Letters to the Editor

NNTs Misleading for Onychomycosis Treatments


Am Fam Physician. 2018 Jun 1;97(11):online.

Original Article: Topical Antifungals for Treatment of Onychomycosis [FPIN's Help Desk Answers]

Issue Date: November 1, 2016

See additional reader comments at: https://www.aafp.org/afp/2016/1101/p734.html

To the Editor: The authors of this article asked, “What is the rate of resolution of onychomycosis treated with topical antifungal agents?” Although the agents discussed are effective for treating onychomycosis, the number needed to treat (NNT) of 7 to 17 is potentially deceptive. Expressing effectiveness as an actual cure rate would have been more direct, clear, and patient centered.

For example, the study on efinaconazole 10% topical solution demonstrated complete cure rates of only 15% to 18% after one year.1 By comparing efinaconazole cure rates with vehicle cure rates of 3.5% to 5.5%, the NNT is indeed 7 to 10. However, it would also be correct to state that 82% to 85% of patients who used efinaconazole 10% topical solution for 52 weeks did not have a complete cure. Given that the cost of efinaconazole is approximately $600 for a single 4-mL bottle,2 the low absolute cure rate would make the value of this treatment quite low.

Similarly, the study comparing cure rates of tavaborole 5% topical solution with those of placebo yielded an NNT of 13, which might make tavaborole 5% topical solution seem more favorable than if the actual cure rates of 6.5% to 9.1% after 48 weeks of treatment were emphasized.2 Given that the cost of a single 4-mL bottle of tavaborole 5% topical solution is approximately $600,2 and that more than 90% of patients using this treatment would not have a complete cure, the value of this treatment also seems quite low.

Author disclouse: No relevant financial affiliations.

Editor's Note:Estimated retail cost for one treatment course based on information obtained at http://www.goodrx.com (accessed May 4, 2018).



1. 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 [published correction appears in J Am Acad Dermatol. 2014;70(2):399]. J Am Acad Dermatol. 2013;68(4):600–608.

2. 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. J Am Acad Dermatol. 2015;73(1):62–69.

In Reply: We appreciate Dr. Fallert's interest in our article. In fact, we did report the absolute cure rates. The NNT offers clinical utility for physicians to understand how these topical agents for onychomycosis compare with vehicle over 48 weeks of daily treatment. Space constraints kept us from discussing the costs of these treatments and their comparative value. The bottom line is that topical treatment options for onychomycosis have limited effectiveness and high costs. We hope that our article will help guide family physicians in selecting appropriate treatments for their patients.

Author disclosure: No relevant financial affiliations.

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This series is coordinated by Kenny Lin, MD, MPH, Associate Deputy Editor for AFP Online.



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