Emerging Recalcitrant Tinea Pedis and Management Using Antifungal Susceptibility Testing: A Pilot Study

Abstract

Tinea pedis (TP) is a common fungal infection that has become increasingly prevalent with the rise of drug-resistant strains. Traditional antifungal treatments are increasingly less effective, prompting a need for new therapeutic approaches. This pilot study aimed to explore the role of antifungal susceptibility testing (AST) in the management of recalcitrant TP. In this exploratory pilot study, TP Skin specimens were collected and examined microscopically and via culture, with PCR used for species differentiation. Antifungal susceptibility testing (AST) determined MICs for various antifungals, categorizing patients into sensitive, resistant, tolerant, or recalcitrant groups. All patients received clotrimazole 1% cream, with individualized oral antifungal treatments based on AST results and a standard 4-week treatment duration. The study involved 38 patients, with 28 diagnosed with TP. Isolates included T. mentagrophytes complex (67.85%), T. rubrum (25%), E. floccosum (3.57%), M. canis (3.57%). Antifungal susceptibility testing revealed high resistance rates, particularly to terbinafine (43%) and itraconazole (17%). Treatment responses varied, with 64.28% of terbinafine-resistant patients improving, while itraconazole-resistant cases often required a switch to voriconazole. Findings from this pilot study suggest that AST may be a valuable tool in the management of recalcitrant tinea pedis when performed by experienced laboratories in accordance with standardized guidelines. An MIC cut-off value of 2 µg/mL for defining terbinafine resistance is proposed; however, larger studies are required to establish definitive clinical breakpoints. Voriconazole appears to be a promising alternative treatment option in cases resistant to both terbinafine and itraconazole.