Before we get into efficacy, lets start with some basics. There are four approved classes of antifungal drugs for the treatment of onychomycosis: the allylamines, azoles, morpholines, and hydroxypyridinones.
Normally, first line therapy for onychomycosis is Terbinafine (allylamine). Allylamines inhibit squalene epoxidase, a step in the ergosterol biosynthesis pathway.
Traditional topical therapy is considered to be ineffective for the treatment of this disease. But, in June 2014, the FDA approved the first topical triazole for the treatment of onychomycosis of the toenails. The azoles inhibit lanosterol 14α-demethylase, another step in the ergosterol biosynthesis pathway. Itraconazole is part of this group as well (which is considered second line therapy).
The question is: does efinaconazole work?
In two phase III multicenter randomized trials (patients were randomized to treatment with efinaconazole or placebo once daily for 48 weeks) complete cure was achieved by 18% and 15% of patients treated with efinaconazole compared with only 3% and 6% of patients treated with placebo. Mycological cure rate was 55.2% and 53.4% respectively.
Adverse reactions: 76% (compared to 63% with placebo) of these patients experienced localized adverse reactions: blisters, contact dermatitis, erythema, and ingrown nail – these reactions were not severe enough to stop the trials.
Terbinafine, which is first line, has a 38% complete cure rate and a 70% mycological cure rate.
So, it seems to be that efinaconazole is not as effective as Terbinafine. For this reason, Terbinafine continues to be first line for the treatment of onychomycosis. Efinaconazole, however, be a useful adjunct to oral therapy or as an option for those who have underlying liver disease.