In vitro Susceptibility to Itraconazole, Clotrimazole, Ketoconazole and Terbinafine of 100 Isolates of Trichophyton rubrum

BACKGROUND: A reference method for dermatophyte in vitro susceptibility testing is lacking. With the advent of new antimycotics, susceptibility testing has received increasing attention as an important laboratory tool for aiding the selection of appropriate drug therapy. METHODS: One hundred strains of Trichophyton rubrum were tested against four antifungal agents, itraconazole, clotrimazole, ketoconazole and terbinafine, by using a modification of the proposed standard M38-P of the National Committee for Clinical Laboratory Standards and two types of standardized inocula, 1.4 x 10(4) and 5 x 10(3) CFU/ml. RESULTS: Terbinafine was revealed to be the most effective antifungal drug. Of the three azole derivatives tested, clotrimazole showed the highest antifungal activity, while the minimum inhibitory concentrations (MICs) of itraconazole and ketoconazole were similar. Inoculum size did not affect the MIC of any of the antifungal agents tested. CONCLUSION: Our preliminary data provide promising results for the development of a reference method for dermatophyte susceptibility testing based on the microdilution technique, although more dermatophytes should be tested and the method evaluated in different laboratories.