungual onychomycosis (DSO) of the toenails affecting 20% to 60% of 1 or more target great toenails (TGTs), tested positive for fungus using potassium hydroxide (KOH) wet mounts and positive for Trichophyton rubrum and Trichophyton mentagrophytes on fungal culture diagnostic tests, had distal TGT thickness of 3 mm or less, and had 3 mm or more of clear nail between the proximal nail fold and the most proximal visible mycotic border.5 Those with active tinea pedis requiring treatment or with a history of chronic moccasin-type tinea pedis were excluded. Participants were randomized to receive either tavaborole or vehicle (2:1). Treatments were applied once daily to all infected toenails for a total of 48 weeks, and nail debridement (defined as partial or complete removal of the toenail) was not permitted. Notably, controlled trimming of the nail was allowed to 1 mm of the leading nail edge. Regular assessments of each toenail for disease involvement, onycholysis, and subungual hyperkeratosis were made at screening, baseline, week 2, week 6, and every 6 weeks thereafter until week 52. Subungual TGT samples were taken at screening and every 12 weeks during the study for examination at a mycology laboratory, which performed KOH and fungal culture tests. A follow-up assessment was made at week 52.5
The primary end point was complete cure of the TGT at week 52, with secondary end points of completely or almost clear TGT nail (≤10% dystrophic nail), completely or almost clear TGT nail (≤10% dystrophic nail) plus negative mycology, and negative mycology of TGT.5 Examples of TGTs in participants who achieved complete cure and almost clear nails with negative mycology before and after treatment with tavaborole are shown in Figure 1. An example of a patient considered to have treatment failure is shown in Figure 2. This patient showed marked improvement in nail appearance and had a negative culture result but had a positive KOH test, which demonstrates the stringency in which topical agents are judged in onychomycosis trials.5
Efinaconazole
Efinaconazole is a topical triazole antifungal specifically indicated to treat onychomycosis. Two identical randomized, vehicle-controlled, double-blind, multicenter trials were performed to assess the safety and efficacy of efinaconazole solution 10%.7 The first study (NCT01008033) involved 870 participants and was conducted at a total of 74 sites in Japan (33 sites), Canada (7 sites), and the United States (34 sites) between December 2009 and September 2011. The second study (NCT01007708) had 785 participants and was conducted at 44 sites in Canada (8 sites) and the United States (36 sites) between December 2009 and October 2011.
Participants aged 18 to 70 years with a clinical diagnosis of DSO affecting 1 or more TGT were eligible to participate.7 Other eligibility criteria included an uninfected toenail length 3 mm or more from the proximal nail fold, a maximum toenail thickness of 3 mm, positive KOH wet mounts, and positive dermatophyte or mixed dermatophyte/candida cultures. Dermatophytes included T rubrum and T mentagrophytes. Those with severe moccasin-type tinea pedis were excluded. Participants were randomized to receive efinaconazole or vehicle (3:1). Once-daily treatments were self-applied to nails for 48 weeks. Clinical assessments were made at baseline and every 12 weeks until week 48, with a follow-up assessment at week 52. No nail trimming protocol was provided.7
The primary end point of the efinaconazole phase 3 trials was complete cure at week 52, with secondary end points including mycologic cure, treatment success (≤5% mycotic nail), and complete or almost complete cure (negative culture and KOH, ≤5% mycotic nail). An example of a complete cure from baseline to week 52 is shown in Figure 3.7
Ciclopirox
Ciclopirox was the first topical therapy to be approved for the treatment of onychomycosis. Ciclopirox is a broad-spectrum antifungal agent that inhibits metal-dependent enzymes, which are responsible for the degradation of toxic peroxides in fungal cells. The safety and efficacy of ciclopirox nail lacquer topical solution 8% also was investigated in 2 identical phase 3 clinical trials.8 The first study was conducted at 9 sites in the United States between June 1994 and June 1996 and included 223 participants. The second study was conducted at 9 sites in the United States between July 1994 and April 1996 and included 237 participants.
Eligible participants were required to have DSO in at least one TGT, positive KOH wet mount with positive dermatophyte culture, and 20% to 65% nail involvement.8 Those with tinea pedis were not excluded. Participants were randomized to receive once-daily treatment with ciclopirox or vehicle (1:1)(applied to all toenails and affected fingernails) for 48 weeks. The product was to be removed by the patient with alcohol on a weekly basis. Trimming was allowed as necessary, and mechanical debridement by the physician could be performed monthly. Assessments were made every 4 weeks, and mycologic examinations were performed every 12 weeks. Participants who were clinically cured were assessed further in a 12- to 24-week posttreatment follow-up period.8
The primary end point of complete cure and secondary end points of treatment success (negative culture and KOH, ≤10% mycotic nail), mycologic cure, and negative mycologic culture were assessed at week 48.8
Phase 3 Clinical Trial Similarities and Differences
The phase 3 clinical trials used to investigate the safety and efficacy of tavaborole,5 efinaconazole,7 and ciclopirox8 were similar in their overall design. All trials were randomized, double-blind, vehicle-controlled studies in patients with DSO. Each agent was assessed using a once-daily application for a treatment period of 48 weeks.
Primary differences among study designs included the age range of participants, the range of mycotic nail involvement, the presence/absence of tinea pedis, and the nail trimming/debridement protocols used. Differences were observed in the patient eligibility criteria of these trials. Both mycotic area and participant age range were inconsistent for each agent (eTable). Participants with larger mycotic areas usually have a poorer prognosis, as they tend to have a greater fungal load.9 A baseline mycotic area of 20% to 60%,5 20% to 50%,7 and 20% to 65%8 at baseline was required for the tavaborole, efinaconazole, and ciclopirox trials, respectively. Variations in mycotic area between trials can affect treatment efficacy, as clinical cures can be reached quicker by patients with smaller areas of infection. Of note, the average mycotic area of involvement was not reported in the tavaborole studies but was 36% and 40% for the efinaconazole and ciclopirox studies, respectively.5,8 It also is more difficult to achieve complete cure in older patients, as they have poor circulation and reduced nail growth rates.1,10 The participant age range was 18 to 88 years in the tavaborole trials, with 8% of the participants older than 70 years,5 compared to 18 to 71 years in both the efinaconazole and ciclopirox trials.7,8 The average age of participants in each study was approximately 54, 51, and 50 years for tavaborole, efinaconazole, and ciclopirox, respectively. Because factors impacting treatment failure can increase with age, efficacy results can be confounded by differing age distributions across different studies.
Another important feature that differed between the clinical trials was the approach to nail trimming—defined as shortening of the free edge of the nail distal to the hyponychium—which varies from debridement in that the nail plate is removed or reduced in thickness proximal to the hyponychium. In the tavaborole trials, trimming was controlled to within 1 mm of the free edge of the nail,5 whereas the protocol used for the ciclopirox trials allowed nail trimming as necessary as well as moderate debridement before treatment application and on a monthly basis.8 Debridement is an important component in all ciclopirox trials, as it is used to reduce fungal load.11 No trimming control was provided during the efinaconazole trials; however, debridement was prohibited.7 These differences can dramatically affect the study results, as residual fungal elements and portions of infected nails are removed during the trimming process in an uncontrolled manner, which can affect mycologic testing results as well as the clinical efficacy results determined through investigator evaluation. Discrepancies regarding nail trimming approach inevitably makes the trial results difficult to compare, as mycologic cure is not translatable between studies.
Furthermore, somewhat unusually, complete cure rate variations were observed between different study centers in the efinaconazole trials. Japanese centers in the first efinaconazole study (NCT01008033) had higher complete cure rates in both the efinaconazole and vehicle treatment arms, which is notable because approximately 29% of participants in this study were Asian, mostly hailing from 33 Japanese centers. The reason for these confounding results is unknown and requires further analysis.
Lastly, the presence or absence of tinea pedis can affect the response to onychomycosis treatment. In the tavaborole trials, patients with active interdigital tinea pedis or exclusively plantar tinea pedis or chronic moccasin-type tinea pedis requiring treatment were excluded from the studies.5 In contrast, only patients with severe moccasin-type tinea pedis were excluded in efinaconazole trials.7 The ciclopirox studies had no exclusions based on presence of tinea pedis.8 These differences are noteworthy, as tinea pedis can serve as a reservoir for fungal infection if not treated and can lead to recurrence of onychomycosis.12
Conclusion
In recent years, disappointing efficacy has resulted in the failure of several topical agents for onychomycosis during their development; however, there are several aspects to consider when examining efficacy data in onychomycosis studies. Obtaining a complete cure in onychomycosis is difficult. Because patients applying treatments at home are unlikely to undergo mycologic testing to confirm complete cure, visual inspections are helpful to determine treatment efficacy.
Despite similar overall designs, notable differences in the study designs of the phase 3 clinical trials investigating tavaborole, efinaconazole, and ciclopirox are likely to have had an effect on the reported results, making the efficacy of the agents difficult to compare. It is particularly tempting to compare the primary end point results of each trial, especially considering tavaborole and efinaconazole had primary end points with the same parameters; however, there are several other factors (eg, age range of study population, extent of infection, nail trimming, patient demographics) that may have affected the outcomes of the studies and precluded a direct comparison of any end points. Without head-to-head investigations, there is room for prescribing clinicians to interpret results differently.
Acknowledgment
Writing and editorial assistance was provided by ApotheCom Associates, LLC, Yardley, Pennsylvania, and was supported by Sandoz, a Novartis division.
- Elewski BE. Onychomycosis: pathogenesis, diagnosis, and management. Clin Microbiol Rev. 1998;11:415-429.
- Thomas J, Jacobson GA, Narkowicz CK, et al. Toenail onychomycosis: an important global disease burden. J Clin Pharm Ther. 2010;35:497-519.
- Scher RK. Onychomycosis: a significant medical disorder. J Am Acad Dermatol. 1996;35(3, pt 2):S2-S5.
- Del Rosso JQ. The role of topical antifungal therapy for onychomycosis and the emergence of newer agents. J Clin Aesthet Dermatol. 2014;7:10-18.
- Elewski BE, Aly R, Baldwin SL, et al. Efficacy and safety of tavaborole topical solution, 5%, a novel boron-based antifungal agent, for the treatment of toenail onychomycosis: results from 2 randomized phase-III studies. J Am Acad Dermatol. 2015;73:62-69.
- Rock FL, Mao W, Yaremchuk A, et al. An antifungal agent inhibits an aminoacyl-tRNA synthetase by trapping tRNA in the editing site. Science. 2007;316:1759-1761.
- Elewski BE, Rich P, Pollak R, et al. Efinaconazole 10% solution in the treatment of toenail onychomycosis: two phase III multicenter, randomized, double-blind studies. J Am Acad Dermatol. 2013;68:600-608.
- Gupta AK, Joseph WS. Ciclopirox 8% nail lacquer in the treatment of onychomycosis of the toenails in the United States. J Am Pod Med Assoc. 2000;90:495-501.
- Carney C, Tosti A, Daniel R, et al. A new classification system for grading the severity of onychomycosis: Onychomycosis Severity Index. Arch Dermatol. 2011;147:1277-1282.
- Gupta AK. Onychomycosis in the elderly. Drugs Aging. 2000;16:397-407.
- Gupta AK, Malkin KF. Ciclopirox nail lacquer and podiatric practice. J Am Podiatr Med Assoc. 2000;90:502-507.
- Scher RK, Baran R. Onychomycosis in clinical practice: factors contributing to recurrence. Br J Dermatol. 2003;149(suppl 65):5-9.
Onychomycosis is a fungal nail infection primarily caused by dermatophytes.1 If left untreated, the infection can cause nail destruction and deformities,1 resulting in pain and discomfort,2 impaired foot mobility,3 and an overall reduced quality of life.1 Onychomycosis is a chronic condition that requires long treatment periods due to the slow growth rates of toenails.1 To successfully cure the condition, fungal eradication must be achieved.
Prior to the US Food and Drug Administration (FDA) approval of tavaborole and efinaconazole, ciclopirox was the only approved topical treatment for onychomycosis.4 The recent approval of tavaborole and efinaconazole has increased treatment options available to patients and has started to pave the way for future topical treatments. This article discusses the 3 approved topical treatments for onychomycosis and focuses on the design of the phase 3 clinical trials that led to their approval.
Topical Agents Used to Treat Onychomycosis
Tavaborole, efinaconazole, and ciclopirox have undergone extensive clinical investigation to receive FDA approval. Results from pivotal phase 3 studies establishing the efficacy and safety of each agent formed the basis for regulatory submission. Although it may seem intuitive to compare the relative performance of these agents based on their respective phase 3 clinical trial data, there are important differences in study methodology, conduct, and populations that prevent direct comparisons. The FDA provides limited guidance to the pharmaceutical industry on how to conduct clinical trials for potential onychomycosis treatments. Comparative efficacy and safety claims are limited based on cross-study comparisons. The details of the phase 3 trial designs are summarized in the Table.
Tavaborole
Tavaborole is a boron-based treatment with a novel mechanism of action.5 Tavaborole binds to the editing domain of leucyl–transfer ribonucleic acid synthetase via an integrated boron atom and inhibits fungal protein synthesis.6 Two identical randomized, double-blind, vehicle-controlled, parallel-group, phase 3 clinical trials evaluating tavaborole were performed.5 The first study (registered at www.clinicaltrials.gov with the identifier NCT01270971) included 594 participants from27 sites in the United States and Mexico and was conducted between December 2010 and November 2012. The second study (NCT01302119) included 604 participants from 32 sites in the United States and Canada and was conducted between February 2011 and January 2013.
Eligible participants 18 years and older had distal subungual onychomycosis (DSO) of the toenails affecting 20% to 60% of 1 or more target great toenails (TGTs), tested positive for fungus using potassium hydroxide (KOH) wet mounts and positive for Trichophyton rubrum and Trichophyton mentagrophytes on fungal culture diagnostic tests, had distal TGT thickness of 3 mm or less, and had 3 mm or more of clear nail between the proximal nail fold and the most proximal visible mycotic border.5 Those with active tinea pedis requiring treatment or with a history of chronic moccasin-type tinea pedis were excluded. Participants were randomized to receive either tavaborole or vehicle (2:1). Treatments were applied once daily to all infected toenails for a total of 48 weeks, and nail debridement (defined as partial or complete removal of the toenail) was not permitted. Notably, controlled trimming of the nail was allowed to 1 mm of the leading nail edge. Regular assessments of each toenail for disease involvement, onycholysis, and subungual hyperkeratosis were made at screening, baseline, week 2, week 6, and every 6 weeks thereafter until week 52. Subungual TGT samples were taken at screening and every 12 weeks during the study for examination at a mycology laboratory, which performed KOH and fungal culture tests. A follow-up assessment was made at week 52.5
The primary end point was complete cure of the TGT at week 52, with secondary end points of completely or almost clear TGT nail (≤10% dystrophic nail), completely or almost clear TGT nail (≤10% dystrophic nail) plus negative mycology, and negative mycology of TGT.5 Examples of TGTs in participants who achieved complete cure and almost clear nails with negative mycology before and after treatment with tavaborole are shown in Figure 1. An example of a patient considered to have treatment failure is shown in Figure 2. This patient showed marked improvement in nail appearance and had a negative culture result but had a positive KOH test, which demonstrates the stringency in which topical agents are judged in onychomycosis trials.5
Efinaconazole
Efinaconazole is a topical triazole antifungal specifically indicated to treat onychomycosis. Two identical randomized, vehicle-controlled, double-blind, multicenter trials were performed to assess the safety and efficacy of efinaconazole solution 10%.7 The first study (NCT01008033) involved 870 participants and was conducted at a total of 74 sites in Japan (33 sites), Canada (7 sites), and the United States (34 sites) between December 2009 and September 2011. The second study (NCT01007708) had 785 participants and was conducted at 44 sites in Canada (8 sites) and the United States (36 sites) between December 2009 and October 2011.
Participants aged 18 to 70 years with a clinical diagnosis of DSO affecting 1 or more TGT were eligible to participate.7 Other eligibility criteria included an uninfected toenail length 3 mm or more from the proximal nail fold, a maximum toenail thickness of 3 mm, positive KOH wet mounts, and positive dermatophyte or mixed dermatophyte/candida cultures. Dermatophytes included T rubrum and T mentagrophytes. Those with severe moccasin-type tinea pedis were excluded. Participants were randomized to receive efinaconazole or vehicle (3:1). Once-daily treatments were self-applied to nails for 48 weeks. Clinical assessments were made at baseline and every 12 weeks until week 48, with a follow-up assessment at week 52. No nail trimming protocol was provided.7
The primary end point of the efinaconazole phase 3 trials was complete cure at week 52, with secondary end points including mycologic cure, treatment success (≤5% mycotic nail), and complete or almost complete cure (negative culture and KOH, ≤5% mycotic nail). An example of a complete cure from baseline to week 52 is shown in Figure 3.7
Ciclopirox
Ciclopirox was the first topical therapy to be approved for the treatment of onychomycosis. Ciclopirox is a broad-spectrum antifungal agent that inhibits metal-dependent enzymes, which are responsible for the degradation of toxic peroxides in fungal cells. The safety and efficacy of ciclopirox nail lacquer topical solution 8% also was investigated in 2 identical phase 3 clinical trials.8 The first study was conducted at 9 sites in the United States between June 1994 and June 1996 and included 223 participants. The second study was conducted at 9 sites in the United States between July 1994 and April 1996 and included 237 participants.
Eligible participants were required to have DSO in at least one TGT, positive KOH wet mount with positive dermatophyte culture, and 20% to 65% nail involvement.8 Those with tinea pedis were not excluded. Participants were randomized to receive once-daily treatment with ciclopirox or vehicle (1:1)(applied to all toenails and affected fingernails) for 48 weeks. The product was to be removed by the patient with alcohol on a weekly basis. Trimming was allowed as necessary, and mechanical debridement by the physician could be performed monthly. Assessments were made every 4 weeks, and mycologic examinations were performed every 12 weeks. Participants who were clinically cured were assessed further in a 12- to 24-week posttreatment follow-up period.8
The primary end point of complete cure and secondary end points of treatment success (negative culture and KOH, ≤10% mycotic nail), mycologic cure, and negative mycologic culture were assessed at week 48.8
Phase 3 Clinical Trial Similarities and Differences
The phase 3 clinical trials used to investigate the safety and efficacy of tavaborole,5 efinaconazole,7 and ciclopirox8 were similar in their overall design. All trials were randomized, double-blind, vehicle-controlled studies in patients with DSO. Each agent was assessed using a once-daily application for a treatment period of 48 weeks.
Primary differences among study designs included the age range of participants, the range of mycotic nail involvement, the presence/absence of tinea pedis, and the nail trimming/debridement protocols used. Differences were observed in the patient eligibility criteria of these trials. Both mycotic area and participant age range were inconsistent for each agent (eTable). Participants with larger mycotic areas usually have a poorer prognosis, as they tend to have a greater fungal load.9 A baseline mycotic area of 20% to 60%,5 20% to 50%,7 and 20% to 65%8 at baseline was required for the tavaborole, efinaconazole, and ciclopirox trials, respectively. Variations in mycotic area between trials can affect treatment efficacy, as clinical cures can be reached quicker by patients with smaller areas of infection. Of note, the average mycotic area of involvement was not reported in the tavaborole studies but was 36% and 40% for the efinaconazole and ciclopirox studies, respectively.5,8 It also is more difficult to achieve complete cure in older patients, as they have poor circulation and reduced nail growth rates.1,10 The participant age range was 18 to 88 years in the tavaborole trials, with 8% of the participants older than 70 years,5 compared to 18 to 71 years in both the efinaconazole and ciclopirox trials.7,8 The average age of participants in each study was approximately 54, 51, and 50 years for tavaborole, efinaconazole, and ciclopirox, respectively. Because factors impacting treatment failure can increase with age, efficacy results can be confounded by differing age distributions across different studies.
Another important feature that differed between the clinical trials was the approach to nail trimming—defined as shortening of the free edge of the nail distal to the hyponychium—which varies from debridement in that the nail plate is removed or reduced in thickness proximal to the hyponychium. In the tavaborole trials, trimming was controlled to within 1 mm of the free edge of the nail,5 whereas the protocol used for the ciclopirox trials allowed nail trimming as necessary as well as moderate debridement before treatment application and on a monthly basis.8 Debridement is an important component in all ciclopirox trials, as it is used to reduce fungal load.11 No trimming control was provided during the efinaconazole trials; however, debridement was prohibited.7 These differences can dramatically affect the study results, as residual fungal elements and portions of infected nails are removed during the trimming process in an uncontrolled manner, which can affect mycologic testing results as well as the clinical efficacy results determined through investigator evaluation. Discrepancies regarding nail trimming approach inevitably makes the trial results difficult to compare, as mycologic cure is not translatable between studies.
Furthermore, somewhat unusually, complete cure rate variations were observed between different study centers in the efinaconazole trials. Japanese centers in the first efinaconazole study (NCT01008033) had higher complete cure rates in both the efinaconazole and vehicle treatment arms, which is notable because approximately 29% of participants in this study were Asian, mostly hailing from 33 Japanese centers. The reason for these confounding results is unknown and requires further analysis.
Lastly, the presence or absence of tinea pedis can affect the response to onychomycosis treatment. In the tavaborole trials, patients with active interdigital tinea pedis or exclusively plantar tinea pedis or chronic moccasin-type tinea pedis requiring treatment were excluded from the studies.5 In contrast, only patients with severe moccasin-type tinea pedis were excluded in efinaconazole trials.7 The ciclopirox studies had no exclusions based on presence of tinea pedis.8 These differences are noteworthy, as tinea pedis can serve as a reservoir for fungal infection if not treated and can lead to recurrence of onychomycosis.12
Conclusion
In recent years, disappointing efficacy has resulted in the failure of several topical agents for onychomycosis during their development; however, there are several aspects to consider when examining efficacy data in onychomycosis studies. Obtaining a complete cure in onychomycosis is difficult. Because patients applying treatments at home are unlikely to undergo mycologic testing to confirm complete cure, visual inspections are helpful to determine treatment efficacy.
Despite similar overall designs, notable differences in the study designs of the phase 3 clinical trials investigating tavaborole, efinaconazole, and ciclopirox are likely to have had an effect on the reported results, making the efficacy of the agents difficult to compare. It is particularly tempting to compare the primary end point results of each trial, especially considering tavaborole and efinaconazole had primary end points with the same parameters; however, there are several other factors (eg, age range of study population, extent of infection, nail trimming, patient demographics) that may have affected the outcomes of the studies and precluded a direct comparison of any end points. Without head-to-head investigations, there is room for prescribing clinicians to interpret results differently.
Acknowledgment
Writing and editorial assistance was provided by ApotheCom Associates, LLC, Yardley, Pennsylvania, and was supported by Sandoz, a Novartis division.
Onychomycosis is a fungal nail infection primarily caused by dermatophytes.1 If left untreated, the infection can cause nail destruction and deformities,1 resulting in pain and discomfort,2 impaired foot mobility,3 and an overall reduced quality of life.1 Onychomycosis is a chronic condition that requires long treatment periods due to the slow growth rates of toenails.1 To successfully cure the condition, fungal eradication must be achieved.
Prior to the US Food and Drug Administration (FDA) approval of tavaborole and efinaconazole, ciclopirox was the only approved topical treatment for onychomycosis.4 The recent approval of tavaborole and efinaconazole has increased treatment options available to patients and has started to pave the way for future topical treatments. This article discusses the 3 approved topical treatments for onychomycosis and focuses on the design of the phase 3 clinical trials that led to their approval.
Topical Agents Used to Treat Onychomycosis
Tavaborole, efinaconazole, and ciclopirox have undergone extensive clinical investigation to receive FDA approval. Results from pivotal phase 3 studies establishing the efficacy and safety of each agent formed the basis for regulatory submission. Although it may seem intuitive to compare the relative performance of these agents based on their respective phase 3 clinical trial data, there are important differences in study methodology, conduct, and populations that prevent direct comparisons. The FDA provides limited guidance to the pharmaceutical industry on how to conduct clinical trials for potential onychomycosis treatments. Comparative efficacy and safety claims are limited based on cross-study comparisons. The details of the phase 3 trial designs are summarized in the Table.
Tavaborole
Tavaborole is a boron-based treatment with a novel mechanism of action.5 Tavaborole binds to the editing domain of leucyl–transfer ribonucleic acid synthetase via an integrated boron atom and inhibits fungal protein synthesis.6 Two identical randomized, double-blind, vehicle-controlled, parallel-group, phase 3 clinical trials evaluating tavaborole were performed.5 The first study (registered at www.clinicaltrials.gov with the identifier NCT01270971) included 594 participants from27 sites in the United States and Mexico and was conducted between December 2010 and November 2012. The second study (NCT01302119) included 604 participants from 32 sites in the United States and Canada and was conducted between February 2011 and January 2013.
Eligible participants 18 years and older had distal subungual onychomycosis (DSO) of the toenails affecting 20% to 60% of 1 or more target great toenails (TGTs), tested positive for fungus using potassium hydroxide (KOH) wet mounts and positive for Trichophyton rubrum and Trichophyton mentagrophytes on fungal culture diagnostic tests, had distal TGT thickness of 3 mm or less, and had 3 mm or more of clear nail between the proximal nail fold and the most proximal visible mycotic border.5 Those with active tinea pedis requiring treatment or with a history of chronic moccasin-type tinea pedis were excluded. Participants were randomized to receive either tavaborole or vehicle (2:1). Treatments were applied once daily to all infected toenails for a total of 48 weeks, and nail debridement (defined as partial or complete removal of the toenail) was not permitted. Notably, controlled trimming of the nail was allowed to 1 mm of the leading nail edge. Regular assessments of each toenail for disease involvement, onycholysis, and subungual hyperkeratosis were made at screening, baseline, week 2, week 6, and every 6 weeks thereafter until week 52. Subungual TGT samples were taken at screening and every 12 weeks during the study for examination at a mycology laboratory, which performed KOH and fungal culture tests. A follow-up assessment was made at week 52.5
The primary end point was complete cure of the TGT at week 52, with secondary end points of completely or almost clear TGT nail (≤10% dystrophic nail), completely or almost clear TGT nail (≤10% dystrophic nail) plus negative mycology, and negative mycology of TGT.5 Examples of TGTs in participants who achieved complete cure and almost clear nails with negative mycology before and after treatment with tavaborole are shown in Figure 1. An example of a patient considered to have treatment failure is shown in Figure 2. This patient showed marked improvement in nail appearance and had a negative culture result but had a positive KOH test, which demonstrates the stringency in which topical agents are judged in onychomycosis trials.5
Efinaconazole
Efinaconazole is a topical triazole antifungal specifically indicated to treat onychomycosis. Two identical randomized, vehicle-controlled, double-blind, multicenter trials were performed to assess the safety and efficacy of efinaconazole solution 10%.7 The first study (NCT01008033) involved 870 participants and was conducted at a total of 74 sites in Japan (33 sites), Canada (7 sites), and the United States (34 sites) between December 2009 and September 2011. The second study (NCT01007708) had 785 participants and was conducted at 44 sites in Canada (8 sites) and the United States (36 sites) between December 2009 and October 2011.
Participants aged 18 to 70 years with a clinical diagnosis of DSO affecting 1 or more TGT were eligible to participate.7 Other eligibility criteria included an uninfected toenail length 3 mm or more from the proximal nail fold, a maximum toenail thickness of 3 mm, positive KOH wet mounts, and positive dermatophyte or mixed dermatophyte/candida cultures. Dermatophytes included T rubrum and T mentagrophytes. Those with severe moccasin-type tinea pedis were excluded. Participants were randomized to receive efinaconazole or vehicle (3:1). Once-daily treatments were self-applied to nails for 48 weeks. Clinical assessments were made at baseline and every 12 weeks until week 48, with a follow-up assessment at week 52. No nail trimming protocol was provided.7
The primary end point of the efinaconazole phase 3 trials was complete cure at week 52, with secondary end points including mycologic cure, treatment success (≤5% mycotic nail), and complete or almost complete cure (negative culture and KOH, ≤5% mycotic nail). An example of a complete cure from baseline to week 52 is shown in Figure 3.7
Ciclopirox
Ciclopirox was the first topical therapy to be approved for the treatment of onychomycosis. Ciclopirox is a broad-spectrum antifungal agent that inhibits metal-dependent enzymes, which are responsible for the degradation of toxic peroxides in fungal cells. The safety and efficacy of ciclopirox nail lacquer topical solution 8% also was investigated in 2 identical phase 3 clinical trials.8 The first study was conducted at 9 sites in the United States between June 1994 and June 1996 and included 223 participants. The second study was conducted at 9 sites in the United States between July 1994 and April 1996 and included 237 participants.
Eligible participants were required to have DSO in at least one TGT, positive KOH wet mount with positive dermatophyte culture, and 20% to 65% nail involvement.8 Those with tinea pedis were not excluded. Participants were randomized to receive once-daily treatment with ciclopirox or vehicle (1:1)(applied to all toenails and affected fingernails) for 48 weeks. The product was to be removed by the patient with alcohol on a weekly basis. Trimming was allowed as necessary, and mechanical debridement by the physician could be performed monthly. Assessments were made every 4 weeks, and mycologic examinations were performed every 12 weeks. Participants who were clinically cured were assessed further in a 12- to 24-week posttreatment follow-up period.8
The primary end point of complete cure and secondary end points of treatment success (negative culture and KOH, ≤10% mycotic nail), mycologic cure, and negative mycologic culture were assessed at week 48.8
Phase 3 Clinical Trial Similarities and Differences
The phase 3 clinical trials used to investigate the safety and efficacy of tavaborole,5 efinaconazole,7 and ciclopirox8 were similar in their overall design. All trials were randomized, double-blind, vehicle-controlled studies in patients with DSO. Each agent was assessed using a once-daily application for a treatment period of 48 weeks.
Primary differences among study designs included the age range of participants, the range of mycotic nail involvement, the presence/absence of tinea pedis, and the nail trimming/debridement protocols used. Differences were observed in the patient eligibility criteria of these trials. Both mycotic area and participant age range were inconsistent for each agent (eTable). Participants with larger mycotic areas usually have a poorer prognosis, as they tend to have a greater fungal load.9 A baseline mycotic area of 20% to 60%,5 20% to 50%,7 and 20% to 65%8 at baseline was required for the tavaborole, efinaconazole, and ciclopirox trials, respectively. Variations in mycotic area between trials can affect treatment efficacy, as clinical cures can be reached quicker by patients with smaller areas of infection. Of note, the average mycotic area of involvement was not reported in the tavaborole studies but was 36% and 40% for the efinaconazole and ciclopirox studies, respectively.5,8 It also is more difficult to achieve complete cure in older patients, as they have poor circulation and reduced nail growth rates.1,10 The participant age range was 18 to 88 years in the tavaborole trials, with 8% of the participants older than 70 years,5 compared to 18 to 71 years in both the efinaconazole and ciclopirox trials.7,8 The average age of participants in each study was approximately 54, 51, and 50 years for tavaborole, efinaconazole, and ciclopirox, respectively. Because factors impacting treatment failure can increase with age, efficacy results can be confounded by differing age distributions across different studies.
Another important feature that differed between the clinical trials was the approach to nail trimming—defined as shortening of the free edge of the nail distal to the hyponychium—which varies from debridement in that the nail plate is removed or reduced in thickness proximal to the hyponychium. In the tavaborole trials, trimming was controlled to within 1 mm of the free edge of the nail,5 whereas the protocol used for the ciclopirox trials allowed nail trimming as necessary as well as moderate debridement before treatment application and on a monthly basis.8 Debridement is an important component in all ciclopirox trials, as it is used to reduce fungal load.11 No trimming control was provided during the efinaconazole trials; however, debridement was prohibited.7 These differences can dramatically affect the study results, as residual fungal elements and portions of infected nails are removed during the trimming process in an uncontrolled manner, which can affect mycologic testing results as well as the clinical efficacy results determined through investigator evaluation. Discrepancies regarding nail trimming approach inevitably makes the trial results difficult to compare, as mycologic cure is not translatable between studies.
Furthermore, somewhat unusually, complete cure rate variations were observed between different study centers in the efinaconazole trials. Japanese centers in the first efinaconazole study (NCT01008033) had higher complete cure rates in both the efinaconazole and vehicle treatment arms, which is notable because approximately 29% of participants in this study were Asian, mostly hailing from 33 Japanese centers. The reason for these confounding results is unknown and requires further analysis.
Lastly, the presence or absence of tinea pedis can affect the response to onychomycosis treatment. In the tavaborole trials, patients with active interdigital tinea pedis or exclusively plantar tinea pedis or chronic moccasin-type tinea pedis requiring treatment were excluded from the studies.5 In contrast, only patients with severe moccasin-type tinea pedis were excluded in efinaconazole trials.7 The ciclopirox studies had no exclusions based on presence of tinea pedis.8 These differences are noteworthy, as tinea pedis can serve as a reservoir for fungal infection if not treated and can lead to recurrence of onychomycosis.12
Conclusion
In recent years, disappointing efficacy has resulted in the failure of several topical agents for onychomycosis during their development; however, there are several aspects to consider when examining efficacy data in onychomycosis studies. Obtaining a complete cure in onychomycosis is difficult. Because patients applying treatments at home are unlikely to undergo mycologic testing to confirm complete cure, visual inspections are helpful to determine treatment efficacy.
Despite similar overall designs, notable differences in the study designs of the phase 3 clinical trials investigating tavaborole, efinaconazole, and ciclopirox are likely to have had an effect on the reported results, making the efficacy of the agents difficult to compare. It is particularly tempting to compare the primary end point results of each trial, especially considering tavaborole and efinaconazole had primary end points with the same parameters; however, there are several other factors (eg, age range of study population, extent of infection, nail trimming, patient demographics) that may have affected the outcomes of the studies and precluded a direct comparison of any end points. Without head-to-head investigations, there is room for prescribing clinicians to interpret results differently.
Acknowledgment
Writing and editorial assistance was provided by ApotheCom Associates, LLC, Yardley, Pennsylvania, and was supported by Sandoz, a Novartis division.
- Elewski BE. Onychomycosis: pathogenesis, diagnosis, and management. Clin Microbiol Rev. 1998;11:415-429.
- Thomas J, Jacobson GA, Narkowicz CK, et al. Toenail onychomycosis: an important global disease burden. J Clin Pharm Ther. 2010;35:497-519.
- Scher RK. Onychomycosis: a significant medical disorder. J Am Acad Dermatol. 1996;35(3, pt 2):S2-S5.
- Del Rosso JQ. The role of topical antifungal therapy for onychomycosis and the emergence of newer agents. J Clin Aesthet Dermatol. 2014;7:10-18.
- Elewski BE, Aly R, Baldwin SL, et al. Efficacy and safety of tavaborole topical solution, 5%, a novel boron-based antifungal agent, for the treatment of toenail onychomycosis: results from 2 randomized phase-III studies. J Am Acad Dermatol. 2015;73:62-69.
- Rock FL, Mao W, Yaremchuk A, et al. An antifungal agent inhibits an aminoacyl-tRNA synthetase by trapping tRNA in the editing site. Science. 2007;316:1759-1761.
- Elewski BE, Rich P, Pollak R, et al. Efinaconazole 10% solution in the treatment of toenail onychomycosis: two phase III multicenter, randomized, double-blind studies. J Am Acad Dermatol. 2013;68:600-608.
- Gupta AK, Joseph WS. Ciclopirox 8% nail lacquer in the treatment of onychomycosis of the toenails in the United States. J Am Pod Med Assoc. 2000;90:495-501.
- Carney C, Tosti A, Daniel R, et al. A new classification system for grading the severity of onychomycosis: Onychomycosis Severity Index. Arch Dermatol. 2011;147:1277-1282.
- Gupta AK. Onychomycosis in the elderly. Drugs Aging. 2000;16:397-407.
- Gupta AK, Malkin KF. Ciclopirox nail lacquer and podiatric practice. J Am Podiatr Med Assoc. 2000;90:502-507.
- Scher RK, Baran R. Onychomycosis in clinical practice: factors contributing to recurrence. Br J Dermatol. 2003;149(suppl 65):5-9.
- Elewski BE. Onychomycosis: pathogenesis, diagnosis, and management. Clin Microbiol Rev. 1998;11:415-429.
- Thomas J, Jacobson GA, Narkowicz CK, et al. Toenail onychomycosis: an important global disease burden. J Clin Pharm Ther. 2010;35:497-519.
- Scher RK. Onychomycosis: a significant medical disorder. J Am Acad Dermatol. 1996;35(3, pt 2):S2-S5.
- Del Rosso JQ. The role of topical antifungal therapy for onychomycosis and the emergence of newer agents. J Clin Aesthet Dermatol. 2014;7:10-18.
- Elewski BE, Aly R, Baldwin SL, et al. Efficacy and safety of tavaborole topical solution, 5%, a novel boron-based antifungal agent, for the treatment of toenail onychomycosis: results from 2 randomized phase-III studies. J Am Acad Dermatol. 2015;73:62-69.
- Rock FL, Mao W, Yaremchuk A, et al. An antifungal agent inhibits an aminoacyl-tRNA synthetase by trapping tRNA in the editing site. Science. 2007;316:1759-1761.
- Elewski BE, Rich P, Pollak R, et al. Efinaconazole 10% solution in the treatment of toenail onychomycosis: two phase III multicenter, randomized, double-blind studies. J Am Acad Dermatol. 2013;68:600-608.
- Gupta AK, Joseph WS. Ciclopirox 8% nail lacquer in the treatment of onychomycosis of the toenails in the United States. J Am Pod Med Assoc. 2000;90:495-501.
- Carney C, Tosti A, Daniel R, et al. A new classification system for grading the severity of onychomycosis: Onychomycosis Severity Index. Arch Dermatol. 2011;147:1277-1282.
- Gupta AK. Onychomycosis in the elderly. Drugs Aging. 2000;16:397-407.
- Gupta AK, Malkin KF. Ciclopirox nail lacquer and podiatric practice. J Am Podiatr Med Assoc. 2000;90:502-507.
- Scher RK, Baran R. Onychomycosis in clinical practice: factors contributing to recurrence. Br J Dermatol. 2003;149(suppl 65):5-9.
Practice Points
- Despite similar overall designs, notable differences in the study designs of phase 3 clinical trials investigating tavaborole, efinaconazole, and ciclopirox for the treatment of onychomycosis are likely to have had an effect on the reported results, making the efficacy of these agents difficult to compare.
- The primary difference between studies for tavaborole, efinaconazole, and ciclopirox include the age range of participants, the range of mycotic nail involvement, the presence/absence of tinea pedis, and the nail trimming/debridement protocols used.
- Without head-to-head investigations, there is room for prescribing clinicians to interpret study results for these agents differently.
