Combination therapy in experimental invasive aspergillosis

Techniques for the Assessment of In Vitro and In Vivo Antifungal Combinations

Systemic fungal infections are associated with high mortality rates despite adequate treatment. Moreover, acquired resistance to antifungals is increasing, which further complicates the therapeutic management. One strategy to overcome antifungal resistance is to use antifungal combinations. In vitro, several techniques are used to assess drug interactions, such as the broth microdilution checkerboard, agar-diffusion methods, and time-kill curves. Currently, the most widely used technique is the checkerboard method. The aim of all these techniques is to determine if the interaction between antifungal agents is synergistic, indifferent, or antagonistic. However, the interpretation of the results remains difficult. Several methods of analysis can be used, based on different theories. The most commonly used method is the calculation of the fractional inhibitory concentration index. Determination of the usefulness of combination treatments in patients needs well-conducted clinical trials, which are difficult. It is therefore important to study antifungal combinations in vivo, in experimental animal models of fungal infections. Although mammalian models have mostly been used, new alternative animal models in invertebrates look promising. To evaluate the antifungal efficacy, the most commonly used criteria are the mortality rate and the fungal load in the target organs.

Combination therapy for the treatment of pulmonary mold infections

INTRODUCTION

Pulmonary mold infections are caused by ubiquitous organisms found in soil, water, and decaying vegetation, including Aspergillus spp., the Mucormycetes, hyaline molds, and dematiaceous (black) molds. Areas covered: These infections are often a challenge to diagnose and even more difficult to treat. Recently, antifungal combination therapy has emerged as a promising strategy to treat some forms of invasive mycoses, including pulmonary mold infections. Historically, this approach has been limited due to non-uniform interpretation criteria, variations in pharmacodynamic/pharmacokinetic properties of antifungals used in combination, and an inability to predict clinical success based on in vitro data and animal models. However, recent advances have helped mitigate some of these challenges. Expert commentary: In this paper, we explore what is known about the antifungal combination therapy in the treatment of pulmonary mold infections and explore how it may impact clinical practice. We pay particular attention to novel combinations and the challenges associated with the development of new antifungal agents.

Combining two antifungal agents does not enhance survival of Galleria mellonella larvae infected with Madurella mycetomatis

OBJECTIVE

To determine whether combination therapy would improve therapeutic outcome in eumycetoma caused by Madurella mycetomatis.

METHODS

Survival, colony-forming units (CFU), melanisation and histopathology in M. mycetomatis-infected Galleria mellonella larvae treated with amphotericin B, itraconazole, terbinafine or combinations thereof were determined.

RESULTS

Compared to larvae treated with 5% glucose, enhanced survival was obtained when M. mycetomatis-infected larvae were treated with amphotericin B, but not when they were treated with itraconazole or terbinafine. Combination therapy did not increase survival compared to 5% glucose-treated larvae, itraconazole-treated larvae or terbinafine-treated larvae. Compared to amphotericin B monotreatment, a significant decrease in survival was noted when this therapy was combined with either itraconazole or terbinafine. CFU, melanisation and histopathology did not differ between monotherapy, combination therapy or 5% glucose-treated larvae.

CONCLUSIONS

Combining different classes of antifungal agents did not enhance the survival of M. mycetomatis-infected G. mellonella larvae. Instead of improving the therapeutic outcome, combining either itraconazole or terbinafine with amphotericin B resulted in significantly lower survival rates of infected larvae than amphotericin B monotherapy. This experimental study does not provide support for the use of combined amphotericin B and itraconazole, combined itraconazole and terbinafine or combined terbinafine and amphotericin B and should be confirmed in other animal models.

Invasive pulmonary aspergillosis

In susceptible patients, invasive aspergillosis has a high incidence and a mortality of up to 80%. The diagnosis of this condition is difficult, especially in the early stages of the disease and, as a consequence, antifungal therapy, despite its expense and toxicity, is often initiated empirically. Until recently, there were very few effective antifungal agents for established invasive aspergillosis, but the introduction of two new drugs, voriconazole and caspofungin, has increased the treatment options. These newer antifungal therapies, combined with improved early diagnosis due to the introduction of newer microbiologic techniques, offer the hope that there will be a significant improvement in the substantial morbidity and mortality associated with invasive aspergillosis over the next 5 years.

[Combined effect of micafangin and itraconazole on severe aspergillosis of the bilateral pleural cavities in a patient with Wegener's granulomatosis]

Visceral fungal infections are difficult to manage in patients with collagen diseases and immunocompromised hosts. In particular aspergillosis can be a life-threatening complication in these patients. Here we report that combined use of two antifungal agents (micafangin and itraconazole) was effective against severe aspergillosis of the bilateral pleural cavities in a 48-year old male patient diagnosed with Wegener's granulomatosis. Immunosuppressive therapy with corticosteroids and cyclophosphamides improved his nasal and pulmonary symptoms, but inflammation of the bilateral pleural cavities caused bronchial fistulas. Aspergillus fumigatus then infected the bilateral pulmonary cavities through these fistulas. This patient was treated with combined therapy of ITCZ and MCFG was given to this patient because of the risk of renal dysfunction associated with AMPH-B. After 5 weeks of treatment his clinical findings had improved and the fungus was suppressed.

Efficacy and pharmacodynamics of flucytosine monotherapy in a nonneutropenic murine model of invasive aspergillosis

The therapeutic efficacy of flucytosine (5FC) monotherapy and the pharmacodynamic index predictive of efficacy were evaluated in a nonneutropenic mouse model of acute invasive aspergillosis. Mice were infected intravenously with an Aspergillus fumigatus isolate (the median MICs of 5FC were 128 mug/ml under the standard condition, 0.5 microg/ml at pH 6.0, and 0.031 microg/ml at pH 5.0) 2 h prior to the start of therapy and were treated for 7 days with different 5FC dosing regimens. The total doses ranged from 50 to 800 mg/kg of body weight/day and were administered at 6-, 12-, and 24-h intervals. The efficacy was assessed by means of survival. The survival rates of the treatment groups ranged from 40 to 90%, while the survival rate of the control group was 20%. The efficacy found depended primarily on the total daily dose. However, the power of our sample size may have been too low to exclude an effect of dose fractionation. The pharmacodynamic index that most strongly correlated with the efficacy was the area under the serum concentration-time curve and MIC ratio (R(2) = 0.86). We conclude that 5FC monotherapy is efficacious in a murine Aspergillus fumigatus infection model.

Invasive pulmonary aspergillosis in solid organ and bone marrow transplant recipients

BACKGROUND

Invasive pulmonary aspergillosis (IPA) remains a major cause of mortality in transplant recipients. New strategies in therapy are needed.

METHODS

We prospectively followed all solid organ and bone marrow transplant recipients from January 1998 to January 2003 who showed pulmonary infiltrates. We retrospectively analyzed all of the patients diagnosed as having IPA. Clinical and epidemiological data were collected. Influence of new treatment strategies on survival was also analyzed.

RESULTS

Thirty-one cases of API were found: 8 definite, 18 probable, 5 possible among recipients of liver (11), bone marrow (9), kidney (7), kidney-pancreas (3), and heart (1) transplants. Five patients (16%) were previously receiving antifungal prophylaxis. The most common symptoms were fever (74%) and dyspnea and dry cough (48%). Six cases (19%) showed dissemination to extrapulmonary sites: central nervous system (CNS) in five and bone in one. The most common radiographic patterns were alveolar infiltrates (58%); the lesions were usually diffuse and bilateral (58%). The most common Aspergillus species identified was A. fumigatus (74%). The test to detect Aspergillus antigen (galactomannan) in serum performed in 13 cases, was positive in eight (61%). The crude mortality rate was 61% (19 of 31), but in patients on mechanical ventilation, it was 94% (OR 88, IC 95%: 7.1-1094), and in patients with CNS involvement, it was 100%. The influence of the different treatment regimens on survival was analyzed in definite and probable cases: Group 1 (12) included patients who received conventional monotherapy and group 2 (12) patients received combination antifungal therapy or liposomal amphotericin B (1-AMB) at high doses. The mortality in group 1 was 83% (10 of 12), and in group 2 it was 42% (5 of 12) (P < 0.05).

CONCLUSIONS

The mortality rate of IPA remains high, especially among patients with CNS involvement or those under mechanical ventilation. Combined antifungal therapy or monotherapy with 1-AMB at high doses significantly reduced mortality compared with conventional monotherapy.

Antifungal combination therapy: clinical potential

Combination antifungal therapy has been an area of research and clinical interest since systemic antifungals became available decades ago. In vitro and clinical data were generated for some of the more common invasive fungal infections, especially candidiasis, but until very recently few clinical studies were performed. The first invasive fungal infection to be examined in clinical trials with adequate statistical power was cryptococcal meningitis and several of these trials stand out as classical studies in the clinical evaluation of combination antifungal therapy. More recently, since the availability of the newer antifungal agents, including the echinocandins and extended-spectrum triazoles, there has been a growing interest in examining combination antifungal therapy for invasive fungal disease, especially invasive aspergillosis. This is by no means a comprehensive review of all existing experimental data. Instead, the focus is on the clinical data that have been generated to date and on providing insights into potential future clinical directions. For instance, recent clinical data for cryptococcosis confirm that amphotericin B plus flucytosine is the most active combination for patients with cryptococcal meningitis. A recently completed clinical trial in candidaemia suggests a trend towards improved outcomes among patients receiving amphotericin B plus fluconazole versus fluconazole alone. In aspergillosis, several experimental models suggest benefit of a variety of antifungal combinations, but have not been confirmed in prospective clinical trials. Ultimately, the goal is to provide the reader with a comprehensive but useful review to this complicated and often confusing therapeutic dilemma.

The contribution of animal models of aspergillosis to understanding pathogenesis, therapy and virulence

Animal models of aspergillosis have been used extensively to study various aspects of pathogenesis, innate and acquired host-response, disease transmission and therapy. Several different animal models of aspergillosis have been developed. Because aspergillosis is an important pulmonary disease in birds, avian models have been used successfully to study preventative vaccines. Studies done to emulate human disease have relied on models using common laboratory animal species. Guinea pig models have primarily been used in therapy studies of invasive pulmonary aspergillosis (IPA). Rabbits have been used to study IPA and systemic disease, as well as fungal keratitis. Rodent, particularly mouse, models of aspergillosis predominate as the choice for most investigators. The availability of genetically defined strains of mice, immunological reagents, cost and ease of handling are factors. Both normal and immunosuppressed animals are used routinely. These models have been used to determine efficacy of experimental therapeutics, comparative virulence of different isolates of Aspergillus, genes involved in virulence, and susceptibility to infection with Aspergillus. Mice with genetic immunological deficiency and cytokine gene-specific knockout mice facilitate studies of the roles cells, and cytokines and chemokines, play in host-resistance to Aspergillus. Overall, these models have been critical to the advancement of therapy, and our current understanding of pathogenesis and host-resistance.

Advances and challenges in management of invasive mycoses

Invasive mycoses pose a major diagnostic and therapeutic challenge. Advances in antifungal agents and diagnostic methods offer the potential for improved outcomes in patients with these infections, which are often lethal. Many fungal pathogens occur almost exclusively in opportunistic settings--in the immunocompromised host--and these infections are the focus of this review. Several areas of ongoing challenge remain, including the emergence of resistant organisms and the absence of reliable markers for early identification of patients at risk of developing invasive fungal disease. This Seminar reviews the changing epidemiology of invasive mycoses, new diagnostic methods, and recent therapeutic options and current management strategies for these opportunistic pathogens.

Successful antifungal combination therapy with voriconazole and caspofungin

A 12-year-old boy in third remission of an acute lymphoblastic leukaemia developed infection of lung and paranasal sinuses with Aspergillus flavus in neutropenia. Because of the high risk of leukaemia-relapse bone marrow transplantation (BMT) from a matched unrelated donor was carried out despite invasive pulmonary aspergillosis (IPA). It is the first reported patient with IPA, who was successfully treated by the antifungal combination therapy with voriconazole and caspofungin therapy during myeloablative BMT. Despite 6 weeks of aplasia, a dramatic decrease of lesions highly suggestive of aspergillosis was observed after BMT. Since discharge-oral voriconazole monotherapy has been continued.

Interaction between posaconazole and amphotericin B in concomitant treatment against Candida albicans in vivo

The interaction of posaconazole and amphotericin B was evaluated in concomitant treatment of Candida albicans systemic infections in immunocompetent mice by using four strains of C. albicans with different susceptibilities to fluconazole. Posaconazole and amphotericin B were each tested at four dose levels alone and in all possible combinations against each C. albicans strain. Survival curves of mice treated with combinations of posaconazole and amphotericin B were statistically compared with those of mice treated with the component monotherapies. Of the 64 total combinations evaluated against the C. albicans strains (16 combinations per strain), 20.3% were more effective in prolonging mouse survival than both of the monotherapies, 45.3% were more effective than one of the monotherapies, and 32.8% were similar to both monotherapies. No evidence of antagonism was observed between posaconazole and amphotericin B in this mouse model, consistent with in vitro results against the same strains.

Considerations in Clinical Trials of Combination Antifungal Therapy

The cure rate for serious fungal diseases with currently available agents used as monotherapy is not optimal. The introduction of new classes of antifungal drugs in the last few years naturally leads to the hypothesis that antifungal drugs used in combination may be more effective than the same drugs used alone. The design and interpretation of combination therapy studies raise challenges beyond those encountered when drugs are studied as monotherapy in the treatment of a disease. The definition of combination therapy, the study design, the selection of appropriate patient populations, and the selection of end points, as well as practical considerations, are all important in the design and interpretation of clinical trials of combination therapies. Although combination therapies hold the promise of improved efficacy, it is important to prove this hypothesis, because they also may be associated with increased toxicity and increased drug costs. A careful consideration of study design factors before the initiation of a trial will help obtain the most useful information for patients in this important area.

Combinations of antifungal agents in therapy--what value are they?

Concurrent or sequential antifungal treatment for invasive mycoses has been typically considered as an option to improve results of monotherapy. However, data on the efficacy of combination therapy are sparse and consist largely of results from studies in vitro and experimental animal models. These studies have yielded controversial results depending on the criteria used to evaluate the antifungal interaction. Several combinations that showed synergy in vitro failed to do so in animal models. Overall, apart from cryptococcal infections, combined antifungal therapy is not significantly better than monotherapy in terms of clinical efficacy. It is questionable whether combination therapy should be used in most cases as there is a lack of evidence from well-designed clinical trials. However, combination therapy could be an alternative to monotherapy for patients with invasive infections that are difficult to treat, such as those due to multi-resistant species and for those who fail to respond to standard treatment.

Toward more effective antifungal therapy: the prospects of combination therapy

The availability of new antifungal agents with unique mechanisms of action and improved tolerability has widened the possibilities for the use of combination antifungal therapy for difficult-to-treat opportunistic mycoses. However, the use of this therapy is largely governed by empiricism, especially in patients with invasive mould infections, for whom there is a tremendous need to improve outcomes. Because of the difficulties associated with the design and conduct of clinical trials of combination antifungal therapy for opportunistic mycoses, the majority of the studies evaluating antifungal combinations are still performed in the laboratory or using animal models of infection. However, the methods used to assess combined antifungal effects in vitro and in animals are poorly standardized, and there is little evidence that data generated from these studies can be translated in treating human mycotic infections. Despite the empiricism of combination antifungal therapy, certain principles help guide the use and study of these regimens.

Resolution of orbitocerebral aspergillosis during combination treatment with voriconazole and amphotericin plus adjunctive cytokine therapy

Orbitocerebral aspergillosis has a very high fatality rate and cure is unusual. We describe the successful management of a child with cereberal aspergillosis who had a dramatic response to therapy with a combination of liposomal amphotericin and voriconazole with adjunctive cytokine therapy during immunosuppresive chemotherapy for acute lymphoblastic leukaemia.

Combination chemotherapy for invasive fungal infections: what laboratory and clinical studies tell us so far

Despite potential benefits, few objective clinical data (with the exception of cryptococcocal meningitis) are available supporting the routine use of combination antifungal regimens in patients with invasive mycoses, importantly aspergillosis or candidiasis. There is considerable debate on what constitutes synergy or antagonism in vitro and whether these laboratory findings are translated to beneficial interactions in patients. Given the lack of rigorous clinical data, a better understanding of the important concepts for the justification of the clinical and pharmacoeconomic threshold of antifungal therapy is needed. Such concepts include standardized methods for screening antifungal combinations in culture or in animals and collaborative efforts to collect clinical data on the efficacy and safety of combination regimens.

Disseminated aspergillosis due to Aspergillus flavus in an experimental model: efficacy of azole therapy

The aim of this investigation was to create a reproducible experimental model of disseminated Aspergillus flavus aspergillosis, and to compare the relative therapeutic efficacies of itraconazole and fluconazole in this model. Temporarily immunosuppressed male Wistar rats received intravenous challenge by A. flavus conidia. Treatment was initiated 24 h later with oral itraconazole (1 mg kg-1 BW day-1), oral fluconazole (1 mg kg-1 BW day-1) or excipient only (infected-untreated rats); this was continued for 10 days. At this time, although 100% mortality had occurred among all infected-untreated rats, no mortality was noted among the control-uninfected, infected-itraconazole-treated or infected-fluconazole-treated rats. After killing, essential organs were processed for microbiological and histopathological studies. Aspergillus flavus was recovered in high colony counts from the organs of infected-untreated rats (lungs > liver > brain > kidneys), but in significantly lower colony counts, or not at all, from the organs of itraconazole-treated and fluconazole-treated rats. Histopathological alterations were pronounced in tissues of infected-untreated rats, but less so in treated rats. These data suggest that administration of itraconazole or fluconazole sufficiently early may prevent, or retard, progression of lesions in disseminated aspergillosis.

Antifungal pharmacotherapy for invasive mould infections

The incidence of invasive mould infections is increasing and is associated with significant morbidity and mortality. Among the most prevalent of these infections are those caused by Aspergillus and Fusarium species. Invasive disease caused by moulds frequently presents as a pulmonary infection, but haematogenous infection can occur. Some moulds cause cutaneous disease through either direct inoculation of the skin or secondary spread to the skin after dissemination from another body site. Early diagnosis can often be difficult and, unfortunately, diagnosis occurs late in the course of illness in many cases. Treatment options have historically been limited by the need for intravenous administration (amphotericin B), significant toxicities (amphotericin B), lack of reliable in vitro activity (e.g., amphotericin B in Fusarium and Scedosporium apiospermum infections) and relative lack of clinical experience with newer agents. The recent approval of voriconazole (Vfend, Pfizer) introduces a treatment option that demonstrates both in vitro and in vivo activity against a variety of moulds. With the recent development of the new echinocandin class of antifungal agents and newer broad-spectrum azole antifungal agents with in vitro mould activity, there is a renewed emphasis on fungal treatment strategies. Antimould therapy presents challenges in adverse effect avoidance and management, drug interactions and pharmacoeconomic considerations. Furthermore, combination therapy is being explored with these various new antifungal agents. The administration of an optimal fungicidal therapy early in the course of the illness and control of the underlying disease are vital to prevent complications and mortality from these tenacious mycoses.

Itraconazole preexposure attenuates the efficacy of subsequent amphotericin B therapy in a murine model of acute invasive pulmonary aspergillosis

Antagonism has been described in vitro and in vivo for azole-polyene combinations against Aspergillus species. Using an established murine model of invasive pulmonary aspergillosis, we evaluated the efficacy of several amphotericin B (AMB) dosages given alone or following preexposure to itraconazole (ITC). Mice were immunosuppressed with cortisone acetate and cyclophosphamide. During immunosuppression, animals were administered either ITC solution (50 mg/kg of body weight) or saline by oral gavage twice daily for 3 days prior to infection. Infection was induced by intranasally inoculating mice with a standardized conidial suspension (1 x 10(8) CFU/ml) of Aspergillus fumigatus strain AF 293. AMB was then administered by daily intraperitoneal injections (0.25, 0.5, 1.0, and 3.0 mg/kg) starting 24 h after inoculation and continuing for a total of 72 h. Drug pharmacokinetics of AMB and ITC in plasma were determined by high-performance liquid chromatography. Four different endpoints were used to examine the efficacy of antifungal therapy: (i) viable counts from harvested lung tissue (in CFU per milliliter), (ii) the whole-lung chitin assay, (iii) mortality at 96 h, and (iv) histopathology of representative lung sections. At AMB doses of >0.5 mg/kg/day, fewer ITC-preexposed mice versus non-ITC-preexposed mice were alive at 96 h (0 to 20 versus 60%, respectively). At all time points, the fungal lung burden was consistently and significantly higher in animals preexposed to ITC, as measured by the CFU counts (P = 0.001) and the chitin assay (P = 0.03). Higher doses of AMB did not overcome this antagonism. ITC preexposure was associated with poorer mycological efficacy and survival in mice treated subsequently with AMB for invasive pulmonary aspergillosis.

Efficacy of caspofungin alone and in combination with voriconazole in a Guinea pig model of invasive aspergillosis

The antifungal activity of caspofungin acetate (CAS) alone and in combination with voriconazole (VRC) was evaluated in an immunosuppressed transiently neutropenic guinea pig model of invasive aspergillosis. Guinea pigs were immunosuppressed with triamcinolone at 20 mg/kg of body weight/day subcutaneously beginning 4 days prior to lethal intravenous challenge with Aspergillus fumigatus and were made temporarily neutropenic with cyclophosphamide administered at 150 mg/kg intraperitoneally (i.p.) 1 day prior to challenge. Therapy with i.p. CAS at 1 and 2.5 mg/kg/day (with and without oral VRC at 5 mg/kg/day), oral VRC at 5 mg/kg/day, or i.p. amphotericin B (AMB) at 1.25 mg/kg/day was begun 24 h after challenge and was continued for 5 days. Mortality occurred in 12 of 12 untreated controls, whereas mortality occurred in 4 of 12 and 6 of 12 guinea pigs treated with CAS at 1 and 2.5 mg/kg/day, respectively, and in 3 of 12 guinea pigs treated with AMB. No mortality occurred among animals treated with CAS at 1 mg/kg/day plus VRC at 5 mg/kg/day, CAS at 2.5 mg/kg/day plus VRC at 5 mg/kg/day, or VRC at 5 mg/kg/day alone. Both CAS regimens increased the survival times and reduced the colony counts in tissue compared with those for the controls. Treatment with VRC and AMB significantly reduced the colony counts in the tissues of selected animals compared with those in the tissues of the controls. Treatment with VRC and AMB also resulted in reductions in colony counts in tissues compared with those in the tissues of animals treated with CAS (the difference was not statistically significant) and improved the survival times but did not sterilize tissues. Combination therapies with CAS plus VRC at either dose reduced colony counts in tissues 1,000-fold over those for the controls and were the only regimens that significantly reduced the numbers of positive cultures. The combinations of CAS plus VRC were highly effective in this model and should be further evaluated for use against invasive aspergillosis.

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.

Efficacies of two new antifungal agents, the triazole ravuconazole and the echinocandin LY-303366, in an experimental model of invasive aspergillosis

The efficacy of ravuconazole, a new triazole antifungal agent, and the echinocandin LY-303366 were evaluated in an immunosuppressed, temporarily leukopenic rabbit model of invasive aspergillosis. Oral therapy with ravuconazole at a dosage of 30 mg/kg of body weight per day or the echinocandin LY-303366, given intravenously in a dosage of 5 or 10 mg/kg, was begun 24 h after a lethal or sublethal challenge, and results were compared with those for amphotericin B therapy and untreated controls. Prophylaxis was also studied with LY-303366 given at a dosage of 5 or 10 mg/kg/day 48 h before lethal or sublethal challenge. Ravuconazole eliminated mortality, cleared aspergillus antigen from the serum, and eliminated Aspergillus fumigatus organisms from tissues of both lethally and sublethally challenged immunosuppressed animals with invasive aspergillosis. Although LY-303366, at both doses, prolonged survival and reduced aspergillus antigenemia, it did not eliminate aspergillus organisms from organ tissues. The half-lives of ravuconazole and LY-303366 in rabbits were 13 and 12.5 h, respectively, and no accumulation of either drug was seen after 6 days of treatment. Although LY-303366 showed activity in this rabbit model of invasive aspergillosis, ravuconazole was the more active agent, comparable to amphotericin B. Additional studies are needed to determine the potential of ravuconazole for use in the treatment of this infection.

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.

Invasive aspergillosis. Disease spectrum, treatment practices, and outcomes. I3 Aspergillus Study Group

A review of representative cases of invasive aspergillosis was conducted to describe current treatment practices and outcomes. Eighty-nine physicians experienced with aspergillosis completed case forms on 595 patients with proven or probable invasive aspergillosis diagnosed using modifications of the Mycoses Study Group criteria. Pulmonary disease was present in 56%, with disseminated infection in 19%. The major risk factors for aspergillosis were bone marrow transplantation (32%) and hematologic malignancy (29%), but patients had a variety of underlying conditions including solid organ transplants (9%), AIDS (8%), and pulmonary diseases (9%). Overall, high antifungal failure rates occurred (36%), and complete antifungal responses were noted in only 27%. Treatment practices revealed that amphotericin B alone (187 patients) was used in most severely immunosuppressed patients while itraconazole alone (58 patients) or sequential amphotericin B followed by itraconazole (93 patients) was used in patients who were less immunosuppressed than patients receiving amphotericin B alone. Response rate for patients receiving amphotericin B alone was poor, with complete responses noted in only 25% and death due to or with aspergillosis in 65%. In contrast, patients receiving itraconazole alone or following amphotericin B had death due to or with Aspergillus in 26% and 36%, respectively. These results confirm that mortality from invasive aspergillosis in severely immunosuppressed patients remains high even with standard amphotericin B. Improved responses were seen in the less immunosuppressed patients receiving sequential amphotericin B followed by itraconazole and those receiving itraconazole alone. New approaches and new therapies are needed to improve the outcome of invasive aspergillosis in high-risk patients.

Effect of sequential combination of amphotericin B and azole antifungal agents against Aspergillus fumigatus

Patients with aspergillosis have a poor prognosis because there are no effective antifungal agents except for amphotericin B. However, administration of amphotericin B is limited in immunocompromised patients due to its toxicity, which includes impairment of renal function. We attempted to evaluate the efficacy of a sequential combination of antifungal agents against Aspergillus fumigatus strain. The in vitro effects of sequential combinations of antifungal agents against five strains of Aspergillus fumigatus were determined by assessing changes in the wet weight of mycelial cells. The effect of a sequential combination was examined by pretreating mycelial cells with an antifungal agent, followed by the addition of a second antifungal agent. Pretreatment with amphotericin B (AMPH) followed by miconazole (MCZ) or fluconazole (FLCZ) resulted in better in vitro effects compared with the effect of simultaneous use of the agents. In contrast, pretreatment of mycelial cells with azole antifungal agents, other than MCZ, followed by AMPH, resulted in an increase in the wet weight compared with that recorded after simultaneous incubation with AMPH and azole antifungal agents. Our results showed that combined treatment, of AMPH followed by MCZ or FLCZ, inhibited the growth of A. fumigatus, suggesting that such a regimen may be effective against aspergillosis.

Antifungal agents. Part I. Amphotericin B preparations and flucytosine

Traditionally, amphotericin B has been the cornerstone of antifungal treatment. Toxicity, however, is a major dose-limiting factor of amphotericin B deoxycholate. Nevertheless, it continues to have a major role in the treatment of deep-seated mycotic infections. Recently, less nephrotic lipid formulations, including amphotericin B lipid complex, amphotericin B cholesteryl sulfate, and liposomal amphotericin B, have been introduced. The pharmacologic properties, main indications, recommended dosages, related costs, and adverse effects of these various preparations are summarized in this review. Orally administered flucytosine is useful in certain infections, particularly cryptococcal meningitis, but it should be used with caution in patients with renal insufficiency.

Antifungal combination therapy: where we stand

Amphotericin B has been used in combination, simultaneously or sequentially, with fluconazole and itraconazole. However, there are no data from clinical trials to suggest the most appropriate use of these drug combinations. In vitro work has consistently described antagonism of polyenes and azoles, but new work suggests that hydrophilic azoles (e.g. fluconazole) with amphotericin B may not result in antagonistic effects, whereas lipophilic azoles (e.g. ketoconazole, itraconazole) antagonize the antifungal effects of amphotericin B. Experimental studies in animals with invasive candidiasis show that fluconazole and amphotericin B are not antagonistic and may be additive in their effects. In contrast, itraconazole and amphotericin B are antagonistic in this same murine candidiasis model. In animals infected with Aspergillus, itraconazole plus amphotericin B seem to be antagonistic when used simultaneously and possibly when used sequentially. Nevertheless, initial therapy with amphotericin B followed by itraconazole in patients with aspergillosis is a common clinical strategy. Recent data and concepts concerning the combined use of available antifungal drugs are discussed in this paper.

Efficacy of deoxycholate amphotericin B and unilamellar liposomal amphotericin B in prophylaxis of experimental Aspergillus fumigatus endocarditis

OBJECTIVE

To evaluate and compare in vivo the protective efficacy of unilamellar liposomal amphotericin B (L-AmB) with that of deoxycholate amphotericin B (D-AmB) in experimental endocarditis.

MATERIAL AND METHODS

In the rabbit model of experimental Aspergillus fumigatus endocarditis, two doses of each antifungal agent (1.5 mg/kg each) were administered intravenously at 4 hours and at 30 minutes before challenge with an inoculum of A. fumigatus. Three days later, the animals were sacrificed, and the aortic vegetations were analyzed.

RESULTS

All 19 animals that did not receive chemoprophylaxis acquired endocarditis. In contrast, endocarditis developed in 2 of 10 animals pretreated with D-AmB (P < 0.01) and 3 of 8 animals pretreated with L-AmB (P < 0.01). Both D-AmB and L-AmB prevented the development of endocarditis due to A. fumigatus and decreased the concentration of fungi in the aortic vegetations by more than 1 log10.

CONCLUSION

In the rabbit experimental model of Aspergillus endocarditis, D-AmB and L-AmB were equally effective in reducing the incidence of the infection and the tissue burden of fungi.

Combination therapy with amphotericin B and fluconazole against invasive candidiasis in neutropenic-mouse and infective-endocarditis rabbit models

Although there are an increasing number of new antifungal agents available, the morbidity and mortality due to invasive mycoses remain high. The high rates of polyene toxicities and the development of azole resistance have raised the issue of using antifungal agents of these classes in combination, despite theoretical concerns regarding antagonism between such agents. This study was designed to evaluate the in vivo efficacy of combined therapy with amphotericin B and fluconazole against Candida albicans. Two distinct animal models were used in this study: a neutropenic-mouse model of hematogenously disseminated candidiasis and the infective-endocarditis rabbit model. Treatment efficacy was assessed by determining reductions in mortality as well as decreases in tissue fungal densities. In the neutropenic-mouse model, amphotericin B, as well as combination therapy, significantly prolonged survival compared to untreated controls (P < 10(-5) and P = 0.001, respectively). The fungal densities in the kidneys of neutropenic mice were significantly reduced with either amphotericin B monotherapy or amphotericin B-fluconazole combined therapy compared to those of controls (P < 10(-6)). Fluconazole monotherapy also reduced fungal densities in the kidneys; however, this decrease was not statistically significant (P = 0.17). In contrast, treatment with either fluconazole alone or combined with amphotericin B (but not amphotericin B monotherapy) significantly decreased fungal densities in the brain (P = 0.025). In the rabbit endocarditis model, amphotericin B monotherapy or combined therapy significantly decreased fungal densities in cardiac vegetations (P < 0.01 versus the controls). Although no significant antagonism was seen when fluconazole was given in combination with amphotericin B, combination therapy did not augment the antifungal activity of amphotericin B.

Recent progress and current problems in treatment of invasive fungal infections in neutropenic patients

Invasive fungal infections, including disseminated candidiasis and invasive pulmonary aspergillosis, are important causes of morbidity and mortality in neutropenic patients. The recent development of fluconazole, itraconazole, lipid formulations of amphotericin B, and recombinant cytokines have expanded our therapeutic armamentarium. Clinical trials have elucidated new strategies for utilizing these compounds in the prevention and treatment of opportunistic mycoses. The population of more severely immunocompromised patients, however, continues to expand and the spectrum of drug-resistant fungi, including but not limited to Candida spp, Fusarium spp, Zygomycetes, and dematiaceous moulds, continues to evolve, thus presenting new challenges to recent therapeutic advances. Development of new antifungal chemotherapeutic agents and novel approaches for augmentation of host response will be required to meet these new mycologic challenges.

Efficacy of UK-109496, a new azole antifungal agent, in an experimental model of invasive aspergillosis

The efficacy of UK-109496, a new azole antifungal agent, was evaluated in an immunosuppressed, temporarily leukopenic rabbit model of invasive aspergillosis. Oral therapy with UK-109496 at a dosage of 10 or 15 mg/kg of body weight every 8 h was begun 24 h after a lethal or sublethal challenge, and results were compared with those for amphotericin B therapy and untreated controls. UK-109496 eliminated mortality and also reduced the tissue burden of Aspergillus fumigatus 10- to 100-fold in liver and kidney tissues and to a lesser degree in lung tissue, and at the higher dose, no viable organisms were recovered from brain tissue from these animals. Both dosages of UK-109496 decreased or eliminated circulating antigen. The half-life of UK-109496 in rabbits was 2.5 to 3 h, and no accumulation of drug was seen even after 15 doses in either uninfected or infected animals. Thus, UK-109496 shows activity in this rabbit model of invasive aspergillosis. Additional studies are needed to determine the potential of the drug for use in the treatment of this infection.

Invasive aspergillosis in systemic lupus erythematosus

Invasive aspergillosis is seldomly described in systemic lupus erythematosus. We present two cases of aspergillosis and review 21 cases reported between 1957 and 1994. The typical clinical presentation is fever and cough in a hospitalized SLE patient previously treated with corticosteroids, immunosuppressors, and broad-spectrum antibiotics. Unlike aspergillosis in other conditions, granulocytopenia is uncommon. Chest radiographs show diffuse or patchy infiltration of lung fields. Diagnosis was suspected premortem in 2 patients. Aspergillus fumigatus was identified or isolated in sputum or parenchimal tissues in the majority of cases. Twenty-two patients died (95%). The finding of hyphae in the sputum of a systemic lupus erythematosus patient with a suggestive clinical picture should lead to bronchoscopy, bronchoalveolar lavage, and lung biopsy. Proof of diagnosis will come from the demonstration of hyphae in tissues and isolation of aspergillus from tissue cultures. Long-term therapy with amphotericin B alone or in combination with fluorocytosine or itraconazole may help improve survival.

Combination therapy of murine invasive candidiasis with fluconazole and amphotericin B

A study was performed to assess the in vivo relevance of the in vitro antagonism between fluconazole and amphotericin B against Candida albicans. Combinations of fluconazole and amphotericin B were explored for their efficacies against acute (100% mortality in 2 to 5 days) or less acute (100% mortality in 30 days) invasive candidiasis infections in mice with healthy immune systems and immunocompromised mice. Treatment efficacy was assessed by protection from mortality and/or a reduction in the fungal burden in tissue. In models of acute infection in mice with healthy immune systems or less acute infection in immunocompromised mice, combinations of fluconazole and amphotericin B were superior to fluconazole alone, and the effects were at least additive. Combination therapy was at least as efficacious as amphotericin B alone. In a different model of less acute infection in mice with healthy immune systems, combinations of fluconazole and amphotericin B showed no interactions and were no better than either drug alone. We conclude that combination therapy with fluconazole and amphotericin B is not antagonistic in vivo, in contrast to published in vitro studies, and, consequently, suggest that combination therapy should be considered in the management of clinical candidiasis.

Monoclonal antibodies against a 97-kilodalton antigen from Aspergillus flavus

We prepared a panel of five monoclonal antibodies (MAbs) directed against Aspergillus flavus that all reacted against one 97-kDa antigen by western blot (immunoblot). Flow cytometry demonstrated that these antibodies bound (in increasing degrees) to all morphologic stages of A. flavus growth: conidia, swollen conidia, and hyphae. Cross-reactivity among species was examined by enzyme-linked immunosorbent assay of fungal culture filtrates. Four MAbs reacted with 10 of 11 A. flavus isolates, and the fifth one reacted with 9 of them. One MAb also reacted with A. fumigatus, two reacted with A. niger, A. wentii, and A. nidulans, and all five reacted with A. ochraceus. None reacted with A. terreus, A. glaucus, A. versicolor, or a Penicillium species. Each MAb bound to A. flavus hyphae in formalin-fixed paraffin sections of a muscle biopsy from a confirmed human case of invasive aspergillosis. In summary, these MAbs identified a 97-kDa antigen found on A. flavus that is both surface bound and an exoantigen. Either the same or a cross-reacting antigen is present in A. fumigatus and other Aspergillus species.