Cure Rates of Control Interventions in Randomized Trials of Onychomycosis Treatments

The efficacy of antifungals for onychomycosis has been determined in randomized controlled trials (RCTs); interestingly, their control arms have demonstrated some therapeutic effects. These controls constitute either placebos (inert pills) or vehicles (all but the antifungal component of the creams). We sought to determine whether RCT controls exhibited statistically relevant efficacy rates (ie, beyond the placebo effect), whether oral and topical controls differed in their efficacies, and whether the efficacy rates of the controls correlated with those of the active comparator associated with that control.

All RCTs of oral and topical monotherapies for dermatophyte toenail onychomycosis were identified through a systematic literature search. For the meta-analyses of cure rates, the double arcsine transformation was used. The N - 1 χ2 test was used to determine whether the cure rates significantly differed between topical and oral controls. Correlation was investigated using Kendall rank correlation tests.

The pooled mycological, complete, and clinical cure rates of the control interventions (19 trials) were 9%, 1%, and 6%, respectively. The pooled efficacy rates for oral and topical controls were as follows: mycological cure rate, 7% and 12% (P = .0016); complete cure rate, 1% for both; and clinical cure rate, 4% and 8%, respectively (P = .0033). For oral RCTs, the respective cure rates of the active therapies were not correlated with controls. However, for topical RCTs, as the mycological and clinical cure rates of the active therapy increased, so did those of the topical vehicle associated with the active therapy in question, and vice versa.

The topical vehicle cure rates were often higher than the oral placebo cure rates, likely due to the presence of nonantifungal chemicals (eg, moisturizers, urea) with antifungal and debriding properties, which are not present in oral controls.