New azasteroidal antifungal antibiotics from Geotrichum flavo-brunneum. III. Biological activity.

The A25822 antibiotic complex consists of seven biologically active factors. A comparative study of these factors determined that factor B possessed the greatest antifungal activity. The minimal inhibitory concentration of A25822B against isolates of Candida albicans was less than 0.3 similar to 5.0 mug/ml, Trichophyton mentagrophytes was inhibited at less than 0.0312 mug/ml. Other pathogenic fungi such as Cryptococcus neoformans, Histoplasma capsulatum, Blastomyces dermatitidis, Sporotrichum schenckii, and Microsporium gypseum were very susceptible to A25822B. Only limited antibacterial activity of A25822B was found. Parenteral or oral administration of 50 mg/kg of A25822B significantly extended the average survival time of mice infected with C. albicans. Doses of 20 mg/kg of A25822B caused a greater than ten-fold reduction in the number of Candida cells recovered from kidneys of infected mice. A solution of 0.5% or 0.25% A25822B applied topically was effective against an experimental dermatophyte infection on guinea pigs. A peak blood level of 3 mug/ml was achieved in mice following a 100 mg/kg dose of A25822B. Combination of A25822B with a polyene antibiotic in vitro showed antagonism.