The novel fungal CYP51 inhibitor VT-1598 displays classic dose-dependent antifungal activity in murine models of invasive aspergillosis.

Aspergillus spp. infections remain a global concern, with ∼30% attributable mortality of invasive aspergillosis (IA). VT-1598 is a novel fungal CYP51 inhibitor designed for exquisite selectivity versus human CYP enzymes to achieve a maximal therapeutic index and therefore maximal antifungal efficacy. Previously, its broad-spectrum in vitro antifungal activity was reported. We report here the pharmacokinetics (PK) and pharmacodynamics (PD) of VT-1598 in neutropenic mouse models of IA. The plasma area-under-the-curve (AUC) of VT-1598 increased nearly linearly between 5 and 40 mg/kg after 5 days of QD administration (155 and 1033 µg*h/ml, respectively), with a further increase with 40 mg/kg BID dosing (1354 µg*h/ml). When A. fumigatus isolates with in vitro susceptibilities of 0.25 and 1.0 µg/ml were used in a disseminated IA model, VT-1598 treatment produced no decrease in kidney fungal burden at QD 10 mg/kg, intermediate decreases at QD 20 mg/kg and maximum or near maximum decreases at 40 mg/kg QD and BID. The PK/PD relationships of AUCfree/MIC for 1-log killing for the two strains were 5.1 and 1.6 h, respectively, similar to values reported for approved CYP51 inhibitors. In a survival study where animals were observed for 12 days after the last treatment, survival was 100% at the doses tested (20 and 40 mg/kg QD), and fungal burden remained suppressed even though drug wash-out was complete. Similar dose-dependent reductions in lung fungal burden were observed in a pulmonary model of IA. These data strongly support further exploration of VT-1598 for the treatment of this lethal mold infection.

Pharmacokinetics and Pharmacodynamics of Murepavadin in Neutropenic Mouse Models.

Murepavadin (POL7080) represents the first member of a novel class of outer membrane protein-targeting antibiotics. It specifically interacts with LptD and inhibits lipopolysaccharide (LPS) transport. Murepavadin is being developed for the treatment of serious infections by Pseudomonas aeruginosa We determined the plasma protein binding and the pharmacokinetics of murepavadin in plasma and epithelial lining fluid (ELF; pulmonary) in infected animals, and we determined the exposure-response relationship. Treatment of CD-1 neutropenic mice was started 2 h after infection using murepavadin at different dosing frequencies for 24 h, and the number of CFU per lung was determined. The sigmoid maximum-effect model was used to fit the dose-response, and the pharmacodynamic index (PDI) response was used to determine the PDI values, resulting in a static effect and 1-log kill reduction. Using R2 as an indicator of the best fit, the area under the concentration-time curve for the unbound fraction of the drug (fAUC)/MIC ratio correlated best with efficacy. The mean AUC required to provide a static effect was 36.83 mg h/liter (fAUC = 8.25 mg h/liter), and that to provide a 1-log reduction was 44.0 mg h/liter (fAUC = 9.86 mg h/liter). The mean static fAUC/MIC was determined to be 27.78, and that for a 1-log reduction was 39.85. These data may serve to determine doses in humans that are likely to be efficacious.

The novel fungal CYP51 inhibitor VT-1598 is efficacious alone and in combination with liposomal amphotericin B in a murine model of cryptococcal meningitis.

Objectives: Annual global deaths from cryptococcal meningitis (CM) are estimated at 180 000 and mortality is as high as 30%, even with optimal therapy. VT-1598 is a novel fungal CYP51 inhibitor with potent intrinsic antifungal activity against Cryptococcus. We report here VT-1598's in vivo antifungal activity in a murine model of CM. Methods: Single-dose plasma and brain pharmacokinetics in mice and MIC for Cryptococcus neoformans H99 were determined prior to efficacy studies. Short-course monotherapy and combination doses were explored with the endpoint of brain fungal burden. A survival study was also conducted using monotherapy treatment with fungal burden measured after a 6 day drug washout. Results: Oral doses of VT-1598 had good plasma and brain exposure and resulted in significant (P < 0.0001) and dose-dependent reductions in brain fungal burden, reaching a 6 log10 reduction. Unlike either positive drug control (fluconazole or liposomal amphotericin B), both mid and high doses of VT-1598 reduced fungal burden to below levels measured at the start of treatment. When VT-1598 was dosed in the survival study, no VT-1598-treated animal succumbed to the infection. Whereas fluconazole showed a 2.5 log10 increase in fungal burden after the 6 day washout, the VT-1598 mid- and high-dose animals showed almost no regrowth (<0.5 log10). In a separate fungal burden study using suboptimal doses of VT-1598 and liposomal amphotericin B to probe for combination effects, each combination had a positive effect relative to corresponding monotherapies. Conclusions: These pre-clinical in vivo data strongly support clinical investigation of VT-1598 as a novel therapy for this lethal infection.

In vitro susceptibility of Clostridium difficile to SMT19969 and comparators, as well as the killing kinetics and post-antibiotic effects of SMT19969 and comparators against C. difficile.

OBJECTIVES: SMT19969 is a novel antimicrobial under clinical development for the treatment of Clostridium difficile infection (CDI). The objective was to determine the comparative susceptibility of 82 C. difficile clinical isolates (which included ribotype 027 isolates and isolates with reduced metronidazole susceptibility) to SMT19969, fidaxomicin, vancomycin and metronidazole and to determine the killing kinetics and post-antibiotic effects of SMT19969, fidaxomicin and vancomycin against C. difficile. METHODS: MICs were determined by agar incorporation. Killing kinetics and post-antibiotic effects were determined against C. difficile BI1, 630 and 5325 (ribotypes 027, 012 and 078, respectively). RESULTS: SMT19969 showed potent inhibition of C. difficile (MIC90=0.125 mg/L) and was markedly more active than either metronidazole (MIC90 = 8 mg/L) or vancomycin (MIC90 = 2 mg/L). There were no differences in susceptibility to SMT19969 between different ribotypes. Fidaxomicin was typically one doubling dilution more active than SMT19969 and both agents maintained activity against isolates with reduced susceptibility to metronidazole. In addition, SMT19969 was bactericidal against the C. difficile strains tested, with reductions in viable counts to below the limit of detection by 24 h post-inoculation. Vancomycin was bacteriostatic against all three strains. Fidaxomicin was bactericidal although reduced killing was observed at concentrations <20 × MIC against C. difficile BI1 (ribotype 027) compared with other strains tested. CONCLUSIONS: These data demonstrate that SMT19969 is associated with potent and bactericidal activity against the strains tested and support further investigation of SMT19969 as potential therapy for CDI.

Aspergillus fumigatus proteases, Asp f 5 and Asp f 13, are essential for airway inflammation and remodelling in a murine inhalation model.

BACKGROUND: In susceptible individuals, exposure to Aspergillus fumigatus can lead to the development of atopic lung diseases such as allergic bronchopulmonary aspergillosis (ABPA) and severe asthma with fungal sensitization (SAFS). Protease allergens including Asp f 5 and Asp f 13 from Aspergillus fumigatus are thought to be important for initiation and progression of allergic asthma. OBJECTIVE: To assess the importance of secreted protease allergens Asp f 5 (matrix metalloprotease) and Asp f 13 (serine protease) in Aspergillus fumigatus-induced inflammation, airway hyperactivity, atopy and airway wall remodelling in a murine model following chronic exposure to secreted allergens. METHODS: BALB/c mice were repeatedly intranasally dosed over the course of 5 weeks with culture filtrate from wild-type (WT), Asp f 5 null (∆5) or Asp f 13 null (∆13) strains of Aspergillus fumigatus. Airway hyper-reactivity was measured by non-invasive whole-body plethysmography, Th2 response and airway inflammation by ELISA and cell counts, whilst airway remodelling was assessed by histological analysis. RESULTS: Parent WT and ∆5 culture filtrates showed high protease activity, whilst protease activity in ∆13 culture filtrate was low. Chronic intranasal exposure to the three different filtrates led to comparable airway hyper-reactivity and Th2 response. However, protease allergen deleted strains, in particular ∆13 culture filtrate, induced significantly less airway inflammation and remodelling compared to WT culture filtrate. CONCLUSION: Aspergillus fumigatus-secreted allergen proteases, Asp f 5 and Asp f 13, are important for recruitment of inflammatory cells and remodelling of the airways in this murine model. However, deletion of a single allergen protease fails to alleviate airway hyper-reactivity and allergic immune response. Targeting protease activity of Aspergillus fumigatus in conditions such as SAFS or ABPA may have beneficial effects in preventing key aspects of airway pathology.

DL-2-hydroxyisocaproic acid attenuates inflammatory responses in a murine Candida albicans biofilm model.

Chronic biofilm infections are often accompanied by a chronic inflammatory response, leading to impaired healing and increased, irreversible damage to host tissues. Biofilm formation is a major virulence factor for Candida albicans and a challenge for treatment. Most current antifungals have proved ineffective in eradicating infections attributed to biofilms. The biofilm structure protects Candida species against antifungals and provides a way for them to evade host immune systems. This leads to a very distinct inflammatory response compared to that seen in planktonic infections. Previously, we showed the superior efficacy of dl-2-hydroxyisocaproic acid (HICA) against various bacteria and fungi. However, the immunomodulatory properties of HICA have not been studied. Our aim was to investigate the potential anti-inflammatory response to HICA in vivo. We hypothesized that HICA reduces the levels of immune mediators and attenuates the inflammatory response. In a murine model, a robust biofilm was formed for 5 days in a diffusion chamber implanted underneath mouse skin. The biofilm was treated for 12 h with HICA, while caspofungin and phosphate-buffered saline (PBS) were used as controls. The pathophysiology and immunoexpression in the tissues surrounding the chamber were determined by immunohistochemistry. Histopathological examination showed an attenuated inflammatory response together with reduced expression of matrix metalloproteinase 9 (MMP-9) and myeloperoxidase (MPO) compared to those of chambers containing caspofungin and PBS. Interestingly, the expression of developmental endothelial locus 1 (Del-1), an antagonist of neutrophil extravasation, increased after treatment with HICA. Considering its anti-inflammatory and antimicrobial activity, HICA may have enormous therapeutic potential in the treatment of chronic biofilm infections and inflammation, such as those seen with chronic wounds.

Pharmacokinetics and pharmacodynamics of anidulafungin for experimental Candida endophthalmitis: insights into the utility of echinocandins for treatment of a potentially sight-threatening infection.

Candida chorioretinitis and endophthalmitis are relatively common manifestations of disseminated candidiasis. Anidulafungin is increasingly used for the treatment of disseminated candidiasis, but its efficacy for Candida endophthalmitis is not known. A nonneutropenic model of hematogenous Candida endophthalmitis was used. Anidulafungin at 5, 10, and 20 mg/kg was initiated at 48 h postinoculation. The fungal densities in the kidney and vitreous humor were determined. Anidulafungin concentrations in the plasma and vitreous humor were measured using high-performance liquid chromatography (HPLC). A pharmacokinetic-pharmacodynamic model was used to link anidulafungin concentrations with the observed antifungal effect. The area under the concentration-time curve (AUC) associated with stasis was determined in the both the kidney and the vitreous humor. The results were bridged to humans to identify likely dosages that are associated with significant antifungal activity within the eye. Inoculation of Candida albicans resulted in logarithmic growth in both the vitreous humor and the kidney. The pharmacokinetics of anidulafungin were linear. There was dose-dependent penetration of the anidulafungin into the vitreous humor. The exposure-response relationships in the kidney and vitreous were completely discordant. AUCs of 270 and 100 were required for stasis in the eye and kidney, respectively. The currently licensed regimen results in an AUC for an average patient that is associated with stasis in the kidney but minimal antifungal activity in the eye. We conclude that anidulafungin penetrates the eye in a dose-dependent manner and that dosages higher than those currently licensed are required to achieve significant antifungal activity in the eye.

The efficacy of aerosol treatment with non-ionic surfactant vesicles containing amphotericin B in rodent models of leishmaniasis and pulmonary aspergillosis infection.

Amphotericin B (AMB) is used to treat both fungal and leishmanial infections, which are of major significance to human health. Clinical use of free AMB is limited by its nephrotoxicity, whereas liposomal AMB is costly and requires parenteral administration, thus development of novel formulations with enhanced efficacy, minimal toxicity and that can be applied via non-invasive routes is required. In this study we analysed the potential of non-ionic surfactant vesicles (NIV) given by nebulisation to deliver AMB to the lungs, liver and skin. Treatment with AMB-NIV resulted in significantly higher drug levels in the lungs and skin (p<0.05) compared to similar treatment with AMB solution but significantly lower plasma levels (p<0.05). Treatment with AMB-NIV resulted in a significant reduction in fungal lung burdens in a rat model of invasive pulmonary aspergillosis (p<0.05) compared to treatment with the carrier alone. Treatment with AMB-NIV but not AMB solution significantly suppressed Leishmania donovani liver parasite burdens (p<0.05) but could not inhibit the growth of cutaneous Leishmania major lesions. The results of this study indicate that aerosolised NIV enhanced pulmonary and hepatic delivery whilst minimising systemic exposure and toxicity.

Disseminated Candidiasis caused by Candida albicans with amino acid substitutions in Fks1 at position Ser645 cannot be successfully treated with micafungin.

The clinical utility of the echinocandins is potentially compromised by the emergence of drug resistance. We investigated whether Candida albicans with amino acid substitutions at position Ser645 in Fks1 can be treated with either a conventional or an elevated dosage of micafungin. We studied Candida albicans (wild-type SC5314; MIC, 0.06 mg/liter) and four fks1 mutants (one FKS1/fks1 heterozygote mutant [MIC, 0.5 mg/liter] and three fks1/fks1 homozygous mutants [MICs for all, 2 mg/liter]) with a variety of amino acid substitutions at Ser645. The pharmacokinetic and pharmacodynamic relationships were characterized in a persistently neutropenic murine model of disseminated candidiasis. A mathematical model was fitted to all pharmacokinetic and pharmacodynamic data. This mathematical model was then used to "humanize" the murine pharmacokinetics, and the predicted antifungal effect was determined. The estimated maximal rate of growth and ultimate fungal densities in the kidney for each of the strains were similar. The administration of micafungin at 1 mg/kg of body weight to the wild type resulted in moderate antifungal activity, whereas the administration of 5 and 20 mg/kg resulted in rapid fungicidal activity. In contrast, the FKS1/fks heterozygote was killed only with 20 mg/kg, and the homozygous fks1 mutants failed to respond to any dosage. The bridging study revealed that human dosages of 100 and 400 mg/day were active only against the wild type, with no activity against either the heterozygote or the homozygote mutants. Ser645 Fks1 Candida albicans mutants cannot be treated with either conventional or elevated dosages of micafungin and should be deemed resistant.

Pathogenicity of Aspergillus fumigatus mutants assessed in Galleria mellonella matches that in mice.

Aspergillus fumigatus is a clinically important fungus with the ability to cause invasive aspergillosis with high mortality rates in immunocompromised patients and chronic pulmonary aspergillosis in immunocompetent individuals. Virulence of mutants has traditionally been assessed using mammalian hosts such as mice and rats and more recently the fruit fly, Drosophila melanogaster, demonstrated the potential to act as an in vivo host suitable for screening Aspergillus mutants. In this study using a larger thermotolerant invertebrate, Galleria mellonella, the virulence of individual gene deletants of Aspergillus fumigatus (cpcA, sidA, sidC, sidD, sidF and paba,) were compared to the parental and gene-replacement strains, if available. A range of infectious challenges consisting of from 3 × 10(3)-3 × 10(6) spores/larva was followed by observation of larval survival with mean survival time used as a surrogate of microbial pathogenicity. Mutants cpcA, sidA, sidF and paba were avirulent and sidC and sidD showed attenuated virulence. Virulence assessment in G. mellonella correlated closely with the historic data generated using mice and Drosophila. Pre-screening Aspergillus mutants using G. mellonella could significantly reduce the number of mammals required to assess changes in virulence.

In vitro antifungal activity of isavuconazole against 345 mucorales isolates collected at study centers in eight countries.

Although mucormycoses (formerly zygomycoses) are relatively uncommon, they are associated with high mortality and treatment options are limited. Isavuconazole is a novel, water soluble, broad-spectrum azole in clinical development for the treatment of invasive aspergillosis and candidiasis. The objective of this report was to collate data on the in vitro activity of isavuconazole against a collection of 345 diverse mucorales isolates, collected and tested at eight study centers in europe, mexico and North America. Each study center undertook minimum inhibitory concentration (MIC) susceptibility testing of their isolates, according to EUCAST or CLSI guidelines. Across all study centers, isavuconazole exhibited MIC(50 )values of 1-4 mg/l and MIC(90 )values of 4-16 mg/l against the five genera. There were also marked differences in MIC distributions, which could be ascribed to differences in inoculum and/or endpoint. EUCAST guidelines appeared to generate modal MICs 2-fold higher than CLSI. These results confirm that isavuconazole possesses at least partial antifungal activity against mucorales.

Don't throw your blood clots away: use of blood clot may improve sensitivity of PCR diagnosis in invasive aspergillosis.

BACKGROUND: The diagnosis of invasive aspergillosis (IA) remains challenging and frequently is not made until after death. Histopathological examination remains central to confirmation of diagnosis but often requires invasive procedures to obtain tissue for the examination. Detection of aspergillus DNA by quantitative PCR (qPCR) offers the potential for earlier diagnosis due to higher sensitivity, but PCR in clinical use is poorly reproducible, with different centres reporting variable results and often using different extraction and analytical methods. AIMS: To optimise the performance of aspergillus PCR as a diagnostic modality. METHODS: A rat inhalation model of invasive aspergillosis was used to optimise the methodology of diagnostic aspergillus PCR. Infected animals were terminally bled at 4 days post-infection; samples of EDTA blood, serum and the residual clot were pooled for subsequent analysis. DNA was extracted from each fraction using a variety of methods and an optimised qPCR reaction using an Aspergillus fumigatus primer set performed. RESULTS: Significantly more aspergillus DNA was detected from the clot than EDTA and serum samples. Enzymatic and mechanical pretreatment reduced the yield of fungal DNA. There was some evidence that the average Ct values were greater for the EZ1 BioRobot than the MagNA Pure automated extractor, but this did not reach statistical significance at the 5% level (p = 0.078). CONCLUSIONS: Automated extraction from the clot present in a blood sample will increase DNA yield and improve the diagnostic sensitivity of the test.

Efficacy of isavuconazole, voriconazole and fluconazole in temporarily neutropenic murine models of disseminated Candida tropicalis and Candida krusei.

OBJECTIVES: The aim of this study was to assess the dose-response of isavuconazole, voriconazole and fluconazole in disseminated Candida tropicalis and Candida krusei infections. METHODS: Mice were immunosuppressed using either one dose [temporarily neutropenic (TN)] or two doses [persistently neutropenic (PN)] of cyclophosphamide. Treatment was started 5 h after infection with oral isavuconazole (6, 15, 30, 60, 90, 120 or 150 mg/kg equivalent active compound), intravenous voriconazole (5, 20 or 40 mg/kg plus grapefruit gavage twice daily) or oral fluconazole (15, 50 or 150 mg/kg) all administered twice daily. Kidney burden was assessed for C. tropicalis, and kidney and brain burden for C. krusei. RESULTS: Vehicle controls developed a non-lethal infection with high burdens in both models. In the TN models, isavuconazole, voriconazole and fluconazole (>50 mg/kg) reduced kidney burden compared with controls; >60 mg/kg isavuconazole and 50 mg/kg fluconazole were superior to alternative treatments (other than voriconazole 40 mg/kg). Isavuconazole (all doses) reduced brain burden (P<0.05) in the C. krusei model; fluconazole (all doses) and voriconazole (5 and 20 mg/kg) did not. In the C. krusei kidney burden model, isavuconazole 120 and 150 mg/kg and voriconazole 40 mg/kg were superior to controls and fluconazole. In the C. tropicalis model, PN isavuconazole (all doses), voriconazole (>5 mg/kg) and fluconazole (all doses) reduced kidney burden (P<0.05). Only isavuconazole (all doses) and 40 mg/kg voriconazole were effective against C. krusei in the brain, isavuconazole and voriconazole reduced tissue burden (P<0.05). Fluconazole had no significant effect on brain burden even at 150 mg/kg. CONCLUSIONS: Isavuconazole significantly reduced kidney burden in mice infected with C. tropicalis and both kidney and brain burdens in mice infected with C. krusei. Isavuconazole was as effective as voriconazole and much more effective than fluconazole at reducing brain burden.

Aspergillus flavus: human pathogen, allergen and mycotoxin producer.

Aspergillus infections have grown in importance in the last years. However, most of the studies have focused on Aspergillus fumigatus, the most prevalent species in the genus. In certain locales and hospitals, Aspergillus flavus is more common in air than A. fumigatus, for unclear reasons. After A. fumigatus, A. flavus is the second leading cause of invasive aspergillosis and it is the most common cause of superficial infection. Experimental invasive infections in mice show A. flavus to be 100-fold more virulent than A. fumigatus in terms of inoculum required. Particularly common clinical syndromes associated with A. flavus include chronic granulomatous sinusitis, keratitis, cutaneous aspergillosis, wound infections and osteomyelitis following trauma and inoculation. Outbreaks associated with A. flavus appear to be associated with single or closely related strains, in contrast to those associated with A. fumigatus. In addition, A. flavus produces aflatoxins, the most toxic and potent hepatocarcinogenic natural compounds ever characterized. Accurate species identification within Aspergillus flavus complex remains difficult due to overlapping morphological and biochemical characteristics, and much taxonomic and population genetics work is necessary to better understand the species and related species. The flavus complex currently includes 23 species or varieties, including two sexual species, Petromyces alliaceus and P. albertensis. The genome of the highly related Aspergillus oryzae is completed and available; that of A. flavus in the final stages of annotation. Our understanding of A. flavus lags far behind that of A. fumigatus. Studies of the genomics, taxonomy, population genetics, pathogenicity, allergenicity and antifungal susceptibility of A. flavus are all required.

Infrared body temperature measurement of mice as an early predictor of death in experimental fungal infections.

Temperatures of mice were measured using an infrared high performance non-contact thermometer, after the device had been calibrated using implantable microchips containing temperature transponders. Mice were infected with three species of Candida (isolates) and the resultant disseminated infections monitored. Mouse temperatures could be reliably measured using the infrared device and this measurement caused little distress to the mice. We were further able to demonstrate that mice rarely recovered if their body temperature dropped below 33.3 degrees C (sensitivity 68%, specificity 97%). Adoption of a 33.3 degrees C endpoint in fungal sepsis experiments measured by infrared non-contact thermometer would significantly reduce the suffering in the terminal stages of this type of infection model.

Activity of micafungin (FK463) against an itraconazole-resistant strain of Aspergillus fumigatus and a strain of Aspergillus terreus demonstrating in vivo resistance to amphotericin B.

We compared the activity of four doses of micafungin (FK463) with that of amphotericin B, liposomal amphotericin B and itraconazole in a murine model of disseminated aspergillosis. Temporarily neutropenic mice were infected with a lethal dose of either an itraconazole-resistant Aspergillus fumigatus isolate or Aspergillus terreus, a species that is less susceptible to amphotericin B. Treatment was started 24 h after infection and lasted for 7 days. Mice were treated with either amphotericin B (0.5 or 5 mg/kg), liposomal amphotericin (5 or 25 mg/kg), itraconazole (25 or 75 mg/kg) or FK463 (either 1, 2, 5 or 10 mg/kg). Treatment of the A. fumigatus model with either amphotericin B, liposomal amphotericin or FK463 prolonged survival. Doses of FK463 5 and 10 mg/kg had a 100% survival. Treatment of A. terreus infection with either itraconazole or FK463, but not amphotericin B, also prolonged survival. Doses of liposomal amphotericin of 5 and 25 mg/kg were ineffective against A. terreus infection. No treatment regime was able to totally clear the liver or kidneys in either model. The data indicate that FK463 may have a clinical role in the treatment of life-threatening invasive aspergillosis.

In vitro interaction of terbinafine with itraconazole, fluconazole, amphotericin B and 5-flucytosine against Aspergillus spp.

We investigated the in vitro interaction of terbinafine with itraconazole, fluconazole, amphotericin B and 5-flucytosine, against Aspergillus spp. We tested three isolates of Aspergillus fumigatus (one resistant to itraconazole), and two each of Aspergillus flavus, Aspergillus niger and Aspergillus terreus. We employed a broth microdilution-based method derived from an in vivo validated method capable of detecting itraconazole resistance in A. fumigatus. We studied the effect on the MICs by calculation of the fractional inhibitory concentration (FIC) and fractional fungicidal concentration (FFC) (99.99% kill). Itraconazole and terbinafine were synergic or additive in all strains (FIC = 0.15-1.0). Fluconazole and terbinafine were synergic with A. fumigatus, A. terreus and A. flavus (FIC = 0.3-0.5) and indifferent with A. niger (FIC = 2) isolates. Amphotericin B and terbinafine were mostly indifferent or antagonistic (FIC = 1.0-4.02). Flucytosine and terbinafine were usually indifferent or antagonistic (FIC = 0.63-8.5). FFCs were generally in accord with FICs. The use of terbinafine in combination therapy for Aspergillus infections with azoles seems promising, whereas terbinafine and amphotericin B or flucytosine in combination were less effective.

Treatment of Absidia corymbifera infection in mice with amphotericin B and itraconazole.

The activities of amphotericin B and itraconazole were studied in a temporarily neutropenic murine model of disseminated Absidia corymbifera infection, caused by two different strains. Amphotericin B MICs were 0.25 mg/L for both strains and itraconazole MICs were 1 and 2 mg/L. Amphotericin B was effective in vivo with both isolates. Itraconazole was less effective.

Susceptibility testing of Aspergillus flavus: inoculum dependence with itraconazole and lack of correlation between susceptibility to amphotericin B in vitro and outcome in vivo.

We have attempted to validate in Aspergillus flavus the main in vitro methodologies that have been used to detect resistance in Aspergillus fumigatus. We developed a murine model with two A. flavus isolates, one that was apparently resistant in vitro to amphotericin B (AFL5) and another that was resistant to itraconazole (AFL8). No correlation was found for amphotericin B in AFL5, since the in vivo response was compatible with a susceptible isolate. Modification of the in vitro susceptibility test methodology for amphotericin B was unsuccessful. Although AFL8 was apparently resistant to itraconazole in vitro, it was found to be susceptible in vivo. Additional in vitro work has detected weaknesses in the in vitro susceptibility methodology validated for A. fumigatus when applied to A. flavus. The principal problems are that changes in the inoculum have a large effect on the MICs of itraconazole for some A. flavus strains and that a trailing end point and spore sediment often appear when an inoculum with a higher colony count is used. We propose a modified method using a final inoculum of 2.5 x 10(4) CFU per ml of RPMI 1640 medium with 2% glucose buffered to pH 7.0 in a microtiter format, incubated for 48 h with no growth end point. Validation of this methodology requires one or more itraconazole-resistant A. flavus isolates, which have yet to be identified.

In vivo activity of amphotericin B lipid complex in immunocompromised mice against fluconazole-resistant or fluconazole-susceptible Candida tropicalis.

We compared four doses of amphotericin B lipid complex (ABLC) with three doses of fluconazole in temporarily neutropenic mice in a murine model of disseminated candidiasis due to four different isolates of Candida tropicalis. The mice were infected with a 90% lethal dose of four strains of C. tropicalis for which the fluconazole MICs ranged from 1 to >125 mg/liter 3 days after receiving 200 mg of cyclophosphamide/kg of body weight. Treatment was started 18 h after infection and lasted for 7 days. ABLC (1, 2, 5, and 10 mg/kg) was administered once a day intravenously, fluconazole was administered by oral gavage once daily (25 and 50 mg/kg/day) or twice daily (125 mg/kg). MICs determined in five different ways with 24- and 48-h endpoints were also compared. The overall survival rates were controls, 14%; fluconazole, 64%; and ABLC, 82%. Treatment with ABLC at 2 to 10 mg/kg increased survival compared to controls (P = <0.0001) and was also superior to fluconazole at 25 and 50 mg/kg (P = 0.006). In the fluconazole-resistant C. tropicalis model (MIC, 128 microg/ml), ABLC at 2 to 10 mg/kg was superior to fluconazole at 250 mg/kg and ABLC at 10 mg/kg was superior to all fluconazole doses (P = <0.05). Fluconazole at 250 mg/kg daily was superior to both 25 and 50 mg/kg at reducing mortality with most isolates. ABLC was superior to fluconazole (P = <0.01), and fluconazole at 250 mg/kg was superior to fluconazole at both 25 and 50 mg/kg (P = 0.02) in all models at reducing C. tropicalis counts in the kidneys. Neither drug consistently sterilized the brain or kidneys. A 48-h endpoint reading with the NCCLS susceptibility testing microtiter variation overestimates resistance to fluconazole. ABLC is an effective treatment for fluconazole-resistant C. tropicalis at all doses tested.