Synergistic antimicrobial activity by combining an allylamine with benzoyl peroxide with expanded coverage against yeast and bacterial species

Background Dermatophyte infections can be polymicrobial. Topical antifungal therapies offer limited coverage of yeasts and Gram-positive and Gram-negative bacteria. Moreover, the increased usage of these topical antimicrobial agents has resulted in the development of resistant cases. Benzoyl peroxide (BP), used in concert with antimicrobial agents containing an accessible tertiary amine, has previously been shown to increase radical activity and biological effect. Objectives To determine the applicability of using the tertiary amine terbinafine in concert with BP in dermatophyte and mixed skin infections by means of in vitro testing. Methods In this preliminary in vitro study, the effect of BP, alone and in combination with terbinafine, was tested against Candida albicans, Pseudomonas aeruginosa and Staphylococcus aureus isolates following a checkerboard modification of the National Committee for Clinical Laboratory Standards M27-A2 and M7-A6. The individual minimum inhibitory concentrations of terbinafine, BP, and the combination, were determined against each isolate. Results The combination of BP with terbinafine led to additive activities against the majority of Candida albicans isolates tested and additionally expanded the bacterial coverage of terbinafine. Conclusions The combination of antifungal agents bearing a tertiary amine with BP may have benefit in polymicrobial infections, given its wider antimicrobial coverage. Further appreciation of this mechanism of catalysis of BP radical formation by certain antimicrobials and other tertiary amine-containing compounds may lead to the discovery of improved treatments for several dermatological conditions.