Activity of the new antifungal triazole, posaconazole, against Cryptococcus neoformans

The new antifungal derivative posaconazole was tested against three clinical isolates of Cryptococcus neoformans var. neoformans using a broth microdilution procedure performed according to the guidelines established by the NCCLS. Posaconazole MICs were 0.125, 0.25 and 1.0 mg/L for isolates 491, 2337 and 486, respectively. To investigate the in vivo activity of this new compound, we established an experimental model of systemic cryptococcosis in CD1 mice by iv injection of cells of each strain of C. neoformans. Low (3 mg/kg/day) and high (10 mg/kg/day) doses of posaconazole were compared with amphotericin B given at 0.3 mg/kg/day for 10 consecutive days. Survival studies showed that all treatment regimens were effective in prolonging the survival of mice infected with C. neoformans 486 (P < 0.001). Only posaconazole at 10 mg/kg and amphotericin B were effective in prolonging the survival in mice infected with C. neoformans 2337 (P from <0.01 to <0.001), while neither agent was effective in mice infected with C. neoformans 491. Tissue burden experiments performed 24 h after the end of therapy revealed that posaconazole at 10 mg/kg was effective at reducing the fungal burden in both lung and brain tissues of all three strains of C. neoformans. In particular, for C. neoformans 491 and 2337 posaconazole was superior to amphotericin B at reducing the fungal burden in the brain (P < 0.05). The efficacy of posaconazole was also confirmed by determining the capsular antigen serum levels of treated mice versus untreated mice. Our study underlines the excellent activity of posaconazole against this pathogenic yeast.

Electrophoretic karyotyping and antifungal susceptibility patterns of Candida parapsilosis clinical isolates causing deep and superficial fungal infections

Forty-six isolates of Candida parapsilosis, each from a single patient, were collected from July 1993 through March 1999 at the University of Ancona Hospitals and Clinics. Twenty-eight strains were isolated from superficial lesioned sites, including skin, nails and other sources while 18 strains were isolated from blood. The isolates were typed by electrophoretic karyotyping (EK) and tested for their susceptibility to fluconazole (FLC), itraconazole (ITC), flucytosine (5-FC), and amphotericin B (AMB). Our data confirmed that EK is a useful technique for DNA typing of isolates of Candida parapsilosis and showed that the source of isolation is not associated with a given DNA type. Although strains belonging to this species of Candida are susceptible to the most common antifungals, including the triazoles, the degree of ITC susceptibility was dose dependent (MIC ranging from 0.25-0.5 microgram/ml) for 98% of the isolates.

Interactions of posaconazole and flucytosine against Cryptococcus neoformans

A checkerboard methodology, based on standardized methods proposed by the National Committee for Clinical Laboratory Standards for broth microdilution antifungal susceptibility testing, was applied to study the in vitro interactions of flucytosine (FC) and posaconazole (SCH 56592) (FC-SCH) against 15 isolates of Cryptococcus neoformans. Synergy, defined as a fractional inhibitory concentration (FIC) index of <0.50, was observed for 33% of the isolates tested. When synergy was not achieved, there was still a decrease in the MIC of one or both drugs when they were used in combination. Antagonism, defined as a FIC of >4.0, was not observed. The in vitro efficacy of combined therapy was confirmed by quantitative determination of the CFU of C. neoformans 486, an isolate against which the FC-SCH association yielded a synergistic interaction. To investigate the potential beneficial effects of this combination therapy in vivo, we established two experimental murine models of cryptococcosis by intracranial or intravenous injection of cells of C. neoformans 486. At 1 day postinfection, the mice were randomized into different treatment groups. One group each received each drug alone, and one group received the drugs in combination. While combination therapy was not found to be significantly more effective than each single drug in terms of survival, tissue burden experiments confirmed the potentiation of antifungal activity with the combination. Our study demonstrates that SCH and FC combined are significantly more active than either drug alone against C. neoformans in vitro as well in vivo. These findings suggest that this therapeutic approach could be useful in the treatment of cryptococcal infections.

Interactions between triazoles and amphotericin B against Cryptococcus neoformans

The interaction of amphotericin B (AmB) and azole antifungal agents in the treatment of fungal infections is still a controversial issue. A checkerboard titration broth microdilution-based method that adhered to the recommendations of the National Committee for Clinical Laboratory Standards was applied to study the in vitro interactions of AmB with fluconazole (FLC), itraconazole (ITC), and the new investigational triazole SCH 56592 (SCH) against 15 clinical isolates of Cryptococcus neoformans. Synergy, defined as a fractional inhibitory concentration (FIC) index of < or =0.50, was observed for 7% of the isolates in studies of the interactions of both FLC-AmB and ITC-AmB and for 33% of the isolates in studies of the SCH-AmB interactions; additivism (FICs, >0.50 to 1.0) was observed for 67, 73, and 53% of the isolates in studies of the FLC-AmB, ITC-AmB, and SCH-AmB interactions, respectively; indifference (FICs, >1.0 to < or =2.0) was observed for 26, 20, and 14% of the isolates in studies of the FLC-AmB, ITC-AmB, and SCH-AmB interactions, respectively. Antagonism (FIC >2.0) was not observed. When synergy was not achieved, there was still a decrease, although not as dramatic, in the MIC of one or both drugs when they were used in combination. To investigate the effects of FLC-AmB combination therapy in vivo, we established an experimental model of systemic cryptococcosis in BALB/c mice by intravenous injection of cells of C. neoformans 2337, a clinical isolate belonging to serotype D against which the combination of FLC and AmB yielded an additive interaction in vitro. Both survival and tissue burden studies showed that combination therapy was more effective than FLC alone and that combination therapy was at least as effective as AmB given as a single drug. On the other hand, when cells of C. neoformans 2337 were grown in FLC-containing medium, a pronounced increase in resistance to subsequent exposures to AmB was observed. In particular, killing experiments conducted with nonreplicating cells showed that preexposure to FLC abolished the fungicidal activity of the polyene. However, this apparent antagonism was not observed in vivo. Rather, when the two drugs were used sequentially for the treatment of systemic murine cryptococcosis, a reciprocal potentiation was often observed. Our study shows that (i) the combination of triazoles and AmB is significantly more active than either drug alone against C. neoformans in vitro and (ii) the concomitant or sequential use of FLC and AmB for the treatment of systemic murine cryptococcosis results in a positive interaction.

In vitro activities of the new antifungal triazole SCH 56592 against common and emerging yeast pathogens

A broth microdilution method performed in accordance with the National Committee for Clinical Laboratory Standards guidelines was used to compare the in vitro activity of the new antifungal triazole SCH 56592 (SCH) to that of fluconazole (FLC), itraconazole (ITC), and ketoconazole (KETO) against 257 clinical yeast isolates. They included 220 isolates belonging to 12 different species of Candida, 15 isolates each of Cryptococcus neoformans and Saccharomyces cerevisiae, and seven isolates of Rhodotorula rubra. The MICs of SCH at which 50% (MIC(50)) and 90% (MIC(90)) of the isolates were inhibited were 0.06 and 2.0 microg/ml, respectively. In general, SCH was considerably more active than FLC (MIC(50) and MIC(90) of 1.0 and 64 microg/ml, respectively) and slightly more active than either ITC (MIC(50) and MIC(90) of 0.25 and 2.0 microg/ml, respectively) and KETO (MIC(50) and MIC(90) of 0.125 and 4.0 microg/ml, respectively). Our in vitro data suggest that SCH has significant potential for clinical development.

In-vitro interactions of itraconazole with flucytosine against clinical isolates of Cryptococcus neoformans

Treatment failures can occur in AIDS patients infected with Cryptococcus neoformans, despite aggressive antifungal therapy. Combination regimens with additive or synergic drugs could provide additional options for treating cryptococcosis. We studied the effects of itraconazole combined with flucytosine against 16 strains of C. neoformans var. neoformans. Combination therapy revealed different results for the various strains, including synergy (fractional inhibitory concentration (FIC) index 0.5, 63% of the interactions), addition (FIC >0.5 to 1.0, 31% of the interactions) and indifference (FIC >1.0 to <2.0, 6% of the interactions). Antagonism (FIC >2.0) was not observed. The efficacy of combination therapy was confirmed by quantitative cfu and killing curve assays. In particular, killing curves conducted in replicating cells showed that the addition of itraconazole prevented the development of flucytosine-resistant mutants of C. neoformans. These data show that the combination of itraconazole and flucytosine is significantly more active than either drug alone against C. neoformans in vitro.

In-vitro activity of five antifungal agents against uncommon clinical isolates of Candida spp

A broth microdilution method and an agar dilution method were used for testing fluconazole, itraconazole, ketoconazole, flucytosine and amphotericin B against 98 clinical isolates belonging to seven species of Candida. The approximate rank order of fluconazole MICs was Candida lusitaniae approximately Candida kefyr < Candida famata approximately Candida guilliermondii < Candida pelliculosa approximately C. lipolytica approximately Candida inconspicua. Candida lypolitica and C. pelliculosa were the species least susceptible to itraconazole and ketoconazole. Flucytosine MICs revealed the highest prevalence of resistant strains among C. lipolytica and C. lusitaniae. All isolates were susceptible to amphotericin B.

In vitro activity of five antifungal agents against clinical isolates of Saccharomyces cerevisiae

We evaluated the in vitro activity of fluconazole, itraconazole, ketoconazole, 5-fluorocytosine and amphotericin B against 30 clinical isolates of Saccharomyces cerevisiae by a broth microdilution method, following the NCCLS recommendation. Testing was performed either in RPMI-1640 or yeast nitrogen base (YNB). YNB supported the growth of all isolates tested, while results in RPMI-1640 were not obtained for six isolates (20%). The MIC of all three azoles in YNB were one or two dilutions higher than those obtained in RPMI-1640 (P=0.0001 for fluconazole and itraconazole, P=0.03 for ketoconazole). Elevated MICs were observed for all three azoles, while all the isolates were susceptible to 5-fluorocytosine and amphotericin B. All MIC values were confirmed by spectrophotometric reading. Six strains of S. cerevisiae isolated from the faeces and consecutive blood cultures from an AIDS patient over a 7-month period were typed by electrophoretic karyotyping (EK). EK showed the maintenance of the same karyotype over time suggesting that the faecal isolate changed from a colonizing to infection-causing strain. The relative resistance of S. cerevisiae to azole drugs as well as its ability to cause widespread infections may promote the emergence of this species as a pathogen in immunosuppressed patients.

In-vitro interaction of terbinafine with amphotericin B, fluconazole and itraconazole against clinical isolates of Candida albicans

A chequerboard titration broth microdilution method, performed according to the recommendations of the National Committee for Clinical Laboratory Standards, was applied to study the in-vitro interaction of terbinafine with amphotericin B, fluconazole and itraconazole against 30 strains of Candida albicans isolated from the oral cavities of AIDS patients. MICs were determined spectrophotometrically at 490 nm and read at either 24 h or 48 h. The end-point was defined as the drug concentration resulting in > or = 90% inhibition of growth relative to control growth. Synergy, defined as a fractional inhibitory concentration (FIC) index of < or = 0.50, was observed in 93% (28 of 30) of terbinafine-amphotericin B interactions, in 47% (14 of 30) of terbinafine-fluconazole interactions and in 43% (13 of 30) of terbinafine-itraconazole interactions; antagonism (FIC > 2.0) was not observed. Where synergy was not achieved, there was still a decrease, although not as dramatic, in the MIC of one or both drugs when used in combination. Reading the MICs on day 2 did not significantly affect the mode of interaction of terbinafine-triazoles, while for terbinafine-amphotericin B the proportion of synergic interactions dropped from 93% (28 of 30) to 30% (nine of 30; P = 0.0001). Antagonism was not observed for any drug combination even at 48 h. Minimum fungicidal concentrations (MFCs) of all drugs alone and in combination were determined against five isolates. Neither terbinafine nor the two triazoles showed fungicidal activity when tested alone or in combination. The fungicidal activity of amphotericin B was slightly enhanced when combined with terbinafine, there being a decrease of two-fold dilutions in the amphotericin B MFCs against all five isolates tested. Thus terbinafine enhances the activities of amphotericin B and triazoles against C. albicans in vitro. Clearly, clinical studies are warranted to elucidate further the potential utility of these combination therapies.

Genotypic identification of sequential Candida albicans isolates from AIDS patients by polymerase chain reaction techniques

Random amplification of polymorphic DNA and inter-repeat polymerase chain reaction (IR-PCR) were compared with restriction fragment length polymorphism (RFLP) analysis as methods for DNA typing of Candida albicans. Forty-seven strains of Candida albicans isolated from the oral cavities of five AIDS patients undergoing fluconazole therapy were analyzed. There was an excellent correspondence between the DNA types obtained by both PCR-based techniques and by RFLP. With the exception of one patient who was infected with three DNA types of Candida albicans during a five-year observation period, the patients each harboured only one major strain, which became progressively less susceptible to fluconazole. Each DNA type was unique to a patient. The data suggest that these typing methods are suitable for investigating the epidemiology of oropharyngeal candidiasis in this patient group.