Efinaconazole 10% and Tavaborole 5% Penetrate Across Poly-ureaurethane 16%: Results of In Vitro Release Testing and Clinical Implications of Onychodystrophy in Onychomycosis.

Background: Poly-ureaurethane has been previously described for the management of dry, brittle, and in general, dystrophic nails. The polymer yields a waterproof, breathable barrier to protect the nail plate and prevent further damage to the nail, while regulating transonychial water loss (TOWL). Because nail dystrophy and dessication are contributing factors to onychomycosis, a barrier that protects the nail but also allows a topical antifungal to permeate its shield is potentially an advantageous combination. Oral antifungals such as terbinafine, itraconazole, and fluconazole, as well as the newer topical antifungals efinaconazole and tavaborole (although formulated to penetrate the nail unit and work with the porosity and inherent electrical charge of the nail plate), do not take into account nail damage that has been created from years of harboring a dermatophyte infection. Up to 50% of cases presumed to be onychomycosis are in fact onychodystrophy without fungal infection, and laboratory testing for fungus should be obtained prior to initiating antifungal treatment. Whether a nail has onychomycosis, or onychodystrophy due to other causes, barrier function and structural integrity are compromised in diseased nails, and should be addressed. A poly-ureaurethane barrier that protects against wetting/drying, fungal reservoirs, and microtrauma, followed by the addition of oral or topical antifungals after laboratory fungal confirmation may optimize outcomes in the treatment of onychomycosis.


Objective: The purpose of this work was to determine through in vitro release testing (IVRT) whether poly-ureaurethane 16% allows for penetration of efinaconazole 10% or tavaborole 5%. Results could spur subsequent clinical studies which would have implications for the addition of an antifungal based on fungal confirmation, after addresssing the underlying nail dystrophy primarily.


Methods: A vertical diffusion cell system was used to evaluate the ability of efinaconazole 10% and tavaborole 5% to penetrate across poly-ureaurethane 16%. The diffusion cells had a 1.0 cm surface area and approximately 8 mL receptor volume. Poly-ureaurethane 16% was applied to a 0.45 μm nylon membrane and allowed to dry before use. Efinaconazole 10% or tavaborole 5% was then applied to the poly-ureaurethane 16% coated membrane, and samples were pulled from the receptor chamber at various times. Reverse phase chromatography was then used to assess the penetration of each active ingredient across the membrane.


Results: The flux and permeability of efinaconazole or tavaborole across poly-ureaurethane 16% were determined from efinaconazole 10% or tavaborole 5%, respectively. The flux and permeability of efinaconazole were determined to be 503.9 +/- 31.9 μg/cm/hr and 14.0 +/- 0.9 nm/sec. The flux and permeability of tavaborole were determined to be 755.5 +/- 290.4 μg/cm/hr and 42.0 +/- 16.1 nm/sec.


Conclusion: In addition to the treatment of onychoschizia, onychorrhexis, and other signs of severe dessication of the nail plate, a barrier that regulates TOWL should be considered in the management onychomycosis to address barrier dysfunction and to promote stabilization of the damaged nail. Previously published flux values across the nail are reported to be 1.4 μg/cm/day for efinaconazole and 204 μg/cm/day for tavaborole. These values are substantially lower than the herein determined flux for both molecules across poly-ureaurethane 16%. A comparison of the data suggests that poly-ureaurethane 16%, if used prior to efinaconazole or tavaborole, would not limit the ability of either active ingredient to access the nail, and therefore, would be unlikely to reduce their antifungal effect. Onychodystrophy is inherent in, and often precedes onychomycosis, and consideration should be given for initiation of treatment in the same sequence: stabilizing and protecting the nail plate barrier primarily, and subsequently adding oral or topical antifungals after laboratory confirmation. Future clinical studies will be needed to determine combination efficacy for in vivo use.

J Drugs Dermatol. 2016;15(9):1116-1120.