Antifungal therapy in a murine model of disseminated infection by Cryptococcus gattii

Consensus guidelines for optimising antifungal drug delivery and monitoring to avoid toxicity and improve outcomes in patients with haematological malignancy and haemopoietic stem cell transplant recipients, 2021

Antifungal agents can have complex dosing and the potential for drug interaction, both of which can lead to subtherapeutic antifungal drug concentrations and poorer clinical outcomes for patients with haematological malignancy and haemopoietic stem cell transplant recipients. Antifungal agents can also be associated with significant toxicities when drug concentrations are too high. Suboptimal dosing can be minimised by clinical assessment, laboratory monitoring, avoidance of interacting drugs, and dose modification. Therapeutic drug monitoring (TDM) plays an increasingly important role in antifungal therapy, particularly for antifungal agents that have an established exposure-response relationship with either a narrow therapeutic window, large dose-exposure variability, cytochrome P450 gene polymorphism affecting drug metabolism, the presence of antifungal drug interactions or unexpected toxicity, and/or concerns for non-compliance or inadequate absorption of oral antifungals. These guidelines provide recommendations on antifungal drug monitoring and TDM-guided dosing adjustment for selected antifungal agents, and include suggested resources for identifying and analysing antifungal drug interactions. Recommended competencies for optimal interpretation of antifungal TDM and dose recommendations are also provided.

Pharmacokinetics and Pharmacodynamics of Posaconazole

Posaconazole is typically used for preventing invasive yeast and mold infections such as invasive aspergillosis in high-risk immunocompromised patients. The oral suspension was the first released formulation and many pharmacokinetic and pharmacodynamic studies of this formulation have been published. Erratic absorption profiles associated with this formulation were widely reported. Posaconazole exposure was found to be significantly influenced by food and many gastrointestinal conditions, including pH and motility. As a result, low posaconazole plasma concentrations were obtained in large groups of patients. These issues of erratic absorption urged the development of the subsequently marketed delayed-release tablet, which proved to be associated with higher and more stable exposure profiles. Shortly thereafter, an intravenous formulation was released for patients who are not able to take oral formulations. Both new formulations require a loading dose on day 1 to achieve high posaconazole concentrations more quickly, which was not possible with the oral suspension. So far, there appears to be no evidence of increased toxicity correlated to the higher posaconazole exposure achieved with the regimen for these formulations. The higher systemic availability of posaconazole for the delayed-release tablet and intravenous formulation have resulted in these two formulations being preferable for both prophylaxis and treatment of invasive fungal disease. This review aimed to integrate the current knowledge on posaconazole pharmacokinetics, pharmacodynamics, major toxicity, existing resistance, clinical experience in special populations, and new therapeutic strategies in order to get a clear understanding of the clinical use of this drug.

Efficacy of voriconazole in vitro and in invertebrate model of cryptococcosis

Cryptococcosis is a common opportunistic infection in patients with advanced HIV infection and may also affect immunocompetent patients. The available antifungal agents are few and other options are needed for the cryptococcosis treatment. In this work, we first analyzed the virulence of twelve C. neoformans and C. gattii strains assessing capsule thickness, biofilms formation, and survival and morbidity in the invertebrate model of Galleria mellonella and then we evaluated the antifungal activity of voriconazole (VRC) in vitro and in vivo also using G. mellonella. Our results showed that all Cryptococcus spp. isolates were able to produce capsule and biofilms, and were virulent using G. mellonella model. The VRC has inhibitory activity on planktonic cells with MIC values ranging from 0.03 to 0.25 μg/mL on Cryptococcus spp.; and these isolates were more tolerant to fluconazole (ranging from 0.25 to 16 μg/mL), the triazol agent often recommended alone or in combination with amphotericin B in the cryptococcosis therapy. In contrast, mature biofilms were less susceptible to the VRC treatment. The VRC (10 or 20 mg/kg) treatment of infected G. mellonella larvae significantly increased the larval survival when compared to the untreated group for the both Cryptococcus species and significantly decreased the fungal burden and dissemination in the larval tissue. Our findings corroborate with the literature data, supporting the potential use of VRC as an alternative for cryptococcosis treatment. Here, we emphasize the use of G. mellonella larval model as an alternative animal model for studies of antifungal efficacy on mycosis, including cryptococcosis.

Antifungal Drugs: Special Problems Treating Central Nervous System Infections

Treating fungal infections in the central nervous system (CNS) remains a challenge despite the availability of new antifungal agents. Therapy is limited by poor understanding of the kinetic properties of antifungal drugs in the CNS compounded by lack of data for many agents. In some cases, clinical response rates do not correspond to data on drug concentrations in the cerebral spinal fluid and/or brain parenchyma. In order to better characterize the use of antifungal agents in treating CNS infections, a review of the essential principles of neuroPK are reviewed. Specific data regarding antifungal drug concentrations in the cerebral spinal fluid and brain tissue are described from human data where available. Alternative dosing regimens and the role of antifungal drug concentration monitoring in treating fungal infections in the CNS are also discussed. Having a better understanding of these key concepts will help guide clinicians in determining the best treatment courses for patients with these devastating infections.

A new method for studying cryptococcosis in a murine model using 99mTc-Cryptococcus gattii

Cryptococcus gattii is one of the etiologic agents of cryptococcosis, a systemic mycosis that occurs in healthy and immunosuppressed humans and animals worldwide. Primary pulmonary infection caused by C. gattii is usually followed by fungal dissemination to the central nervous system, resulting in high mortality rates. In this context, animal models of cryptococcosis are useful in the study of fungal pathogenesis and host response against the pathogen, and for testing novel therapeutic options. The most frequently applied method to study fungal dissemination from the lungs to other organs is by culturing tissues, which is not accurate for the detection and quantification of fungal load at early stages of the infection. To overcome this problem, the purpose of this study was to develop a new method for the quantification of Cryptococcus dissemination. One C. gattii strain was efficiently radiolabeled with technetium-99m (99mTc), without affecting viability of the cells. Further, the 99mTc-C. gattii (111 MBq) strain was used to infect mice by intratracheal and intravenous route for biodistribution studies. 99mTc-C. gattii was successfully used in detection of the yeast in the brain of mice 6 hours postinoculation, while the detection using colony forming units was possible only 24 hours postinfection. Our results provided an alternative method that could be applied in further investigations regarding the efficacy of antifungals, fungal virulence, and host-pathogen interactions.

Cladophialophora bantiana osteomyelitis in a renal transplant patient

Cladophialophora bantiana is a neurotropic dematiaceous fungus which rarely causes disseminated disease. We report a case of proven C. bantiana osteomyelitis in a renal transplant recipient, complicated with probable cerebral disease. Stable disease was reached after combined antifungal therapies, immune enhancement and amputation of the infected lower limb.

Tissue penetration of antifungal agents

Understanding the tissue penetration of systemically administered antifungal agents is critical for a proper appreciation of their antifungal efficacy in animals and humans. Both the time course of an antifungal drug and its absolute concentrations within tissues may differ significantly from those observed in the bloodstream. In addition, tissue concentrations must also be interpreted within the context of the pathogenesis of the various invasive fungal infections, which differ significantly. There are major technical obstacles to the estimation of concentrations of antifungal agents in various tissue subcompartments, yet these agents, even those within the same class, may exhibit markedly different tissue distributions. This review explores these issues and provides a summary of tissue concentrations of 11 currently licensed systemic antifungal agents. It also explores the therapeutic implications of their distribution at various sites of infection.

Modest efficacy of voriconazole against murine infections by Sporothrix schenckii and lack of efficacy against Sporothrix brasiliensis

The efficacy of voriconazole (VRC) was evaluated against two strains of each of the two most common species causing sporotrichosis, Sporothrix schenckii sensu stricto and Sporothrix brasiliensis, using a murine model of disseminated infection. Voriconazole was administered at doses of 20 or 40 mg kg(-1) per day by gavage. The drug showed some efficacy, especially at 40 mg kg(-1) per day, in prolonging the survival and reducing fungal load in spleen and liver in mice infected with S. schenckii, whereas in animals infected with S. brasiliensis the drug did not work.

Efficacy of posaconazole in murine experimental sporotrichosis

We developed a murine model of systemic sporotrichosis by using three strains of each of the two commonest species causing sporotrichosis, i.e., Sporothrix schenckii sensu stricto and Sporothrix brasiliensis, in order to evaluate the efficacy of posaconazole (PSC). The drug was administered at a dose of 2.5 or 5 mg/kg of body weight twice a day by gavage, and one group was treated with amphotericin B (AMB) as a control treatment. Posaconazole, especially at 5 mg/kg, showed good efficacy against all the strains tested, regardless of their MICs, as measured by prolonged survival, tissue burden reduction, and histopathology.