The role of antifungal susceptibility testing in the therapy of candidiasis

Prior to the introduction of azoles, no real need for antifungal susceptibility testing (AFST) existed, as amphotericin B was the only agent available to treat systemic candidiasis. Introduction of fluconazole and itraconazole provided alternate, less toxic antifungal therapies. Intrinsic resistance of Candida krusei, decreased susceptibility of Candida glabrata, and development of resistance by Candida albicans (in mucosal disease in AIDS) to azoles led to development of our current AFST methodologies. The goal of AFST, like that of antibacterial susceptibility testing, is to predict clinical response, or at least to forecast failure. Although the ability of AFST to predict clinical outcome (clinical correlation) is still being fully elucidated, current methodologies do appear to reliably predict clinical resistance to azoles. Ready access to AFST is currently limited, affecting its timely use, but even with this lack of timeliness, AFST can still play an important role in patient care. Important potential roles include: 1) use in the development of local antibiograms to aid empiric selection of antifungals; 2) testing of isolates from candidemia or deep infection to aid in selection of long-term therapies; and, 3) the testing of isolates from recurrent mucosal disease to aid in selection of alternative regimens.