Lack of correlation of 24- vs. 48-h itraconazole minimum inhibitory concentrations with microbiological and survival outcomes in a guinea pig model of disseminated candidiasis

Minimal Inhibitory Concentration (MIC)-Phenomena in Candida albicans and Their Impact on the Diagnosis of Antifungal Resistance

Antifungal susceptibility testing (AFST) of clinical isolates is a tool in routine diagnostics to facilitate decision making on optimal antifungal therapy. The minimal inhibitory concentration (MIC)-phenomena (trailing and paradoxical effects (PXE)) observed in AFST complicate the unambiguous and reproducible determination of MICs and the impact of these phenomena on in vivo outcome are not fully understood. We aimed to link the MIC-phenomena with in vivo treatment response using the alternative infection model Galleria mellonella. We found that Candida albicans strains exhibiting PXE for caspofungin (CAS) had variable treatment outcomes in the Galleria model. In contrast, C. albicans strains showing trailing for voriconazole failed to respond in vivo. Caspofungin- and voriconazole-susceptible C. albicans strains responded to the respective antifungal therapy in vivo. In conclusion, MIC data and subsequent susceptibility interpretation of strains exhibiting PXE and/or trailing should be carried out with caution, as both effects are linked to drug adaptation and treatment response is uncertain to predict.

Evaluation of the possible influence of trailing and paradoxical effects on the clinical outcome of patients with candidemia

OBJECTIVE

Paradoxical growth (PG) and trailing effect (TE) are frequently observed during antifungal susceptibility testing (AFST). These two phenomena interfere with the determination of the minimal inhibitory concentration (MIC). The aim of this study was to assess the clinical impact of TE and PG.

METHODS

We analysed the frequency of TE and PG of 690 Candida isolates collected from a population-based study performed in Spain (CANDIPOP) and correlated the results with clinical outcome of the patients.

RESULTS

Around 70% (484/690) of the isolates exhibited TE to azoles. Candida tropicalis showed the highest presence of TE (39/53 isolates exhibited residual growth >25% of control). No TE was seen in most of the isolates from the psilosis complex. PG was mainly associated with echinocandins. In patients treated with fluconazole within the first 48 hours after blood sampling (n = 221), the presence of TE to azoles tended to be associated with lower 30-day mortality (odds ratio (OR) 0.55, 95% confidence interval (CI) 0.25-1.00) but not with clinical failure (OR 0.85, 95% CI 0.45-1.54). In the subgroup of 117 patients treated with echinocandins, the presence of PG was not associated with patient's response to antifungal treatment (OR for 30-day mortality 1.63, 95% CI 0.76-4.03; OR for clinical failure 1.17, 95% CI 0.53-2.70).

CONCLUSIONS

TE or PG are widely expressed among Candida spp., although they do not seem to influence clinical outcome.

Therapeutic drug monitoring (TDM) of antifungal agents: guidelines from the British Society for Medical Mycology

The burden of human disease related to medically important fungal pathogens is substantial. An improved understanding of antifungal pharmacology and antifungal pharmacokinetics-pharmacodynamics has resulted in therapeutic drug monitoring (TDM) becoming a valuable adjunct to the routine administration of some antifungal agents. TDM may increase the probability of a successful outcome, prevent drug-related toxicity and potentially prevent the emergence of antifungal drug resistance. Much of the evidence that supports TDM is circumstantial. This document reviews the available literature and provides a series of recommendations for TDM of antifungal agents.