In Vitro Combination Effect of Topical and Oral Anti-Onychomycosis Drugs on Trichophyton rubrum and Trichophyton interdigitale

Abstract

To evaluate the combination effects of anti-onychomycosis drugs, the minimum inhibitory concentrations of topical (efinaconazole, luliconazole, and tavaborole) and oral (itraconazole and terbinafine) drugs for Trichophyton rubrum and Trichophyton interdigitale (8 each, with a total of 16 strains) were determined using the microdilution checkerboard technique based on the Clinical and Laboratory Standard Institute guidelines. No antagonism was observed between the topical and oral drugs against all the tested strains. Efinaconazole with terbinafine exerted a synergistic effect on 43.8% of the strains tested (7/16 strains) and efinaconazole with itraconazole on 12.5% (2/16 strains). Conversely, luliconazole showed no synergistic effect with terbinafine but was synergistically effective with itraconazole against 31.3% of the strains (5/16 strains). Tavaborole showed no synergistic effect with terbinafine and was synergistically effective with itraconazole against 18.8% of the strains (3/16 strains). The results suggest that a combination of topical and oral drugs could be a potential clinical option for onychomycosis treatment, and overall, the efinaconazole and oral drug combination would be the most advantageous among the tested combinations.

Keywords: FIC index; anti-onychomycosis drug; combination antifungal effect.

Figure 1

Combination antifungal effect of topical drugs and oral drugs against T. rubrum and T. interdigitale (each 8 strains) (a) with terbinafine, (b) with itraconazole. Figures in the bar express number of strains observed in each combination effect.