In vitro and in vivo activities of piritetrate (M-732), a new antidermatophytic thiocarbamate

Piritetrate (M-732), a new topical antifungal agent belonging chemically to the thiocarbamates, was demonstrated to possess a potent selective antidermatophytic activity. In terms of its MICs in susceptibility testing, mainly done by using Sabouraud dextrose agar plates, piritetrate exhibited several- to 10-fold-stronger antidermatophytic activity than tolnaftate, a reference thiocarbamate. Furthermore, piritetrate was found to show a broader antifungal spectrum than tolnaftate; relatively many species and strains of dematiaceous fungi, dimorphic fungi, and some other filamentous fungi as well as a few strains of Cryptococcus neoformans were fairly susceptible to piritetrate, while almost all the tested species and strains were resistant to tolnaftate. All the tested species of the genus Candida were, however, resistant to both compounds. Variables which can influence antimicrobial activity caused few changes in the MICs of either compound against Trichophyton mentagrophytes; however, an increase in the inoculum size resulted in a significant increase in the MICs. The antidermatophytic activities of piritetrate and tolnaftate were fungistatic but not fungicidal. Piritetrate also exhibited a more potent in vitro anti-T. mentagrophytes activity than clotrimazole or tolciclate. Piritetrate and tolnaftate had no antibacterial activity. The in vivo activity of topically administered piritetrate against experimental dermal infection of guinea pigs with T. mentagrophytes was more effective than that of tolnaftate both mycologically and clinically. Piritetrate manifested no acute toxicity in laboratory animals when administered even in large quantities by the oral, intraperitoneal, and topical routes.