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Purpose: Evaluate the appropriateness of use of in vitro antifungal susceptibility testing in the treatment of Candida infections.
Methods: All in vitro antifungal susceptibility test results performed for patients with infection due to Candida species from 2005 to 2011 were retrospectively reviewed. Information collected from the medical record included antifungal therapy before and after availability of susceptibility test results, results of the testing, appropriateness of use, and presence of an infectious disease service consult. Definitions for appropriate and inappropriate application of the antifungal susceptibility test results were developed and applied to each case.
Results: Of the 96 susceptibility tests performed, 64 (66.7%) were classified as “appropriate” and 32 (33.3%) as “inappropriate” in influencing prescribing decisions. The most common “appropriate” use involved a change in antifungal therapy in direct response to the susceptibility results. The primary reason for “inappropriate” use was no change in therapy despite the opportunity to refine therapy based upon the results. In those instances of inappropriate use, 28 of 32 (87.5%) were associated with an infectious disease consult, compared to 61 of 64 (95.3%) appropriate uses. The 96 susceptibility tests involved a total of 106 Candida infections with 113 infected sites. Candida glabrata was the most common yeast, present in 53 of 106 (50%) infections, and 43 of 113 (38.1%) of Candida-infected sites were bloodstream-based. Of the 22 infections caused by Candida albicans, 3 were resistant to fluconazole.
Conclusions: In vitro antifungal susceptibility test results are not always utilized appropriately in the optimization of antifungal therapy. Infectious disease consultation does not appear to improve the appropriate use of these test results. Continued quality improvement is needed to guide the appropriate use of in vitro susceptibility testing for antifungal agents.