In vitro activities of voriconazole, fluconazole, and itraconazole against 566 clinical isolates of Cryptococcus neoformans from the United States and Africa

The Antifungal Activity of HMA, an Amiloride Analog and Inhibitor of Na+/H+ Exchangers

One path toward identifying effective and easily accessible antifungals is to repurpose commonly used drugs. Amiloride, a widely used diuretic, inhibits different isoforms of Na⁺/H⁺ exchangers, Na⁺ channels, and Na⁺/Ca²⁺ exchangers. Here, we found that amiloride had poor antifungal activity against isolates of Cryptococcus prompting the examination of the amiloride analog, HMA [5-(N,N-hexamethylene)amiloride]. HMA possesses strong activity against Na⁺/H⁺ exchangers (NHEs) and little K⁺-associated toxicity since HMA has only minimal inhibitory effects toward epithelial sodium channels (ENaC), the diuretic and antikaliuretic target of amiloride. Although HMA produced a robust dose-dependent growth inhibition of several fungal isolates, susceptibility assays revealed modest MICs against isolates of Cryptococcus. A checkerboard dilution strategy resulted in fractional inhibitory concentrations (FIC) < 0.5, suggesting that HMA displays synergy with several antifungal azole drugs including posaconazole, voriconazole, and ketoconazole. Itraconazole and ravuconazole showed moderate synergy with HMA across all tested fungal isolates. In combination with HMA, ravuconazole had MICs of 0.004-0.008 μg/ml, a ∼16-fold reduction compared to MICs of ravuconazole when used alone and significantly more effective than the overall MIC₉₀ (0.25 μg/ml) reported for ravuconazole against 541 clinical isolates of Cryptococcus neoformans. In combination with azole drugs, MICs of HMA ranged from 3.2 μM (1 μg/ml) to 26 μM (16 μg/ml), HMA was not cytotoxic at concentrations ≤ 8 μg/ml, but MICs were above the reported HMA K_i of 0.013-2.4 μM for various Na⁺/H⁺ exchangers. Our results suggest that HMA has limited potential as a monotherapy and may have additional targets in fungal/yeast cells since strains lacking NHEs remained sensitive to HMA. We determined that the hydrophobic substituent at the 5-amino group of HMA is likely responsible for the observed antifungal activity and synergy with several azoles since derivatives with bulky polar substitutions showed no activity against Cryptococcus, indicating that other 5-substituted HMA derivatives could possess stronger antifungal activity. Moreover, substitution of other positions around the pyrazine core of HMA has not been investigated but could reveal new leads for antifungal drug development.

Increased Antifungal Drug Resistance in Clinical Isolates of Cryptococcus neoformans in Uganda

Cryptococcal antigen screening is recommended among people living with AIDS when entering HIV care with a CD4 count of <100 cells/μl, and preemptive fluconazole monotherapy treatment is recommended for those with subclinical cryptococcal antigenemia. Yet, knowledge is limited of current antimicrobial resistance in Africa. We examined antifungal drug susceptibility in 198 clinical isolates collected from Kampala, Uganda, between 2010 and 2014 using the CLSI broth microdilution assay. In comparison with two previous studies from 1998 to 1999 that reported an MIC50 of 4 μg/ml and an MIC90 of 8 μg/ml prior to widespread human fluconazole and agricultural azole fungicide usage, we report an upward shift in the fluconazole MIC50 to 8 μg/ml and an MIC90 value of 32 μg/ml, with 31% of isolates with a fluconazole MIC of ≥ 16 μg/ml. We observed an amphotericin B MIC50 of 0.5 μg/ml and an MIC90 of 1 μg/ml, of which 99.5% of isolates (197 of 198 isolates) were still susceptible. No correlation between MIC and clinical outcome was observed in the context of amphotericin B and fluconazole combination induction therapy. We also analyzed Cryptococcus susceptibility to sertraline, with an MIC50 of 4 μg/ml, suggesting that sertraline is a promising oral, low-cost, available, novel medication and a possible alternative to fluconazole. Although the CLSI broth microdilution assay is ideal to standardize results, limit human bias, and increase assay capacity, such assays are often inaccessible in low-income countries. Thus, we also developed and validated an assay that could easily be implemented in a resource-limited setting, with similar susceptibility results (P = 0.52).

Approaches to the early treatment of invasive fungal infection

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

Antifungal susceptibility of Cryptococcus neoformans isolates in HIV-infected patients to fluconazole, itraconazole and voriconazole in Spain: 1994-1996 and 1997-2005

The antifungal drug susceptibility of 70 Cryptococcus neoformans isolates obtained in Spain from 1994 to 1996 (23 isolates) and from 1997 to 2005 (47 isolates) was investigated. The MICs of fluconazole, itraconazole and voriconazole were determined by the modified Clinical and Laboratory Standards Institute (CLSI; formerly National Committee for Clinical Laboratory Standards) broth microdilution method. The MIC(50) and MIC(90) for itraconazole and voriconazole did not change significantly from 1994 to 2005. The MIC(50) of fluconazole remained stable and the MIC(90) decreased by 2 log(2) dilution in the isolates collected from 1997 to 2005. We conclude that the in vitro resistance to fluconazole decreased over an 11-year period. In addition, a tendency for the development of possible cross-resistance between the three triazoles was observed.

Antifungal drug susceptibility of Cryptococcus neoformans from clinical sources in Nairobi, Kenya

The serotypes and mating types of 80 clinical isolates of Cryptococcus neoformans from Kenya were studied and subjected to broth microdilution susceptibility testing to amphotericin B (AMP), flucytosin, fluconazole (FLC), itraconazole (ITC) and miconazole (MCZ). The isolates included C. neoformans var. grubii- 75 of 80 (serotype A; 93.7%), C. neoformans var. neoformans- three of 80 (3.8%) and C. neoformans var. gattii- two (serotype B; 2.5%). Mating experiment confirmed all the isolates to be alpha-mating type. Seventy-eight (97.5%) of the isolates had minimum inhibitory concentration (MIC) of < or =0.5 microg ml(-1) to AMP and at 1 microg ml(-1), 100% of the isolates were inhibited. Flucytosin resistance was observed in 21% with MIC in which 90% of the isolates were inhibited (MIC90) of 64 microg ml(-1). Only 23.8% of the strains were susceptible to FLC with 65% susceptible dose-dependent (SDD) and 11.2% resistant. Itraconazole susceptibility was 61.3% while the rest were either SDD or resistant. The MIC90 for ITC and MCZ were 0.5 and 2 microg ml(-1) respectively. The study reports the serotypes, mating types and highlights the existence of azoles resistance in C. neoformans in Nairobi which calls for antifungal drug resistance surveillance as prophylactic use of FLC increases because of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) epidemic in sub-Saharan Africa.

Long-term outcome of therapy for 59 cats and 11 dogs with cryptococcosis

OBJECTIVE

To determine the outcome of therapy in cats and dogs with naturally occurring cryptococcosis. Design Retrospective study of 59 cats and 11 dogs at the University Veterinary Centre Sydney from 1986 to 2004.

METHOD

Following detailed analysis of case notes potential associations between patient characteristics, cryptococcal species, retroviral status (cats), disease severity and type of therapy were examined in relation to duration and success of therapy. Treatment protocols based on amphotericin B, fluconazole and itraconazole were compared.

RESULTS

Seventy-six percent of feline patients were successfully treated. For cats, the presence of central nervous system disease was the only factor found to influence outcome. Cats with neurological involvement, disseminated disease or refractory disease treated with amphotericin B containing protocols did as well, on average, as cats with less severe disease treated with azole monotherapy. Amphotericin B was thus an effective agent for treating severe cases of cryptococcosis. The median cumulative dose of amphotericin B for cats cured at the first attempt was 16 mg/kg (range 7 to 23 mg/kg). The median duration of treatment required to effect a cure at first attempt was significantly shorter for fluconazole (4 months; range 1 to 8 months) than for itraconazole (9 months; range 3 to 24 months; P = 0. 0191; Mann Whitney U test). The success rate for treatment of canine cases was 55%. No factor appeared to influence disease outcome in dogs. Large cumulative doses of amphotericin B could be administered via the subcutaneous route in both species and generally with minimal nephrotoxicity. Recrudescence occurred in a significant proportion of animals, in some cases despite a reduction of serum latex cryptococcal antigen agglutination test to zero.

CONCLUSION

Although the prognosis of cryptococcosis should be described as guarded, a majority of the canine and especially feline patients can be expected to be cured, although treatment is protracted and expensive.

Cryptococcus gattii infection: characteristics and epidemiology of cases identified in a South African province with high HIV seroprevalence, 2002-2004

We describe 46 Cryptococcus gattii-infected persons identified by population-based surveillance conducted in South Africa. Most patients with C. gattii infection presented with meningitis. The mortality rate during hospitalization was 36%. We found no significant differences between persons with and persons without C. gattii infection with regard to clinical presentation, acquired immunodeficiency syndrome diagnosis, concomitant conditions, or prior opportunistic infections. C. gattii isolates had low MICs to the tested antifungal drugs.

Efficacy of voriconazole in experimental Cryptococcus neoformans infection

Voriconazole is a third generation triazole with improved activity against many fungal pathogens. We examined the efficacy of voriconazole in a murine infection model and evaluated the drug's effect on cellular characteristics and serum polysaccharide levels. The antifungal reduced serum polysaccharide and significantly prolonged the survival of lethally infected animals.

Emerging azole antifungals

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

Management of intracranial fungal infections in patients with haematological malignancies

The incidence of, and mortality associated with, invasive fungal infections remains far higher than hoped. As a consequence of the overall increase in the incidence of such infections over time, the incidence of central nervous system (CNS) fungal infections is also increasing and, despite improvements in diagnostic techniques and the introduction of novel antifungal agents, therapy for CNS infections is still associated with discouragingly poor results. In patients with haematological malignancies, opportunistic infections with Candida or Aspergillus remain the most common infections affecting the CNS; however, opportunistic infections with less well-known fungi are becoming more common and must be considered in the differential diagnosis. New techniques for the early diagnosis of invasive fungal infections are emerging. Pharmacologic options for treating invasive fungal infections have also improved during the past few years, with new drugs becoming available that have broader antifungal spectra and better safety profiles. Other novel treatment approaches, such as combination therapy, are also being explored. Early investigations have produced encouraging results; however, large, prospective studies involving many patients are necessary to validate the widespread use of these approaches. This review analyses the existing guidelines for treatment of CNS fungal infections and the literature available on the use of new drugs to generate sets of recommendations for treatment of these life-threatening infections in patients with haematological malignancies.

DNA fingerprinting pattern and susceptibility to antifungal drugs in Cryptococcus neoformans variety grubii isolates from Barcelona city and rural environmental samples

Cryptococcus neoformans var. grubii (serotype A) was isolated from 12 soil samples mixed with pigeon droppings (16.9%) from 71 soil samples in Barcelona and rural areas of Catalonia. C. neoformans was not isolated from indoor dust and Eucalyptus debris. PCR fingerprinting was performed in 22 representative isolates and all of them corresponded to the VNI pattern. Susceptibility testing for the 22 isolates of C. neoformans var. grubii showed that all of them were susceptible to amphotericin B. Three isolates presented MICs (Minimal Inhibitory Concentrations) > or = 1 microg/ml to Itraconazole, five MICs > or = 1 microg/ml to ketoconazole and four were fluconazole resistant, (MICs > or = 64 microg/ml), while three of them were shown to have MICs > or = 1 microg/ml to voriconazole. In spite that all isolates presented the same DNA fingerprinting pattern, the susceptibility to antifungals is very variable. The possibility of acquiring cryptococcosis infection with primarily resistant environment strains is feasible.

Voriconazole: review of a broad spectrum triazole antifungal agent

Voriconazole is a second-generation triazole antifungal agent, structurally derived from fluconazole with an extended spectrum of activity against a wide variety of yeasts and moulds. Developed for the treatment of life-threatening fungal infections, it appears to be an effective therapy option for invasive aspergillosis, fluconazole-resistant candidiasis and refractory or less-common invasive fungal infections. It is available for both oral and intravenous administration and is characterised by an acceptable safety and tolerability spectrum.

New agents for invasive mycoses in children

PURPOSE OF REVIEW

Invasive fungal infections are an important cause of morbidity and mortality in immunocompromised children of all ages. This review summarizes information on new antifungal agents, including current data on their clinical use in children, as well as alternative strategies such as antifungal combination and immunomodulation therapy.

RECENT FINDINGS

Novel antifungal agents, such as the echinocandins and the second-generation triazoles, were recently introduced that exhibit promising efficacy against Candida spp., Aspergillus spp., and other opportunistic fungal pathogens. These compounds are generally well tolerated and show substantial efficacy as salvage treatment and equal or even superior efficacy compared with older azoles or amphotericin B as first-line or empiric therapy for fungal infections. Clinical studies of pharmacokinetics and efficacy of the new agents in the pediatric population are, however, limited.

SUMMARY

The response rates observed with the recently introduced drugs, although superior in some cases compared with older antifungal agents, are still far from satisfactory. The development of new antifungal compounds as well as the use of alternative approaches of combination therapy and immunomodulation should be pursued through well-designed laboratory and clinical studies in pediatric patients.

Primary Cutaneous Cryptococcosis in a Lung Transplant Recipient

Cryptococcal skin lesions are found in 10 to 15% of patients with disseminated cryptococcosis. Primary skin inoculation by Cryptococcus neoformans is rare but has been reported. We report the first known case of primary cutaneous cryptococcosis in a lung transplant recipient. Our patient, a 57-year-old man, underwent left single-lung transplantation and presented with a nonhealing ulcer 50 months later. Skin histopathology and culture confirmed C. neoformans. Serum and cerebrospinal fluid cryptococcal antigen tests were negative. The lesion healed after treatment with fluconazole. To date, disseminated disease is not evident. Primary cutaneous cryptococcosis has been reported in kidney and liver recipients but not in lung transplantation recipients. Nonhealing ulcers in immunocompromised patients mandate aggressive diagnostic procedures. Differential diagnosis of these cutaneous lesions should consider fungi, including C. neoformans.

Systemic Antifungal Therapy: New Options, New Challenges

The frequency of invasive fungal infections has increased dramatically in recent decades because of an expanding population at risk. Until now, treatment options for invasive mycoses have been primarily amphotericin B and the azoles, fluconazole and itraconazole. Traditional agents are limited by an inadequate spectrum of activity, drug resistance, toxicities, and drug-drug interactions. The recent approval of caspofungin and voriconazole clearly has expanded the number of existing antifungal drugs available. However, the enthusiasm that accompanies their availability is counterbalanced by limited clinical experience, high drug acquisition costs, and distinctive toxicities. The pharmacologic characteristics, extent of clinical experience (efficacy and toxicity), and drug acquisition costs among available systemic antifungal agents are compared, with emphasis on the new agents. Also, recommendations on the role of each agent are provided according to the most common indications for systemic antifungal therapy: invasive candidiasis, invasive aspergillosis, and febrile neutropenia.

Antifungal susceptibility of clinical and environmental isolates of Cryptococcus neoformans to four antifungal drugs determined by two techniques

A total of 64 Cryptococcus neoformans strains, including clinical and environmental Brazilian isolates var. neoformans and var. gattii, were tested for susceptibility to amphotericin B, 5-flucytosine, fluconazole and itraconazole. The tests were performed according to the recommendations of National Committee of Clinical Laboratory Standards and the method of macrodilution in liquid medium of Shadomy et al. [Manual de Microbiologia Clínica, 4th ed. Buenos Aires: Editorial Medica Panamericana, 1987: 1229-38]. For most drugs there was a significant difference between the readings taken at 24 and 48 h with both methods. When the minimum inhibitory concentrations obtained by the two techniques were compared, significant differences were observed for amphotericin B and fluconazole. Overall, differences in drug susceptibility with respect to the origin of the isolates or the variety of the fungus were not observed. As an exception, the gattii variety exhibited a high resistance rate to amphotericin B when the technique of Shadomy et al. was applied, a fact possibly related to the greater difficulty for treatment of the disease caused by this fungal variety.

Voriconazole: a new triazole antifungal agent

Voriconazole is a second-generation azole antifungal agent that shows excellent in vitro activity against a wide variety of yeasts and molds. It can be given by either the intravenous or the oral route; the oral formulation has excellent bioavailability. The side effect profile of voriconazole is unique in that non-sight-threatening, transient visual disturbances occur in approximately 30% of patients given the drug. Rash (which can manifest as photosensitivity) and hepatitis also occur. The potential for drug-drug interactions is high and requires that careful attention be given to dosage regimens and monitoring of serum levels and effects of interacting drugs. Voriconazole has been approved for the treatment of invasive aspergillosis and refractory infections with Pseudallescheria/Scedosporium and Fusarium species, and it will likely become the drug of choice for treatment of serious infections with those filamentous fungi.

Review of the safety and efficacy of voriconazole

Voriconazole is a new triazole antifungal agent structurally related to fluconazole, but with improved potency and spectrum of activity. Voriconazole has good in vitro activity against Candida species, Cryptococcus neoformans, Aspergillus spp. and other mould spp. Initial clinical studies and case reports demonstrate efficacy with voriconazole against invasive aspergillosis and infections caused by C. neoformans, Scedosporium apiospermum, Blastomyces dermatitidis, Coccidioides immitis and Histoplasma capsulatum. Voriconazole is available both as oral and iv. preparations and exhibits complex pharmacokinetics. This drug is metabolised by the cytochrome (CYP) P450 enzyme system and therefore, has potential drug interactions. This review evaluates the current literature regarding the safety and efficacy of voriconazole.

Investigational antifungal agents

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

New investigational antifungal agents for treating invasive fungal infections

Systemic fungal infections have been recognised as a major cause of morbidity and mortality during the last two decades. There are only a few therapeutic options for these infections. Severe toxicity, such as impairment of renal function, limits the use of amphotericin B. Flucytosine is associated with side effects and drug resistance. Fluconazole and itraconazole are safer, though emergence of resistance and innate resistance in some fungal pathogens is a concern in their use. Therefore, there is a need for developing novel drugs and/or treatment strategies to combat these infections. In recent years, increased efforts by the pharmaceutical industry and academia have led to the discovery of new re-engineered or reconsidered antifungal agents that are more efficacious, safer and have a broad spectrum of activity. Lipid formulations of polyene antifungal agents, amphotericin B and nystatin, have the advantage of improved therapeutic index. Activity against resistant fungi, high bioavailability, safety and longer half-life are the properties that encourage development of the newer triazoles (e.g., voriconazole, ravuconazole and posaconazole). Echinocandin-like lipopeptide antibiotics are among the antifungal agents with a novel mode of action. In addition to these lead investigational compounds, development of newer antifungal agents is underway.

Novel triazole antifungal agents

The risk of opportunistic infections is greatly increased in patients who are immunocompromised due to AIDS, cancer chemotherapy and organ or bone marrow transplantation. Candida albicans is often associated with serious systemic fungal infections, however other Candida species such as Candida krusei, Candida tropicalis and Candida glabrata, as well as Cryptococcus neoformans and filamentous fungi such as Aspergillus, have also emerged as clinically significant fungal pathogens. Two triazole antifungal agents, fluconazole and itraconazole, were introduced over a decade ago and since then have been used extensively for the prophylaxis and treatment of a variety of fungal infections. Although both drugs are effective and have their place in therapy, limitations regarding the utility of these agents do exist. For example, fluconazole is not effective for the prophylaxis or treatment of Aspergillus species and has limited activity against C. krusei and C. glabrata. The use of itraconazole has been limited secondary to concerns regarding unpredictable bioavailability. The rising incidence of fungal infections and the reported increase of non-albicans candidal infections noted over the past two decades highlight the need for new antifungal agents with improved spectra of activity. Several new triazole agents are in various phases of preclinical and clinical trials and may be available for human use in the near future. Three such agents voriconazole, posaconazole and ravuconazole are reviewed and compared with existing agents.