In vitro studies of activities of the antifungal triazoles SCH56592 and itraconazole against Candida albicans, Cryptococcus neoformans, and other pathogenic yeasts

A Comprehensive Overview of the Antibiotics Approved in the Last Two Decades: Retrospects and Prospects

Due to the overuse of antibiotics, bacterial resistance has markedly increased to become a global problem and a major threat to human health. Fortunately, in recent years, various new antibiotics have been developed through both improvements to traditional antibiotics and the discovery of antibiotics with novel mechanisms with the aim of addressing the decrease in the efficacy of traditional antibiotics. This manuscript reviews the antibiotics that have been approved for marketing in the last 20 years with an emphasis on the antibacterial properties, mechanisms, structure-activity relationships (SARs), and clinical safety of these antibiotics. Furthermore, the current deficiencies, opportunities for improvement, and prospects of antibiotics are thoroughly discussed to provide new insights for the design and development of safer and more potent antibiotics.

In vitro activity of the antifungal azoles itraconazole and posaconazole against Leishmania amazonensis

Leishmaniasis, caused by protozoan parasites of the Leishmania genus, is one of the most prevalent neglected tropical diseases. It is endemic in 98 countries, causing considerable morbidity and mortality. Pentavalent antimonials are the first line of treatment for leishmaniasis except in India. In resistant cases, miltefosine, amphotericin B and pentamidine are used. These treatments are unsatisfactory due to toxicity, limited efficacy, high cost and difficult administration. Thus, there is an urgent need to develop drugs that are efficacious, safe, and more accessible to patients. Trypanosomatids, including Leishmania spp. and Trypanosoma cruzi, have an essential requirement for ergosterol and other 24-alkyl sterols, which are absent in mammalian cells. Inhibition of ergosterol biosynthesis is increasingly recognized as a promising target for the development of new chemotherapeutic agents. The aim of this work was to investigate the antiproliferative, physiological and ultrastructural effects against Leishmania amazonensis of itraconazole (ITZ) and posaconazole (POSA), two azole antifungal agents that inhibit sterol C14α-demethylase (CYP51). Antiproliferative studies demonstrated potent activity of POSA and ITZ: for promastigotes, the IC50 values were 2.74 µM and 0.44 µM for POSA and ITZ, respectively, and for intracellular amastigotes, the corresponding values were 1.63 µM and 0.08 µM, for both stages after 72 h of treatment. Physiological studies revealed that both inhibitors induced a collapse of the mitochondrial membrane potential (ΔΨm), which was consistent with ultrastructural alterations in the mitochondrion. Intense mitochondrial swelling, disorganization and rupture of mitochondrial membranes were observed by transmission electron microscopy. In addition, accumulation of lipid bodies, appearance of autophagosome-like structures and alterations in the kinetoplast were also observed. In conclusion, our results indicate that ITZ and POSA are potent inhibitors of L. amazonensis and suggest that these drugs could represent novel therapies for the treatment of leishmaniasis, either alone or in combination with other agents.

Advances in synthetic approach to and antifungal activity of triazoles

Several five membered ring systems, e.g., triazole, oxadiazole dithiazole and thiadiazole with three heteroatoms at symmetrical or asymmetrical positions have been studied because of their interesting pharmacological properties. In this article our emphasis is on synthetic development and pharmacological activity of the triazole moiety which exhibit a broad spectrum of pharmacological activity such as antifungal, antibacterial, anti-inflammatory and anticancer etc. Triazoles have increased our ability to treat many fungal infections, for example, candidiasis, cryptococcal meningitis, aspergillosis etc. However, mortality due to these infections even with antifungal therapy is still unacceptably high. Therefore, the development of new antifungal agents targeting specific fungal structures or functions is being actively pursued. Rapid developments in molecular mycology have led to a concentrated search for more target antifungals. Although we are entering a new era of antifungal therapy in which we will continue to be challenged by systemic fungal diseases, the options for treatment will have greatly expanded.

Therapeutic efficacy of posaconazole against Candida glabrata in a murine model of vaginitis

The frequency of mucosal infections caused by Candida glabrata has increased significantly. Candida glabrata infections are often resistant to many azole antifungal agents, especially fluconazole. The purpose of this study was to compare the efficacies of posaconazole (PSC) and fluconazole (FLC) in the treatment of experimental C. glabrata vaginitis caused by isolates with different FLC susceptibilities. A battery of 36 vaginal isolates of C. glabrata was tested against PSC and FLC to determine their in vitro susceptibilities. The 48-h geometric mean MICs for all isolates tested were 0.156 and 4.238 μg ml(-1) for PSC and FLC respectively. Two strains of C. glabrata for which FLC MICs were different were selected for in vivo study. The treatment regimens for the vaginal murine infection model were PSC or FLC at 10 or 20 mg kg(-1) of body weight/day and 20 mg kg(-1) twice a day. Regimens with PSC at 20 mg kg(-1) once or twice a day were effective in reducing the load of both the FLC-susceptible and -resistant isolates of C. glabrata. FLC at 20 mg kg(-1) twice a day was effective in reducing the load of both the isolates of C. glabrata. PSC displayed a more effective in vivo activity than FLC in the treatment of murine C. glabrata vaginitis.

Approaches to the early treatment of invasive fungal infection

Invasive fungal infections account for significant morbidity and mortality in the seriously immunocompromised host, especially those suffering from hematologic malignancies and the recipients of hematopoietic cell transplant. One of the reasons for the continuing high mortality rates due to invasive fungal infection is the delay in administering appropriate therapy. As preemptive antifungal therapy is not feasible for lack of a predictive test, early empiric therapy is currently the only approach likely to result in improvement in survival. Here, we present our approach to both invasive candidiasis and invasive mold infection. Therapy should be initiated at the first signs and symptoms of disease, utilizing knowledge of local fungal epidemiology, the patient's recent antifungal agent exposure, and the diagnostic tests immediately available, to select an appropriate antifungal agent most likely to be effective against the suspected fungal species.

Synthesis and antiviral activity of azoles obtained from carbohydrates

Herein we describe the synthesis of 1,2,4-triazolyl-3-thione;1,3,4-oxadiazole, and imidazo[2,1-b]thiazole derivatives from carbohydrates. The antiviral activity of these compounds was tested against Dengue and Junin virus (the etiological agent of Argentine hemorrhagic fever). The 3-(p-bromobenzoyl)-5-(1,2-O-isopropylidene-3-O-methyl-alpha-d-xylofuranos-5-ulos-5-yl)imidazo[2,1-b]thiazole was able to inhibit the replication of both viruses in Vero cells at concentration significantly lower than the CC(50).

Posaconazole (Noxafil, SCH 56592), a new azole antifungal drug, was a discovery based on the isolation and mass spectral characterization of a circulating metabolite of an earlier lead (SCH 51048)

Posaconazole (SCH 56592) is a novel triazole antifungal drug that is marketed in Europe and the United States under the trade name 'Noxafil' for prophylaxis against invasive fungal infections. SCH 56592 was discovered as a possible active metabolite of SCH 51048, an earlier lead. Initial studies have shown that serum concentrations determined by a microbiological assay were higher than those determined by HPLC from animals dosed with SCH 51048. Subsequently, several animals species were dosed with (3)H-SCH 51048 and the serum was analyzed for total radioactivity, SCH 51048 concentration and antifungal activity. The antifungal activity was higher than that expected based on SCH 51048 serum concentrations, confirming the presence of active metabolite(s). Metabolite profiling of serum samples at selected time intervals pinpointed the peak that was suspected to be the active metabolite. Consequently, (3)H-SCH 51048 was administered to a large group of mice, the serum was harvested and the metabolite was isolated by extraction and semipreparative HPLC. LC-MS/MS analysis suggested that the active metabolite is a secondary alcohol with the hydroxyl group in the aliphatic side chain of SCH 51048. All corresponding monohydroxylated diastereomeric mixtures were synthesized and characterized. The HPLC retention time and LC-MS/MS spectra of the diastereomeric secondary alcohols of SCH 51048 were similar to those of the isolated active metabolite. Finally, all corresponding individual monohydroxylated diasteriomers were synthesized and evaluated for in vitro and in vivo antifungal potencies, as well as pharmacokinetics. SCH 56592 emerged as the candidate with the best overall profile.

Recent advances in antifungal chemotherapy

For over 50 years, amphotericin B deoxycholate (AmBD) has been the 'gold standard' in antifungal chemotherapy, despite its frequent toxicities. However, improved treatment options for invasive fungal infections (IFIs) have been developed during the last 15 years. Newer antifungal agents, including less toxic lipid preparations of AmBD, triazoles and the echinocandins, have been added to our armamentarium against IFIs. Some of these newer drugs can now replace AmBD as primary therapy (e.g. caspofungin for candidiasis, voriconazole for aspergillosis), whilst others offer new therapeutic options for difficult-to-treat IFIs (e.g. posaconazole for zygomycosis, fusariosis and chromoblastomycosis). It is interesting that extended use of newer antifungals such as fluconazole, despite decreasing the mortality attributed to candidiasis, resulted in selection of species resistant to several antifungals (Candida krusei, Candida glabrata); whilst several publications suggest that prolonged use of voriconazole may expose severely immunocompromised patients to the risk of zygomycosis (breakthrough). On the other hand, the differences in the mode of action of newer antifungals such as echinocandins raise the question whether combination antifungal therapy is more effective than monotherapy. Finally, the availability of an oral formulation with excellent biosafety of several newer antifungals (e.g. posaconazole) makes them candidates for prophylactic or prolonged maintenance therapy.

Multiple resistance mechanisms to azole antifungals in yeast clinical isolates

The use of antifungal agents, especially the azole class, has increased in parallel with a higher incidence of fungal infections, particularly in immunocompromised patients. This situation has favored the appearance of Candida species, prominent among them C. albicans and C. globrata, with acquired resistance to these agents. This review focuses on the latest developments in investigations of molecular mechanisms contributing to azole resistance. Multiple resistance mechanisms have been described that can coexist in resistant clinical isolates. Understanding resistance mechanisms is of value not only for the design of new antifungal agents but also the development of strategies of overcome or delay the emergence of resistance.

Posaconazole: clinical pharmacology and potential for management of fungal infections

Posaconazole is a novel lipophilic antifungal triazole that inhibits cytochrome P450-dependent 14-alpha demethylase in the biosynthetic pathway of ergosterol. Inhibition of this enzyme leads to an accumulation of toxic 14-alpha methylsterols and a depletion of ergosterol, resulting in a perturbation of the function of the fungal cell membrane and blockage of cell growth and division. In vitro, posaconazole has potent and broad-spectrum activity against opportunistic, endemic and dermatophytic fungi. This activity extends to organisms that are often refractory to existing triazoles, amphotericin B or echinocandins, such as Candida glabrata, Candida krusei, Aspergillus terreus, Fusarium spp. and the Zygomycetes. A large variety of animal models of invasive fungal infections have provided consistent evidence of efficacy against these organisms in vivo, both in normal and immunocompromised animals. Posaconazole is available as an oral suspension and optimal exposure is achieved when the drug is administered in two to four divided doses along with food or a nutritional supplement. The compound has a large volume of distribution, in the order of 5 l/kg, and a half-life of approximately 20 h. Posaconazole is not metabolized to a significant extent through the cytochrome P450 enzyme system and is primarily excreted in an unchanged form in the feces. Although it is inhibitory, cytochrome P3A4 has no effect on 1A2, 2C8, 2C9, 2D6 and 2E1 isoenzymes, and therefore, a limited spectrum of drug-drug interactions can be expected. Pharmacokinetic studies in special populations revealed no necessity for dosage adjustment based on differences in age, gender, race, renal or hepatic function. Posaconazole has demonstrated strong antifungal efficacy in Phase II and III clinical trials in immunocompromised patients with oropharyngeal and esophageal candidiasis. Posaconazole also showed promising efficacy as salvage therapy in a large Phase II study including 330 patients with invasive fungal infections intolerant to or refractory to standard therapies. Posaconazole appears to be well tolerated in a manner comparable with that of fluconazole and it is currently under regulatory review in the USA and Europe for the treatment of refractory invasive fungal infections. This drug profile reviews the preclinical and clinical pharmacology of posaconazole and its potential role for prevention and treatment of invasive fungal infections.

Therapeutic efficacy of posaconazole against isolates ofCandida albicanswith different susceptibilities to fluconazole in a vaginal model

A battery of 34 vaginal isolates of Candida albicans was tested against posaconazole (POS) and fluconazole (FLU) to determine their in vitro susceptibilities and to obtain FLU-susceptible and FLU-resistant strains for the murine in vivo studies. FLU-resistant strains were chosen on the basis of their 48-h MICs. The 48-h geometric mean MICs for all isolates tested were 0.016 and 0.656 microg/ml for POS and FLU, respectively. The treatment regimens for the vaginal murine infection model were POS or FLU at 10 or 20 mg/kg of body weight/day and 20 mg/kg twice a day. All regimens with POS were effective in reducing fungal burden of both the fluconazole-susceptible and resistant isolates of C. albicans. All FLU regimens were effective against infection induced by the fluconazole-susceptible strain. While FLU at 10 mg/kg was ineffective against fungal burden of the resistant strain, treatment with FLU at 20 mg/kg once or twice a day was effective against this strain. Both POS and FLU at 20 mg/kg twice a day were able to clear C. albicans from vaginas of mice infected with the fluconazole-susceptible strain. POS displayed a more effective in vivo activity than FLU in the treatment of murine C. albicans vaginitis produced by isolates with different susceptibilities to FLU.

Posaconazole Oral Suspension

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Emerging azole antifungals

Systemic and superficial fungal infections have progressively emerged over the past few decades as an increasing cause of human disease, especially in the immunocompromised host. Control of fungal disease has proved difficult because few risk factors are potentially preventable; the population at highest risk for fungal disease, the immunocompromised patient, has been steadily increasing. There is a clear need for additional safe and effective therapeutic agents for the treatment of systemic fungal disease. A new generation of triazoles that includes voriconazole, posaconazole, ravuconazole and albaconazole has emerged and are presently in different phases of clinical investigation. These new triazoles have demonstrated a broad spectrum of activity, in particular against fungal pathogens previously resistant to previously available antifungals. This review highlights the emerging azole antifungals, both those available and in clinical development, and discusses their prospects for the future.

In vitro activities of new and established triazoles against opportunistic filamentous and dimorphic fungi

The in vitro activities of three new triazoles were determined and compared to those of itraconazole and fluconazole against 306 clinical isolates of Blastomyces dermatitidis, Cladophialophora carrionii, Coccidioides immitis, Fonsecaea pedrosoi, Fusarium spp., Histoplasma capsulatum, Paecilomyces lilacinus, Pseudallescheria boydii and Sporothrix schenckii. Minimum inhibitory concentrations (MIC) were determined by a broth macrodilution method of the National Committee for Clinical Laboratory Standards M38-A procedure. Itraconazole (geometric mean MIC, 0.16-0.65 microg/ml), voriconazole (geometric mean MIC, 0.18-1.44 microg/ml), ravuconazole (geometric mean MIC, 0.18-1.09 microg/ml), and posaconazole (geometric mean MIC, 0.18-1.38 microg/ml), had relatively uniform values showing potent in vitro inhibitory activity against B. dermatitidis, C. carrionii, C. immitis, F. pedrosoi, H. capsulatum, and S. schenckii. The in vitro activity was variable with strains of P. boydii, P. lilacinus and Fusarium spp.

Antifungal chemotherapeutics

This review addresses trends in outcome and risk factors for invasive fungal infections, current antifungal agents and new therapeutic strategies. Current prospects for new therapies rest upon caspofungin, the first of a new class of antifungal molecules, the echinocandins, and new extended-spectrum azoles, voriconazole, posaconazole and ravuconazole. Approval by the Food and Drug Administration of the USA and the European Medicine Agency was given in 2001-2002 to voriconazole and caspofungin. Voriconazole clearly demonstrated a decrease in mortality in invasive aspergillosis and fusariosis fungal infections.

Analysis of the influence of Tween concentration, inoculum size, assay medium, and reading time on susceptibility testing of Aspergillus spp

The influence of several test variables on susceptibility testing of Aspergillus spp. was assessed. A collection of 28 clinical isolates was tested against amphotericin B, itraconazole, voriconazole, and terbinafine. Inoculum size (10(4) CFU/ml versus 10(5) CFU/ml) and glucose supplementation (0.2% versus 2%) did not have significant effects on antifungal susceptibility testing results and higher inoculum size and glucose concentration did not falsely elevate MICs. In addition, antifungal susceptibility testing procedure with an inoculum size of 10(5) CFU/ml distinctly differentiated amphotericin B or itraconazole-resistant Aspergillus strains in vivo from the susceptible ones. Time of incubation significantly affected the final values of MICs, showing major increases (two to six twofold dilutions, P < 0.01 by analysis of variance) between MIC readings at 24 and 48 h, but no differences were observed between antifungal susceptibility testing results obtained at 48 h and at 72 h. Significantly higher MICs were uniformly associated with higher concentrations of Tween (P < 0.01), used as a dispersing agent in the preparation of inoculum suspensions. The geometric mean MICs showed increases of between 1.5- and 10-fold when the Tween concentration varied from 0.1% (the geometric means for amphotericin B, itraconazole, voriconazole, and terbinafine were 1.29, 0.69, 1.06, and 0.64 mug/ml, respectively) to 5% (the geometric means for amphotericin B, itraconazole, voriconazole, and terbinafine were 1.97, 5.79, 1.60, and 4.66 mug/ml, respectively). The inhibitory effect of Tween was clearly increased with inoculum sizes of 10(5) CFU/ml and was particularly dramatic for itraconazole, terbinafine, and Aspergillus terreus. The inoculum effect was not observed when the Tween concentration was below 0.5% (P > 0.01).

Antifungal activity of posaconazole compared with fluconazole and amphotericin B against yeasts from oropharyngeal candidiasis and other infections

OBJECTIVES

The in vitro antifungal activity of posaconazole was compared with that of fluconazole and amphotericin B.

MATERIALS AND METHODS

A microdilution method (M27-A2) was used with 331 clinical yeast isolates.

RESULTS

The geometric mean MICs of posaconazole, fluconazole and amphotericin B were 0.16, 0.91 and 0.15 mg/L, respectively. Posaconazole was markedly more active than fluconazole and was active against 9/11 fluconazole-resistant Candida albicans, and five Candida glabrata had an MIC of posaconazole of 16 mg/L.

CONCLUSIONS

These data indicate that posaconazole is a potentially effective antifungal agent for the treatment of mycoses caused by yeasts.

New agents for the treatment of systemic fungal infections – current status

Systemic antifungal chemotherapy is enjoying its most dynamic era. More antifungal agents are under development than ever before, including agents in entirely new classes. Major goals of current investigations are to identify compounds with a wide spectrum of activity, minimal toxicity and a high degree of target specificity. The antifungal drugs in development include new azoles {voriconazole, posaconazole (formerly SCH-56592), ravuconazole (formerly BMS-207147)}, lipid formulations of amphotericin B, a lipid formulation of nystatin, echinocandins {anidulafungin (formerly, LY-303366, VER-002), caspofungin (formerly MK-991), micafungin (formerly FK-463)}, antifungal peptides other than echinocandins, and sordarin derivatives. This discussion reviews the currently available antifungal agents and summarises the developmental issues that surround these new systemic antifungal drugs.

Antifungal activities of posaconazole and granulocyte-macrophage colony-stimulating factor ex vivo and in mice with disseminated infection due to Scedosporium prolificans

Invasive infection due to Scedosporium prolificans is characterized by drug resistance and a high rate of mortality. The effects of posaconazole (POS), an investigational antifungal triazole, murine granulocyte-macrophage colony-stimulating factor (GM-CSF), and their combination against S. prolificans were evaluated ex vivo and in a newly developed murine model of disseminated infection due to this organism. When POS was combined with polymorphonuclear leukocytes from untreated or GM-CSF-treated mice (P < 0.01) ex vivo, it had increased activity in terms of the percentage of hyphal damage. Immunocompetent BALB/c mice were infected with 4 x 10(4) conidia of S. prolificans via the lateral tail vein. At 24 h postinfection the mice were treated with GM-CSF (5 microg/kg of body weight/day subcutaneously), POS (50 mg/kg/day by gavage), both agents, or saline only. Half of the brain, lung, liver, and kidney from each animal were cultured; and the other half of each organ was processed for histopathology. The mean survival times were 7.0 +/- 0.3 days for the controls, 7.4 +/- 0.4 days for POS-treated mice, 8.0 +/- 0.3 days for GM-CSF-treated mice (P = 0.08 compared with the results for the controls), and 7.3 +/- 0.3 days for POS-GM-CSF-treated mice. Fungal burdens (determined as the numbers of CFU per gram of tissue) were found in descending orders of magnitude in the kidneys, brains, livers, and lungs. The burdens were significantly reduced in the brains of GM-CSF-treated mice (P < 0.05) and the livers of POS-treated mice (P < 0.05). The numbers of lesions in the organs closely corresponded to the fungal burdens. GM-CSF tended to prolong survival (P = 0.08 compared with the results for the controls). While the combination of POS and GM-CSF showed enhanced activity ex vivo, it did not increase the activities of the two agents against this highly refractory filamentous fungus in mice.

Cryptococcus neoformans methionine synthase: expression analysis and requirement for virulence

This paper describes (i) the expression profile of the methionine synthase gene (MET6) in the human pathogenic fungus Cryptococcus neoformans and (ii) the phenotypes of a C. neoformans met6 mutant. In contrast to the MET3 gene, which showed no significant change in expression in any environmental condition tested, the MET6 gene showed a substantial induction in response to methionine and a dramatic transcriptional induction in response to homocysteine. Like a met3 mutant, the met6 mutant was a methionine auxotroph. However, relative to a met3 mutant, the met6 mutant grew very slowly and was less heat-shock resistant. In contrast to a met3 mutant, the met6 mutant lost viability when starved of methionine, and it was deficient in capsule formation. Like a met3 mutant, the met6 mutant was avirulent. In contrast to a met3 mutant, the met6 mutant was hypersensitive to fluconazole and to the calcineurin inhibitors FK506 and cyclosporin A. A synergistic fungicidal effect was also found between each of these drugs and met6. The phenotypic differences between the met3 and met6 mutants may be due to the accumulation in met6 mutants of homocysteine, a toxic metabolic intermediate that inhibits sterol biosynthesis.

Activity of posaconazole in treatment of experimental disseminated zygomycosis

Three isolates of zygomycetes were used to produce a disseminated infection in nonimmunocompromised mice. Against all zygomycete strains, amphotericin B significantly prolonged survival. Itraconazole was inactive against Rhizopus microsporus and Rhizopus oryzae but was partially active against Absidia corymbifera. Posaconazole had no beneficial effects against R. oryzae but showed partial activity against A. corymbifera. Posaconazole had a clear dose-response effect against R. microsporus.

Susceptibility testing of fungi--current status and open questions

The increase of fungal infections and the improvement of therapeutical options demand reliable antifungal susceptibility testing. In vitro susceptibility testing of fungi--in contrast to bacteria--is not yet established as a routine method. The NCCIS (National Committee for Clinical Laboratory Standards) guidelines for susceptibility testing of yeasts (and proposed for hyphomycetes) are most important for standardization. Meanwhile, essential parts of this test procedure are accepted, but it should still be improved. The concept of using only one test medium for all drugs and test organisms is not realized so far. There are also some test situations that prevent the NCCLS standard from being applied. Based on our experience, this article describes the NCCLS methods and their modifications. It places emphasis on lipophilic drugs showing controversies despite standardization. Furthermore, the prediction of MICs on the clinical outcome is discussed. Since there are some pitfalls in testing antifungals, this should be done in experienced laboratories only. The MIC has to be regarded as only one, but an important, factor in the management of fungal diseases. Host-, drug-, and pathogen-specific data should be considered simultaneously.

Use of high-performance liquid chromatographic and microbiological analyses for evaluating the presence or absence of active metabolites of the antifungal posaconazole in human plasma

Posaconazole (SCH 56592) is a novel broad spectrum triazole antifungal agent that is currently in phase III clinical trials for the treatment of systemic fungal infections. This study was initiated to determine if orally administered posaconazole to humans would result in the formation of active metabolite(s). Plasma samples from a multiple-rising dose study in healthy volunteers were analyzed by validated HPLC and microbiological methods. The HPLC analysis involved extraction with a mixture of organic solvent (methylene chloride-hexane) followed by separation on a C18 column and quantification by UV absorbance at 262 nm. The microbiological assay was performed utilizing an agar diffusion method using Candida pseudorropicalis ATCC 46764 as the test organism. Potency was determined by comparing the growth inhibition zones produced by the test sample to those produced by standard concentrations prepared in plasma. Individual and mean plasma concentration-time profiles were similar for both HPLC and microbiological assays. The area under the plasma concentration-time curves of the microbiological and HPLC results were similar with a mean (RSD) ratio of 105.5% 15.3%), indicating that there was no relevant biologically active metabolite of posaconazole in human plasma.

Mutations in Aspergillus fumigatus resulting in reduced susceptibility to posaconazole appear to be restricted to a single amino acid in the cytochrome P450 14alpha-demethylase

To better understand the molecular basis of posaconazole (POS) resistance in Aspergillus fumigatus, resistant laboratory isolates were selected. Spontaneous mutants arose at a frequency of 1 in 10(8) and fell into two susceptibility groups, moderately resistant and highly resistant. Azole resistance in A. fumigatus was previously associated with decreased drug accumulation. We therefore analyzed the mutants for changes in levels of transcripts of genes encoding efflux pumps (mdr1 and mdr2) and/or alterations in accumulation of [(14)C]POS. No changes in either pump expression or drug accumulation were detected. Similarly, there was no change in expression of cyp51A or cyp51B, which encode the presumed target site for POS, cytochrome P450 14alpha-demethylase. DNA sequencing revealed that each resistant isolate carried a single point mutation in residue 54 of cyp51A. Mutations at the same locus were identified in three clinical A. fumigatus isolates exhibiting reduced POS susceptibility but not in susceptible clinical strains. To verify that these mutations were responsible for the resistance phenotype, we introduced them into the chromosome of a POS-susceptible A. fumigatus strain under the control of the glyceraldehyde phosphate dehydrogenase promoter. The transformants exhibited reductions in susceptibility to POS comparable to those exhibited by the original mutants, confirming that point mutations in the cyp51A gene in A. fumigatus can confer reduced susceptibility to POS.

In vitro and in vivo activities of posaconazole against Coccidioides immitis

Posaconazole (SCH 56592) was tested against 25 strains of Coccidioides immitis to determine their in vitro susceptibilities. The geometric mean 48-h MIC of posaconazole (POSA) was 0.5 microg/ml, the MIC range was 0.25 to 1 microg/ml, and the MIC at which 50% of the isolates tested are inhibited (MIC50) and the MIC90 were 0.5 and 1 microg/ml, respectively. The geometric mean 48-h MIC of itraconazole (ITRA) was 0.23 microg/ml, the MIC range was 0.125 to 0.5 microg/ml, and the MIC50 and MIC90 were both 0.25 microg/ml. Two strains of C. immitis were selected for in vivo studies on the basis of the POSA 48-h MICs for the isolates. POSA orally administered at 0.01, 0.1, 0.5, 1, 5, and 10 mg/kg of body weight/day was compared with ITRA administered at 10 and 30 mg/kg three times a day. The spleens and livers of mice that died or survived to day 50 were removed to measure the fungal burdens. Mice had >or=90% survival when they were treated with >or=0.5 mg of POSA per kg or 30 mg of ITRA per kg. Cultures of whole spleens and livers from mice treated with 10 mg of POSA per kg showed >or=70% sterilization. No sterilization of whole spleens and livers from mice treated with ITRA was seen. POSA displayed potent in vivo activity against the two strains of C. immitis tested.

In vitro activities of posaconazole, itraconazole, voriconazole, amphotericin B, and fluconazole against 37 clinical isolates of zygomycetes

In vitro antifungal susceptibility testing results of a new antifungal triazole, posaconazole (POS), were compared to results with amphotericin B (AMB), itraconazole (ITC), voriconazole (VRC), and fluconazole (FLC) against clinical agents of zygomycosis. The MICs of POS at which 50% and 90% of the isolates were inhibited were 0.25 and 4 microg/ml, respectively. POS was significantly more active than VRC and FLC and slightly more active than ITC. The results suggest that POS has significant potential for clinical development against the zygomycetes.

In vitro activity of nystatin compared with those of liposomal nystatin, amphotericin B, and fluconazole against clinical Candida isolates

We investigated the in vitro activity of nystatin and liposomal nystatin against 103 Candida isolates to determine the effect of both time and medium on MICs. We also compared the nystatin MICs with those of amphotericin B and fluconazole. Testing was performed in accordance with the National Committee for Clinical Laboratory Standards M27-A microdilution methodology with RPMI 1640, RPMI 1640 supplemented with glucose to 2% (RPMI-2), and antibiotic medium 3 supplemented with glucose to 2% (AM3). While nystatin MICs were similar to or slightly lower than liposomal nystatin MICs in RPMI 1640 and RPMI-2, they were markedly higher than liposomal nystatin MICs in AM3. Use of AM3 and determination of the MIC after 24 h of incubation provided a slightly wider range of liposomal nystatin MICs (0.06 to >16 microg/ml). Under these conditions, the MICs at which 90% of isolates were inhibited of nystatin and liposomal nystatin were 2 and 1 microg/ml, respectively. Nystatin and liposomal nystatin in general showed good activity against all Candida spp. tested. Although the MICs of nystatin and liposomal nystatin tended to rise in parallel with the amphotericin B MICs, nystatin and liposomal nystatin MICs of 1 to 2 and 0.5 to 1 microg/ml, respectively, were obtained for seven and six, respectively, of nine isolates for which amphotericin B MICs were >or=0.25 microg/ml. No correlation between fluconazole and nystatin or liposomal nystatin MICs was observed. As amphotericin B MICs of >or=0.25 microg/ml correlate with in vitro resistance, these results suggest that liposomal nystatin might have activity against some amphotericin B-resistant isolates. In vivo testing in animal models is required for clarification of this issue.

New single-isomer compounds on the horizon

In 1992, the Food and Drug Administration (FDA) issued new guidelines governing stereoisomerism in new-drug development. The guidelines strongly encourage the development of single isomers and discourage stereoisomeric (eg, racemic) mixtures. As a result, most new chiral drugs are being developed as single enantiomers (ie, single isomers). There are three mechanisms for the identification and development of new single-isomer drugs: chiral switches (CS), chiral metashifts (CM), and new single-isomer chemical entities (NSICEs). In a CS, one of the two enantiomers of an established racemate is developed as a new drug, with the expectation that the single-isomer form has advantages over the racemic parent in terms of efficacy and/or adverse effects. Many new CS drugs are in development, eg, (S)-oxybutynin for urinary incontinence and escitalopram for depression. In a CM, a chiral metabolite of a drug is developed, in single-isomer form, as an agent with advantages over the parent. Among the current CM drugs in development are (+)-norcisapride (safer GI prokinetic agent than the racemic parent cisapride) and (S)-desmethylzopiclone (antianxiety agent, metabolite of the sedative-hypnotic zopiclone). Many NSICEs are in development, eg, rosuvastatin as an antihypercholesterolemic, posaconazole as an antifungal, sitafloxacin as a fluoroquinolone antibacterial, pregabalin as an anticonvulsant, abarelix as an antineoplastic, etc. As in the development of any new drug, not every single-isomer candidate will reach the clinic, but there is no doubt that the move to single-isomer agents is an important step forward in the search for better and safer drugs.

Recent advances in the epidemiology, prevention, diagnosis, and treatment of fungal pneumonia

Although pneumonia caused by fungi is not a common occurrence in the general population, disease in an enlarging immunocompromised population is encountered with increasing frequency. Fungal pneumonias are most frequently caused by Aspergillus spp., dimorphic fungi and Cryptococcus neoformans. Recent studies have identified risk factors of thrombocytopenia, environmental events (such as construction or renovation) and immunosuppressive drug therapies as being specific risk factors for invasive fungal disease in select patient populations. Diagnostic strategies to detect circulating antigens and polymerase chain reaction based detection systems have been explored to improve identification prior to the progressive advanced disease. Advances in prophylactic strategies include increased use of aerosolized formulations of amphotericin B, usually in conjunction with new and old systemic antifungal agents. Despite recent published guidelines for treatment of fungal pneumonia based on etiology, mortality remains high in some infections with advanced disease. Caspofungin, a new echinocandin antifungal, has recently been approved by the US Food and Drug Administration for the treatment of invasive Aspergillus infections in patients unresponsive to or unable to receive amphotericin B. A triazole antifungal, voriconazole, has shown promise in phase III clinical trials in patients with refractory fungal infections and is expected to be available in early 2002. Other echinocandin and triazole antifungals are under development in attempts to provide improved effective therapy for fungal pneumonia.

Simultaneous high-performance liquid chromatographic determination of SCH 59884 (phosphate ester prodrug of SCH 56592), SCH 207962 and SCH 56592 in dog plasma

SCH 59884 is an IV prodrug of SCH 56592, the broad-spectrum azole antifungal agent that is active both orally and intravenously in animal models of infection. SCH 56592 is in phase III clinical trials for the treatment of serious systemic fungal infections. SCH 59884 is a carboxylate ester of SCH 56592 with gamma-butyric acid phosphate. Following IV administration of SCH 59884, the compound is rapidly dephosphorylated to SCH 207962 which is then hydrolyzed to SCH 56592. A high-performance liquid chromatographic (HPLC) method was developed for the simultaneous determination of SCH 59884, SCH 207962 and SCH 56592 in plasma of dogs, a species used for safety evaluation. The HPLC analysis involved protein precipitation with methanol followed by separation on a C-18 column and quantitation by UV absorbance at 260 nm. The lower limits of quantification were 0.1 microg/ml for SCH 59884 and 0.05 microg/ml for SCH 207962 and SCH 56592 in dog plasma. The linearity for the three compounds was satisfactory as indicated by correlation coefficients (r) of >0.98, back-calculated concentrations and visual examination of the calibration curves. The precision and accuracy were satisfactory as shown by coefficients of variation (CV) ranging from 2.4 to 10.6%, and bias values ranging from -8.4 to 13.3%. Moreover, SCH 59884 and SCH 207962 were stable in dog plasma after being subjected to three freeze-thaw cycles. SCH 56592 had been shown earlier to be stable under these conditions. The assay was shown to be specific, accurate, precise, and reliable for use in pharmacokinetic and toxicokinetic studies.

Evaluation of Etest method for determining posaconazole MICs for 314 clinical isolates of Candida species

The performance of the Etest for posaconazole (SCH 56592) susceptibility testing of 314 isolates of Candida spp. was assessed against the National Committee for Clinical Laboratory Standards (NCCLS) microdilution broth method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35 degrees C. MICs were determined by Etest for all 314 isolates with RPMI agar containing 2% glucose (RPG agar) and were read after incubation for 48 h at 35 degrees C. The Candida isolates included C. albicans (n = 174), C. glabrata (n = 57), C. tropicalis (n = 31), C. parapsilosis (n = 39), C. krusei (n = 5), C. guilliermondii (n = 6), and C. lusitaniae (n = 2). The Etest results correlated well with reference MICs. Overall agreement was 95%, and agreements for individual species were as follows: C. krusei, 100%; C. albicans, 98%; C. tropicalis, 97%; C. glabrata, 93%; C. parapsilosis, 85%; C. guilliermondii, 83%; and C. lusitaniae, 50%. The problem of trailing end points was minimized with RPG agar, and good agreement with broth dilution MICs was obtained when discernible growth within an established ellipse was ignored. The Etest method using RPG agar appears to be a useful method for determining posaconazole susceptibilities of Candida species.

In vitro activities of posaconazole (Sch 56592) compared with those of itraconazole and fluconazole against 3,685 clinical isolates of Candida spp. and Cryptococcus neoformans

Posaconazole is a new investigational triazole with broad-spectrum antifungal activity. The in vitro activities of posaconazole were compared with those of itraconazole and fluconazole against 3,685 isolates of Candida spp. (3,312 isolates) and C. neoformans (373 isolates) obtained from over 70 different medical centers worldwide. The MICs of the antifungal drugs were determined by broth microdilution tests performed according to the National Committee for Clinical Laboratory Standards method using RPMI 1640 as the test medium. Posaconazole was very active against all Candida spp. (MIC at which 90% of the isolates were inhibited [MIC(90)], 0.5 microg/ml; 97% of MICs were < or =1 microg/ml) and C. neoformans (MIC(90), 0.5 microg/ml; 100% of MICs were < or =1 microg/ml). Candida albicans was the most susceptible species of Candida (MIC(90), 0.06 microg/ml), and Candida glabrata was the least susceptible (MIC(90), 4 microg/ml). Posaconazole was more active than itraconazole and fluconazole against all Candida spp. and C. neoformans. These results provide further evidence for the spectrum and potency of posaconazole against a large and geographically diverse collection of clinically important fungal pathogens.

Investigational antifungal agents

Several new antifungal agents, including novel compounds in familiar classes and entirely new classes targeting previously untapped mechanisms, are in various stages of the drug development process. Many new triazole antifungal agents are being studied, including voriconazole, posaconazole, and ravuconazole. The echinocandin antifungals, which represent a new class of antifungal agents, possess activity against a variety of fungal pathogens. The sodarin derivatives and nikkomycins are two additional classes of antifungals in early stages of development; future studies will determine their therapeutic usefulness.

In vitro antifungal activity of posaconazole against various pathogenic fungi

The antifungal activity of posaconazole (SCH56592), a new triazole antifungal, against stock cultures and fresh clinical isolates of a wide range of pathogenic fungi was compared with that of itraconazole, fluconazole and amphotericin B. Posaconazole inhibited growth of all the fungal species tested except Fusarium spp. at 1 mg/l or lower concentrations, showing a broad-spectrum antifungal activity. The activities of posaconazole for all the fungal species far surpassed those of fluconazole and were even superior to those of itraconazole for Aspergillus spp. as well as for many other fungal species.

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.

Antifungal activity and pharmacokinetics of posaconazole (SCH 56592) in treatment and prevention of experimental invasive pulmonary aspergillosis: correlation with galactomannan antigenemia

The antifungal efficacy, safety, and pharmacokinetics of posaconazole (SCH 56592) (POC) were investigated in treatment and prophylaxis of primary pulmonary aspergillosis due to Aspergillus fumigatus in persistently neutropenic rabbits. Antifungal therapy consisted of POC at 2, 6, and 20 mg/kg of body weight per os; itraconazole (ITC) at 2, 6, and 20 mg/kg per os; or amphotericin B (AMB) at 1 mg/kg intravenously. Rabbits treated with POC showed a significant improvement in survival and significant reductions in pulmonary infarct scores, total lung weights, numbers of pulmonary CFU per gram, numbers of computerized-tomography-monitored pulmonary lesions, and levels of galactomannan antigenemia. AMB and POC had comparable therapeutic efficacies by all parameters. By comparison, animals treated with ITC had no significant changes in outcome variables in comparison to those of untreated controls (UC). Rabbits receiving prophylactic POC at all dosages showed a significant reduction in infarct scores, total lung weights, and organism clearance from lung tissue in comparison to results for UC (P < 0.01). There was dosage-dependent microbiological clearance of A. fumigatus from lung tissue in response to POC. Serum creatinine levels were greater (P < 0.01) in AMB-treated animals than in UC and POC- or ITC-treated rabbits. There was no elevation of serum hepatic transaminase levels in POC- or ITC-treated rabbits. The pharmacokinetics of POC and ITC in plasma demonstrated dose dependency after multiple dosing. The 2-, 6-, and 20-mg/kg dosages of POC maintained plasma drug levels above the MICs for the entire 24-h dosing interval. In summary, POC at > or =6 mg/kg/day per os generated sustained concentrations in plasma of > or =1 microg/ml that were as effective in the treatment and prevention of invasive pulmonary aspergillosis as AMB at 1 mg/kg/day and more effective than cyclodextrin ITC at > or =6 mg/kg/day per os in persistently neutropenic rabbits.

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 and in vivo activities of SCH 56592 (posaconazole), a new triazole antifungal agent, against Aspergillus and Candida

SCH 56592 (posaconazole), a new triazole antifungal agent, was tested in vitro, and its activity was compared to that of itraconazole against 39 Aspergillus strains and to that of fluconazole against 275 Candida and 9 Cryptococcus strains. The SCH 56592 MICs for Aspergillus ranged from </=0.002 to 0.5 microg/ml, and those of itraconazole ranged from </=0.008 to 1 microg/ml. The SCH 56592 MICs for Candida and Cryptococcus strains ranged from </=0. 004 to 16 microg/ml, and those of fluconazole ranged from </=0.062 to >64 microg/ml. SCH 56592 showed excellent activity against Aspergillus fumigatus and Aspergillus flavus in a pulmonary mouse infection model. When administered therapeutically, the 50% protective doses (PD(50)s) of SCH 56592 ranged from 3.6 to 29.9 mg/kg of body weight, while the PD(50)s of SCH 56592 administered prophylactically ranged from 0.9 to 9.0 mg/kg; itraconazole administered prophylactically was ineffective (PD(50)s, >75 mg/kg). SCH 56592 was also very efficacious against fluconazole-susceptible, -susceptible dose-dependent, or -resistant Candida albicans strains in immunocompetent or immunocompromised mouse models of systemic infection. The PD(50)s of SCH 56592 administered therapeutically ranged from 0.04 to 15.6 mg/kg, while the PD(50)s of SCH 56592 administered prophylactically ranged from 1.5 to 19.4 mg/kg. SCH 56592 has excellent potential for therapy against serious Aspergillus or Candida infections.

Chiral high-performance liquid chromatographic analysis of antifungal SCH 56592 and evaluation of its chiral inversion in animals and humans

SCH 56592 is a novel triazole antifungal agent that is active both orally and intravenously in animal models of infection. This compound is in Phase II-III clinical trials for the treatment of systemic fungal infections. SCH 56592 is a single enantiomer with four stereogenic centers; therefore, it was necessary to evaluate the possible chiral inversion of this drug candidate in animals and humans. Thus, chiral high-performance liquid chromatographic (HPLC) methods have been developed to separate SCH 56592 from its diastereomers and to evaluate its chiral inversion in rats, dogs, cynomolgus monkeys, and humans. Chiral HPLC analysis involved the use of a Chiralcel OD column set at 39 degrees C with a mobile phase of hexane-ethanol-diethylamine and a fluorescence detector set at an excitation wavelength of 270 nm and an emission wavelength of 390 nm. Plasma or serum samples were subjected to solid phase extraction on a C(2) cartridge followed by HPLC analysis. The method was sensitive with a limit of quantitation of 0.1 microg/ml in dog serum. The linearity was satisfactory, as shown by correlations of >0.997 and by visual examination of the calibration curves. The precision and accuracy were satisfactory, as indicated by coefficients of variation (CV) ranging from 1.1 to 12.1% and bias values ranging from -11.0 to 9.0%. Chiral HPLC analysis indicated that SCH 56592 was not subjected to chiral inversion in rats, dogs, cynomolgus monkeys, and humans.

New drugs and novel targets for treatment of invasive fungal infections in patients with cancer

Invasive fungal infections have emerged as important causes of morbidity and mortality in profoundly immunocompromised patients with cancer. Current treatment strategies for these infections are limited by antifungal resistance, toxicity, drug interactions, and expense. In order to overcome these limitations, new antifungal compounds are being developed, which may improve our therapeutic armamentarium for prevention and treatment of invasive mycoses in high-risk patients with neoplastic diseases.

High-performance liquid chromatographic analysis of the anti-fungal agent SCH 56592 in dog serum

SCH 56592 is a novel triazole antifungal agent that is active both orally and intravenously. This compound is in phase II-III clinical trials for the treatment of systemic fungal infections. A high-performance liquid chromatographic (HPLC) method was developed for the analysis of SCH 56592 in serum of dogs, a species used for safety evaluation. The HPLC analysis involved protein precipitation with methanol followed by separation on a C18 column and quantitation by UV absorbance at 262 nm. The method was sensitive with a limit of quantification of 0.05 microg/ml in dog serum. The linearity was satisfactory as indicated by correlations of >0.996, in addition to visual examination of the calibration curves. The precision and accuracy were satisfactory as indicated by coefficients of variation (C.V.) ranging from 2.0 to 3.8%, and bias values ranging from -6.5 to 10%. Moreover, SCH 56592 was stable in dog serum after being subjected to three freeze-thaw cycles. The assay was shown to be sensitive, specific, accurate, precise, and reliable for use in pharmacokinetic or toxicokinetic studies.

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 and in-vivo activities of SCH56592 against Cryptococcus neoformans

The in-vitro and in-vivo activities of SCH56592, a triazole antifungal agent, against Cryptococcus neoformans were studied. MIC(90)s for 16 strains of C. neoformans measured by microdilution method (NCCLS M27-A) were 1 mg/L of SCH56592, 16 mg/L of fluconazole, 32 mg/L of flucytosine, and 0.5 mg/L of amphotericin B. In a murine model of pulmonary cryptococcosis, 10 mg/kg of SCH56592 was more effective than fluconazole. The fungal burden of the lung of animals treated with SCH56592 was significantly reduced (7.40 +/- 0.21 log(10) cfu/g), as compared with fluconazole (7.77 +/- 0.07 log(10) cfu/g) and control (7.79 +/- 0.1 log(10) cfu/g) (P < 0.01). For C. neoformans-infected mice following 7 days treatment with 10 mg/kg of SCH56592 there was a higher concentration in lung (3.36 +/- 0.62 ng/ml) than in plasma (2.16 +/- 0.86 ng/mL), and this was maintained for 12 h after administration.

Current and emerging azole antifungal agents

Major developments in research into the azole class of antifungal agents during the 1990s have provided expanded options for the treatment of many opportunistic and endemic fungal infections. Fluconazole and itraconazole have proved to be safer than both amphotericin B and ketoconazole. Despite these advances, serious fungal infections remain difficult to treat, and resistance to the available drugs is emerging. This review describes present and future uses of the currently available azole antifungal agents in the treatment of systemic and superficial fungal infections and provides a brief overview of the current status of in vitro susceptibility testing and the growing problem of clinical resistance to the azoles. Use of the currently available azoles in combination with other antifungal agents with different mechanisms of action is likely to provide enhanced efficacy. Detailed information on some of the second-generation triazoles being developed to provide extended coverage of opportunistic, endemic, and emerging fungal pathogens, as well as those in which resistance to older agents is becoming problematic, is provided.