Usefulness of Antifungal Reference In Vitro Susceptibility Tests as a Guide in Therapeutic Management

Purpose of Review: This review provides information on the utility of reference antifungal susceptibility testing methods in the clinical setting. Recent Findings: Clinical and Laboratory Standards Institute (CLSI)/European Committee for Antimicrobial Susceptibility Testing breakpoints (BPs) as predictors of therapy response (reported as either “cured” or “failure”) and epidemiological cutoff endpoints (ECVs/ECOFFS) of mutants (harboring specific resistance mechanisms) have been established. Summary: Although ECVs are available for other species and agents and for commercial methods, only reference triazole and echinocandin BPs have been established. Therefore, correlations of in vitro/in vivo results in this review were based on BPs or ECVs for Candida spp. and/or Aspergillus fumigatus. We also included CLSI ECVs for the Cryptococcus neoformans complex and tentative values for Candida auris. Overall, BPs/ECVs appear to be useful, but most available data are for correlations between BPs and minimal inhibitory concentrations (MICs) for susceptible isolates. Although ECVs can discriminate between MICs for WT (wild type) and mutants (non-WT), an MIC overlap could be present.