Utility of real-time antifungal susceptibility testing for fluconazole in the treatment of candidemia

Challenges and research priorities to progress the impact of antimicrobial stewardship

Antimicrobial stewardship programmes have been playing an important role in patient care and hospital policies. These programmes are now recognised as formal strategies for curbing the upward trend in antibiotic resistance and for improving the appropriate antimicrobial and antifungal use. The role of such programs in the era of antimicrobial resistance presents several unique challenges and opportunities, most notably in the diagnostic and therapeutic setting. Controversies remain regarding the most effective interventions and the appropriate design to evaluate their impact. In this review, based on rounds of discussion, we explain the most important challenges faced by antibiotic stewardship and antifungal stewardship programmes. We also try to suggest areas for further research.

Antifungal stewardship in daily practice and health economic implications

During recent years, inappropriate antifungal use has contributed to the global increase in antifungal resistance and has played a role in the shift in the aetiology of invasive fungal infections. Moreover, overuse of antifungals may also lead to higher toxicity associated with unnecessary medication exposure and to increased healthcare costs. Antifungal stewardship (AFS) programmes consist of multidisciplinary interventions, led by specialists in infectious disease, microbiology and pharmacy that cooperate and communicate with the major prescribing departments in order to optimise antifungal therapies evaluating the indication, dose, streamlining and duration. Herein, we review the available evidence for the use of AFS and their impact on health economics. We also describe our AFS program, the successive steps we followed and the main difficulties we found.

Echinocandin and triazole antifungal susceptibility profiles for clinical opportunistic yeast and mold isolates collected from 2010 to 2011: application of new CLSI clinical breakpoints and epidemiological cutoff values for characterization of geographic and temporal trends of antifungal resistance

The SENTRY Antimicrobial Surveillance Program monitors global susceptibility and resistance rates of newer and established antifungal agents. We report the echinocandin and triazole antifungal susceptibility patterns for 3,418 contemporary clinical isolates of yeasts and molds. The isolates were obtained from 98 laboratories in 34 countries during 2010 and 2011. Yeasts not presumptively identified by CHROMagar, the trehalose test, or growth at 42°C and all molds were sequence identified using internal transcribed spacer (ITS) and 28S (yeasts) or ITS, translation elongation factor (TEF), and 28S (molds) genes. Susceptibility testing was performed against 7 antifungals (anidulafungin, caspofungin, micafungin, fluconazole, itraconazole, posaconazole, and voriconazole) using CLSI methods. Rates of resistance to all agents were determined using the new CLSI clinical breakpoints and epidemiological cutoff value criteria, as appropriate. Sequencing of fks hot spots was performed for echinocandin non-wild-type (WT) strains. Isolates included 3,107 from 21 Candida spp., 146 from 9 Aspergillus spp., 84 from Cryptococcus neoformans, 40 from 23 other mold species, and 41 from 9 other yeast species. Among Candida spp., resistance to the echinocandins was low (0.0 to 1.7%). Candida albicans and Candida glabrata that were resistant to anidulafungin, caspofungin, or micafungin were shown to have fks mutations. Resistance to fluconazole was low among the isolates of C. albicans (0.4%), Candida tropicalis (1.3%), and Candida parapsilosis (2.1%); however, 8.8% of C. glabrata isolates were resistant to fluconazole. Among echinocandin-resistant C. glabrata isolates from 2011, 38% were fluconazole resistant. Voriconazole was active against all Candida spp. except C. glabrata (10.5% non-WT), whereas posaconazole showed decreased activity against C. albicans (4.4%) and Candida krusei (15.2% non-WT). All agents except for the echinocandins were active against C. neoformans, and the triazoles were active against other yeasts (MIC90, 2 μg/ml). The echinocandins and triazoles were active against Aspergillus spp. (MIC90/minimum effective concentration [MEC90] range, 0.015 to 2 μg/ml), but the echinocandins were not active against other molds (MEC90 range, 4 to >16 μg/ml). Overall, echinocandin and triazole resistance rates were low; however, the fluconazole and echinocandin coresistance among C. glabrata strains warrants continued close surveillance.

Progress in antifungal susceptibility testing of Candida spp. by use of Clinical and Laboratory Standards Institute broth microdilution methods, 2010 to 2012

Antifungal susceptibility testing of Candida has been standardized and refined and now may play a useful role in managing Candida infections. Important new developments include validation of 24-h reading times for all antifungal agents and the establishment of species-specific epidemiological cutoff values (ECVs) for the systemically active antifungal agents and both common and uncommon species of Candida. The clinical breakpoints (CBPs) for fluconazole, voriconazole, and the echinocandins have been revised to provide species-specific interpretive criteria for the six most common species. The revised CBPs not only are predictive of clinical outcome but also provide a more sensitive means of identifying those strains with acquired or mutational resistance mechanisms. This brief review serves as an update on the new developments in the antifungal susceptibility testing of Candida spp. using Clinical and Laboratory Standards Institute (CLSI) broth microdilution (BMD) methods.

Validation of 24-hour flucytosine MIC determination by comparison with 48-hour determination by the Clinical and Laboratory Standards Institute M27-A3 broth microdilution reference method

Flucytosine and itraconazole are the only antifungal agents for which the Clinical Laboratory and Standards Institute recommendations include MIC breakpoint readings at 48 h only. Here we show good essential and categorical agreement between the flucytosine MIC readings at 48 and 24 h for Candida species.

Evaluation of antifungal therapy in patients with candidaemia based on susceptibility testing results: implications for antimicrobial stewardship programmes

BACKGROUND

Definitive antifungal therapy is typically based on Candida species and clinical status, rather than susceptibility reports. Antifungal susceptibility testing is available, but the impact on treatment decisions is unknown. The purpose of this study was to assess antifungal therapy in hospitalized patients with candidaemia during the time period between the start of empirical therapy and after antifungal susceptibility testing reports are available.

METHODS

A retrospective study of 161 hospitalized patients with candidaemia was conducted. Patients who received fluconazole or an echinocandin were evaluated for changes in empirical antifungal therapy prior to and after susceptibility reporting.

RESULTS

One hundred and sixty-one patients aged 59 ± 16 years (male, 54%; Caucasian, 52%; APACHE II score ≥ 15, 48%; and intensive care unit, 50%) were identified, of whom 130 (81%) had fluconazole-susceptible candidaemia. Fifty-eight patients (36%) were initiated on fluconazole and 103 (64%) on an echinocandin. The mean time from culture to the susceptibility report was 5 ± 2 days. Prior to availability of the susceptibility report, 20 fluconazole-initiated patients (34%) were switched to an echinocandin, while 14 echinocandin-initiated patients (14%) were switched to fluconazole. Once a susceptibility report was available, 35 of 89 (39%) patients with fluconazole-susceptible candidaemia on an echinocandin were de-escalated to fluconazole. Eleven patients on fluconazole just prior to a susceptibility report were identified with a fluconazole-resistant Candida species.

CONCLUSIONS

Using antifungal susceptibility testing, patients given fluconazole with fluconazole-resistant Candida species were identified. Less than 40% of echinocandin-treated patients with fluconazole-susceptible organisms were de-escalated to fluconazole. Antifungal susceptibility testing may help to identify patients in need of clinical intervention.

Validation of 24-hour posaconazole and voriconazole MIC readings versus the CLSI 48-hour broth microdilution reference method: application of epidemiological cutoff values to results from a global Candida antifungal surveillance program

We performed 24- and 48-h MIC determinations of posaconazole and voriconazole against more than 16,000 clinical isolates of Candida species. By using the 24- and 48-h epidemiological cutoff values (ECVs), the categorical agreement between the 24-h and reference 48-h broth microdilution results ranged from 97.1% (C. parapsilosis and voriconazole) to 99.8% (C. krusei and voriconazole), with 0.0 to 2.9% very major discrepancies (VMD). The essential agreement (within 2 log(2) dilutions) between the 24- and 48-h results was 99.6% for both posaconazole and voriconazole. The MIC results obtained for both posaconazole and voriconazole after only 24 h of incubation may be used to determine the susceptibilities of Candida spp. to these important antifungal agents. The applications of ECVs to this large collection of Candida isolates suggests the potential to develop 24-h species-specific clinical breakpoints for both posaconazole and voriconazole.

Wild-type MIC distribution and epidemiological cutoff values for Aspergillus fumigatus and three triazoles as determined by the Clinical and Laboratory Standards Institute broth microdilution methods

Antifungal susceptibility testing of Aspergillus species has been standardized by both the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Recent studies suggest the emergence of strains of Aspergillus fumigatus with acquired resistance to azoles. The mechanisms of resistance involve mutations in the cyp51A (sterol demethylase) gene, and patterns of azole cross-resistance have been linked to specific mutations. Studies using the EUCAST broth microdilution (BMD) method have defined wild-type (WT) MIC distributions, epidemiological cutoff values (ECVs), and cross-resistance among the azoles. We tested a collection of 637 clinical isolates of A. fumigatus for which itraconazole MICs were < or = 2 microg/ml against posaconazole and voriconazole using the CLSI BMD method. An ECV of < or = 1 microg/ml encompassed the WT population of A. fumigatus for itraconazole and voriconazole, whereas an ECV of < or = 0.25 microg/ml was established for posaconazole. Our results demonstrate that the WT distribution and ECVs for A. fumigatus and the mold-active triazoles were the same when determined by the CLSI or the EUCAST BMD method. A collection of 43 isolates for which itraconazole MICs fell outside of the ECV were used to assess cross-resistance. Cross-resistance between itraconazole and posaconazole was seen for 53.5% of the isolates, whereas cross-resistance between itraconazole and voriconazole was apparent in only 7% of the isolates. The establishment of the WT MIC distribution and ECVs for the azoles and A. fumigatus will be useful in resistance surveillance and is an important step toward the development of clinical breakpoints.

Recent experience with fungaemia: change in species distribution and azole resistance

Owing to a rise in frequency and change in pattern of cases with fungaemia at our tertiary care centre, we conducted a prospective study for 4 months to understand the epidemiology and outcome of this infection. Detailed case histories including management protocol and outcomes were noted. Records of 140 cases with fungaemia (27.1% adult and 72.9% paediatric patients) were analysed. Although C. tropicalis was the most common yeast isolated, significantly higher isolation of C. guilliermondii (30.4%) and C. pelliculosa (17.6%) was noted in paediatric patients; and C. albicans (26.3%) and C. glabrata (10.5%) in adult patients. Rare species isolated included C. ustus (0.7%) and Trichosporon asahii (2.1%). Mortality was high (56.9% and 47.4%, respectively), in both groups of patients. Resistance to azoles (fluconazole, itraconazole, voriconazole) emerged in C. albicans (12.5-18.8%) and C. tropicalis (10.2-13.6%). Antifungal susceptibility testing report modified the therapy from fluconazole to amphotericin B in 8 patients; 5 survived. In conclusion, the study highlighted the rise of non-albicans Candida species in our hospital with differential distribution in paediatric and adult wards and emergence of azole resistance.

Validation of 24-hour fluconazole MIC readings versus the CLSI 48-hour broth microdilution reference method: results from a global Candida antifungal surveillance program

We performed 24- and 48-h MIC determinations and disk diffusion testing of fluconazole against more than 11,000 clinical isolates of Candida species. By using the reference MIC breakpoints, the categorical agreement between the 24-h and reference 48-h broth microdilution results ranged from 93.8% (all Candida species) to 94.9% (all Candida species minus Candida krusei), with only 0.1% very major errors (VME). The essential agreement (within 2 log(2) dilutions) between the 24-h and 48-h results was 99.6%. The categorical agreement between the 24-h disk diffusion results and the 24-h MIC results, using the previously established breakpoints, was 94.4%, with 0.1% VME. Both the MIC and the disk diffusion results obtained for fluconazole after only 24 h of incubation may be used to determine the susceptibilities of Candida spp. to this widely used antifungal agent.

Association of fluconazole pharmacodynamics with mortality in patients with candidemia

Recent studies of nonneutropenic patients with candidemia or candidiasis suggest that fluconazole pharmacodynamic parameters correlate with clinical outcomes; however, additional data of correlation to mortality in patients with candidemia would be valuable. We assessed the impact of MICs for Candida, fluconazole pharmacodynamics, and patient characteristics on all-cause mortality with use of a prospective cohort of 96 hospitalized patients with candidemia. Among 84 patients for whom Candida isolates were available for testing, the most frequent Candida species isolated were Candida albicans (44%), followed by Candida parapsilosis (20.2%), and Candida glabrata (20.2%). Fluconazole resistance (MIC of >or=64 microg/ml) was present in 7 (8.3%) to 10 (11.9%) of 84 isolates, depending on the MIC endpoint determination method (50% or 80% inhibition read at 24 or 48 h). Overall mortality occurred in 27 (28.1%) of 96 patients, and nonsurvivors were more likely to have fluconazole-resistant isolates (25% versus 6.7%; P = 0.02). Multivariable analysis demonstrated an association between fluconazole resistance and mortality, but it did not reach statistical significance (odds ratio, 5.3; 95% confidence interval, 0.8 to 33.4; P = 0.08). By pharmacodynamic analysis, a fluconazole area under the concentration-time curve/MIC of <11.5 or MIC of >or=64 was associated with increased patient mortality (P <or= 0.09). These data support previous findings of an antifungal exposure-response relationship to mortality in patients with candidemia. In addition, similar MICs were obtained using a 24- or 48-h MIC endpoint determination, thus providing the opportunity to assess earlier the impact of isolate susceptibility on therapy.

To test or not to test: a cost minimization analysis of susceptibility testing for patients with documented Candida glabrata fungemias

This cost minimization analysis investigated the financial impact of the treatment of fungemias due to Candida glabrata from a hospital perspective using three competing alternatives: (i) performing in-house susceptibility testing on all C. glabrata isolates and changing patients to less expensive fluconazole therapy for isolates that test susceptible; (ii) susceptibility testing at outside laboratories with delayed deescalation to fluconazole if isolates test susceptible; and (iii) no routine susceptibility testing with full echinocandin treatment course. Sensitivity analyses and Monte Carlo simulation enhanced the robustness of the model through variation of all assumptions and costs. In the base case, the use of in-house testing displayed a cost advantage over the options of send-out testing and no susceptibility testing ($2,226 versus $2,410 versus $3,136, respectively). Sensitivity analyses determined that the cost of echinocandin therapy and the turnaround time for send-out testing had the potential to impact the base case model. The decision model indicated that in-house susceptibility testing of C. glabrata isolates should result in lower overall treatment costs in patients with documented C. glabrata fungemias.

Epidemiology of invasive candidiasis: a persistent public health problem

Invasive candidiasis (IC) is a leading cause of mycosis-associated mortality in the United States. We examined data from the National Center for Health Statistics and reviewed recent literature in order to update the epidemiology of IC. IC-associated mortality has remained stable, at approximately 0.4 deaths per 100,000 population, since 1997, while mortality associated with invasive aspergillosis has continued to decline. Candida albicans remains the predominant cause of IC, accounting for over half of all cases, but Candida glabrata has emerged as the second most common cause of IC in the United States, and several less common Candida species may be emerging, some of which can exhibit resistance to triazoles and/or amphotericin B. Crude and attributable rates of mortality due to IC remain unacceptably high and unchanged for the past 2 decades. Nonpharmacologic preventive strategies should be emphasized, including hand hygiene; appropriate use, placement, and care of central venous catheters; and prudent use of antimicrobial therapy. Given that delays in appropriate antifungal therapy are associated with increased mortality, improved use of early empirical, preemptive, and prophylactic therapies should also help reduce IC-associated mortality. Several studies have now identified important variables that can be used to predict risk of IC and to help guide preventive strategies such as antifungal prophylaxis and early empirical therapy. However, improved non-culture-based diagnostics are needed to expand the potential for preemptive (or early directed) therapy. Further research to improve diagnostic, preventive, and therapeutic strategies is necessary to reduce the considerable morbidity and mortality associated with IC.

Interpretive breakpoints for fluconazole and Candida revisited: a blueprint for the future of antifungal susceptibility testing

Developing interpretive breakpoints for any given organism-drug combination requires integration of the MIC distribution, pharmacokinetic and pharmacodynamic parameters, and the relationship between in vitro activity and outcome from both in vivo and clinical studies. Previously, the Subcommittee for Antifungal Testing of the Clinical and Laboratory Standards Institute (CLSI [formerly National Committee for Clinical Laboratory Standards]) proposed MIC interpretive breakpoints for fluconazole and Candida spp. These breakpoints were considered to be somewhat weak, because the clinical data supporting them came largely from mucosal infections and there were very few infections involving strains with elevated fluconazole MICs. We readdress the issue of fluconazole breakpoints for Candida by using published clinical and microbiologic data to provide further validation of the breakpoints proposed by the CLSI in 1997. We also address interpretive breakpoints for agar disk diffusion testing of fluconazole. The MIC distribution for fluconazole was determined with a collection of 13,338 clinical isolates. The overall MIC at which 90% of the isolates were inhibited was 8 microg/ml: 91% were susceptible (S) at a MIC of or= 64 microg/ml). Similar results were obtained for 2,190 isolates from randomized clinical trials. Analysis of available data for 1,295 patient-episode-isolate events (692 represented mucosal infections and 603 represented invasive infections) from 12 published clinical studies demonstrated an overall success rate of 77%, including 85% for those episodes in which the fluconazole MIC was or= 64 microg/ml) isolates. Pharmacodynamic analysis demonstrated a strong relationship between MIC, fluconazole dose, and outcome. A dose/MIC ratio of approximately 25 was supportive of the following susceptibility breakpoints for fluconazole and Candida spp.: S, MIC or= 64 microg/ml. The corresponding disk test breakpoints are as follows: S, >or=19 mm; SDD, 15 to 18 mm; R, Collapse

Key Words Collapse

MESH Headings

• Antifungal Agents/administration & dosage
• Antifungal Agents/pharmacology
• Antifungal Agents/therapeutic use
• Candida/drug effects
• Candidiasis/drug therapy
• Clinical Trials as Topic
• Dose-Response Relationship, Drug
• Drug Resistance, Fungal
• Fluconazole/pharmacokinetics
• Fluconazole/pharmacology
• Fluconazole/therapeutic use
• Humans
• Microbial Sensitivity Tests/standards
• Treatment Outcome

Collapse

Grants Collapse

Affiliation(s)

M A Pfaller Department of Pathology, Medical Microbiology Division, C606 GH, University of Iowa College of Medicine, Iowa City, 52242, USA.
D J Diekema
D J Sheehan

Collapse

Initial management of candidemia at an academic medical center: Evaluation of the IDSA guidelines

Treatment of candidemia is more complicated because of the changing epidemiology of Candida and introduction of newer antifungal agents. Utilization and benefit of practice guidelines and infectious disease consultation for the management of candidemia has not been previously described in the routine clinical setting. We prospectively studied the impact of the Infectious Disease Society of America (IDSA) guidelines for the management of candidemia and infectious disease consultation on clinical outcomes in 119 patients with candidemia at a tertiary care hospital. Medical records were reviewed to capture data concerning use of antifungal agents, management of central venous catheters, and infectious disease consultation. Initial antifungal therapy was consistent with the IDSA guidelines in 76% of patients. Variation from the guidelines was independently associated with higher mortality (24% versus 57%, P = 0.003). Infectious disease consultation was independently associated with lower mortality (18% versus 39%, P < 0.01). Use of the IDSA guidelines and infectious disease consultation service was found to improve patient outcomes in patients with candidemia at our institution. Further studies should be performed to validate newer guidelines in a clinical setting at other institutions.