In vivo fluconazole pharmacodynamics and resistance development in a previously susceptible Candida albicans population examined by microbiologic and transcriptional profiling

From bench to bedside: Perspectives on the utility of pharmacokinetics/pharmacodynamics in predicting the efficacy of antifungals in invasive candidiasis

The aim of this perspective is to give an overlook on the utility of pharmacokinetics/pharmacodynamics (PK/PD) in predicting the efficacy of antifungals in invasive candidiasis. Overall, from the available literature it appears that bridging data of PK/PD of antifungals from the laboratory to the clinic for the treatment of invasive candidiasis are feasible only partially. Fluconazole is the only antifungal agent having the pharmacodynamic threshold of efficacy identified in experimental animal models convincingly validated in the clinical setting of invasive candidiasis as well. Conversely, for voriconazole and posaconazole data on this topic are very limited. For the echinocandins, robust PK/PD identified in the laboratory represented the rationale for defining differential clinical breakpoints of echinocandins against different species of Candida by the regulatory agencies. However, translation of the findings in the clinical setting provided conflicting results. Data on PK/PD of amphotericin B and flucytosine in models of invasive candidiasis are quite limited, and clinical studies assessing the role of drug exposure on efficacy are currently lacking. The expectation is that prospective studies could test more and more frequently the validity of experimental PK/PD data of antifungals in the clinical setting of invasive candidiasis. The findings could represent a step forward in addressing adequate antifungal stewardship programmes.

Overview of antifungal dosing in invasive candidiasis

In the past, most antifungal therapy dosing recommendations for invasive candidiasis followed a 'one-size fits all' approach with recommendations for lowering maintenance dosages for some antifungals in the setting of renal or hepatic impairment. A growing body of pharmacokinetic/pharmacodynamic research, however now points to a widespread 'silent epidemic' of antifungal underdosing for invasive candidiasis, especially among critically ill patients or special populations who have altered volume of distribution, protein binding and drug clearance. In this review, we explore how current adult dosing recommendations for antifungal therapy in invasive candidiasis have evolved, and special populations where new approaches to dose optimization or therapeutic drug monitoring may be needed, especially in light of increasing antifungal resistance among Candida spp.

Strong Synergism of Palmatine and Fluconazole/Itraconazole Against Planktonic and Biofilm Cells of Candida Species and Efflux-Associated Antifungal Mechanism

Fungal infections caused by Candida albicans and non-albicans Candida [NAC] species are becoming a growing threat in immunodeficient population, people with long-term antibiotic treatment and patients enduring kinds of catheter intervention. The resistance to one or more than one conventional antifungal agents contributes greatly to the widespread propagation of Candida infections. The severity of fungal infection requires the discovery of novel antimycotics and the extensive application of combination strategy. In this study, a group of Candida standard and clinical strains including C. albicans as well as several NAC species were employed to evaluate the antifungal potentials of palmatine (PAL) alone and in combination with fluconazole (FLC)/itraconazole (ITR) by microdilution method, checkerboard assay, gram staining, spot assay, and rhodamine 6G efflux test. Subsequently, the expressions of transporter-related genes, namely CDR1, CDR2, MDR1, and FLU1 for C. albicans, CDR1 and MDR1 for Candida tropicalis and Candida parapsilosis, ABC1 and ABC2 for Candida krusei, CDR1, CDR2, and SNQ2 for Candida glabrata were analyzed by qRT-PCR. The susceptibility test showed that PAL presented strong synergism with FLC and ITR with fractional inhibitory concentration index (FICI) in a range of 0.0049-0.75 for PAL+FLC and 0.0059-0.3125 for PAL+ITR in planktonic cells, 0.125-0.375 for PAL+FLC and 0.0938-0.3125 for PAL+ITR in biofilms. The susceptibility results were also confirmed by gram staining and spot assay. After combinations, a vast quantity of rhodamine 6G could not be pumped out as considerably intracellular red fluorescence was accumulated. Meanwhile, the expressions of efflux-associated genes were evaluated and presented varying degrees of inhibition. These results indicated that PAL was a decent antifungal synergist to promote the antifungal efficacy of azoles (such as FLC and ITR), and the underlying antifungal mechanism might be linked with the inhibition of efflux pumps and the elevation of intracellular drug content.

Effect of fluconazole prophylaxis on Candida fluconazole susceptibility in premature infants

OBJECTIVES

Extremely premature infants are at high risk of developing invasive candidiasis; fluconazole prophylaxis is safe and effective for reducing invasive candidiasis in this population but further study is needed. We sought to better understand the effect of prophylactic fluconazole on a selection of fluconazole-resistant Candida species.

METHODS

We evaluated the susceptibility to fluconazole of Candida isolates from premature infants (<750 g birth weight) enrolled in a multicentre, randomized, placebo-controlled trial of fluconazole prophylaxis. Candida species were isolated through surveillance cultures at baseline (study day 0-7), period 1 (study day 8-28) and period 2 (study day 29-49). Fluconazole MICs were determined for all Candida isolates.

RESULTS

Three hundred and sixty-one infants received fluconazole (n = 188) or placebo (n = 173). After the baseline period, Candida colonization was significantly lower in the fluconazole group compared with placebo during periods 1 (5% versus 27%; P < 0.001) and 2 (3% versus 27%; P < 0.001). After the baseline period, two infants (1%) were colonized with at least one fluconazole-resistant Candida in each group. Median fluconazole MIC was similar in both treatment groups at baseline and period 1. However, in period 2, median MIC was higher in the fluconazole group compared with placebo (1.00 versus 0.50 mg/L, P = 0.01). There was no emergence of resistance observed and no patients developed invasive candidiasis with a resistant Candida isolate.

CONCLUSIONS

Fluconazole prophylaxis decreased Candida albicans and 'non-albicans' Candida colonization and was associated with a slightly higher fluconazole MIC for colonizing Candida isolates.

Antifungal pharmacodynamics: Latin America's perspective

The current increment of invasive fungal infections and the availability of new broad-spectrum antifungal agents has increased the use of these agents by non-expert practitioners, without an impact on mortality. To improve efficacy while minimizing prescription errors and to reduce the high monetary cost to the health systems, the principles of pharmacokinetics (PK) and pharmacodynamics (PD) are necessary. A systematic review of the PD of antifungals agents was performed aiming at the practicing physician without expertise in this field. The initial section of this review focuses on the general concepts of antimicrobial PD. In vitro studies, fungal susceptibility and antifungal serum concentrations are related with different doses and dosing schedules, determining the PD indices and the magnitude required to obtain a specific outcome. Herein the PD of the most used antifungal drug classes in Latin America (polyenes, azoles, and echinocandins) is discussed.

Novel strategies against Candida biofilms: interest of synthetic compounds

A biofilm is a consortium of microbial cells that are attached to a substratum or an interface. It should be considered a reservoir that may induce serious infections. Indeed, Candidaspp. biofilms may be involved in the persistence or worsening of some chronic inflammatory diseases as well as in systemic infections, which may lead to high morbidity and mortality rates. New strategies are currently being explored, utilizing several synthetic compounds to prevent or fight these Candida biofilms. This article focuses on active synthetic compounds classified with regards to their modes of action: inhibition of early adherence phase, inhibition or control of biofilm maturation and finally elimination of already formed biofilms. Some of them show promise in fighting biofilm.

Nylon-3 polymers active against drug-resistant Candida albicans biofilms

Candida albicans is the most common fungal pathogen in humans, and most diseases produced by C. albicans are associated with biofilms. We previously developed nylon-3 polymers with potent activity against planktonic C. albicans and excellent C. albicans versus mammalian cell selectivity. Here we show that these nylon-3 polymers have strong and selective activity against drug-resistant C. albicans in biofilms, as manifested by inhibition of biofilm formation and by killing of C. albicans in mature biofilms. The best nylon-3 polymer (poly-βNM) is superior to the antifungal drug fluconazole for all three strains examined. This polymer is slightly less effective than amphotericin B (AmpB) for two strains, but the polymer is superior against an AmpB-resistant strain.

Pharmacokinetics and pharmacodynamics of antifungals in children and their clinical implications

Invasive fungal infections are a significant cause of morbidity and mortality in children. Successful management of these systemic infections requires identification of the causative pathogen, appropriate antifungal selection, and optimisation of its pharmacokinetic and pharmacodynamic properties to maximise its antifungal activity and minimise toxicity and the emergence of resistance. This review highlights salient scientific advancements in paediatric antifungal pharmacotherapies and focuses on pharmacokinetic and pharmacodynamic studies that underpin current clinical decision making. Four classes of drugs are widely used in the treatment of invasive fungal infections in children, including the polyenes, triazoles, pyrimidine analogues and echinocandins. Several lipidic formulations of the polyene amphotericin B have substantially reduced the toxicity associated with the traditional amphotericin B formulation. Monotherapy with the pyrimidine analogue flucytosine rapidly promotes the emergence of resistance and cannot be recommended. However, when used in combination with other antifungal agents, therapeutic drug monitoring of flucytosine has been shown to reduce high peak flucytosine concentrations, which are strongly associated with toxicity. The triazoles feature large inter-individual pharmacokinetic variability, although this pattern is less pronounced with fluconazole. In clinical trials, posaconazole was associated with fewer adverse effects than other members of the triazole family, though both posaconazole and itraconazole display erratic absorption that is influenced by gastric pH and the gastric emptying rate. Limited data suggest that the clinical response to therapy may be improved with higher plasma posaconazole and itraconazole concentrations. For voriconazole, pharmacokinetic studies among children have revealed that children require twice the recommended adult dose to achieve comparable blood concentrations. Voriconazole clearance is also affected by the cytochrome P450 (CYP) 2C19 genotype and hepatic impairment. Therapeutic drug monitoring is recommended as voriconazole pharmacokinetics are highly variable and small dose increases can result in marked changes in plasma concentrations. For the echinocandins, the primary source of pharmacokinetic variability stems from an age-dependent decrease in clearance with increasing age. Consequently, young children require larger doses per kilogram of body weight than older children and adults. Routine therapeutic drug monitoring for the echinocandins is not recommended. The effectiveness of many systemic antifungal agents has been correlated with pharmacodynamic targets in in vitro and in murine models of invasive candidiasis and aspergillosis. Further study is needed to translate these findings into optimal dosing regimens for children and to understand how these agents interact when multiple antifungal agents are used in combination.

Structure-activity relationships among antifungal nylon-3 polymers: identification of materials active against drug-resistant strains of Candida albicans

Fungal infections are a major challenge to human health that is heightened by pathogen resistance to current therapeutic agents. Previously, we were inspired by host-defense peptides to develop nylon-3 polymers (poly-β-peptides) that are toxic toward the fungal pathogen Candida albicans but exert little effect on mammalian cells. Based on subsequent analysis of structure-activity relationships among antifungal nylon-3 polymers, we have now identified readily prepared cationic homopolymers active against strains of C. albicans that are resistant to the antifungal drugs fluconazole and amphotericin B. These nylon-3 polymers are nonhemolytic. In addition, we have identified cationic-hydrophobic copolymers that are highly active against a second fungal pathogen, Cryptococcus neoformans, and moderately active against a third pathogen, Aspergillus fumigatus.

Proteomic Analysis of Cellular and Membrane Proteins in Fluconazole-Resistant Candida glabrata

Objectives

Candida glabrata is one of the most common causes of Candida bloodstream infections worldwide. Some isolates of C glabrata may be intermediately resistant to azoles, with some strains developing resistance during therapy or prophylaxis with fluconazole. In this study, we used a proteomic approach to identify differentially expressed proteins between fluconazoleresistant and -susceptible strains.

Methods

Membrane and cellular proteins were extracted from fluconazolesusceptible and fluconazole-resistant C glabrata strains. Differentially expressed proteins were compared using two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis. Proteins with >1.5-fold difference in expression were identified by liquid chromatography tandem mass spectrometry (LC-MS/MS).

Results

A total of 65 proteins were differentially expressed in the cellular and membrane fractions. Among the 39 cellular proteins, 11 were upregulated and 28 were downregulated in fluconazole-resistant strains in comparison with fluconazole-susceptible strains. In the membrane fraction, a total of 26 proteins were found, of which 19 were upregulated and seven were downregulated. A total of 31 proteins were identified by LC-MS/MS that are involved in glycolysis, carbohydrate transport, energy transfer, and other metabolic pathways. Heat shock proteins were identified in various spots.

Conclusion

Heat shock and stress response proteins were upregulated in the membrane fraction of the fluconazole-resistant C glabrata strain. Compared with susceptible strains, fluconazole-resistant strains showed increased expression of membrane proteins and decreased expression of cellular proteins.

Proteomic Analysis of Intracellular and Membrane Proteins From Voriconazole-Resistant Candida glabrata

Objectives

The proteomic analysis of voriconazole resistant Candida glabrata strain has not yet been investigated. In this study, differentially expressed proteins of intracellular and membrane fraction from voriconazole-susceptible, susceptible dose-dependent (S-DD), resistant C. glabrata strains were compared with each other and several proteins were identified.

Methods

The proteins of intracellular and membrane were isolated by disrupting cells with glass bead and centrifugation from voriconazole susceptible, S-DD, and resistant C. glabrata strains. The abundance of expressed proteins was compared using two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and proteins showing continuous twofold or more increase or reduction of expression in resistant strains compared to susceptible and S-DD strain were analyzed by liquid chromatography/mass spectrometry-mass spectrometry method.

Results

Of 34 intracellular proteins, 15 proteins showed expression increase or reduction (twofold or more). The identified proteins included regulation, energy production, carbohydrate transport, amino acid transport, and various metabolism related proteins. The increase of expression of heat shock protein 70 was found. Among membrane proteins, 12, 31 proteins showed expression increase or decrease in the order of susceptible, S-DD, and resistant strains. This expression included carbohydrate metabolism, amino acid synthesis, and response to stress-related proteins. In membrane fractions, the change of expression of 10 heat shock proteins was observed, and 9 heat shock protein 70 (Hsp70) showed the reduction of expression.

Conclusion

The expression of Hsp70 protein in membrane fraction is related to voriconazole resistant C. glabrata strains.

Nylon-3 polymers with selective antifungal activity

Host-defense peptides inhibit bacterial growth but show little toxicity toward mammalian cells. A variety of synthetic polymers have been reported to mimic this antibacterial selectivity; however, achieving comparable selectivity for fungi is more difficult because these pathogens are eukaryotes. Here we report nylon-3 polymers based on a novel subunit that display potent antifungal activity (MIC = 3.1 μg/mL for Candida albicans ) and favorable selectivity (IC10 > 400 μg/mL for 3T3 fibroblast toxicity; HC10 > 400 μg/mL for hemolysis).

Impact of prior inappropriate fluconazole dosing on isolation of fluconazole-nonsusceptible Candida species in hospitalized patients with candidemia

Prior use of fluconazole is a modifiable risk factor for the isolation of fluconazole-nonsusceptible Candida species. Optimization of the use of fluconazole by appropriate dose or duration may be able to minimize the risk of resistance. The objective of this study was to evaluate the effects of prior fluconazole therapy, including the dose and duration, on fluconazole susceptibility among Candida species isolated from hospitalized patients with candidemia. A retrospective cohort study of hospitalized patients with a first occurrence of nosocomial candidemia, from 2006 to 2009, was carried out. The relationships between the initial dose and duration of prior fluconazole therapy and the isolation of fluconazole-nonsusceptible Candida species were assessed. An initial fluconazole dose greater than 2 mg/kg and less than 6 mg/kg of body weight was considered suboptimal. A total of 177 patients were identified, of whom 133 patients aged 61 ± 16 years (56% male, 51% Caucasian, 51% with an APACHE II score of ≥ 15) had candidemia more than 2 days after the hospital admission day. Nine of 107 (8%) patients with fluconazole-susceptible Candida species and 9 of 26 (35%) patients with fluconazole-nonsusceptible Candida species had prior fluconazole exposure (risk ratio [RR], 3.03; 95% confidence interval [95% CI], 1.57 to 5.86; P, 0.0022). Preexposure with an initial dose of fluconazole greater than 2 mg/kg and less than 6 mg/kg occurred in 3 of 9 (33%) and 8 of 9 (89%) patients with fluconazole-susceptible and fluconazole-nonsusceptible Candida species, respectively (P, 0.0498). We conclude that patients with candidemia due to fluconazole-nonsusceptible Candida species were more likely to have received prior fluconazole therapy. Suboptimal initial dosing of prior fluconazole therapy was associated with candidemia with fluconazole-nonsusceptible Candida species.

Efflux: how bacteria use pumps to control their microenvironment

Efflux pumps are a potent and clinically important cause of antibiotic resistance. The particular focus of this chapter is on the efflux pump as a target for antimicrobial therapy and the development of new antibacterials to address the efflux problem.Tigecycline is an example of how old antibiotics, in this case tetracyclines, which have become substrates for efflux pumps, can be extensively modified to restore antimicrobial activity and clinical efficacy.

Transcriptional profiling of azole-resistant Candida parapsilosis strains

Herein we describe the changes in the gene expression profile of Candida parapsilosis associated with the acquisition of experimentally induced resistance to azole antifungal drugs. Three resistant strains of C. parapsilosis were obtained following prolonged in vitro exposure of a susceptible clinical isolate to constant concentrations of fluconazole, voriconazole, or posaconazole. We found that after incubation with fluconazole or voriconazole, strains became resistant to both azoles but not to posaconazole, although susceptibility to this azole decreased, whereas the strain incubated with posaconazole displayed resistance to the three azoles. The resistant strains obtained after exposure to fluconazole and to voriconazole have increased expression of the transcription factor MRR1, the major facilitator transporter MDR1, and several reductases and oxidoreductases. Interestingly, and similarly to what has been described in C. albicans, upregulation of MRR1 and MDR1 is correlated with point mutations in MRR1 in the resistant strains. The resistant strain obtained after exposure to posaconazole shows upregulation of two transcription factors (UPC2 and NDT80) and increased expression of 13 genes involved in ergosterol biosynthesis. This is the first study addressing global molecular mechanisms underlying azole resistance in C. parapsilosis; the results suggest that similarly to C. albicans, tolerance to azoles involves the activation of efflux pumps and/or increased ergosterol synthesis.

The contribution of mouse models to our understanding of systemic candidiasis

Some Candida species are common commensals, which can become opportunistic pathogens in susceptible hosts. In severely ill patients, Candida species, particularly Candida albicans, can cause life-threatening systemic infections. These infections are difficult to diagnose, as symptoms are similar to those of systemic bacterial infections. These difficulties can lead to delays in initiation in antifungal therapy, which contributes to the high mortality rates (> 40%) associated with these infections. In order to investigate systemic Candida infection, mouse models have been developed that mimic human disease, the most common being the intravenous infection model and the gastrointestinal colonization and dissemination model. This review discusses the two models and the contributions that they have made to our understanding of fungal virulence, host response to infection and the development of novel antifungal therapies and diagnostics.

Antifungal activity of amphotericin B conjugated to carbon nanotubes

Amphotericin B (AMB) has long been considered the most effective drug in the treatment of serious invasive fungal infections. There are, however, major limitations to its use, due to several adverse effects, including acute infusional reactions and, most relevant, a dose-dependent nephrotoxicity. At least some of these effects are attributed to the aggregation of AMB as a result of its poor water solubility. To overcome this problem, reformulated versions of the drug have been developed, including a micellar dispersion of AMB with sodium deoxycholate (AMBD), its encapsulation into liposomes, or its incorporation into lipidic complexes. The development of nanobiotechnologies provides novel potential drug delivery systems that make use of nanomaterials such as functionalized carbon nanotubes (f-CNTs), which are emerging as an innovative and efficient tool for the transport and cellular translocation of therapeutic molecules. In this study, we prepared two conjugates between f-CNTs and AMB. The antifungal activity of these conjugates was tested against a collection of reference and clinical fungal strains, in comparison to that of AMB alone or AMBD. Measured minimum inhibition concentration (MIC) values for f-CNT-AMB conjugates were either comparable to or better than those displayed by AMB and AMBD. Furthermore, AMBD-resistant Candida strains were found to be susceptible to f-CNT-AMB 1. Additional studies, aimed at understanding the mechanism of action of the conjugates, suggest a nonlytic mechanism, since the compounds show a major permeabilizing effect on the tested fungal strains only after extended incubation. Interestingly, the f-CNT-AMB 1 does not show any significant toxic effect on Jurkat cells at antifungal concentrations.

Once-weekly liposomal amphotericin B as Candida prophylaxis in very low birth weight premature infants: a prospective, randomized, open-label, placebo-controlled pilot study

OBJECTIVE

This study was conducted to evaluate once-weekly liposomal amphotericin B (L-AmB) for Candida prophylaxis in very low birth weight (VLBW) neonates.

METHODS

This prospective, randomized, open-label, placebo-controlled study included neonates who were <32 weeks' gestational age, <7 days old, and weighing <1500 g at birth. Subjects were randomized to receive L-AmB 5 mg/kg per week or placebo (dextrose water) and were followed until 6 weeks of age. Surveillance cultures were obtained at baseline, at 72 hours, and weekly thereafter. Study drug was continued until 6 weeks after birth or the discontinuation of high-risk treatments and invasive devices, whichever occurred first. Blood cultures were obtained as clinically indicated. The primary end point was development of Candida colonization by 6 weeks' postnatal age; secondary end points included development of invasive candidiasis and occurrence of treatment-related adverse events. Safety variables included renal and hepatic function tests, incidence of grade III-IV intraventricular hemorrhage (IVH) and necrotizing enterocolitis (NEC), and mortality.

RESULTS

Forty subjects were enrolled and randomized to receive L-AmB (12 males, 8 females; 50% white) or placebo (12 males, 8 females; 35% white). Subjects were evenly distributed by gestational age, age at enrollment, birth weight, race, and sex. Consent was withdrawn after completion of study treatment in 1 subject (L-AmB); 1 subject in each study arm died during the study; and 3 subjects were transferred back to their referring institutions (1 L-AmB, 2 placebo). Thus, 17 subjects in each arm completed all study procedures, although all 40 subjects were evaluable. Colonization before administration of study drug was noted in 4 L-AmB subjects (20%) and 1 placebo subject (5%); 1 (5%) and 3 (15%) subjects in the respective groups developed colonization while receiving study drug. No L-AmB subjects and 1 placebo subject developed candidiasis. One subject in each group died; these deaths were not considered related to study drug or fungal infection. There were no clinical differences between groups in the incidence of grade III-IV IVH, NEC, hypokalemia, nephrotoxicity, need for platelet or packed red blood cell transfusion, or mortality.

CONCLUSIONS

L-AmB 5 mg/kg once weekly was generally well tolerated in these VLBW infants. The data did not allow evaluation of efficacy. A larger, multicenter, randomized clinical trial of L-AmB for Candida prophylaxis that is appropriately powered is warranted.

Aneuploid chromosomes are highly unstable during DNA transformation of Candida albicans

Candida albicans strains tolerate aneuploidy, historically detected as karyotype alterations by pulsed-field gel electrophoresis and more recently revealed by array comparative genome hybridization, which provides a comprehensive and detailed description of gene copy number. Here, we first retrospectively analyzed 411 expression array experiments to predict the frequency of aneuploidy in different strains. As expected, significant levels of aneuploidy were seen in strains exposed to stress conditions, including UV light and/or sorbose treatment, as well as in strains that are resistant to antifungal drugs. More surprisingly, strains that underwent transformation with DNA displayed the highest frequency of chromosome copy number changes, with strains that were initially aneuploid exhibiting approximately 3-fold more copy number changes than strains that were initially diploid. We then prospectively analyzed the effect of lithium acetate (LiOAc) transformation protocols on the stability of trisomic chromosomes. Consistent with the retrospective analysis, the proportion of karyotype changes was highly elevated in strains carrying aneuploid chromosomes. We then tested the hypothesis that stresses conferred by heat and/or LiOAc exposure promote chromosome number changes during DNA transformation procedures. Indeed, a short pulse of very high temperature caused frequent gains and losses of multiple chromosomes or chromosome segments. Furthermore, milder heat exposure over longer periods caused increased levels of loss of heterozygosity. Nonetheless, aneuploid chromosomes were also unstable when strains were transformed by electroporation, which does not include a heat shock step. Thus, aneuploid strains are particularly prone to undergo changes in chromosome number during the stresses of DNA transformation protocols.

Efflux-mediated antifungal drug resistance

Fungi cause serious infections in the immunocompromised and debilitated, and the incidence of invasive mycoses has increased significantly over the last 3 decades. Slow diagnosis and the relatively few classes of antifungal drugs result in high attributable mortality for systemic fungal infections. Azole antifungals are commonly used for fungal infections, but azole resistance can be a problem for some patient groups. High-level, clinically significant azole resistance usually involves overexpression of plasma membrane efflux pumps belonging to the ATP-binding cassette (ABC) or the major facilitator superfamily class of transporters. The heterologous expression of efflux pumps in model systems, such Saccharomyces cerevisiae, has enabled the functional analysis of efflux pumps from a variety of fungi. Phylogenetic analysis of the ABC pleiotropic drug resistance family has provided a new view of the evolution of this important class of efflux pumps. There are several ways in which the clinical significance of efflux-mediated antifungal drug resistance can be mitigated. Alternative antifungal drugs, such as the echinocandins, that are not efflux pump substrates provide one option. Potential therapeutic approaches that could overcome azole resistance include targeting efflux pump transcriptional regulators and fungal stress response pathways, blockade of energy supply, and direct inhibition of efflux pumps.

In vivo pharmacodynamic target investigation for micafungin against Candida albicans and C. glabrata in a neutropenic murine candidiasis model

Previous studies using in vivo candidiasis models have demonstrated that the concentration-associated pharmacodynamic indices, the maximum concentration of a drug in serum/MIC and 24-h area under the curve (AUC)/MIC, are associated with echinocandin treatment efficacy. The current investigations used a neutropenic murine model of disseminated Candida albicans and C. glabrata infection to identify the 24-h AUC/MIC index target associated with a stasis and killing endpoint for the echinocandin, micafungin. The kinetics after intraperitoneal micafungin dosing were determined in neutropenic infected mice. Peak levels and AUC values were linear over the 16-fold dose range studied. The serum drug elimination half-life ranged from 7.5 to 16 h. Treatment studies were conducted with 4 C. albicans and 10 C. glabrata isolates with micafungin MICs varying from 0.008 to 0.25 microg/ml to determine whether similar 24-h AUC/MIC ratios were associated with efficacy. The free drug AUC/MICs associated with stasis and killing (1-log) endpoints were near 10 and 20, respectively. The micafungin exposures associated with efficacy were similar for the two Candida species. Furthermore, the free drug micafungin exposures required to produce stasis and killing endpoints were similar to those recently reported for another echinocandin, anidulafungin, against the identical Candida isolates in this model.

In vivo pharmacodynamic characterization of anidulafungin in a neutropenic murine candidiasis model

Multiple in vivo studies have characterized the pharmacodynamics of drugs from the triazole and polyene antifungal drug classes. Fewer studies have investigated these pharmacodynamic relationships for the echinocandin drug class. We used a neutropenic murine model of disseminated Candida albicans, Candida tropicalis, and Candida glabrata infection to characterize the time course of activity of the new echinocandin anidulafungin. The pharmacokinetic-pharmacodynamic (PK-PD) indices (the percentage of time that the drug concentration was above the MIC, the ratio of the area under the concentration-time curve from 0 to 24 h [AUC(0-24)] to the MIC, and the ratio of the maximum serum drug concentration [C(max)] to the MIC) were correlated with in vivo efficacy, as measured by organism numbers in kidney cultures after 96 h of therapy. The kinetics following intraperitoneal anidulafungin dosing in neutropenic infected mice were monitored. Peak levels and AUCs were linear over the 16-fold dose range studied. The drug elimination half-life in serum ranged from 14 to 24 h. Single-dose postantifungal-effect studies demonstrated prolonged suppression of organism regrowth after serum anidulafungin levels had fallen below the MIC. Of the four dosing intervals studied, treatment with the more widely spaced dosing regimens was most efficacious, suggesting the C(max)/MIC ratio as the PK-PD index most predictive of efficacy. Nonlinear regression analysis suggested that both the C(max)/MIC and AUC/MIC ratios were strongly predictive of treatment success. Studies were then conducted with 13 additional C. albicans, C. tropicalis, and C. glabrata isolates with various anidulafungin susceptibilities (MICs of anidulafungin for these strains, 0.015 to 2.0 microg/ml) to determine if similar C(max)/MIC and AUC(0-24)/MIC ratios for these isolates were associated with efficacy. The anidulafungin exposures associated with efficacy were similar among Candida species.

Monitoring plasma voriconazole levels may be necessary to avoid subtherapeutic levels in hematopoietic stem cell transplant recipients

BACKGROUND

Low voriconazole levels have been associated with a higher failure rate in patients with confirmed fungal infections.

METHODS

Steady-state plasma trough voriconazole levels were measured after at least 5 days of therapy in 87 patients with hematologic malignancies on 201 separate occasions (1-5 levels per patient; median, 2). Most patients (90%) had undergone allogeneic hematopoietic stem cell transplantation. The daily voriconazole dose, administered in 2 divided doses, was 200 mg (n = 4), 400 mg (n = 151), 500 mg (n = 20), 600 mg (n = 18), and 800 mg (n = 8); corresponding to 2.0-16.3 (median, 5.4) mg/kg. Plasma voriconazole levels were 0-12.5 microg/mL (median, 1.2). Voriconazole was undetectable (<0.2 mug/mL) in 15%.

RESULTS

The correlation between dose and levels was weak (r = 0.14; P = .045). The median absolute daily drug dose (400 mg) was identical in groups of patients with levels of 0, 0.2 to 0.5, >0.5 to 2.0, >2.0 to 5.0, and >5.0. Whereas the daily drug dose in mg/kg was significantly higher when the levels were >5.0 microg/mL, there was no consistent relation between dose and level below that threshold. In adult patients getting standard doses of voriconazole orally, the drug levels are highly variable. Based on limited available data, between a quarter and two-thirds of these levels could potentially be associated with a lower likelihood of response or a higher likelihood of failure.

CONCLUSIONS

Future voriconazole studies should incorporate prospective therapeutic drug monitoring and consideration should be given to checking levels in patients receiving the drug for confirmed, life-threatening fungal infections.