Quality control guidelines for National Committee for Clinical Laboratory Standards--recommended broth macrodilution testing of ketoconazole and itraconazole.

Ketoconazole and itraconazole were tested in a multilaboratory study to establish quality control (QC) guidelines for yeast antifungal susceptibility testing. Two isolates that had been previously identified as QC isolates for amphotericin B, fluconazole, and flucytosine (Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258) were tested in accordance with the National Committee for Clinical Laboratory Standards M27-P guidelines. Each isolate was tested 20 times with the two antifungal agents in the five laboratories by using a lot of RPMI 1640 unique to each laboratory as well as a lot common to all five laboratories, thus generating 200 MICs per drug per organism. Overall, 96 to 99% of the MICs for each drug fell within the desired 3-log2 dilution range (mode +/- 1 log2 dilution). By using these data, 3-log2 dilution QC ranges encompassing 98% of the observed MICs for three of the organism-drug combinations and 94% of the observed MICs for the fourth combination were established. These QC ranges are 0.064 to 0.25 micrograms/ml for both ketoconazole and itraconazole against C. parapsilosis ATCC 22019 and 0.125 to 0.5 micrograms/ml for both ketoconazole and itraconazole against C. krusei ATCC 6258.