Combined therapy with fluconazole and flucytosine in murine cryptococcal meningitis

Invasion of the central nervous system by Cryptococcus neoformans requires a secreted fungal metalloprotease

Cryptococcus spp. cause life-threatening fungal infection of the central nervous system (CNS), predominantly in patients with a compromised immune system. Why Cryptococcus neoformans has this remarkable tropism for the CNS is not clear. Recent research on cerebral pathogenesis of C. neoformans revealed a predominantly transcellular migration of cryptococci across the brain endothelium; however, the identities of key fungal virulence factors that function specifically to invade the CNS remain unresolved. Here we found that a novel, secreted metalloprotease (Mpr1) that we identified in the extracellular proteome of C. neoformans (CnMpr1) is required for establishing fungal disease in the CNS. Mpr1 belongs to a poorly characterized M36 class of fungalysins that are expressed in only some fungal species. A strain of C. neoformans lacking the gene encoding Mpr1 (mpr1Δ) failed to breach the endothelium in an in vitro model of the human blood-brain barrier (BBB). A mammalian host infected with the mpr1Δ null strain demonstrated significant improvement in survival due to a reduced brain fungal burden and lacked the brain pathology commonly associated with cryptococcal disease. The in vivo studies further indicate that Mpr1 is not required for fungal dissemination and Mpr1 likely targets the brain endothelium specifically. Remarkably, the sole expression of CnMPR1 in Saccharomyces cerevisiae resulted in a robust migration of yeast cells across the brain endothelium, demonstrating Mpr1's specific activity in breaching the BBB and suggesting that Mpr1 may function independently of the hyaluronic acid-CD44 pathway. This distinct role for Mpr1 may develop into innovative treatment options and facilitate a brain-specific drug delivery platform.

IMPORTANCE

Cryptococcus neoformans is a medically relevant fungal pathogen causing significant morbidity and mortality, particularly in immunocompromised individuals. An intriguing feature is its strong neurotropism, and consequently the hallmark of cryptococcal disease is a brain infection, cryptococcal meningoencephalitis. For C. neoformans to penetrate the central nervous system (CNS), it first breaches the blood-brain barrier via a transcellular pathway; however, the identities of fungal factors required for this transmigration remain largely unknown. In an effort to identify extracellular fungal proteins that could mediate interactions with the brain endothelium, we undertook a proteomic analysis of the extracellular proteome and identified a secreted metalloprotease (Mpr1) belonging to the M36 class of fungalysins. Here we found that Mpr1 promotes migration of C. neoformans across the brain endothelium and into the CNS by facilitating attachment of cryptococci to the endothelium surface, thus underscoring the critical role of M36 proteases in fungal pathogenesis.

Glycoprotein targeted therapeutics: a new era of anti-herpes simplex virus-1 therapeutics

Herpes simplex virus type-1 (HSV-1) is among the most common human pathogens worldwide. Its entry into host cells is an intricate process that relies heavily on the ability of the viral glycoproteins to bind host cellular proteins and to efficiently mediate fusion of the virus envelope with the cell membrane. Acquisition of HSV-1 results in a lifelong latent infection. Because of the cycles of reactivation from a latent state, much emphasis has been placed on the management of infection through the use of DNA synthesis inhibitors. However, new methods are needed to provide more effective treatment at earlier phases of the viral infection and to prevent the development of drug resistance by the virus. This review outlines the infection process and the common therapeutics currently used against the fundamental stages of HSV-1 replication and fusion. The remainder of this article will focus on a new approach for HSV-1 infection control and management, the concept of glycoprotein-receptor targeting.

[Guidelines for the treatment of Invasive Candidiasis and other yeasts. Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC). 2010 Update]

These guidelines are an update of the recommendations of the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC) that were issued in 2004 (Enferm Infecc Microbiol Clin. 2004, 22:32-9) on the treatment of Invasive Candidiasis and infections produced by other yeasts. This 2010 update includes a comprehensive review of the new drugs that have appeared in recent years, as well as the levels of evidence for recommending them. These guidelines have been developed following the rules of the SEIMC by a working group composed of specialists in infectious diseases, clinical microbiology, critical care medicine, paediatrics and oncology-haematology. It provides a series of general recommendations regarding the management of invasive candidiasis and other yeast infections, as well as specific guidelines for prophylaxis and treatment, which have been divided into four sections: oncology-haematology, solid organ transplantation recipients, critical patients, and paediatric patients.

Combinatorial approaches to the prevention and treatment of HIV-1 infection

The discovery of the human immunodeficiency virus type 1 (HIV-1) in 1982 soon led to the identification and development of antiviral compounds to be used in treatment strategies for infected patients. Early in the epidemic, drug monotherapies frequently led to treatment failures because the virus quickly developed resistance to the single drug. Following the advent of highly active antiretroviral therapy (HAART) in 1995, dramatic improvements in HIV-1-infected patient health and survival were realized as more refined combination therapies resulted in reductions in viral loads and increases in CD4+ T-cell counts. In the absence of an effective vaccine, prevention of HIV-1 infection has also gained traction as an approach to curbing the pandemic. The development of compounds as safe and effective microbicides has intensified and has focused on blocking the transmission of HIV-1 during all forms of sexual intercourse. Initial preclinical investigations and clinical trials of microbicides focused on single compounds effective against HIV-1. However, the remarkable successes achieved using combination therapy to treat systemic HIV-1 infection have subsequently stimulated the study and development of combination microbicides that will simultaneously inhibit multiple aspects of the HIV-1 transmission process by targeting incoming viral particles, virus-infected cells, and cells susceptible to HIV-1 infection. This review focuses on existing and developing combination therapies, covering preclinical development, in vitro and in vivo efficacy studies, and subsequent clinical trials. The shift in focus within the microbicide development field from single compounds to combination approaches is also explored.

Combination flucytosine and high-dose fluconazole compared with fluconazole monotherapy for the treatment of cryptococcal meningitis: a randomized trial in Malawi

BACKGROUND

Cryptococcal meningitis is a major cause of human immunodeficiency virus (HIV)-associated morbidity and mortality in Africa. Improved oral treatment regimens are needed because amphotericin B is neither available nor feasible in many centers. Fluconazole at a dosage of 1200 mg per day is more fungicidal than at a dosage of 800 mg per day, but mortality rates remain unacceptably high. Therefore, we examined the effect of adding oral flucytosine to fluconazole.

METHODS

From 13 February through 2 December 2008, HIV-seropositive, antiretroviral-naive patients experiencing their first episode of cryptococcal meningitis were randomized to receive (1) 14 days of fluconazole (1200 mg per day) alone or (2) in combination with flucytosine (100 mg/kg per day) followed by fluconazole (800 mg per day), with both groups undergoing 10 weeks of follow-up. The primary end point was early fungicidal activity, derived from quantitative cerebrospinal fluid cultures on days 1, 3, 7, and 14. Secondary end points were safety and 2- and 10-week mortality.

RESULTS

Forty-one patients were analyzed. Baseline mental status, cryptococcal burden, opening pressure, CD4(+) cell count, and HIV load were similar between groups. Combination therapy was more fungicidal than fluconazole alone (mean early fungicidal activity +/- standard deviation -0.28 +/- 0.17 log colony-forming units [CFU]/mL per day vs -0.11 +/- 0.09 log CFU/mL per day; P < .001). The combination arm had fewer deaths by 2 weeks (10% vs 37%) and 10 weeks (43% vs 58%). More patients had grade III or IV neutropenia with combination therapy (5 vs 1, within the first 2 weeks; P = .20), but there was no increase in infection-related adverse events.

CONCLUSIONS

The results suggest that optimal oral treatment for cryptococcal meningitis is high-dose fluconazole with flucytosine. Efforts are needed to increase availability of flucytosine in Africa. Clinical trials registration. isrctn.org Identifier: ISRCTN02725351.

Clinical practice guidelines for the management of cryptococcal disease: 2010 update by the infectious diseases society of america

Cryptococcosis is a global invasive mycosis associated with significant morbidity and mortality. These guidelines for its management have been built on the previous Infectious Diseases Society of America guidelines from 2000 and include new sections. There is a discussion of the management of cryptococcal meningoencephalitis in 3 risk groups: (1) human immunodeficiency virus (HIV)-infected individuals, (2) organ transplant recipients, and (3) non-HIV-infected and nontransplant hosts. There are specific recommendations for other unique risk populations, such as children, pregnant women, persons in resource-limited environments, and those with Cryptococcus gattii infection. Recommendations for management also include other sites of infection, including strategies for pulmonary cryptococcosis. Emphasis has been placed on potential complications in management of cryptococcal infection, including increased intracranial pressure, immune reconstitution inflammatory syndrome (IRIS), drug resistance, and cryptococcomas. Three key management principles have been articulated: (1) induction therapy for meningoencephalitis using fungicidal regimens, such as a polyene and flucytosine, followed by suppressive regimens using fluconazole; (2) importance of early recognition and treatment of increased intracranial pressure and/or IRIS; and (3) the use of lipid formulations of amphotericin B regimens in patients with renal impairment. Cryptococcosis remains a challenging management issue, with little new drug development or recent definitive studies. However, if the diagnosis is made early, if clinicians adhere to the basic principles of these guidelines, and if the underlying disease is controlled, then cryptococcosis can be managed successfully in the vast majority of patients.

Treatment of invasive fungal infections in immunocompromised and transplant patients: AmBiLoad trial and other new data

Opportunistic invasive fungal infections (IFIs) have changed. Moreover, a significantly greater therapeutic armamentarium is now available, with liposomal amphotericin B (L-AmB) administered in new ways, for example in higher doses, in combination with other compounds or inhaled. The objective of this study was to review these three aspects. The AmBiLoad study was designed to clarify whether higher doses of L-AmB could be more efficacious than the licensed dose of 3-5 mg/kg. It was a multicentric study where patients were randomised to receive a 14-day course of 3 mg/kg/day or 10 mg/kg/day L-AmB. A total of 339 patients were enrolled during the study period (April 2003 to October 2004). Discontinuation of treatment, mainly due to adverse events, was frequent (13% in the standard dose group vs. 24% in the high dose group), and only 66% and 50%, respectively, completed 14 days of randomised treatment. There was no statistically significant difference with regard to favourable overall responses between the treatment groups (50% in the standard dose group vs. 46% in the high dose group; P = 0.65). In addition, there was no significant difference according to type of IFI (invasive aspergillosis, 50% vs. 46% in the standard and high dose groups, respectively). The obvious conclusion of this study was that administration of 10 mg/kg/day L-AmB to patients with IFI does not improve efficacy but increases toxicity and price. In vitro and experimental data suggest that the combination of AmB with other antifungal agents may be more effective than monotherapy; however, data regarding the clinical efficacy of L-AmB in combination with other agents are scarce. The use of inhaled L-AmB has shown promising results for use as antifungal prophylaxis in high-risk patients.

Genetic prerequisites for additive or synergistic actions of 5-fluorocytosine and fluconazole in baker's yeast

During applications of 5-fluorocytosine (5FC) and fluconazole (FLC), additive or synergistic action may even occur when primary resistance to 5FC is established. Here, we analysed conjoint drug action in Saccharomyces cerevisiae strains deficient in genes known to be essential for 5FC or FLC function. Despite clear primary resistance, residual 5FC activity and additive 5FC+FLC action in cells lacking cytosine permease (Fcy2p) or uracil phosphoribosyl transferase (Fur1p) were detected. In contrast, Deltafcy1 mutants, lacking cytosine deaminase, became entirely resistant to 5FC, concomitantly losing 5FC+FLC additivity. Disruption of the orotate phosphoribosyltransferase gene (URA5) in the wild-type led to low-level 5FC tolerance, while an alternative orotate phosphoribosyltransferase, encoded by URA10, contributed to 5FC toxicity only in the Deltaura5 background. Remarkably, combination of Deltaura5 and Deltafur1 resulted in complete 5FC resistance. Thus, yeast orotate phosphoribosyltransferases are involved in 5FC metabolism. Similarly, disruption of the ergosterol Delta(5,6)-desaturase-encoding gene ERG3 resulted only in partial resistance to FLC, and concomitantly a synergistic effect with 5FC became evident. Full resistance to FLC occurred in Deltaerg3 Deltaerg11 double mutants and, simultaneously, synergism or even an additive effect with FLC and 5FC was no longer discernible. Since the majority of spontaneously occurring resistant yeast clones displayed residual sensitivity to either 5FC or FLC and those strains responded to combined drug treatment in a predictable manner, careful resistance profiling based on the findings reported here may help to address yeast infections by combined application of antimycotic compounds.

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.

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.

Cryptococcosis

Cryptococcus neoformans has risen to a worldwide highly recognizable major opportunistic pathogen with deadly consequences. It has become a model fungus to study a variety of paradigms in the host-fungus relationships. Genomic studies are advancing knowledge on its evolution and dissecting its virulence composite. Studies designed to understand host immunology to this fungus are leading to development of active and passive prevention and therapeutic strategies. This article collates and analyzes both new and old knowledge about the pathogen to help frame the meaning of human cryptococcosis as it starts to evolve in the new millennium.

Effects of fluconazole singly and in combination with 5-fluorocytosine or amphotericin B in the treatment of cryptococcal meningoencephalitis in an intracranial murine model

In this study we developed a highly reproducible intracranial murine model of cryptococcosis. Mice (Balb/c, 5-7 weeks old) were challenged intracranially and treated with intermediate (30 mg/kg) or high (90 mg/kg) dose fluconazole, and amphotericin B (0.75 mg/kg), administered singly or in combination with flucytosine (100 mg/kg). Survival and brain CFU analyses were performed. Effect of fluconazole prophylaxis was also determined. Our data show that the developed model mimics clinical signs of cryptococcal meningitis. In single treatment, fluconazole (30 mg/kg) was more efficacious than amphotericin B or flucytosine (P < 0.0001). Combination treatment led to significantly increased anticryptococcal activity, which was highest for high dose fluconazole + flucytosine (P < 0.0001). However, no significant difference was observed between high dose fluconazole treatment with and without flucytosine (P >0.05). Fluconazole prophylaxis led to a significant decrease in brain CFU. In conclusion, high dose fluconazole administered post-infection, or as prophylaxis, may be highly efficacious in the treatment and prevention of meningoencephalitis.

The role of murine models in the development of antifungal therapy for systemic mycoses

Animal testing is crucial to the development of new antifungal compounds. This review describes the role that murine and other animal models have played in the development of three classes of antifungal agents: the polyenes, the triazoles and the echinocandins and the ways in which these models have been either the positive link in the path from in vitro studies to the patient, or have foreclosed later clinical evaluation. Efficacy studies in particular mycoses are discussed, as well as studies designed to determine whether combinations of antifungal drugs may have value over single agents. Copyright 2000 Harcourt Publishers Ltd.

Drug resistance in Cryptococcus neoformans

Cryptococcus neoformans has become a major opportunistic fungal pathogen worldwide. Successful treatment of invasive disease with this fungus has used amphotericin B, flucytosine and various azoles. However, treatment failures continue to occur for a variety of reasons including direct antifungal drug resistance. Issues and mechanisms for antifungal drug resistance in Cryptococcus neoformans are reviewed. Furthermore, approaches and strategies for prevention and treatment of antifungal drug resistance are identified and these include host immune modulation, dose optimization, prophylaxis/empirical regimens, improved drug delivery systems such as lipid preparations of amphotericin B, surgery, combination antifungal treatments and development of new antifungal agents. Copyright 1999 Harcourt Publishers Ltd.

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

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

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.

Amphotericin B colloidal dispersion combined with flucytosine with or without fluconazole for treatment of murine cryptococcal meningitis

Studies with animals and in vitro studies have demonstrated that flucytosine plus amphotericin B or fluconazole has significantly improved mycologic activity against meningitis caused by Cryptococcus neoformans compared to the activity of amphotericin B or fluconazole used alone. However, few doses have been tested in combination. This study evaluated the antifungal efficacy of amphotericin B colloidal dispersion (ABCD) combined with flucytosine with and without fluconazole in a murine model of cryptococcal meningitis. The following dosages were tested: ABCD at 0 to 12.5 mg/kg of body weight given intravenously 3 days/week, flucytosine at 0 to 110 mg/kg/day, and fluconazole at 0 to 50 mg/kg/day. Meningitis was established in male BALB/c mice by intracerebral injection of C. neoformans. Treatment with flucytosine with or without fluconazole dissolved in the sole source of drinking water was started on day 2; animals were sacrificed at 16 days, and the numbers of fungal colonies in the brain were quantified. A survival rate of 100% was achieved with ABCD plus flucytosine without fluconazole; however, the addition of fluconazole was required to prevent weight loss (P < 0.00001) and to achieve the maximum antifungal effect (P < 0.00001). The only region of dose combinations for which the 99% confidence intervals were less than 100 CFU/g of brain was defined by ABCD at 5.0 to 7.5 mg/kg combined with flucytosine at 20 to 60 mg/kg/day and fluconazole at 30 to 40 mg/kg/day. The triple combination of ABCD plus flucytosine and fluconazole was necessary to achieve the greatest antifungal activity.

Effect of severity of meningitis on fungicidal activity of flucytosine combined with fluconazole in a murine model of cryptococcal meningitis

We studied the effect of the severity of meningitis on the response to therapy with fluconazole and flucytosine in a murine model of cryptococcal meningitis. Meningitis was established by intracerebral injection of Cryptococcus neoformans. The severity of meningitis was varied by delaying the onset of treatment from 3 to 7 days. Animals were sacrificed after 14 days of treatment, and the numbers of C. neoformans per gram of brain tissue were quantified. The range of effective dose combinations of fluconazole and flucytosine became progressively reduced as the severity of meningitis increased. The magnitude of treatment effect, as measured by the numbers of CFU/gram of brain tissue, was also reduced with increasing severity of meningitis. In this model, as the severity of meningitis increases, higher doses of fluconazole are required to achieve equivalent levels of activity. The combination of fluconazole and flucytosine appears to have the most-potent antifungal effects. This is most readily observed in animals with more-severe meningitis.

Combination therapy with fluconazole and flucytosine in the murine model of cryptococcal meningitis

This study elucidates the role of combined fluconazole and flucytosine as therapy for cryptococcosis in the murine model of meningitis. Three strains of Cryptococcus neoformans for which the range of fluconazole MICs was wide--2 microg/ml (susceptible strain), 8 microg/ml (moderately susceptible strain), and 32 microg/ml (resistant strain)--were used for infection. One day postinfection, the mice were randomized into eight treatment groups: placebo; flucytosine (40 mg/kg of body weight/day); fluconazole at 3 mg/kg/day (low dosage), 10 mg/kg/day (moderate dosage), or 20 mg/kg/day (high dosage); and combined flucytosine and fluconazole at low, moderate, or high doses of fluconazole. Three major findings were demonstrated: (i) correlation between the MICs for the isolates and the in vivo effectiveness of fluconazole as assessed by the reduction in cryptococcal brain burden, (ii) a dose-response curve (a higher dose of fluconazole was significantly more efficacious than a lower dose [P < 0.001]), and (iii) synergism between fluconazole and flucytosine (therapy with a combination of fluconazole and flucytosine was superior to therapy with either agent alone [P < 0.01]).

Key issues concerning fungistatic versus fungicidal drugs

Are there any fungicidal drugs available today? A critical issue in answering this question is that of definition. The simplest, most stringent definitions identify fungistatic drugs as those that inhibit growth, whereas fungicidal drugs kill fungal pathogens. The immunocompetent host is usually far better equipped to eliminate fungal pathogens than the immunosuppressed host. Therefore, it would be especially desirable to have a truly fungicidal drug, one that absolutely kills and fungi, as a treatment option for the immunosuppressed patient. The critical question would be whether a fungicidal drug can be delivered to the target site in a concentration high enough for a sufficient time to reduce the intralesional fungal counts to zero. By this simple definition, there are no fungicidal drugs available today. However, an accepted alternative definition is that often used by the bacteriologist: Fungicidal drugs are those that lead to a reduction of 99.9% of the initial inocula. Although this less restrictive in vitro standard is more easily met, it has serious limitations. Whether the 99.9% kill should be an acceptable standard remains uncertain. As an alternative, the minimum inhibitory concentration, though indicating static activity, has served well; perhaps it should be the only information reported for fungal susceptibility testing.

Fluconazole distribution to the brain: a crossover study in freely-moving rats using in vivo microdialysis

PURPOSE

The purpose of this study was to determine if the microdialysis sampling technique is feasible to study the central nervous system distributional kinetics of a novel triazole antifungal agent, fluconazole, in an awake, freely-moving rat model, and to determine fluconazole distribution to the extracellular fluid (ECF) of the brain.

METHODS

The relative recovery of the microdialysis probes (CMA-12) was determined in vitro and in vivo by retrodialysis using UK-54,373, a fluorinated analog of fluconazole. Sprague-Dawley rats received 10 mg/kg and 20 mg/kg fluconazole IV bolus doses in a crossover design, and brain extracellular fluid fluconazole concentrations were monitored using microdialysis and on-line HPLC analysis. The plasma fluconazole concentration vs. time data were determined using sequential blood sampling and HPLC analysis.

RESULTS

There was no statistical difference between relative probe recoveries for both fluconazole and UK-54,373, either in vitro or in vivo, and probe recoveries did not change during the course of the in vivo crossover experiment. Fluconazole rapidly distributes into in the brain ECF and the average brain distribution coefficient (brain/plasma AUC ratio) was 0.60 +/- 0.18 and was independent of dose. Plasma pharmacokinetic parameters were linear in the dose range studied.

CONCLUSIONS

Fluconazole rapidly reaches a distributional equilibrium between brain extracellular fluid and plasma, and the distribution to the brain is substantial and not dependent on dose over a two-fold range. Furthermore, the results indicate that microdialysis utilizing UK-54,373 as the in vivo retrodialysis probe calibrator is a feasible method to study the transport of fluconazole into the central nervous system.

Effect of fluconazole on fungicidal activity of flucytosine in murine cryptococcal meningitis

Both animal and in vitro studies have demonstrated that combinations of flucytosine with amphotericin B and with fluconazole have significantly improved activity against cryptococcal meningitis compared with the activity of each drug used alone. However, very few dose levels of these agents have been tested in combination. This study evaluated the efficacy of fluconazole plus flucytosine in a murine model of cryptococcal meningitis over a broad range of dose combinations (fluconazole, 0 to 40 micrograms/g of body weight per day; flucytosine, 0 to 200 micrograms/g/day). Both drugs were dissolved in drinking water, with treatment on days 2 to 11. In this highly reproducible model, fluconazole had a dramatic effect on the fungicidal activity of flucytosine. Flucytosine at dose levels of as much as 200 micrograms/g/day alone or in combination with low doses of fluconazole had minimal fungicidal activity, whereas in combination with fluconazole at 24 to 40 micrograms/g/day, flucytosine showed fungicidal activity in the range of 45 to 65% of the animals treated at doses of 40 to 100 micrograms/g/day. This striking effect of fluconazole is consistent with the results of both in vitro and clinical studies. In the clinic, the use of flucytosine is often limited by severe toxicity, while toxicity is rarely observed with fluconazole. These results suggest that when flucytosine is given with higher doses of fluconazole, the maximum therapeutic effect of the former in the clinic may be observed at dose levels that are far less than the doses commonly employed (150 micrograms/g daily).

In vitro determination of optimal antifungal combinations against Cryptococcus neoformans and Candida albicans

There is currently no rapid, reliable, and reproducible in vitro technique to describe the growth-inhibitory interactions of antifungal drug combinations over a wide range of drug concentrations. We have developed a microdilution plate assay that was used to determine optimal drug combinations and concentrations of one-, two-, and three-drug regimens of amphotericin B (AmphB), fluconazole (FLU), and 5-fluorocytosine (5FC) for growth inhibition of three isolates each of Cryptococcus neoformans and Candida albicans. These growth inhibition data were then used in a multifactorial design technique to (i) generate contour and surface response plots to aid visual interpretation and (ii) develop mathematical equations describing the growth responses of the fungi to a wide range of antifungal concentrations and ratios. Our data indicated that (i) antifungal drug-drug interactions affecting yeast growth are complex functions of the drugs used in combination, their absolute concentrations, and also their relative (proportional) concentrations; (ii) AmphB-FLU combinations had additive effects against C. albicans over wide concentration ranges for each agent but were indifferent (i.e., were less than additive) in their inhibitory effect on C. neoformans; (iii) other two-drug combinations (FLU-5FC or AmphB-5FC) had indifferent effects on the growth of both fungi; and (iv) three-drug combinations (AmphB-FLU-5FC) showed an additive inhibitory effect on the growth of both C. albicans and C. neoformans. The finding that no antagonism was observed in combinations employing AmphB and FLU in this in vitro model is of critical importance since it argues against the current theoretical concept, based on the individual drug's mode of action, of antagonism between these two drugs. These microdilution techniques provide a method to determine rational regimens of antifungal agents in multidrug combinations for future testing to correlate in vitro activity with in vivo response. The use of this approach has made the evaluation of complex antifungal drug-drug interactions possible and provided important new information to the evolving field of antifungal drug combination.

Fluconazole. An update of its pharmacodynamic and pharmacokinetic properties and therapeutic use in major superficial and systemic mycoses in immunocompromised patients

Fluconazole is a triazole antifungal agent which is now an established part of therapy in patients with immune deficiencies. It is effective against oropharyngeal/oesophageal candidiasis (candidosis) when used orally once daily either as treatment or secondary prophylaxis in patients with AIDS or as treatment or primary prophylaxis in neutropenia associated with cancer therapy. Fluconazole also resolves symptoms in up to 60% of patients with cryptococcal meningitis and AIDS. However, in this infection its efficacy as treatment relative to that of amphotericin B is equivocal, and its major role is as the drug of choice for maintenance therapy following amphotericin B induction. In this regard, fluconazole has been proven superior to amphotericin B and to itraconazole 200 mg/day. Comparisons with other drugs used for the treatment of mucosal candidiasis in patients with AIDS show fluconazole to be superior to nystatin, similar to itraconazole and at least as effective as clotrimazole and ketoconazole; it was more so than the latter azole in 1 study. In patients undergoing chemotherapy or bone marrow transplantation, fluconazole as primary prophylaxis has produced greater clinical benefit than a clotrimazole regimen. The incidence of adverse events appears to be somewhat higher in patients with AIDS compared with HIV-negative cohorts, but the qualitative pattern of events is similar. The most frequent events are gastrointestinal complaints, headache and skin rash: rare exfoliative skin reactions and isolated instances of clinically overt hepatic dysfunction have occurred in patients with AIDS. Issues yet to be clarified include: the use of fluconazole in children with AIDS, in whom results have been promising; its efficacy against other fungal infections encountered in immunocompromised patients; whether the drug influences mortality, as has been suggested by one placebo-controlled trial in patients undergoing bone marrow transplant; and the appropriateness of its potential for use as primary prophylaxis against cryptococcal meningitis in patients with AIDS, where it shows efficacy but there is concern over increasing risk of development of secondary resistance. Notwithstanding these undefined aspects of its clinical profile, fluconazole is now confirmed as an important antifungal drug in the management of fungal infections in patients with immune deficiencies. In patients with AIDS it is the present drug of choice as maintenance therapy against cryptococcal meningitis and is a preferred agent for secondary prophylaxis against candidal infections; it is also a favoured agent for primary prophylaxis in patients at risk because of neutropenia associated with chemotherapy or bone marrow transplantation .

Cryptococcosis in the era of AIDS--100 years after the discovery of Cryptococcus neoformans

Although Cryptococcus neoformans and cryptococcosis have existed for several millennia, a century has passed since the discovery of this encapsulated yeast and its devastating disease. With the advent of the AIDS pandemic, cryptococcal meningitis has emerged as a leading cause of infectious morbidity and mortality and a frequently life-threatening opportunistic mycosis among patients with AIDS. Both basic and clinical research have accelerated in the 1990s, and this review attempts to highlight some of these advances. The discussion covers recent findings, current concepts, controversies, and unresolved issues related to the ecology and genetics of C. neoformans; the surface structure of the yeast; and the mechanisms of host defense. Regarding cell-mediated immunity, CD4+ T cells are crucial for successful resistance, but CD8+ T cells may also participate significantly in the cytokine-mediated activation of anticryptococcal effector cells. In addition to cell-mediated immunity, monoclonal antibodies to the major capsular polysaccharide, the glucuronoxylomannan, offer some protection in murine models of cryptococcosis. Clinical concepts are presented that relate to the distinctive features of cryptococcosis in patients with AIDS and the diagnosis, treatment, and prevention of cryptococcosis in AIDS patients.

In vitro evaluation of combination of fluconazole and flucytosine against Cryptococcus neoformans var. neoformans

Amphotericin B and fluconazole are current acceptable therapies for cryptococcal meningitis; however, their effect remains suboptimal. The combination of fluconazole and flucytosine has yielded encouraging clinical results in human immunodeficiency virus patients with cryptococcal meningitis. To investigate the biological basis of this finding, we performed in vitro combination testing of fluconazole and flucytosine against 50 clinical strains of Cryptococcus neoformans var. neoformans. Synergy (fractional inhibitory concentration index of < 1.0) was observed in 62% of cases, while antagonism (fractional inhibitory concentration index of > 2.0) was not observed. For cases in which synergy was not achieved (autonomous or additive effects), the beneficial effect of the combination was still seen (i.e., there was still a decrease, although not as dramatic, in the MIC of one or both drugs when used in combination). The in vitro inhibitory action of flucytosine was greatly enhanced by the addition of fluconazole; the flucytosine MICs for Cryptococcus isolates were markedly decreased to concentrations which were severalfold lower than the achievable cerebrospinal fluid flucytosine concentration. On the other hand, the addition of flucytosine did not greatly enhance the in vitro activity of fluconazole if the initial fluconazole MIC for the isolate was > or = 8 micrograms/ml. Controlled clinical studies are warranted to further elucidate the potential utility of fluconazole-flucytosine combination therapy.

Monoclonal antibodies to Cryptococcus neoformans glucuronoxylomannan enhance fluconazole efficacy

Monoclonal antibody (MAb) 2H1, which binds to the capsular glucuronoxylomannan (GXM) of the fungus Cryptococcus neoformans, prolonged survival and decreased fungal burden in an experimental murine infection. Fluconazole (FLU) is a triazole antibiotic which is effective against C. neoformans. The efficacy of MAb 2H1 in combination with FLU was studied in vitro with the murine macrophage-like cell line J7741.16 and in vivo in mice infected intravenously. In vitro, the combination of MAb 2H1 and FLU was more effective than either agent alone in reducing the number of CFU of C. neoformans cocultured with J774.16 cells. In combination with FLU, GXM-binding MAbs of the immunoglobulin M (IgM), IgG1, IgG2a, IgG2b, IgG3, and IgA isotypes were effective in reducing the numbers of CFU in C. neoformans-J774.16 cocultures. For the in vivo experiments, A/JCr mice were infected intravenously with 5 x 10(5) organisms treated with MAb and FLU. The therapeutic effect of MAb 2H1 was primarily to reduce the number of CFU in the lung and the serum GXM level, whereas FLU was most effective in reducing the number of CFU in the brain. Mice receiving combination therapy had lower numbers of CFU in the lung and serum GXM levels than mice treated with FLU alone. Administration of MAb 2H1 with or without FLU had little or no effect on the number of CFU in the brain. The results provide support for combined therapy.

Fluconazole, D0870, and flucytosine treatment of disseminated Candida tropicalis infections in mice

D0870 is a recently developed triazole with characteristics of a broad spectrum of activity and slow clearance by nonrenal mechanisms. Herein we have evaluated the efficacy of D0870, alone and combined with flucytosine, in a murine model of disseminated Candida tropicalis infection. Four isolates of C. tropicalis were evaluated. Two were highly susceptible in vitro to fluconazole, and two were resistant to fluconazole. All were highly susceptible to flucytosine and D0870. Animals were pretreated with 5-fluorouracil 1 day before infection because C. tropicalis has reduced virulence in immunocompetent mice. This was done to render them neutropenic for > 10 days. Mice were infected intravenously and treated orally with D0870 or fluconazole, alone or combined with flucytosine. Survival and tissue burden of the spleen and kidneys were used to evaluate the efficacy of antifungal therapy. Fluconazole was less effective for treatment of resistant C. tropicalis than susceptible C. tropicalis. D0870 was more potent than fluconazole and was effective in fluconazole-resistant isolates. Flucytosine was consistently effective when used alone but did not consistently add to the benefit of D0870 or fluconazole. D0870 has potential in treatment of candidiasis caused by C. tropicalis, including fluconazole-resistant isolates.

Treatment of exogenous Candida endophthalmitis in rabbits with oral fluconazole

We investigated the efficacy of oral fluconazole, alone or in combination with oral flucytosine (5FC), in treating Candida endophthalmitis using a rabbit model. Albino rabbits were infected with an intravitreal inoculation of 1,000 CFU of susceptible Candida albicans and randomized 5 days later to receive treatment with oral fluconazole alone (80 mg/kg of body weight per day), a combination of fluconazole and 5FC (100 mg/kg/12 h), or no treatment. The treatment effect was assessed at 2 and 4 weeks after therapy by funduscopy, quantitative vitreous culture, and histopathology. Intravitreal levels of fluconazole, 2 to 24 h after the first dose, were measured to be > 10 times the MIC of the drug for C. albicans. Among rabbits treated with fluconazole for 2 weeks, 67% had a > 90% reduction in fungal load (P < 0.05) and 33% were sterile. After 4 weeks, all had a > 99% reduction in fungal load (P < 0.05) and 75% were sterile (P = 0.01). This treatment effect was unchanged 4 weeks after discontinuation of fluconazole. Among rabbits treated with fluconazole and 5FC for 2 weeks, 67% died during therapy. Among the surviving rabbits, 75% had a > 90% reduction in fungal load (P < 0.05) and 25% were sterile. We conclude that oral fluconazole may be useful for treatment of Candida endophthalmitis. Addition of 5FC was associated with high toxicity and minimal additional antifungal effect in our rabbit model.

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.

Fluconazole penetration into the human prostate

Fluconazole concentrations in the serum and prostate of human volunteers undergoing transurethral resection for benign prostatic hypertrophy were measured. There was a high correlation (r = 0.783) between serum (mean = 6.6 micrograms/ml) and tissue (mean = 1.9 micrograms/g) fluconazole concentrations, and these data were used to construct a model for local tissue concentrations.

Flucytosine+fluconazole association in the treatment of a murine experimental model of cryptococcosis

The efficacy of flucytosine (5-FC) and fluconazole (FLU) association in the treatment of a murine experimental model of cryptococcosis, was evaluated. Seven groups of 10 Balb C mice each, were intraperitoneally inoculated with 10(7) cells of Cryptococcus neoformans. Six groups were allocated to receive 5-FC (300 mg/kg) and FLU (16 mg/kg), either combined and individually, by daily gavage beginning 5 days after the infection, for 2 and 4 weeks. One group received distilled water and was used as control. The evaluation of treatments was based on: survival time; macroscopic examination of brain, lungs, liver and spleen at autopsy; presence of capsulated yeasts in microscopic examination of wet preparations of these organs and cultures of brain homogenate. 5-FC and FLU, individually or combined, significantly prolonged the survival time of the treated animals with respect to the control group (p < 0.01). Animals treated for 4 weeks survived significantly longer than those treated for 2 weeks (p < 0.01). No significant differences between the animals treated with 5-FC and FLU combined or separately were observed in the survival time and morphological parameters. The association of 5-FC and FLU does not seem to be more effective than 5-FC or FLU alone, in the treatment of this experimental model of cryptococcosis.

Antibody-mediated protection in mice with lethal intracerebral Cryptococcus neoformans infection

The fungus Cryptococcus neoformans is an important opportunistic pathogen for patients with AIDS. C. neoformans infections frequently involve the brain and are often fatal. In the setting of AIDS C. neoformans infections are incurable and new treatment strategies are urgently needed. Passive administration of antibody is a potential therapeutic option for the prevention and treatment of C. neoformans. The IgG1 murine monoclonal antibody 2H1 to the capsular polysaccharide of C. neoformans was studied for its ability to modify the course of lethal intracerebral cryptococcal infection in mice. Intraperitoneal administration of antibody 2H1 resulted in small, yet significant, prolongations in the average survival of mice given intracerebral infection and reduced the number of C. neoformans colonies in brain tissue. Histopathological examination of brain tissues revealed a diffuse cryptococcal meningitis with fewer organisms in the brains of mice that received antibody 2H1 than in the control group. Thus, systemic administration of a monoclonal antibody can modify the course of lethal intracerebral C. neoformans infection in mice by prolonging survival and decreasing fungal burden in brain tissues.