Caspofungin: antifungal activity in vitro, pharmacokinetics, and effects on fungal load and animal survival in neutropenic rats with invasive pulmonary aspergillosis

Development and Quality Control of a Population Pharmacokinetic Model Library for Caspofungin

BACKGROUND

Caspofungin is an echinocandin antifungal agent commonly used as the first-line therapy for invasive candidiasis, salvage therapy for invasive aspergillosis, and empirical therapy for presumed fungal infections. Pharmacokinetic (PK) variabilities and suboptimal exposure have been reported for caspofungin, increasing the risk of insufficient efficacy.

OBJECTIVE

This work aimed to develop a caspofungin population pharmacokinetic (popPK) library and demonstrate its utility by assessing the probability of target attainment across diverse settings.

METHODS

We established a caspofungin popPK model library following a rigorous literature review, re-implementing selected models in R with rxode2. Quality control procedures included a comparison of different studies and assessing covariate impacts. Model libraries were primarily used to perform Monte Carlo simulations to estimate target attainment and guide personalized dosing in Candida infections.

RESULTS

A total of 13 models, one- or two-compartment models, were included. The most significant covariates were body size (weight and body surface area), liver function, and albumin level. The results show that children and adults showed considerable differences in pharmacokinetics. For C. albicans and C. parapsilosis, none of the populations achieved a PTA of ≥90% at their respective susceptible MIC values. In contrast, for C. glabrata, 70% of the adult studies reached a PTA of ≥90%, while all pediatric studies achieved the same PTA level.

CONCLUSION

At the recommended dosage, adult patients showed notably lower exposure to caspofungin compared to pediatric patients. Considering body size, liver function, and serum albumin is crucial when determining caspofungin dosage regimens. Furthermore, further research is required to comprehensively understand the pharmacokinetics of caspofungin in pediatric patients.

Therapeutic drug monitoring of antifungal therapies: do we really need it and what are the best practices?

INTRODUCTION

Despite advancements, invasive fungal infections (IFI) still carry high mortality rates, often exceeding 30%. The challenges in diagnosis, coupled with limited effective antifungal options, make managing IFIs complex. Antifungal drugs are essential for IFI management, but their efficacy can be diminished by drug-drug interactions and pharmacokinetic variability. Therapeutic Drug Monitoring (TDM), especially in the context of triazole use, has emerged as a valuable strategy to optimize antifungal therapy.

AREAS COVERED

This review provides current evidence regarding the potential benefits of TDM in IFI management. It discusses how TDM can enhance treatment response, safety, and address altered pharmacokinetics in specific patient populations.

EXPERT OPINION

TDM plays a crucial role in achieving optimal therapeutic outcomes in IFI management, particularly for certain antifungal agents. Preclinical studies consistently show a link between therapeutic drug levels and antifungal efficacy. However, clinical research in mycology faces challenges due to patient heterogeneity and the diversity of fungal infections. TDM's potential advantages in guiding Echinocandin therapy for critically ill patients warrant further investigation. Additionally, for drugs like Posaconazole, assessing whether serum levels or alternative markers like saliva offer the best measure of efficacy is an intriguing question.

Therapeutic Drug Monitoring of Antimicrobials in Critically Ill Obese Patients

Obesity is a significant global public health concern that is associated with an elevated risk of comorbidities as well as severe postoperative and nosocomial infections. The treatment of infections in critically ill obese patients can be challenging because obesity affects the pharmacokinetics and pharmacodynamics of antibiotics, leading to an increased risk of antibiotic therapy failure and toxicity due to inappropriate dosages. Precision dosing of antibiotics using therapeutic drug monitoring may help to improve the management of this patient population. This narrative review outlines the pharmacokinetic and pharmacodynamic changes that result from obesity and provides a comprehensive critical review of the current available data on dosage adjustment of antibiotics in critically ill obese patients.

Caspofungin Cerebral Penetration and Therapeutic Efficacy in Experimental Cerebral Aspergillosis

Despite best available therapy, cerebral aspergillosis is an often-lethal complication of disseminated aspergillosis. There is an urgent need to expand the currently limited therapeutic options. In this study, we assessed cerebral drug exposure and efficacy of caspofungin (CAS) using a lethal infant rat model of cerebral aspergillosis. Eleven-day-old Wistar rats were infected by intracisternal injection of Aspergillus fumigatus conidia. Treatment started after 22 h and was continued for 10 days. Regimens were CAS 1 mg/kg/day intraperitoneally (i.p.), liposomal amphotericin B (L-AmB) 5 mg/kg/day i.p., and both drugs combined at the same dose i.p. Infected controls were given NaCl 0.85% i.p. Primary endpoints assessed were survival, cerebral fungal burden, galactomannan index, and drug concentrations in brain homogenate at 2, 3, 5, and 11 days after infection. Compared to those of controls (4.4 ± 2.7 days), survival times were increased by treatment with CAS alone (10.3 ± 1.7 days; P < 0.0001) and CAS combined with L-AmB (9.3 ± 2.8 days; P < 0.0001). In contrast, survival time of L-AmB-treated animals (4.3 ± 3.1 days) was not different from that of controls. Cerebral fungal burden and galactomannan index declined in all animals over time, without significant differences between controls and treated animals. CAS trough levels in brain tissue were between 0.84 and 1.4 μg/g, concentrations we show to be associated with efficacy. AmB trough levels in brain tissue were higher than the MIC of the A. fumigatus isolate. In summary, CAS concentrations in brain tissue suggest it may be therapeutically relevant and it significantly improved survival in this lethal model of cerebral aspergillosis in nonneutropenic rats. The clinical efficacy of CAS treatment for cerebral aspergillosis merits further study. IMPORTANCE Treatment options for cerebral aspergillosis, an often-lethal disease, are limited. The echinocandins (caspofungin is one of them) are not recommended treatment because their brain tissue penetration is often considered insufficient. In a nursing rat model of cerebral aspergillosis that mimics human disease, we found potentially therapeutically relevant concentrations of caspofungin in brain tissue and prolonged survival of caspofungin-treated animals. The efficacy of caspofungin in the treatment of cerebral aspergillosis documented here, if confirmed in other animal models (especially immunosuppressed murine models) and by using additional Aspergillus isolates across a range of CAS minimal effective concentrations (MECs), would suggest that caspofungin merits further study as a treatment option for patients suffering from aspergillosis disseminated to the brain.

Therapeutic Drug Monitoring of Antifungal Agents in Critically Ill Patients: Is There a Need for Dose Optimisation?

Invasive fungal infections are an important cause of morbidity and mortality, especially in critically ill patients. Increasing resistance rates and inadequate antifungal exposure have been documented in these patients, due to clinically relevant pharmacokinetic (PK) and pharmacodynamic (PD) alterations, leading to treatment failure. Physiological changes such as third spacing (movement of fluid from the intravascular compartment to the interstitial space), hypoalbuminemia, renal failure and hepatic failure, as well as common interventions in the intensive care unit, such as renal replacement therapy and extracorporeal membrane oxygenation, can lead to these PK and PD alterations. Consequently, a therapeutic target concentration that may be useful for one patient may not be appropriate for another. Regular doses do not take into account the important PK variations in the critically ill, and the need to select an effective dose while minimising toxicity advocates for the use of therapeutic drug monitoring (TDM). This review aims to describe the current evidence regarding optimal PK/PD indices associated with the clinical efficacy of the most commonly used antifungal agents in critically ill patients (azoles, echinocandins, lipid complexes of amphotericin B, and flucytosine), provide a comprehensive understanding of the factors affecting the PK of each agent, document the PK parameters of critically ill patients compared to healthy volunteers, and, finally, make recommendations for therapeutic drug monitoring (TDM) of antifungals in critically ill patients.

Therapeutic Drug Monitoring of the Echinocandin Antifungal Agents: Is There a Role in Clinical Practice? A Position Statement of the Anti-Infective Drugs Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

PURPOSE

Reduced exposure to echinocandins has been reported in specific patient populations, such as critically ill patients; however, fixed dosing strategies are still used. The present review examines the accumulated evidence supporting echinocandin therapeutic drug monitoring (TDM) and summarizes available assays and sampling strategies.

METHODS

A literature search was conducted using PubMed in December 2020, with search terms such as echinocandins, anidulafungin, caspofungin, micafungin, or rezafungin with pharmacology, pharmacokinetics (PKs), pharmacodynamics (PDs), drug-drug interactions, TDM, resistance, drug susceptibility testing, toxicity, adverse drug reactions, bioanalysis, chromatography, and mass spectrometry. Data on PD/PD (PK/PD) outcome markers, drug resistance, PK variability, drug-drug interactions, assays, and TDM sampling strategies were summarized.

RESULTS

Echinocandins demonstrate drug exposure-efficacy relationships, and maximum concentration/minimal inhibitory concentration ratio (Cmax/MIC) and area under the concentration-time curve/MIC ratio (AUC/MIC) are proposed PK/PD markers for clinical response. The relationship between drug exposure and toxicity remains poorly clarified. TDM could be valuable in patients at risk of low drug exposure, such as those with critical illness and/or obesity. TDM of echinocandins may also be useful in patients with moderate liver impairment, drug-drug interactions, hypoalbuminemia, and those undergoing extracorporeal membrane oxygenation, as these conditions are associated with altered exposure to caspofungin and/or micafungin. Assays are available to measure anidulafungin, micafungin, and caspofungin concentrations. A limited-sampling strategy for anidulafungin has been reported.

CONCLUSIONS

Echinocandin TDM should be considered in patients at known risk of suboptimal drug exposure. However, for implementing TDM, clinical validation of PK/PD targets is needed.

Comparative Pharmacodynamics of Echinocandins against Aspergillus fumigatus Using an In Vitro Pharmacokinetic/Pharmacodynamic Model That Correlates with Clinical Response to Caspofungin Therapy: Is There a Place for Dose Optimization?

Echinocandins have been used as primary therapy of invasive aspergillosis (IA), with suboptimal results at standard dosing. Here, we explored the efficacy of dose escalation in a validated in vitro pharmacokinetic/pharmacodynamic (PK/PD) model. Six echinocandin wild-type (WT) and three non-WT A. fumigatus isolates were tested in an in vitro PK/PD model simulating anidulafungin, caspofungin, and micafungin exposures with a free drug maximum concentration (fCmax) of 0.01 to 16 mg/liter and a half-life (t1/2) of 8 to 22 h. The relationship between the area under the dosing interval time-free drug concentration curve (fAUC0-24)/minimum effective concentration (MEC) and % aberrant mycelium formation was analyzed. PK/PD indices associated with 50 to 99.99% maximal activity (EI50 to EI99.99) were correlated with the clinical outcome of a 50-mg/day standard dose of caspofungin. The probability of target attainment (PTA) was calculated for different dosing regimens of each echinocandin via Monte Carlo analysis. A sigmoidal PK/PD relationship was found for WT isolates with EI99 values of 766, 8.8, and 115 fAUC0-24/CLSI MEC for anidulafungin, caspofungin, and micafungin, respectively. No aberrant mycelia were observed for non-WT isolates, irrespective of their MEC and drug exposure. The EI99, EI99.9, and EI99.99 values corresponded to 2-, 3-, and 4-log10 formation of aberrant mycelia and correlated with survival, favorable, and complete response rates to caspofungin primary therapy in patients with IA. A very low PTA (<13%) was found for the standard doses of all echinocandins, whereas a PTA of ≥90% was found with 100 and 150 mg/day of caspofungin and 1,400 mg/day micafungin against WT isolates. For anidulafungin, the PTA for 1,500 mg/day was 10%. Among the three echinocandins, only caspofungin at 2 or 3 times the licensed dosing was associated with a high PTA. Caspofungin dose escalation might deserve clinical validation.

Pharmacokinetic and Pharmacodynamic Comparison of Intravenous and Inhaled Caspofungin

Background: Aspergillosis is a serious fungal lung infection caused by Aspergillus spp. and is often fatal in immunocompromised patients. Current antifungal drug treatment and delivery results in modest efficacy in these patients may be due to low drug distribution to the lung. A comparison of intravenous (IV) caspofungin and lung-targeted inhaled caspofungin was conducted in rats. The goal was to determine the concentrations of drug at the site of infection and systemic distribution that leads to toxicity. This was performed to understand the difference in the in vitro activity of caspofungin and modest in vivo efficacy. Methods: Caspofungin was delivered to rats through IV injection and nose-only inhalation. Each cohort received a single 2 mg/kg dose of drug. Plasma and tissue samples were analyzed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) and drug levels were compared. Results: The lung drug level was above the minimum effective concentration for 168 hours in the inhaled group but <24 hours in the IV cohort. The lung C_max and area under curve (AUC) in the inhaled group was 20 times higher than in the IV group. Lung-targeted delivery doubled lung drug half-life compared with IV delivery. Systemic distribution to the liver and kidney was 45% lower for the inhaled cohort than the IV group of animals. Conclusions: Based on pharmacokinetic and pharmacodynamic indices, lung-targeted inhaled caspofungin is likely to provide an improved therapeutic benefit without any increase in systemic toxicities. Furthermore, inhaled delivery supports a weekly dosing regimen instead of daily IV dosing.

Chitinase Induction Prior to Caspofungin Treatment of Experimental Invasive Aspergillosis in Neutropenic Rats Does Not Enhance Survival

Host chitinases, chitotriosidase and acidic mammalian chitinase (AMCase), improved the antifungal activity of caspofungin (CAS) against Aspergillus fumigatus in vitro These chitinases are not constitutively expressed in the lung. Here, we investigated whether chitosan derivatives were able to induce chitinase activity in the lungs of neutropenic rats and, if so, whether these chitinases were able to prolong survival of rats with invasive pulmonary aspergillosis (IPA) or of rats with IPA and treated with CAS. An oligosaccharide-lactate chitosan (OLC) derivative was instilled in the left lung of neutropenic rats to induce chitotriosidase and AMCase activities. Rats instilled with OLC or with phosphate-buffered saline (PBS) were subsequently infected with A. fumigatus and then treated with suboptimal doses of CAS. Survival, histopathology, and galactomannan indexes were determined. Instillation of OLC resulted in chitotriosidase and AMCase activities. However, instillation of OLC did not prolong rat survival when rats were subsequently challenged with A. fumigatus In 5 of 7 rats instilled with OLC, the fungal foci in the lungs were smaller than those in rats instilled with PBS. Instillation of OLC did not significantly enhance the survival of neutropenic rats challenged with A. fumigatus and treated with a suboptimal dosage of CAS. Chitotriosidase and AMCase activities can be induced with OLC, but the presence of active chitinases in the lung did not prevent the development of IPA or significantly enhance the therapeutic outcome of CAS treatment.

Generation of Methicillin-Resistant Staphylococcus Aureus Biofilm Infection in an Immunosuppressed Rat Model

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen responsible for many related infections, and immunosuppressed individuals are more susceptible. Its pathogenicity is associated with its virulence factors, resistance to antibiotics, and ability to form biofilm (BF). MRSA-BF infections in immunosuppressed patients pose great difficulties to clinical treatment.

Material/Methods

The study aimed to establish a model of MRSA-BF infection in rats with cyclophosphamide (CTX)-induced immunosuppression. For this, rats were administered CTX on days 1 and 4. White blood cells (WBC) were counted, then rats were inoculated with a clinical MRSA 17546 (t037) on day 5. Rats were sacrificed on days 6–10 and tissue samples were examined by scanning electron microscopy.

Results

Using the dose of CTX: 150 (mg/kg) + 100 (mg/kg) is better than the other 2 programs as the survival rates of the immunocompromised rats were higher than in the other 2 immunosuppressive groups. The survival rate was not different between rats in the clean environment and in the SPF environment. However, the survival rate was affected by the sample acquisitions. Importantly, WBC counts started to decline on day 4, and then started to rise on day 9. Moreover, MRSA-BFs were formed earlier in immunosuppressed rats compared to the normal rats, as shown by scanning electron microscopy.

Conclusions

The study successfully established an immunosuppressed rat model of MRSA-BF infection, which provides methodological and data support for establishment of such animal models and is useful reference for related research. Our results may help further investigation of MRSA-BF infection.

Addition of 17-(allylamino)-17-demethoxygeldanamycin to a suboptimal caspofungin treatment regimen in neutropenic rats with invasive pulmonary aspergillosis delays the time to death but does not enhance the overall therapeutic efficacy

Caspofungin (CAS) which is used as salvage therapy in patients with invasive pulmonary aspergillosis (IPA) inhibits the 1,3-β-D-glucan synthesis in Aspergillus fumigatus. Inhibiting 1,3-β-D-glucan synthesis induces a stress response and in an invertebrate model it was demonstrated that inhibiting this response with geldamycin enhanced the therapeutic efficacy of CAS. Since geldamycin itself is toxic to mammalians, the therapeutic efficacy of combining geldamycin with CAS was not studied in rodent models. Therefore in this study we investigated if the geldamycin derivate 17-(allylamino)-17-demethoxygeldanamycin (17-AAG) was able to enhance the therapeutic efficacy of CAS in vitro and in our IPA model in transiently neutropenic rats. In vitro we confirmed the earlier demonstrated synergy between 17-AAG and CAS in ten A. fumigatus isolates. In vivo we treated A. fumigatus infected neutropenic rats with a sub-optimal dose of 0.75 mg/kg/day CAS and 1 mg/kg/day 17-AAG for ten days. Survival was monitored for 21 days after fungal inoculation. It appeared that the addition 17-AAG delayed death but did not improve overall survival of rats with IPA. Increasing the doses of 17-AAG was not possible due to hepatic toxicity. This study underlines the need to develop less toxic and more fungal specific geldamycin derivatives and the need to test such drugs not only in invertebrate models but also in mammalian models.

Rodent Models of Invasive Aspergillosis due to Aspergillus fumigatus: Still a Long Path toward Standardization

Invasive aspergillosis has been studied in laboratory by the means of plethora of distinct animal models. They were developed to address pathophysiology, therapy, diagnosis, or miscellaneous other concerns associated. However, there are great discrepancies regarding all the experimental variables of animal models, and a thorough focus on them is needed. This systematic review completed a comprehensive bibliographic analysis specifically-based on the technical features of rodent models infected with Aspergillus fumigatus. Out the 800 articles reviewed, it was shown that mice remained the preferred model (85.8% of the referenced reports), above rats (10.8%), and guinea pigs (3.8%). Three quarters of the models involved immunocompromised status, mainly by steroids (44.4%) and/or alkylating drugs (42.9%), but only 27.7% were reported to receive antibiotic prophylaxis to prevent from bacterial infection. Injection of spores (30.0%) and inhalation/deposition into respiratory airways (66.9%) were the most used routes for experimental inoculation. Overall, more than 230 distinct A. fumigatus strains were used in models. Of all the published studies, 18.4% did not mention usage of any diagnostic tool, like histopathology or mycological culture, to control correct implementation of the disease and to measure outcome. In light of these findings, a consensus discussion should be engaged to establish a minimum standardization, although this may not be consistently suitable for addressing all the specific aspects of invasive aspergillosis.

Preclinical Pharmacokinetics and Pharmacodynamic Target of SCY-078, a First-in-Class Orally Active Antifungal Glucan Synthesis Inhibitor, in Murine Models of Disseminated Candidiasis

SCY-078 (MK-3118) is a novel, semisynthetic derivative of enfumafungin and represents the first compound of the triterpene class of antifungals. SCY-078 exhibits potent inhibition of β-(1,3)-d-glucan synthesis, an essential cell wall component of many pathogenic fungi, including Candida spp. and Aspergillus spp. SCY-078 is currently in phase 2 clinical development for the treatment of invasive fungal diseases. In vitro disposition studies to assess solubility, intestinal permeability, and metabolic stability were predictive of good oral bioavailability. Preclinical pharmacokinetic studies were consistent with once-daily administration to humans. After intravenous delivery, plasma clearance in rodents and dogs was low, representing <15% and <25% of hepatic blood flow, respectively. The terminal elimination-phase half-life was 5.5 to 8.7 h in rodents, and it was ∼9.3 h in dogs. The volume of distribution at steady-state was high (4.7 to 5.3 liters/kg), a finding suggestive of extensive tissue distribution. Exposure of SCY-078 in kidney tissue, a target organ for invasive fungal disease such as candidiasis, exceeded plasma by 20- to 25-fold for the area under the concentration-time curve from 0 h to infinity (AUC0-∞) and Cmax SCY-078 achieved efficacy endpoints following oral delivery across multiple murine models of disseminated candidiasis. The pharmacokinetic/pharmacodynamic indices Cmax/MIC and AUC/MIC correlated with outcome. Target therapeutic exposure, expressed as the plasma AUC0-24, was comparable across models, with an upper value of 11.2 μg·h/ml (15.4 μM·h); the corresponding mean value for free drug AUC/MIC was ∼0.75. Overall, these results demonstrate that SCY-078 has the oral and intravenous (i.v.) pharmacokinetic properties and potency in murine infection models of disseminated candidiasis to support further investigation as a novel i.v. and oral treatment for invasive fungal diseases.

Prognostic value of galactomannan: current evidence for monitoring response to antifungal therapy in patients with invasive aspergillosis

Galactomannan (GM) is a polysaccharide present in the cell wall of Aspergillus spp. that is released during growth of the organism. It has been successfully used to aide in the diagnosis of invasive aspergillosis allowing for earlier recognition of disease compared to conventional methods. Since its implementation in the clinic as a diagnostic tool, GM has been used in experimental models to measure therapeutic response. Several clinical studies describe the prognostic value of GM. Herein, we review the evidence supporting the utilization of GM antigen as a biomarker to measure response to systemic antifungal therapy.

Cardiac response to centrally administered echinocandin antifungals

OBJECTIVES

The purpose of this study was to determine the effect of the echinocandin antifungals on the cardiac system, including cardiac output, blood pressure and heart rate, when administered in an in-vivo model.

METHODS

The echinocandin antifungals were administered via central line to male Sprague-Dawley rats. Cardiac imaging and functional measurements were made using a high-resolution in-vivo imaging system. Statistical comparisons of the experimental antifungals versus saline control were made using a Student's t-test.

KEY FINDINGS

In cardiac output (CO) measurements, caspofungin was associated with a bimodal distribution in results at 3 mg/kg. Those with little response, termed 'non-vulnerable' animals (n = 3) had no significant change in CO from baseline (-4.6 ± 10.7%). Other animals, termed 'vulnerable' animals (n = 3 at 3 mg/kg and those dosed at 6 mg/kg (n = 6)), experienced greater than 60% decrease in CO (-66.4 ± 13.1% at 3 mg/kg and -62.9 ± 13.0% at 6 mg/kg, P < 0.05). A dose of 5 mg/kg anidulafungin was associated with no significant changes in CO (-16.1 ± 26%), while 11.5 mg/kg decreased CO by 62.7 ± 19.4% from baseline (P < 0.05). With micafungin 1 mg/kg and 5 mg/kg doses, changes in CO were not significant (-16.7 ± 2.1% and -18.2 ± 1.9%, respectively).

CONCLUSIONS

These studies provide substantial evidence to support ex-vivo Langendorff and in-vitro mitochondrial studies demonstrating a similar pharmacological event. Clinical reports of similar effects also support these findings.

A novel fungus concentration-dependent rat model for acute invasive fungal rhinosinusitis: an experimental study

Background

Acute invasive fungal rhinosinusitis is a lethal infectious process afflicting immunocompromised individuals. Knowledge about this disease is still limited due to the scarcity of animal models designed to study the pathogenesis of this infection. Mast cells are tissue-resident immune cells that participate in a variety of allergic and inflammatory conditions. Limited attention has been given to the role of mast cells in acute invasive fungal rhinosinusitis. Therefore, the objectives of this study were to create a rat model of acute invasive fungal rhinosinusitis based on analyzing the impact of different fungal concentrations on establishing infection, and to observe the changes of mast cells in rats with this disease.

Methods

Sprague–Dawley rats were divided randomly into four groups, three of which were experimental and received different concentrations of Aspergillus fumigatus inoculations, and one was a control group (D). The inoculated Aspergillus fumigatus concentrations were 5 × 10⁷ conidia/ml in group A, 10⁷ conidia/ml in group B, and 10⁶ conidia/ml in group C. Before fungal inoculation, rats were immunosuppressed using cyclophosphamide and cortisone acetate, and had Merocel sponges inserted into the right nares. Hematology and histopathology investigations were then performed.

Results

An acute invasive fungal rhinosinusitis rat model was established successfully with an incidence rate of 90% in group A, 50% in group B and 10% in group C. Aspergillus fumigatus invasion was observed in 20% of the lungs in group A, but was not seen in the remaining groups. In addition, no fungi invaded the orbital tissue, brains, livers, spleens or kidneys of any rat. Compared with the control set, the total number of mast cells in the experimental groups was not significantly increased, but mast cell degranulation, on the other hand, was only found in infected nasal cavities.

Conclusions

This investigation illustrates that various fungal concentrations have different effects on the incidence of acute invasive fungal rhinosinusitis, and it also demonstrates the feasibility of using this model to study the process of fungal rhinosinusoidal invasion. In addition, the results suggest that mast cells may play a role in the protection of sinuses against acute Aspergillus fumigatus infection and in the clearance of established hyphal masses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0713-y) contains supplementary material, which is available to authorized users.

Evidence supporting a role for mammalian chitinases in efficacy of caspofungin against experimental aspergillosis in immunocompromised rats

Objectives

Caspofungin, currently used as salvage therapy for invasive pulmonary aspergillosis (IPA), strangely only causes morphological changes in fungal growth in vitro but does not inhibit the growth. In vivo it has good efficacy. Therefore the question arises how this in vivo activity is reached. Caspofungin is known to increase the amount of chitin in the fungal cell wall. Mammals produce two chitinases, chitotriosidase and AMCase, which can hydrolyse chitin. We hypothesized that the mammalian chitinases play a role in the in vivo efficacy of caspofungin.

Methods

In order to determine the role of chitotriosidase and AMCase in IPA, both chitinases were measured in rats which did or did not receive caspofungin treatment. In order to understand the role of each chitinase in the breakdown of the caspofungin-exposed cells, we also exposed caspofungin treated fungi to recombinant enzymes in vitro.

Results

IPA in immunocompromised rats caused a dramatic increase in chitinase activity. This increase in chitinase activity was still noted when rats were treated with caspofungin. In vitro, it was demonstrated that the action of both chitinases were needed to lyse the fungal cell wall upon caspofungin exposure.

Conclusion

Caspofungin seemed to alter the cell wall in such a way that the two chitinases, when combined, could lyse the fungal cell wall and assisted in clearing the fungal pathogen. We also found that both chitinases combined had a direct effect on the fungus in vitro.

Antifungal therapy in children: an update

Invasive fungal infections are a common problem in children affected by primary or secondary immunodeficiencies. Thanks to an increased knowledge about their mechanisms of action and their pharmacokinetic and toxicity profiles, the use of these drugs in common and uncommon invasive infections in immunocompromised children has improved over the last decades. Choosing the most appropriate antifungal drug is a serious challenge for any clinician, also considering that, in most cases, therapy has to be started before cultures are available, the choice being driven by clinical symptoms and statistical criteria only. In this study, we performed a systematic review of literature, providing antifungal treatment recommendations for paediatric patients which can help clinicians find the most suitable treatment for each specific case. Principal antifungal drugs-ranging from first-generation antimycotics to the latest molecules-are classified according to their targets, and of each group, the pharmacokinetic profile, clinical indications and side effects are extensively described.

Effect of fluid loading during hypovolaemic shock on caspofungin pharmacokinetic parameters in pig

Introduction

Caspofungin treatment is frequently initiated in shock patients. In the present study, we investigated the influence of hypovolaemic shock requiring fluid loading on the plasma and pulmonary pharmacokinetic parameters of caspofungin in the pig.

Methods

After being anaesthetised and mechanically ventilated, 12 pigs were bled to induce a two-hour deep shock and resuscitated using normal saline based on haemodynamic goals. A one-hour infusion of 70 mg of caspofungin was started at the beginning of the resuscitation period. The lungs were removed four hours after caspofungin administration. Sixteen animals served as controls without haemorrhage. Caspofungin concentrations were measured by using high-performance liquid chromatography, and a two-compartment population pharmacokinetic analysis was performed.

Results

In the shock group, the volume of blood removed was 39 ± 7 mL/kg and a volume of 90 ± 17 mL/kg saline was infused throughout the resuscitation period. The extravascular lung water index was higher in the shock group (9.3 ± 1.6 mL/kg vs 5.7 ± 1 mL/kg in the control group; P < 0.01). In the shock group, the median (interquartile range) maximal plasma concentration was 37% lower than in the control group (21.6 μg/mL (20.7 to 22.3) vs 33.1 μg/mL (28.1 to 38.3); P < 0.01). The median area under curve (AUC) from zero to four hours was 25% lower in the shock group than in the control group (60.3 hours × μg/mL (58.4 to 66.4) vs 80.8 hours × μg/mL (78.3 to 96.9); P < 0.01), as was the median lung caspofungin concentration (1.22 μg/g (0.89 to 1.46) vs 1.64 μg/g (1.22 to 2.01); P < 0.01). However, the plasma-to-tissue ratios were not different between the groups, indicating that lung diffusion of caspofungin was not affected after shock followed by fluid loading. Pharmacokinetic analysis showed that the peripheral volume of distribution of caspofungin and intercompartmental clearance were significantly higher in the shock group, as was the total apparent volume of distribution.

Conclusions

Hypovolaemic shock followed by fluid loading in the pig results in a significant increase in the apparent volume of distribution of caspofungin and in a decrease in its plasma and pulmonary exposition. Although our model was associated with capillary leakage and pulmonary oedema, our results should be generalised to the septic shock with caution. Future investigations should focus on monitoring plasma caspofungin concentrations and optimal caspofungin dosing in shock patients.

Assessment of efficacy of antifungals in experimental models of invasive aspergillosis in an era of emerging resistance: the value of real-time quantitative PCR

Experimental models of invasive aspergillosis (IA) have been used to explore pharmacokinetic and pharmacodynamic (PK/PD) properties of antifungal agents. Survival is still considered the golden standard effect measure but has the disadvantage that a large number of animals are needed to determine the dose-response relationships and PK/PD of antifungals. The feasibility of using fungal load by real-time quantitative PCR (qPCR) as an effect measure has been explored recently. The majority of studies reported convincingly demonstrate a larger dynamic range for qPCR compared to conventional assays. However interpretation and translating the results to guidance in clinical decision making need further study. It is expected that the use of qPCR will become the primary outcome measure for assessment of PK/PD relationships of antifungals in experimental models of IA.

Earlier response assessment in invasive aspergillosis based on the kinetics of serum Aspergillus galactomannan: proposal for a new definition

BACKGROUND

Current criteria for assessing treatment response of invasive aspergillosis (IA) rely on nonspecific subjective parameters. We hypothesized that an Aspergillus-specific response definition based on the kinetics of serum Aspergillus galactomannan index (GMI) would provide earlier and more objective response assessment.

METHODS

We compared the 6-week European Organization for Research and Treatment of Cancer/Mycoses Study Group (EORTC/MSG) response criteria with GMI-based response among 115 cancer patients with IA. Success according to GMI required survival with repeatedly negative GMI for ≥2 weeks. Time to response and agreement between the 2 definitions were the study endpoints.

RESULTS

Success according to EORTC/MSG and GMI criteria was observed in 73 patients (63%) and 83 patients (72%), respectively. The GMI-based response was determined at a median of 21 days after treatment initiation (range, 15-41 days), 3 weeks before the EORTC/MSG time point, in 72 (87%) of 83 responders. Agreement between definitions was shown in all 32 nonresponders and in 73 of the 83 responders (91% overall), with an excellent κ correlation coefficient of 0.819. Among 10 patients with discordant response (EORTC/MSG failure, GMI success), 1 is alive without IA 3 years after diagnosis; for the other, aspergillosis could not be detected at autopsy. The presence of other life-threatening complications in the remaining 8 patients indicates that IA had resolved.

CONCLUSIONS

The Aspergillus-specific GMI-based criteria compare favorably to current response definitions for IA and significantly shorten time to response assessment. These criteria rely on a simple, reproducible, objective, and Aspergillus-specific test and should serve as the primary endpoint in trials of IA.

68Ga-siderophores for PET imaging of invasive pulmonary aspergillosis: proof of principle

The diagnosis of invasive pulmonary aspergillosis (IPA) is difficult and lacks specificity and sensitivity. In the pathophysiology of Aspergillus fumigatus, iron plays an essential role as a nutrient during infection. A. fumigatus uses a specific and highly efficient iron uptake mechanism based on iron-complexing ferric ion Fe(III) siderophores, which are a requirement for A. fumigatus virulence. We aimed to evaluate the potential of siderophores radiolabeled with (68)Ga, a positron emitter with complexing properties comparable to those of Fe(III), as a radiopharmaceutical for imaging IPA.

METHODS

(68)Ga radiolabeling of the A. fumigatus siderophores desferri-triacetylfusarinine C (TAFC) and desferri-ferricrocin (FC) was performed at high specific activity. Stability, protein binding, and log P values were determined. In vitro uptake in A. fumigatus cultures was tested under varying conditions. Biodistribution was studied in healthy noninfected BALB/c mice, and uptake was studied in a model of A. fumigatus infection using immunosuppressed Lewis rats.

RESULTS

High-specific-activity (68)Ga labeling could be achieved, and resulting complexes were stable in serum, toward diethylenetriaminepentaacetic acid and Fe(III) challenge. Both siderophores showed hydrophilic properties ((68)Ga-TAFC, log P = -2.59; (68)Ga-FC, log P = -3.17) with low values of protein binding for (68)Ga-TAFC (<2%). Uptake of both siderophores was highly dependent on the mycelial iron load and could be blocked with an excess (10 microM) of siderophore or NaN(3), indicating specific, energy-dependent uptake. In noninfected mice, (68)Ga-TAFC showed rapid renal excretion and low blood values (1.6 +/- 0.37 percentage injected dose per gram [%ID/g] at 30 min); in urine only intact (68)Ga-TAFC was detected. In contrast, (68)Ga-FC revealed high retention in blood (16.1 +/- 1.07 %ID/g at 90 min) and rapid metabolism. In the rat IPA model, lung uptake of (68)Ga-TAFC was dependent on the severity of infection, with less than 0.04 %ID/g in control rats (n = 5) and 0.29 +/- 0.11 %ID/g in mildly infected (n = 3) and 0.95 +/- 0.37 %ID/g in severely infected (n = 4) rats. PET showed focal accumulation in infected lung tissue.

CONCLUSION

Both siderophores bound (68)Ga with high affinity, and (68)Ga-TAFC, especially, showed high stability. (68)Ga-TAFC displayed highly selective accumulation by A. fumigatus subspecies in vitro and in vivo. The high and specific uptake by A. fumigatus proves the potential of (68)Ga-labeled siderophores for the specific detection of A. fumigatus during infection. They hold promise as new PET agents for IPA.

Caspofungin: in pediatric patients with fungal infections

Caspofungin is the first echinocandin to be approved for the treatment of fungal infections in pediatric patients. The antifungal properties of caspofungin result from interference with fungal cell-wall integrity. In vitro, caspofungin is fungicidal against Candida spp. and fungistatic against Aspergillus spp., but has little or no fungicidal or fungistatic activity against Cryptococcus neoformans, the Zygomycetes, Fusarium spp., or Trichosporon beigelii. Caspofungin was effective as empirical antifungal therapy in pediatric patients with persistent fever and neutropenia. Almost half (46%) of caspofungin recipients and one-third (32%) of liposomal amphotericin B recipients achieved an overall favorable response in a randomized, double-blind trial. Caspofungin was also effective in pediatric patients with fungal infections (invasive candidiasis, invasive aspergillosis refractory to or intolerant of standard antifungal agents, or esophageal candidiasis). Positive responses to treatment were seen in 30 of 37 patients with invasive candidiasis, 5 of 10 patients with invasive aspergillosis, and in the one patient with esophageal candidiasis, in a noncomparative, open-label trial. Caspofungin was generally well tolerated in the clinical trials in pediatric patients with febrile neutropenia requiring empirical antifungal treatment, or with fungal infections. Few caspofungin recipients reported serious drug-related adverse events or discontinued treatment as a result of drug-related adverse events.

Echinocandin activity against Aspergillus spp. and the importance of pharmacodynamics

Echinocandins represent a safe and well tolerated option for the therapy of invasive aspergillosis in patients who are unable to tolerate other agents or have refractory disease. In vitro and animal model data provide useful insights into the activity, appropriate dose, and potential role of these agents in invasive aspergillosis. These studies reveal a potentially concerning lack of tissue sterilization when echinocandins are used as monotherapy but clearly show improved survival with increasing doses. Furthermore pharmacodynamic studies suggest that echinocandin doses currently in widespread clinical use may optimize outcomes in invasive aspergillosis. A paucity of clinical data exists examining these agents as monotherapy for invasive aspergillosis and virtually no clinical data exists for using these agents as primary therapy. Further data examining the role of echinocandin monotherapy for invasive aspergillosis is unlikely to be forthcoming in the foreseeable future due to several factors including the aforementioned issues, the relatively small number patients with this infection, and the belief that these agents are potentially best used as part of combination therapy regimens for invasive aspergillosis.

Strain-dependent variation in 18S ribosomal DNA Copy numbers in Aspergillus fumigatus

Enumerating Aspergillus fumigatus CFU can be challenging since CFU determination by plate count can be difficult. CFU determination by quantitative real-time PCR (qPCR), however, is becoming increasingly common and usually relies on detecting one of the subunits of the multicopy rRNA genes. This study was undertaken to determine if ribosomal DNA (rDNA) copy number was constant or variable among different A. fumigatus isolates. FKS1 was used as a single-copy control gene and was validated against single-copy (pyrG and ARG4) and multicopy (arsC) controls. The copy numbers of the 18S rDNA subunit were then determined for a variety of isolates and were found to vary with the strain, from 38 to 91 copies per genome. Investigation of the stability of the 18S rDNA copy number after exposure to a number of different environmental and growth conditions revealed that the copy number was stable, varying less than one copy across all conditions, including in isolates recovered from an animal model. These results suggest that while the ribosomal genes are excellent targets for enumeration by qPCR, the copy number should be determined prior to using them as targets for quantitative analysis.

Paradoxical echinocandin activity: a limited in vitro phenomenon?

The echinocandins have been a welcome addition for the treatment of invasive fungal infections. Despite their excellent safety profile and clinical efficacy, concerns exist regarding an attenuation of activity at higher concentrations, known as the paradoxical effect. In vitro studies have reported this phenomenon against both Candida and Aspergillus species. Recent data have also demonstrated this effect to be species-related and echinocandin specific. Although not completely understood, studies have pointed towards involvement of the protein kinase C cell wall integrity pathway as well as increases in cell wall chitin content as potential mechanisms responsible for this phenomenon. Increases in galactomannan have been reported in vitro and in vivo following echinocandin exposure. Although some in vivo studies of invasive aspergillosis have also reported a paradoxical increase in other markers of invasive disease and fungal burden with echinocandin therapy, these observations are inconsistent. The paradoxical effect has also not been demonstrated clinically. Thus, the clinical implications of the paradoxical attenuation of echinocandin activity at elevated concentrations remain unknown. A complete understanding of this effect may further our knowledge of fungal responses to echinocandin cell wall damage and potentially improve treatment strategies.

Combination therapy of advanced invasive pulmonary aspergillosis in transiently neutropenic rats using human pharmacokinetic equivalent doses of voriconazole and anidulafungin

At present, voriconazole (VOR) is the drug of first choice for treating invasive pulmonary aspergillosis (IPA). However, particularly in advanced stages of disease and in the severely immunocompromised host, the mortality remains substantial. The combination of VOR with an echinocandin may improve the therapeutic outcome. We investigate here whether combining VOR and anidulafungin (ANI) in advanced IPA in transiently neutropenic rats results in a higher therapeutic efficacy. Since VOR is metabolized more rapidly in rodents than in humans, dosage adjustment for VOR is necessary to obtain an area under the plasma concentration-time curve (AUC) in rodents that is equivalent to that of humans. In this study, the pharmacokinetics of VOR and ANI in rats were elucidated, and dosage schedules were applied that produced AUCs similar to those of humans. The developed dose schedules were well tolerated by the rats, without effects on renal and hepatic functions. VOR showed excellent efficacy in early IPA (100% rat survival). In advanced IPA, VOR was less efficacious (50% rat survival), whereas a significant decrease in galactomannan concentrations in lungs and sera was found in surviving rats. ANI administered in advanced IPA resulted in 22% rat survival, and the serum concentrations of fungal galactomannan were slightly but not significantly decreased. The addition of ANI to VOR did not result in significantly increased therapeutic efficacy in advanced IPA, resulting in 67% rat survival and a significant decrease in galactomannan concentration in serum. In conclusion, VOR monotherapy is therapeutically effective in the treatment of advanced-stage IPA and superior to the use of ANI. Combining both agents does not significantly improve the therapeutic outcome.

Establishing in vitro-in vivo correlations for Aspergillus fumigatus: the challenge of azoles versus echinocandins

Two clinical isolates of Aspergillus fumigatus, designated AT and DK, were recently obtained from patients failing caspofungin and itraconazole therapy, respectively. The isolates were tested by microdilution for susceptibility to itraconazole, voriconazole, posaconazole, ravuconazole, and caspofungin and by Etest for susceptibility to amphotericin B and caspofungin. Susceptibility testing documented that the DK isolate was azole resistant (itraconazole and posaconazole MICs, >4 microg/ml; voriconazole MIC, 2 microg/ml; ravuconazole MIC, 4 microg/ml), and the resistance was confirmed in a hematogenous mouse model, with mortality and the galactomannan index as the primary and secondary end points. Sequencing of the cyp51A gene revealed the M220K mutation, conferring multiazole resistance. The Etest, but not microdilution, suggested that the AT isolate was resistant to caspofungin (MIC, >32 microg/ml). In the animal model, this isolate showed reduced susceptibility to caspofungin. Sequencing of the FKS1 gene revealed no mutations; the enzyme retained full sensitivity in vitro; and investigation of the polysaccharide composition showed that the beta-(1,3)-glucan proportion was unchanged. However, gene expression profiling by Northern blotting and real-time PCR demonstrated that the FKS gene was expressed at a higher level in the AT isolate than in the susceptible control isolate. To our knowledge, this is the first report to document the presence of multiazole-resistant clinical isolates in Denmark and to demonstrate reduced susceptibility to caspofungin in a clinical A. fumigatus isolate with increased expression of the FKS gene. Further research to determine the prevalence of resistance in A. fumigatus worldwide, and to develop easier and reliable tools for the identification of such isolates in routine laboratories, is warranted.

Fungicidal versus Fungistatic: what's in a word?

BACKGROUND

Historically clinicians have preferred to use 'cidal' antifungal agents, particularly in critically ill patients. However, data to support the belief that the preferential use of a 'cidal' agent results in better patient outcomes has been lacking.

OBJECTIVE

This review examined the in vitro definitions of fungicidal and fungistatic as well as their strengths and limitations.

METHODS

A Medline search was performed in order to identify literature that examined the in vitro or in vivo impact of fungicidal and fungistatic activity. The study examined three common invasive fungal infections, namely cryptococcal meningitis, candidemia and invasive aspergillosis, where sufficient comparisons of fungicidal and fungistatic agents have been performed to allow for the evaluation of the clinical importance of these in vitro findings.

RESULTS AND CONCLUSION

A clear clinical benefit of fungicidal agents over those with fungistatic activity remains elusive. Patients with cryptococcal meningitis clearly benefit from early fungicidal therapy but require long-term suppression. The data in invasive Candida sp. infections are tantalizing and suggest that fungicidal therapy may be important. However, the data for invasive aspergillosis do not support the hypothesis that fungicidal activity improves outcomes.

Attenuation of echinocandin activity at elevated concentrations: a review of the paradoxical effect

PURPOSE OF REVIEW

The echinocandins have been a welcome addition for the treatment of invasive fungal infections caused by Candida and Aspergillus species. Despite their excellent safety profile and clinical efficacy, concerns exist regarding an attenuation of activity at higher concentrations, known as the paradoxical effect. This article will review the literature describing this effect, the potential mechanisms responsible for it, and the clinical implications of this phenomenon.

RECENT FINDINGS

In-vitro studies have reported a paradoxical effect at higher concentrations against both Candida and Aspergillus species. Recent data have demonstrated this effect in Candida to be species related and echinocandin specific. Although not completely understood, studies have pointed towards involvement of the protein kinase C cell wall integrity and calcineurin pathways as well as increases in cell wall chitin content as potential mechanisms behind the effect. Although some in-vivo studies with echinocandins have reported a paradoxical increase in markers of invasive disease, clinical data are scarce.

SUMMARY

The clinical implications of the paradoxical attenuation of echinocandin activity observed in vitro and in vivo remain unknown. A complete understanding of this effect may further our knowledge of fungal responses to echinocandin cell wall damage and potentially improve treatment strategies.

Caspofungin prolongs survival of transiently neutropenic rats with advanced-stage invasive pulmonary aspergillosis

A high-dose-step-down strategy for caspofungin treatment was evaluated in an experimental model of advanced-stage invasive pulmonary aspergillosis. The therapeutic efficacy of caspofungin in relation to the severity of invasive pulmonary infection caused by Aspergillus fumigatus in transiently neutropenic rats was investigated by using rat survival and the decrease in the fungal burden as the parameters of efficacy. When treatment was started at either 16 h or 24 h after fungal inoculation, caspofungin administered intraperitoneally at 4 mg/kg of body weight/day for 10 days was highly effective (100% and 93% rat survival, respectively). However, only 27% rat survival was obtained when treatment was started at 72 h, when the rats had advanced-stage infection. Increasing the dose from 4 to 10 mg/kg/day could compensate for the decrease in efficacy and resulted in 67% rat survival. The high dose of 10 mg/kg/day for 10 days did not appear to be necessary since a high-dose-step-down dosing schedule with 10 mg/kg/day for 3 days followed by 4 mg/kg/day for 7 days was equally effective. At 10 days after the end of treatment with 10 mg/kg/day caspofungin, the level of neither A. fumigatus DNA nor A. fumigatus galactomannan in the infected left lung was significantly decreased. In contrast, A. fumigatus galactomannan concentrations in serum were significantly decreased. The levels of creatinine, blood urea nitrogen, alanine aminotransferase, and asparate aminotransferase were not elevated during treatment. Caspofungin is effective for the treatment of invasive pulmonary aspergillosis in transiently neutropenic rats and is even effective in rats with advanced-stage infection. In this model, the administration of high-dose-step-down treatment was as effective as treatment with high doses for the whole treatment period.

Effect of caspofungin on metabolite profiles of Aspergillus species determined by nuclear magnetic resonance spectroscopy

Invasive aspergillosis remains a potentially life-threatening infection, the incidence of which is increasing. Current methods used to determine the susceptibilities of Aspergillus strains to antifungal drugs are often unreliable. Nuclear magnetic resonance (NMR) spectroscopy can identify the metabolic complement of microorganisms while monitoring nutrient utilization from the incubation medium. We used 600-MHz (1)H NMR spectroscopy to monitor the metabolic responses of five Aspergillus species cultured in RPMI 1640-2% glucose-morpholinepropanesulfonate buffer to various concentrations of the antifungal drugs amphotericin B (AMB) and caspofungin. The metabolic endpoint (MEP) was determined from nutrient and metabolite resonances, measured as a function of the drug concentration, and was defined as a > or =50% reduction in nutrient consumption or metabolite production. MICs were evaluated by a modification of Clinical and Laboratory Standards Institute broth microdilution method M27-A, and minimal effective concentrations (MECs) were determined by microscopic examination of fungal hyphae. For AMB, the MEPs coincided with the MICs. For caspofungin, the MEPs agreed with the MECs for several Aspergillus strains, but the effect of drug pressure was more complex for others. Expansion of the MEP definition to include any significant changes in metabolite production resulted in agreement with the MEC in most cases. Paradoxical metabolic responses were observed for several Aspergillus strains at either high or low caspofungin concentrations and for one Aspergillus terreus strain with AMB. NMR spectroscopy proved to be a powerful tool for detecting the subtle effects of drug pressure on fungal metabolism and has the potential to provide an alternative method for determining the susceptibilities of Aspergillus species to antifungal drugs.

Factors influencing caspofungin plasma concentrations in patients of a surgical intensive care unit

BACKGROUND

Co-morbidity, medical and surgical interventions often cause alterations to drug plasma concentrations and pharmacokinetic parameters in critically ill patients. In the present study, we investigated parameters influencing plasma caspofungin concentrations in patients of a surgical intensive care unit (SICU).

METHODS

In a monocentre open study, caspofungin trough concentrations (C(24)) were determined for a group of SICU patients. A linear-mixed model was then used to assess factors influencing caspofungin plasma concentrations.

RESULTS

A total of 40 SICU patients were enrolled. Age and body weight ranged from 22 to 76 years and 47 to 108 kg, respectively. All participants received a caspofungin loading dose of 70 mg and a maintenance dose of 50 mg/day. The median duration of therapy was 10 days. Caspofungin C(24) in SICU patients varied more than those determined for healthy subjects reported in previous studies (0.52-4.08 microg/mL versus 1.12-1.78 microg/mL). According to our model, caspofungin C(24) were predicted to be significantly higher in patients with body weight <75 kg (P=0.019) and patients with albumin concentration >23.6 g/L (P=0.030).

CONCLUSIONS

Our results show that body weight and albumin concentration influence caspofungin C(24) in SICU patients and should therefore be considered prognostic factors.

Concentration-dependent effects of caspofungin on the metabolic activity of Aspergillus species

The minimum effective concentration (MEC) used to assess the in vitro antifungal activity of caspofungin against Aspergillus spp. is a qualitative endpoint requiring microscopic examination of hyphae. We therefore developed a tool for the quantitative assessment of caspofungin activity against Aspergillus spp. at clinically applicable concentrations. Susceptibility to caspofungin (0.008 to 8 microg/ml) was studied for 9 A. fumigatus, 8 A. flavus, and 12 A. terreus isolates based on the Clinical and Laboratory Standards Institute M38-A protocol. After 48 h of incubation, the MEC was defined microscopically, and metabolic activity assessed with a modified XTT assay, using 100 microg of the tetrazolium salt XTT/ml and 6.25 muM menadione. A significant reduction in metabolic activity was demonstrated at the MEC (0.25 to 0.5 microg/ml) for all Aspergillus spp. and was more pronounced for A. flavus (median metabolic activity, 25% of control) compared to A. fumigatus and A. terreus (median metabolism, 42 and 53%, respectively), allowing determination of MEC with the XTT assay (93 to 100% agreement with microscopic MEC). Fungal metabolism tended to reach the lowest levels (median, 17 to 38% of control) one to two dilutions higher than the MEC, at the minimum metabolic activity concentration (MMC). For 5 of 9 A. fumigatus isolates, 6 of 12 A. terreus isolates, and 1 of 8 A. flavus isolates, a paradoxical increase in metabolism was observed at concentrations greater than the MMC. Sigmoid (E(max)) or bell-shaped models described accurately (median R(2) = 0.97) the concentration-dependent metabolic changes in the absence or presence, respectively, of paradoxical response. Assessment of metabolic activity may provide useful quantitative endpoints for in vitro studies of caspofungin against Aspergillus spp.

The echinocandins: comparison of their pharmacokinetics, pharmacodynamics and clinical applications

Caspofungin, micafungin and anidulafungin are three drugs of the echinocandin class of antifungals available for intravenous treatment of invasive candidiasis and aspergillosis. They exhibit high in vitro and in vivo activities against Candida spp. and Aspergillus spp. In various clinical studies investigating candidemia and invasive candidiasis, Candida esophagitis, and fever in neutropenia, the clinical efficacy of the echinocandin tested was similar to that of established antifungals. Antifungal activity against strains no longer susceptible to conventional antifungal agents, such as fluconazole and amphotericin B suggests that echinocandins can be used as salvage therapy in life-threatening fungal infections. There is no cross-resistance to other antifungals. Excellent safety and tolerability of treatment with caspofungin has been documented over a total of 4.3 million patient days. Echinocandins are poor substrates of the cytochrome P450 enzyme family and can be safely co-administered with most drugs without the need for dosage adaptation. No dose reduction is required in renal impairment. A reduction in the daily maintenance dose has been recommended for caspofungin, but not for micafungin and anidulafungin in patients presenting with mild to moderate hepatic failure.