Toxicity of amphotericin B plus flucytosine in 194 patients with cryptococcal meningitis

CAF to the Rescue! Potential and Challenges of Combination Antifungal Therapy for Reducing Morbidity and Mortality in Hospitalized Patients With Serious Fungal Infections

The global burden of invasive fungal disease is substantial and escalating. Combination antifungal therapy (CAF) may improve patient outcomes by reducing development of resistance, improving drug penetration and rate of fungal clearance, and allowing for lower and less toxic antifungal drug doses; yet, increased cost, antagonism, drug-drug interactions, and toxicity are concerns. Clinical practice guidelines recommend antifungal monotherapy, rather than CAF, for most invasive fungal diseases due to a lack of comparative randomized clinical trials. An examination of the existing body of CAF research should frame new hypotheses and determine priorities for future CAF clinical trials. We performed a systematic review of CAF clinical studies for invasive candidiasis, cryptococcosis, invasive aspergillosis, and mucormycosis. Additionally, we summarized findings from animal models of CAF and assessed laboratory methods available to evaluate CAF efficacy. Future CAF trials should be prioritized according to animal models showing improved survival and observational clinical data supporting efficacy and safety.

Synthesis and Biological Evaluation of Cyanoacrylamides and 5-Iminopyrrol-2-Ones Against Naegleria fowleri

Primary amoebic meningoencephalitis is caused by the free-living amoeba Naegleria fowleri. The lack of standardized treatment has significantly contributed to the high fatality rates observed in reported cases. Therefore, this study aims to explore the anti-Naegleria activity of eight synthesized cyanoacrylamides and 5-iminopyrrol-2-ones. Notably, QOET-109, QOET-111, QOET-112, and QOET-114 exhibited a higher selectivity index against Naegleria compared to those of the rest of the compounds. Subsequently, these chemicals were assessed against the resistant stage of N. fowleri, demonstrating activity similar to that observed in the vegetative stage. Moreover, characteristic events of programmed cell death were evidenced, including chromatin condensation, increased plasma membrane permeability, mitochondrial damage, and heightened oxidative stress, among others. Finally, this research demonstrated the in vitro activity of the cyanoacrylamide and 5-iminopyrrol-2-one molecules, as well as the induction of metabolic event characteristics of regulated cell death in Naegleria fowleri.

Case report: Successful combination therapy with isavuconazole and amphotericin B in treatment of disseminated Candida tropicalis infection

Disseminated candidiasis is a severe complication in patients with hematological malignancies who have undergone chemotherapy or hematopoietic stem cell transplantation. It has a high mortality rate. When disseminated candidiasis caused by Candida tropicalis involves either the brain or heart, the prognosis is extremely poor. Traditional methods such as cultures are limited in diagnosing disseminated candidiasis. We describe a case report of a 55-year-old man with acute myeloid leukemia who developed candidemia caused by Candida tropicalis after chemotherapy, which disseminated extensively to the heart, brain, skin, liver, spleen and kidneys. In this instance, the patient was rapidly diagnosed with candida infection by metagenomic next generation sequencing, and successfully treated with combination therapy of isavuconazole and amphotericin B. The patient continued with treatment of leukemia while simultaneously receiving antifungal therapy, and both leukemia and disseminated candidiasis were effectively controlled. This case report provides real-world experience for treatment of patients with leukemia complicated by disseminated candidiasis.

Therapeutic drug monitoring of antifungal therapies: do we really need it and what are the best practices?

INTRODUCTION

Despite advancements, invasive fungal infections (IFI) still carry high mortality rates, often exceeding 30%. The challenges in diagnosis, coupled with limited effective antifungal options, make managing IFIs complex. Antifungal drugs are essential for IFI management, but their efficacy can be diminished by drug-drug interactions and pharmacokinetic variability. Therapeutic Drug Monitoring (TDM), especially in the context of triazole use, has emerged as a valuable strategy to optimize antifungal therapy.

AREAS COVERED

This review provides current evidence regarding the potential benefits of TDM in IFI management. It discusses how TDM can enhance treatment response, safety, and address altered pharmacokinetics in specific patient populations.

EXPERT OPINION

TDM plays a crucial role in achieving optimal therapeutic outcomes in IFI management, particularly for certain antifungal agents. Preclinical studies consistently show a link between therapeutic drug levels and antifungal efficacy. However, clinical research in mycology faces challenges due to patient heterogeneity and the diversity of fungal infections. TDM's potential advantages in guiding Echinocandin therapy for critically ill patients warrant further investigation. Additionally, for drugs like Posaconazole, assessing whether serum levels or alternative markers like saliva offer the best measure of efficacy is an intriguing question.

Diagnosis and management of cryptococcal meningitis in HIV-infected adults

Cryptococcal meningitis is a leading cause of morbidity and mortality globally, especially in people with advanced HIV disease. Cryptococcal meningitis is responsible for nearly 20% of all deaths related to advanced HIV disease, with the burden of disease predominantly experienced by people in resource-limited countries. Major advancements in diagnostics have introduced low-cost, easy-to-use antigen tests with remarkably high sensitivity and specificity. These tests have led to improved diagnostic accuracy and are essential for screening campaigns to reduce the burden of cryptococcosis. In the last 5 years, several high-quality, multisite clinical trials have led to innovations in therapeutics that have allowed for simplified regimens, which are better tolerated and result in less intensive monitoring and management of medication adverse effects. One trial found that a shorter, 7-day course of deoxycholate amphotericin B is as effective as the longer 14-day course and that flucytosine is an essential partner drug for reducing mortality in the acute phase of disease. Single-dose liposomal amphotericin B has also been found to be as effective as a 7-day course of deoxycholate amphotericin B. These findings have allowed for simpler and safer treatment regimens that also reduce the burden on the healthcare system. This review provides a detailed discussion of the latest evidence guiding the clinical management and special circumstances that make cryptococcal meningitis uniquely difficult to treat.

Induction therapy with high dose fluconazole plus flucytosine for human immunodeficiency virus‐uninfected cryptococcal meningitis patients: Feasible or not?

BACKGROUND

Cryptococcal meningitis (CM) is increasingly recognised in human immunodeficiency virus (HIV)-uninfected patients with high mortality. The efficacy and safety profiles of induction therapy with high-dose fluconazole plus flucytosine remain unclear.

METHODS

HIV-uninfected CM patients who received high-dose fluconazole (800 mg/d) for initial therapy in Huashan Hospital were included in this retrospective study from January 2013 to December 2018. Efficacy and safety of initial therapy, clinical outcomes and risk factors were evaluated.

RESULTS

Twenty-seven (71.1%) patients who received high-dose fluconazole with flucytosine combination therapy and 11 (28.9%) having fluconazole alone for induction therapy were included. With a median duration of 42 days (IQR, 28-86), the successful response rate of initial therapy was 76.3% (29/38), while adverse drug reactions occurred in 14 patients (36.8%). The rate of persistently positive cerebrospinal fluid (CSF) culture results was 30.6% at 2 weeks, which was significantly associated with CSF CrAg titre >1:1280 (OR 9.56; 95% CI 1.40-103.65; p = .010) and CSF culture of Cryptococcus >3.9 log₁₀ CFU/ml (OR 19.20; 95% CI 1.60-920.54; p = .011), and decreased to 8.6% at 4 weeks. One-year mortality was 15.8% (6/38), and low serum albumin (35 g/L) was found as an independent risk factor for 1-year mortality (HR 6.31; 95% CI 1.150-34.632; p = .034).

CONCLUSIONS

Induction therapy with high-dose fluconazole (800 mg/d), combined with flucytosine, effectively treated HIV-uninfected CM and was well tolerated. Long-term fluconazole treatment with continued monitoring is beneficial for patients with persistent infection.

Therapeutic Drug Monitoring of Antifungal Agents in Critically Ill Patients: Is There a Need for Dose Optimisation?

Invasive fungal infections are an important cause of morbidity and mortality, especially in critically ill patients. Increasing resistance rates and inadequate antifungal exposure have been documented in these patients, due to clinically relevant pharmacokinetic (PK) and pharmacodynamic (PD) alterations, leading to treatment failure. Physiological changes such as third spacing (movement of fluid from the intravascular compartment to the interstitial space), hypoalbuminemia, renal failure and hepatic failure, as well as common interventions in the intensive care unit, such as renal replacement therapy and extracorporeal membrane oxygenation, can lead to these PK and PD alterations. Consequently, a therapeutic target concentration that may be useful for one patient may not be appropriate for another. Regular doses do not take into account the important PK variations in the critically ill, and the need to select an effective dose while minimising toxicity advocates for the use of therapeutic drug monitoring (TDM). This review aims to describe the current evidence regarding optimal PK/PD indices associated with the clinical efficacy of the most commonly used antifungal agents in critically ill patients (azoles, echinocandins, lipid complexes of amphotericin B, and flucytosine), provide a comprehensive understanding of the factors affecting the PK of each agent, document the PK parameters of critically ill patients compared to healthy volunteers, and, finally, make recommendations for therapeutic drug monitoring (TDM) of antifungals in critically ill patients.

Augmenting Azoles with Drug Synergy to Expand the Antifungal Toolbox

Fungal infections impact the lives of at least 12 million people every year, killing over 1.5 million. Wide-spread use of fungicides and prophylactic antifungal therapy have driven resistance in many serious fungal pathogens, and there is an urgent need to expand the current antifungal arsenal. Recent research has focused on improving azoles, our most successful class of antifungals, by looking for synergistic interactions with secondary compounds. Synergists can co-operate with azoles by targeting steps in related pathways, or they may act on mechanisms related to resistance such as active efflux or on totally disparate pathways or processes. A variety of sources of potential synergists have been explored, including pre-existing antimicrobials, pharmaceuticals approved for other uses, bioactive natural compounds and phytochemicals, and novel synthetic compounds. Synergy can successfully widen the antifungal spectrum, decrease inhibitory dosages, reduce toxicity, and prevent the development of resistance. This review highlights the diversity of mechanisms that have been exploited for the purposes of azole synergy and demonstrates that synergy remains a promising approach for meeting the urgent need for novel antifungal strategies.

Progressive Cytopenia Developing during Treatment of Cryptococcosis in a Patient with HIV Infection and Bone Marrow Cryptococcal Infection

Cytopenia is a common complication in patients with human immunodeficiency virus (HIV) infection. Identifying the cause is demanding because of the wide range of possible diagnoses. We herein report an HIV-infected patient with disseminated cryptococcosis involving multiple organs including the blood, brain, lungs, and bone marrow, who developed progressive pancytopenia after initiation of anti-fungal treatment with liposomal amphotericin-B (L-AMB) and flucytosine (5FC). The pancytopenia persisted despite early 5FC discontinuation. A bone marrow biopsy revealed cryptococcal infiltration and the blood examination findings recovered quickly after resuming L-AMB. Thus, this HIV-infected patient's pathological findings and clinical course suggested that the primary cause of the pancytopenia was bone marrow cryptococcosis.

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.

Combination Therapy for HIV-Associated Cryptococcal Meningitis-A Success Story

Cryptococcal meningitis is the leading cause of adult meningitis in patients with HIV, and accounts for 15% of all HIV-related deaths in sub-Saharan Africa. The mainstay of management is effective antifungal therapy, despite a limited arsenal of antifungal drugs, significant progress has been made developing effective treatment strategies by using combination regimens. The introduction of fluconazole as a safe and effective step-down therapy allowed for shorter courses of more fungicidal agents to be given as induction therapy, with higher doses achieving more rapid CSF sterilisation and improved treatment outcomes. The development of early fungicidal activity (EFA), an easily measured surrogate of treatment efficacy, has enabled rapid identification of effective combinations through dose ranging phase II studies, allowing further evaluation of clinical benefit in targeted phase III studies. Recent clinical trials have shown that shorter course induction regimens using one week of amphotericin paired with flucytosine are non-inferior to traditional two-week induction regimens and that the combination of fluconazole and flucytosine offers a viable treatment alternative when amphotericin is unavailable. Access to drugs in many low and middle-income settings remains challenging but is improving, and novel strategies based on single high dose liposomal amphotericin B promise further reduction in treatment complications and toxicities. This review aims to summarise the key findings of the principal clinical trials that have led to the success story of combination therapy thus far.

Molecular Mechanisms of 5-Fluorocytosine Resistance in Yeasts and Filamentous Fungi

Effective management and treatment of fungal diseases is hampered by poor diagnosis, limited options for antifungal therapy, and the emergence of antifungal drug resistance. An understanding of molecular mechanisms contributing to resistance is essential to optimize the efficacy of currently available antifungals. In this perspective, one of the oldest antifungals, 5-fluorocytosine (5-FC), has been the focus of recent studies applying advanced genomic and transcriptomic techniques to decipher the order of events at the molecular level that lead to resistance. These studies have highlighted the complexity of resistance and provided new insights that are reviewed in the present paper.

Pharmacokinetics and tolerance of repeated oral administration of 5-fluorocytosine in healthy dogs

Background

5-fluorocytosine is a pyrimidine and a fluorinated cytosine analog mainly used as an antifungal agent. It is a precursor of 5-fluorouracil, which possesses anticancer properties. To reduce systemic toxicity of 5-fluorouracil during chemotherapy, 5- fluorocytosine can be used as a targeted anticancer agent. Expression of cytosine deaminase by a viral vector within a tumor allows targeted chemotherapy by converting 5-fluorocytosine into the cytotoxic chemotherapeutic agent 5-fluorouracil. However, little is known about the tolerance of 5-fluorocytosine in dogs after prolonged administration.

Results

In three healthy Beagle dogs receiving 100 mg/kg of 5-fluorocytosine twice daily for 14 days by oral route, non-compartmental pharmacokinetics revealed a terminal elimination half-life of 164.5 ± 22.5 min at day 1 and of 179.2 ± 11.5 min, after 7 days of administration. Clearance was significantly decreased between day 1 and day 7 with 0.386 ± 0.031 and 0.322 ± 0.027 ml/min/kg, respectively. Maximal plasma concentration values were below 100 µg/ml, which is considered within the therapeutic margin for human patients. 5-fluorouracil plasma concentration was below the limit of detection at all time points. The main adverse events consisted of depigmented, ulcerated, exudative, and crusty cutaneous lesions 10 to 13 days after beginning 5-fluorocytosine administration. The lesions were localized to the nasal planum, the lips, the eyelids, and the scrotum. Histological analyses were consistent with a cutaneous lupoid drug reaction. Complete healing was observed 15 to 21 days after cessation of 5-fluorocytosine. No biochemical or hematological adverse events were noticed.

Conclusions

Long term administration of 5-fluorocytosine was associated with cutaneous toxicity in healthy dogs. It suggests that pharmacotherapy should be adjusted to reduce the toxicity of 5-fluorocytosine in targeted chemotherapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02927-5.

Moderate levels of 5-fluorocytosine cause the emergence of high frequency resistance in cryptococci

The antifungal agent 5-fluorocytosine (5-FC) is used for the treatment of several mycoses, but is unsuitable for monotherapy due to the rapid development of resistance. Here, we show that cryptococci develop resistance to 5-FC at a high frequency when exposed to concentrations several fold above the minimal inhibitory concentration. The genomes of resistant clones contain alterations in genes relevant as well as irrelevant for 5-FC resistance, suggesting that 5-FC may be mutagenic at moderate concentrations. Mutations in FCY2 (encoding a known permease for 5-FC uptake), FCY1, FUR1, UXS1 (encoding an enzyme that converts UDP-glucuronic acid to UDP-xylose) and URA6 contribute to 5-FC resistance. The uxs1 mutants accumulate UDP-glucuronic acid, which appears to down-regulate expression of permease FCY2 and reduce cellular uptake of the drug. Additional mutations in genes known to be required for UDP-glucuronic acid synthesis (UGD1) or a transcriptional factor NRG1 suppress UDP-glucuronic acid accumulation and 5-FC resistance in the uxs1 mutants.

Pathogenic fungi rapidly develop resistance to the antifungal agent 5-fluorocytosine (5-FC). Here, Chang et al. explore the mechanisms by which Cryptococcus develops 5-FC resistance at a high frequency, including mutations in several genes and altered levels of key metabolites.

Antifungals in Clinical Use and the Pipeline

Over the past 15 years, there has been an increase in the development and utilization of newer antifungal agents. The ideal antifungal, however, in regard to spectrum of activity, pharmacokinetic/pharmacodynamic properties, development of resistance, safety, and drug interaction profile remains elusive. This article reviews pharmacologic aspects of Food and Drug Administration-approved polyenes, flucytosine, azoles, and echinocandins as well as promising pipeline antifungal agents. Unique properties of these newer agents are highlighted. The clinical role of established and investigational antifungal agents as treatment and/or prevention of invasive fungal infections is discussed.

Too Much of a Good Thing: Defining Antimicrobial Therapeutic Targets to Minimize Toxicity

Antimicrobials are a common cause of drug toxicity. Understanding the relationship between systemic antimicrobial exposure and toxicity is necessary to enable providers to take a proactive approach to prevent undesired drug effects. When an exposure threshold has been defined that predicts drug toxicity, therapeutic drug monitoring (TDM) can be performed to assure drug exposure does not exceed the defined threshold. Although some antimicrobials have well-defined dose-dependent toxicities, many other exposure-toxicity relationships have either not been well-defined or, in some cases, not been evaluated at all. In this review, we examine the relationship between exposures and toxicities for antibiotic, antifungal, and antiviral agents. Furthermore, we classify these relationships into four categories: known association between drug exposure and toxicity such that clinical implementation of a specific exposure threshold associated with toxicity for TDM is supported (category 1), known association between drug exposure and toxicity but the specific exposure threshold associated with toxicity is undefined (category 2), association between drug exposure and toxicity has been suggested but relationship is poorly defined (category 3), and no known association between drug exposure and toxicity (category 4). Further work to define exposure-toxicity thresholds and integrate effective TDM strategies has the potential to minimize many of the observed antimicrobial toxicities.

Therapeutic drug monitoring of flucytosine in a cardiac transplant patient receiving continuous veno-venous hemofiltration and intermittent hemodialysis: A case report

Invasive candidiasis is one of the common infections in solid organ transplant recipients. Guidelines recommend echinocandins or liposomal amphotericin with consideration of flucytosine (5-fluorocytosine; 5-FC) as synergistic therapy for treatment of select deep-seated Candida infections, including complex endovascular infections. Flucytosine undergoes extensive renal elimination; however, optimal dosing in patients with renal impairment, or those requiring renal replacement therapy (RRT), is not well-established. We describe a case of a 60-year old female who underwent orthotopic heart transplant complicated by Candida parapsilosis complex fungemia with mediastinitis and development of end-stage renal disease requiring RRT. Flucytosine therapeutic drug monitoring was performed on continuous veno-venous hemofiltration (CVVH) and intermittent hemodialysis (iHD) to guide appropriate dosing. Our results support 5-FC doses of 25 mg/kg daily while undergoing CVVH with a low fluid replacement rate and 21 mg/kg post-iHD or 17 mg/kg daily while receiving thrice weekly iHD.

The Antifungal and Synergistic Effect of Bisphosphonates in Cryptococcus

New treatment strategies are required for cryptococcosis, a leading mycosis in HIV-AIDS patients. Following the identification of Cryptococcus proteins differentially expressed in response to fluconazole, we targeted farnesyl pryrophosphate synthetase (FPPS), an enzyme in the squalene biosynthesis pathway, using nitrogenous bisphosphonates. We hypothesized that these would disrupt squalene synthesis and thereby produce synergy with fluconazole, which acts on a downstream pathway that requires squalene. The susceptibilities of 39 clinical isolates from 6 different species of Cryptococcus were assessed for bisphosphonates and fluconazole, used both independently and in combination. Effective fluconazole-bisphosphonate combinations were then assessed for fungicidal activity, efficacy against biofilms, and ability to resolve cryptococcosis in an invertebrate model. The nitrogenous bisphosphonates risedronate, alendronate, and zoledronate were antifungal against all strains tested. Zoledronate was the most effective (geometric mean MIC = 113.03 mg/liter; risedronate = 378.49 mg/liter; alendronate = 158.4 mg/liter) and was broadly synergistic when combined with fluconazole, with a fractional inhibitory concentration index (FICI) of ≤0.5 in 92% of isolates. Fluconazole and zoledronate in combination were fungicidal in a time-kill assay, inhibited Cryptococcus biofilms, prevented the development of fluconazole resistance, and resolved infection in a nematode model. Supplementation with squalene eliminated bisphosphonate-mediated synergy, demonstrating that synergy was due to the inhibition of squalene biosynthesis. This study demonstrates the utility of targeting squalene synthesis for improving the efficacy of azole-based antifungal drugs and suggests bisphosphonates are promising lead compounds for further antifungal development.

Pharmacokinetics of flucytosine in a critically ill patient on continuous venovenous hemodiafiltration

PURPOSE

To describe the pharmacokinetics of flucytosine in a critically ill patient undergoing continuous venovenous hemodiafiltration (CVVHDF) treated for cryptococcal meningitis.

SUMMARY

A 20-year-old female weighing 93.4 kg with a body mass index of 34.3 kg/m2 with a past medical history of systemic lupus erythematous with diffuse proliferative lupus nephritis (class IV) was admitted to the hospital after several months of worsening dyspnea, fatigue, myalgia, vomiting, and diarrhea. The patient developed worsening renal function and volume overload requiring CVVHDF on hospital day 7. She was diagnosed with cryptococcal meningitis on hospital day 8, and flucytosine 2,500 mg enterally every 12 hours and liposomal amphotericin B 500 mg intravenously every 24 hours were initiated. Flucytosine serum concentrations were collected on day 4 of therapy, and pharmacokinetics were performed on 2 sequential levels. Pharmacokinetic calculations displayed an elimination rate constant of 0.0338 h-1, a volume of distribution between 0.42 and 0.43 L/kg, a half-life of 20.5 hours, and a total drug clearance between 1.32 and 1.36 L/h while on CVVHDF. The nonsequential levels displayed good correlation, and no further monitoring or dosage adjustment was required. The patient completed therapy, with clinical resolution of her infection, and no toxicities due to flucytosine were noted.

CONCLUSION

Flucytosine dosed at 25 mg/kg of actual body weight every 12 hours during CVVHDF conferred therapeutic levels with no appreciable toxicities. Because of its narrow therapeutic index and risk of toxicity, additional pharmacokinetic studies are needed to determine optimal drug dosing of this medication in patients requiring renal replacement therapy.

Griseococcin (1) from Bovistella radicata (Mont.) Pat and antifungal activity

Background

To evaluate the antimicrobial and microbicidel activity of B. radicata fermentation broth, the broth was purified by DEAE-cellulose and sephadex LC-20 column. The compounds were submitted to spectral analyses (HPLC, FT-IR, 1D and 2D NMR etc.).

Results

The purified compounds were identified as the Griseococcin(s) which were naphthoquinone derivatives, the Chemical formula and MW of Griseococcin (1) was determined as C₃₇O₁₀H₄₃N and 661 Da. only Griseococcin (1) has good antimicrobial activity among the Griseococcin(s). The zone of inhibition (ZOI), minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) or minimum fungicidal concentration (MFC) of Griseococcin (1) were used to investigate the antimicrobial activity. Antifungal activity of Griseococcin (1) was significant, especially for main pathogenic fungus Trichophyton rubrum and Trichophyton mentagrophytes, MFC/MIC of Griseococcin (1) was 1, while MFC/MIC of postive control was greater than 4, the fungicidal effect of Griseococcin (1) was better than that of positive control.

Conclusions

In this paper, the secondary metabolite compound Griseococcin (1) from B. radicata was purified. The purified compound can restrain main pathogens (T. rubrum and T. mentagrophytes) leading to tinea pedis. The antifungal activity of Griseococcin (1) was similar to that of the positive control and the fungicidal effect of Griseococcin (1) was better than that of positive control, it might be suitable for pharmaceutical industries.

Natural alkaloid tryptanthrin exhibits novel anticryptococcal activity

Cryptococcal meningitis is a prevalent invasive fungal infection that causes around 180 000 deaths annually. Currently, treatment for cryptococcal meningitis is limited and new therapeutic options are needed. Historically, medicinal plants are used to treat infectious and inflammatory skin infections. Tryptanthrin is a natural product commonly found in these plants. In this study, we demonstrated that tryptanthrin had antifungal activity with minimum inhibitory concentration (MIC) of 2 μg/ml against Cryptococcus species and of 8 μg/ml against Trichophyton rubrum. Further analysis demonstrated that tryptanthrin exerted fungistatic and potent antifungal activity at elevated temperature. In addition, tryptanthrin exhibited a synergistic effect with the calcineurin inhibitors FK506 and cyclosporine A against Cryptococcus neoformans. Furthermore, our data showed that tryptanthrin induced cell cycle arrest at the G1/S phase by regulating the expression of genes encoding cyclins and the SBF/MBF complex (CLN1, MBS1, PCL1, and WHI5) in C. neoformans. Screening of a C. neoformans mutant library further revealed that tryptanthrin was associated with various transporters and signaling pathways such as the calcium transporter (Pmc1) and protein kinase A signaling pathway. In conclusion, tryptanthrin exerted novel antifungal activity against Cryptococcus species through a mechanism that interferes with the cell cycle and signaling pathways.

LAY SUMMARY

The natural product tryptanthrin had antifungal activity against Cryptococcus species by interfering cell cycle and exerted synergistic effects with immunosuppressants FK506 and cyclosporine A. Our findings suggest that tryptanthrin may be a potential drug or adjuvant for the treatment of cryptococcosis.

Saliva for Precision Dosing of Antifungal Drugs: Saliva Population PK Model for Voriconazole Based on a Systematic Review

Precision dosing for many antifungal drugs is now recommended. Saliva sampling is considered as a non-invasive alternative to plasma sampling for therapeutic drug monitoring (TDM). However, there are currently no clinically validated saliva models available. The aim of this study is firstly, to conduct a systematic review to evaluate the evidence supporting saliva-based TDM for azoles, echinocandins, amphotericin B, and flucytosine. The second aim is to develop a saliva population pharmacokinetic (PK) model for eligible drugs, based on the evidence. Databases were searched up to July 2019 on PubMed® and Embase®, and 14 studies were included in the systematic review for fluconazole, voriconazole, itraconazole, and ketoconazole. No studies were identified for isavuconazole, posaconazole, flucytosine, amphotericin B, caspofungin, micafungin, or anidulafungin. Fluconazole and voriconazole demonstrated a good saliva penetration with an average S/P ratio of 1.21 (± 0.31) for fluconazole and 0.56 (± 0.18) for voriconazole, both with strong correlation (r = 0.89-0.98). Based on the evidence for TDM and available data, population PK analysis was performed on voriconazole using Nonlinear Mixed Effects Modeling (NONMEM 7.4). 137 voriconazole plasma and saliva concentrations from 11 patients (10 adults, 1 child) were obtained from the authors of the included study. Voriconazole pharmacokinetics was best described by one-compartment PK model with first-order absorption, parameterized by clearance of 4.56 L/h (36.9% CV), volume of distribution of 60.7 L, absorption rate constant of 0.858 (fixed), and bioavailability of 0.849. Kinetics of the voriconazole distribution from plasma to saliva was identical to the plasma kinetics, but the extent of distribution was lower, modeled by a scale factor of 0.5 (4% CV). A proportional error model best accounted for the residual variability. The visual and simulation-based model diagnostics confirmed a good predictive performance of the saliva model. The developed saliva model provides a promising framework to facilitate saliva-based precision dosing of voriconazole.

Antifungal therapeutic drug monitoring: focus on drugs without a clear recommendation

BACKGROUND

The goal of therapeutic drug monitoring (TDM) is to determine the appropriate exposure of difficult-to-manage medications to optimize the clinical outcomes in patients in various clinical situations. Concerning antifungal treatment, and knowing that this procedure is expensive and time-consuming, TDM is particularly recommended for certain systemic antifungals: i.e., agents with a well-defined exposure-response relationship and unpredictable pharmacokinetic profile or narrow therapeutic index. Little evidence supports the routine use of TDM for polyenes (amphotericin B), echinocandins, fluconazole or new azoles such as isavuconazole, despite the fact that a better understanding of antifungal exposure may lead to a better response.

AIMS

The aim of this work is to review published pharmacokinetic/pharmacodynamic data on systemically administered antifungals, focusing on those for which monitoring is not routinely recommended by experts.

SOURCES

A MEDLINE search of the literature in English was performed introducing the following search terms: amphotericin B, fluconazole, itraconazole, voriconazole, posaconazole, triazoles, caspofungin, micafungin, anidulafungin, echinocandins, pharmacokinetics, pharmacodynamics, and therapeutic drug monitoring. Review articles and guidelines were also screened.

CONTENT

This review collects different pharmacokinetic/pharmacodynamic aspects of systemic antifungals and summarizes recent threshold values for clinical outcomes and adverse events. Although for polyenes, echinocandins, fluconazole and isavuconazole extensive clinical validation is still required for a clear threshold and a routine monitoring recommendation, particular points such as liposome structure or complex pathophysiological conditions affecting final exposure are discussed. For the rest, their better-defined exposure-response/toxicity relationships allow access to useful threshold values and to justify routine monitoring. Additionally, clinical data are needed to better define thresholds that can minimize the development of antifungal resistance.

IMPLICATIONS

General TDM for all systemic antifungals is not recommended; however, this approach may help to establish an adequate antifungal exposure for a favourable response, prevention of toxicity or development of resistance in special clinical circumstances.

Antimicrobial therapeutic drug monitoring in critically ill adult patients: a Position Paper

Purpose

This Position Paper aims to review and discuss the available data on therapeutic drug monitoring (TDM) of antibacterials, antifungals and antivirals in critically ill adult patients in the intensive care unit (ICU). This Position Paper also provides a practical guide on how TDM can be applied in routine clinical practice to improve therapeutic outcomes in critically ill adult patients.

Methods

Literature review and analysis were performed by Panel Members nominated by the endorsing organisations, European Society of Intensive Care Medicine (ESICM), Pharmacokinetic/Pharmacodynamic and Critically Ill Patient Study Groups of European Society of Clinical Microbiology and Infectious Diseases (ESCMID), International Association for Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT) and International Society of Antimicrobial Chemotherapy (ISAC). Panel members made recommendations for whether TDM should be applied clinically for different antimicrobials/classes.

Results

TDM-guided dosing has been shown to be clinically beneficial for aminoglycosides, voriconazole and ribavirin. For most common antibiotics and antifungals in the ICU, a clear therapeutic range has been established, and for these agents, routine TDM in critically ill patients appears meritorious. For the antivirals, research is needed to identify therapeutic targets and determine whether antiviral TDM is indeed meritorious in this patient population. The Panel Members recommend routine TDM to be performed for aminoglycosides, beta-lactam antibiotics, linezolid, teicoplanin, vancomycin and voriconazole in critically ill patients.

Conclusion

Although TDM should be the standard of care for most antimicrobials in every ICU, important barriers need to be addressed before routine TDM can be widely employed worldwide.

Electronic supplementary material

The online version of this article (10.1007/s00134-020-06050-1) contains supplementary material, which is available to authorized users.

Administration and Dosing of Systemic Antifungal Agents in Pediatric Patients

Neonates and immunosuppressed/immunocompromised pediatric patients are at high risk of invasive fungal diseases. Appropriate antifungal selection and optimized dosing are imperative to the successful prevention and treatment of these life-threatening infections. Conventional amphotericin B was the mainstay of antifungal therapy for many decades, but dose-limiting nephrotoxicity and infusion-related adverse events impeded its use. Despite the development of several new antifungal classes and agents in the past 20 years, and their now routine use in at-risk pediatric populations, data to guide the optimal dosing of antifungals in children are limited. This paper reviews the spectra of activity for approved antifungal agents and summarizes the current literature specific to pediatric patients regarding pharmacokinetic/pharmacodynamic data, dosing, and therapeutic drug monitoring.

Therapeutic drug monitoring of systemic antifungal agents: a pragmatic approach for adult and pediatric patients

Introduction: Therapeutic drug monitoring (TDM) has been shown to optimize the management of invasive fungal infections (IFIs), particularly for select antifungal agents with a well-defined exposure-response relationship and an unpredictable pharmacokinetic profile or a narrow therapeutic index. Select triazoles (itraconazole, voriconazole, and posaconazole) and flucytosine fulfill these criteria, while the echinocandins, fluconazole, isavuconazole, and amphotericin B generally do not do so. Given the morbidity and mortality associated with IFIs and the challenges surrounding the use of currently available antifungal agents, TDM plays an important role in therapy.Areas covered: This review seeks to describe the rationale for TDM of antifungal agents, summarize their pharmacokinetic and pharmacodynamic properties, identify treatment goals for efficacy and safety, and provide recommendations for optimal dosing and therapeutic monitoring strategies.Expert opinion: Several new antifungal agents are currently in development, including compounds from existing antifungal classes with enhanced pharmacokinetic or safety profiles as well as agents with novel targets for the treatment of IFIs. Given the predictable pharmacokinetics of these newly developed agents, use of routine TDM is not anticipated. However, expanded knowledge of exposure-response relationships of these compounds may yield a role for TDM to improve outcomes for adult and pediatric patients.

Tolerability profile of the current antifungal armoury

The tolerability of available antifungal agents is essential to the final outcome of the management of invasive mycoses. There are limited classes of antifungal agents for use, and they can have serious direct toxicities and/or drug-drug interactions. In this review, we examine the common toxicities noted for antifungal agents and attempt to both identify the issues around the adverse events and provide clinical context for their occurrence in these fragile patients.

Outcomes of cryptococcosis in renal transplant recipients in a less-resourced health care system

BACKGROUND

Cryptococcosis is the second most common cause of invasive fungal infections in renal transplant recipients in many countries, and data on graft outcome after treatment for this infection is lacking in less-resourced health care settings.

METHODS

Data from 47 renal transplant recipients were retrospectively collected at a single institution during a period of 13 years. Graft dysfunction, graft loss, and mortality rates were evaluated. Predictors of mortality and graft loss were estimated.

RESULTS

A total of 38 (97.4%) patients treated with amphotericin B deoxycholate (AMBd) showed graft dysfunction after antifungal initiation and 8 (18.2%) had kidney graft loss. Graft loss within 30 days after cryptococcosis onset was significantly associated with disseminated infection, greater baseline creatinine levels, and graft dysfunction concomitant to AMBd therapy and an additional nephrotoxic condition. The 30-day mortality rate was 19.2% and it was significantly associated with disseminated and pulmonary infections, somnolence at admission, high CSF opening pressure, positive CSF India ink, creatinine levels greater than 2.0 mg/dL at admission, graft dysfunction in patients treated with AMBd and an additional nephrotoxic condition and graft loss within 30 days.

CONCLUSION

Graft dysfunction was common in renal transplant recipients with cryptococcosis treated with AMBd. The rate of graft loss rate was high, most frequently in patients with concomitant nephrotoxic conditions. Therefore, the clinical focus should be on the use of less nephrotoxic lipid formulations of amphotericin B in this specific population requiring a polyene induction regimen for treatment of severe cryptococcosis in all health care systems caring for transplantation recipients.

Diagnosis and management of Aspergillus diseases: executive summary of the 2017 ESCMID-ECMM-ERS guideline

The European Society for Clinical Microbiology and Infectious Diseases, the European Confederation of Medical Mycology and the European Respiratory Society Joint Clinical Guidelines focus on diagnosis and management of aspergillosis. Of the numerous recommendations, a few are summarized here. Chest computed tomography as well as bronchoscopy with bronchoalveolar lavage (BAL) in patients with suspicion of pulmonary invasive aspergillosis (IA) are strongly recommended. For diagnosis, direct microscopy, preferably using optical brighteners, histopathology and culture are strongly recommended. Serum and BAL galactomannan measures are recommended as markers for the diagnosis of IA. PCR should be considered in conjunction with other diagnostic tests. Pathogen identification to species complex level is strongly recommended for all clinically relevant Aspergillus isolates; antifungal susceptibility testing should be performed in patients with invasive disease in regions with resistance found in contemporary surveillance programmes. Isavuconazole and voriconazole are the preferred agents for first-line treatment of pulmonary IA, whereas liposomal amphotericin B is moderately supported. Combinations of antifungals as primary treatment options are not recommended. Therapeutic drug monitoring is strongly recommended for patients receiving posaconazole suspension or any form of voriconazole for IA treatment, and in refractory disease, where a personalized approach considering reversal of predisposing factors, switching drug class and surgical intervention is also strongly recommended. Primary prophylaxis with posaconazole is strongly recommended in patients with acute myelogenous leukaemia or myelodysplastic syndrome receiving induction chemotherapy. Secondary prophylaxis is strongly recommended in high-risk patients. We strongly recommend treatment duration based on clinical improvement, degree of immunosuppression and response on imaging.

Repurposing and Reformulation of the Antiparasitic Agent Flubendazole for Treatment of Cryptococcal Meningoencephalitis, a Neglected Fungal Disease

Current therapeutic options for cryptococcal meningitis are limited by toxicity, global supply, and emergence of resistance. There is an urgent need to develop additional antifungal agents that are fungicidal within the central nervous system and preferably orally bioavailable. The benzimidazoles have broad-spectrum antiparasitic activity but also have in vitro antifungal activity that includes Cryptococcus neoformans. Flubendazole (a benzimidazole) has been reformulated by Janssen Pharmaceutica as an amorphous solid drug nanodispersion to develop an orally bioavailable medicine for the treatment of neglected tropical diseases such as onchocerciasis. We investigated the in vitro activity, the structure-activity-relationships, and both in vitro and in vivo pharmacodynamics of flubendazole for cryptococcal meningitis. Flubendazole has potent in vitro activity against Cryptococcus neoformans, with a modal MIC of 0.125 mg/liter using European Committee on Antimicrobial Susceptibility Testing (EUCAST) methodology. Computer models provided an insight into the residues responsible for the binding of flubendazole to cryptococcal β-tubulin. Rapid fungicidal activity was evident in a hollow-fiber infection model of cryptococcal meningitis. The solid drug nanodispersion was orally bioavailable in mice with higher drug exposure in the cerebrum. The maximal dose of flubendazole (12 mg/kg of body weight/day) orally resulted in an ∼2 log₁₀CFU/g reduction in fungal burden compared with that in vehicle-treated controls. Flubendazole was orally bioavailable in rabbits, but there were no quantifiable drug concentrations in the cerebrospinal fluid (CSF) or cerebrum and no antifungal activity was demonstrated in either CSF or cerebrum. These studies provide evidence for the further study and development of the benzimidazole scaffold for the treatment of cryptococcal meningitis.

Therapeutic drug monitoring for invasive mould infections and disease: pharmacokinetic and pharmacodynamic considerations

Therapeutic drug monitoring (TDM) may be required to achieve optimal clinical outcomes in the setting of significant pharmacokinetic variability, a situation that applies to a number of anti-mould therapies. The majority of patients receiving itraconazole should routinely be managed with TDM. Voriconazole exhibits highly variable inter-individual pharmacokinetics, and a trough concentration of 1.0-5.5 mg/L is widely accepted although it is derived from relatively low-quality evidence. The case for TDM of posaconazole is currently in a state of flux following the introduction of a newer tablet formulation with improved oral bioavailability, but it may be indicated when used for either prophylaxis or treatment of established disease. The novel broad-spectrum azole drug isavuconazole does not currently appear to require TDM but 'real-world' data are awaited and TDM could be considered in selected clinical cases. For both polyene and echinocandin agents, there are insufficient data regarding the relationship between serum concentrations and therapeutic outcomes to support the routine use of TDM. A number of practical challenges to the implementation of TDM in the treatment of invasive mould infections remain unsolved. The delivery of TDM as a future standard of care will require real-time measurement of drug concentrations at the bedside and algorithms for dosage adjustment. Finally, measures of pharmacodynamic effect are required to deliver therapy that is truly individualized.

Antifungal Efficacy of an Intravenous Formulation Containing Monomeric Amphotericin B, 5-Fluorocytosine, and Saline for Sodium Supplementation

PURPOSE

Amphotericin B (AmB) and 5-fluorocytosine (5-FC) exhibit additive to synergistic activity against systemic mycoses. Incompatibility of prescribed formulations precludes concomitant IV administration, a route with distinct advantages. Previously, we used PEG-DSPE micelles to produce a reformulation of Fungizone (AmB-SD), AmB solubilized by sodium deoxycholate, called mAmB-90. Herein, we describe a second reformulation that facilitates co-delivery of mAmB-90 and 5-FC, and evaluate the effect of PEG-DSPE micelles on the combination's activity against Candida albicans.

METHODS

We assessed the effect of 5-FC addition on the stability, in vitro toxicity, and antifungal efficacy of mAmB-90. The aggregation state and particle size of mAmB-90 combined with 5-FC (FmAmB-90) was evaluated over 48 h. Hemolytic activity was measured in vitro. Antifungal activity was determined in vitro against C. albicans. The efficacy of monotherapy and combination treatment was evaluated in a neutropenic mouse model of disseminated candidiasis.

RESULTS

The aggregation state, particle size, and hemolytic activity of mAmB-90 were unaffected by 5-FC. While antifungal activity was similar in vitro, mAmB-90 alone and combined with 5-FC was more potent than AmB-SD in vivo.

CONCLUSIONS

Short-term stability and in vivo efficacy of our formulation suggest potential to simultaneously deliver AmB and 5-FC for potent antifungal efficacy.

Central Nervous System Infections in the Critically Ill

Central nervous system (CNS) infections are frequently encountered in the intensive care unit setting and are a significant source of morbidity and mortality. The constantly changing trends in microbial resistance, as well as the pharmacokinetic difficulties in providing effective concentrations of antimicrobials at the site of infection represent a unique challenge to clinicians. Achievement of a successful outcome in patientswith CNS infections is reliant on eradication of the offending pathogen and management of any neurologic complications. This requires an anatomic and physiologic understanding of the different types of CNS infection, diagnostic strategies, associated complications, causative organisms, and the principles that govern drug distribution into the CNS. This article serves as a review of the epidemiology, pathophysiology, diagnosis, and treatment options for a variety of CNS infections, with a focus on those commonly encountered in an intensive care setting.

Pharmacokinetic considerations in treating invasive pediatric fungal infections

INTRODUCTION

Despite the increased availability of systemic antifungal agents in recent years, the management of invasive fungal disease is still associated with significant morbidity and mortality. Knowledge of a drug's pharmacokinetic behavior is critical for optimizing existing treatment strategies.

AREAS COVERED

This review examines the pharmacokinetics of the major drug classes used to treat invasive mycoses including the echinocandins, imidazoles, triazoles, nucleoside analogs, and polyenes. It examines the mechanisms behind dose-exposure profiles that differ in children as compared with adults and explores the utility of pharmacogenetic testing and therapeutic drug monitoring.

EXPERT OPINION

Lifesaving medical advances for oncologic and autoimmune conditions have resulted in a significant increase in the frequency of opportunistic fungal infections. Owing to the high rate of treatment failures observed when managing invasive fungal infections, strategies to optimize antifungal therapy are critical when caring for these complex patients. Opportunities to maximize positive outcomes include dose refinement based on age or genetic status, formulation selection, co-administration of interacting medications, and administration with regard to food. The application of therapeutic drug monitoring for dose individualization is a valuable strategy to achieve pharmacodynamic targets.

Therapeutic drug monitoring of anti-infective agents in critically ill patients

Initial adequate anti-infective therapy is associated with significantly improved clinical outcomes for patients with severe infections. However, in critically ill patients, several pathophysiological and/or iatrogenic factors may affect the pharmacokinetics of anti-infective agents leading to suboptimal drug exposure, in particular during the early phase of therapy. Therapeutic drug monitoring (TDM) may assist to overcome this problem. We discuss the available evidence on the use of TDM in critically ill patient populations for a number of anti-infective agents, including aminoglycosides, β-lactams, glycopeptides, antifungals and antivirals. Also, we present the available evidence on the practices of anti-infective TDM and describe the potential utility of TDM to improve treatment outcome in critically ill patients with severe infections. For aminoglycosides, glycopeptides and voriconazole, beneficial effects of TDM have been established on both drug effectiveness and potential side effects. However, for other drugs, therapeutic ranges need to be further defined to optimize treatment prescription in this setting.

Therapeutic drug monitoring of antimicrobials

As pathology services become more centralized and automated, the measurement of therapeutic antimicrobial drugs concentrations is increasingly performed in clinical biochemistry or 'blood science' laboratories. This review outlines key groups of antimicrobial agents: aminoglycosides, glycopeptides, antifungal agents and antituberculosis agents, their role in managing infectious diseases, and the reasons why serum concentration measurement is important.

Drug-induced acid-base disorders

The incidence of acid-base disorders (ABDs) is high, especially in hospitalized patients. ABDs are often indicators for severe systemic disorders. In everyday clinical practice, analysis of ABDs must be performed in a standardized manner. Highly sensitive diagnostic tools to distinguish the various ABDs include the anion gap and the serum osmolar gap. Drug-induced ABDs can be classified into five different categories in terms of their pathophysiology: (1) metabolic acidosis caused by acid overload, which may occur through accumulation of acids by endogenous (e.g., lactic acidosis by biguanides, propofol-related syndrome) or exogenous (e.g., glycol-dependant drugs, such as diazepam or salicylates) mechanisms or by decreased renal acid excretion (e.g., distal renal tubular acidosis by amphotericin B, nonsteroidal anti-inflammatory drugs, vitamin D); (2) base loss: proximal renal tubular acidosis by drugs (e.g., ifosfamide, aminoglycosides, carbonic anhydrase inhibitors, antiretrovirals, oxaliplatin or cisplatin) in the context of Fanconi syndrome; (3) alkalosis resulting from acid and/or chloride loss by renal (e.g., diuretics, penicillins, aminoglycosides) or extrarenal (e.g., laxative drugs) mechanisms; (4) exogenous bicarbonate loads: milk-alkali syndrome, overshoot alkalosis after bicarbonate therapy or citrate administration; and (5) respiratory acidosis or alkalosis resulting from drug-induced depression of the respiratory center or neuromuscular impairment (e.g., anesthetics, sedatives) or hyperventilation (e.g., salicylates, epinephrine, nicotine).

Consensus guidelines for optimising antifungal drug delivery and monitoring to avoid toxicity and improve outcomes in patients with haematological malignancy, 2014

Antifungal agents may be associated with significant toxicity or drug interactions leading to sub-therapeutic antifungal drug concentrations and poorer clinical outcomes for patients with haematological malignancy. These risks may be minimised by clinical assessment, laboratory monitoring, avoidance of particular drug combinations and dose modification. Specific measures, such as the optimal timing of oral drug administration in relation to meals, use of pre-hydration and electrolyte supplementation may also be required. Therapeutic drug monitoring (TDM) of antifungal agents is warranted, especially where non-compliance, non-linear pharmacokinetics, inadequate absorption, a narrow therapeutic window, suspected drug interaction or unexpected toxicity are encountered. Recommended indications for voriconazole and posaconazole TDM in the clinical management of haematology patients are provided. With emerging knowledge regarding the impact of pharmacogenomics upon metabolism of azole agents (particularly voriconazole), potential applications of pharmacogenomic evaluation to clinical practice are proposed.

Pharmacokinetics and pharmacodynamics of antifungals in children and their clinical implications

Invasive fungal infections are a significant cause of morbidity and mortality in children. Successful management of these systemic infections requires identification of the causative pathogen, appropriate antifungal selection, and optimisation of its pharmacokinetic and pharmacodynamic properties to maximise its antifungal activity and minimise toxicity and the emergence of resistance. This review highlights salient scientific advancements in paediatric antifungal pharmacotherapies and focuses on pharmacokinetic and pharmacodynamic studies that underpin current clinical decision making. Four classes of drugs are widely used in the treatment of invasive fungal infections in children, including the polyenes, triazoles, pyrimidine analogues and echinocandins. Several lipidic formulations of the polyene amphotericin B have substantially reduced the toxicity associated with the traditional amphotericin B formulation. Monotherapy with the pyrimidine analogue flucytosine rapidly promotes the emergence of resistance and cannot be recommended. However, when used in combination with other antifungal agents, therapeutic drug monitoring of flucytosine has been shown to reduce high peak flucytosine concentrations, which are strongly associated with toxicity. The triazoles feature large inter-individual pharmacokinetic variability, although this pattern is less pronounced with fluconazole. In clinical trials, posaconazole was associated with fewer adverse effects than other members of the triazole family, though both posaconazole and itraconazole display erratic absorption that is influenced by gastric pH and the gastric emptying rate. Limited data suggest that the clinical response to therapy may be improved with higher plasma posaconazole and itraconazole concentrations. For voriconazole, pharmacokinetic studies among children have revealed that children require twice the recommended adult dose to achieve comparable blood concentrations. Voriconazole clearance is also affected by the cytochrome P450 (CYP) 2C19 genotype and hepatic impairment. Therapeutic drug monitoring is recommended as voriconazole pharmacokinetics are highly variable and small dose increases can result in marked changes in plasma concentrations. For the echinocandins, the primary source of pharmacokinetic variability stems from an age-dependent decrease in clearance with increasing age. Consequently, young children require larger doses per kilogram of body weight than older children and adults. Routine therapeutic drug monitoring for the echinocandins is not recommended. The effectiveness of many systemic antifungal agents has been correlated with pharmacodynamic targets in in vitro and in murine models of invasive candidiasis and aspergillosis. Further study is needed to translate these findings into optimal dosing regimens for children and to understand how these agents interact when multiple antifungal agents are used in combination.

Antifungal pharmacokinetics and pharmacodynamics

Successful treatment of infectious diseases requires choice of the most suitable antimicrobial agent, comprising consideration of drug pharmacokinetics (PK), including penetration into infection site, pathogen susceptibility, optimal route of drug administration, drug dose, frequency of administration, duration of therapy, and drug toxicity. Antimicrobial pharmacokinetic/pharmacodynamic (PK/PD) studies consider these variables and have been useful in drug development, optimizing dosing regimens, determining susceptibility breakpoints, and limiting toxicity of antifungal therapy. Here the concepts of antifungal PK/PD studies are reviewed, with emphasis on methodology and application. The initial sections of this review focus on principles and methodology. Then the pharmacodynamics of each major antifungal drug class (polyenes, flucytosine, azoles, and echinocandins) is discussed. Finally, the review discusses novel areas of pharmacodynamic investigation in the study and application of combination therapy.

Pharmacokinetics and pharmacodynamics of antifungals in children: clinical implications

Invasive fungal disease (IFD) remains life threatening in premature infants and immunocompromised children despite the recent development of new antifungal agents. Optimal dosing of antifungals is one of the few factors clinicians can control to improve outcomes of IFD. However, dosing in children cannot be extrapolated from adult data because IFD pathophysiology, immune response, and drug disposition differ from adults. We critically examined the literature on pharmacokinetics (PK) and pharmacodynamics (PD) of antifungal agents and highlight recent developments in treating pediatric IFD. To match adult exposure in pediatric patients, dosing adjustment is necessary for almost all antifungals. In young infants, the maturation of renal and metabolic functions occurs rapidly and can significantly influence drug exposure. Fluconazole clearance doubles from birth to 28 days of life and, beyond the neonatal period, agents such as fluconazole, voriconazole, and micafungin require higher dosing than in adults because of faster clearance in children. As a result, dosing recommendations are specific to bracketed ranges of age. PD principles of antifungals mostly rely on in vitro and in vivo models but very few PD studies specifically address IFD in children. The exposure-response relationship may differ in younger children compared with adults, especially in infants with invasive candidiasis who are at higher risk of disseminated disease and meningoencephalitis, and by extension severe neurodevelopmental impairment. Micafungin is the only antifungal agent for which a specific target of exposure was proposed based on a neonatal hematogenous Candida meningoencephalitis animal model. In this review, we found that pediatric data on drug disposition of newer triazoles and echinocandins are lacking, dosing of older antifungals such as fluconazole and amphotericin B products still need optimization in young infants, and that target PK/PD indices need to be clinically validated for almost all antifungals in children. A better understanding of age-specific PK and PD of new antifungals in infants and children will help improve clinical outcomes of IFD by informing dosing and identifying future research areas.

Antifungal agents and therapy for infants and children with invasive fungal infections: a pharmacological perspective

Invasive fungal infections, although relatively rare, are life-threatening diseases in premature infants and immunocompromised children. While many advances have been made in antifungal therapeutics in the last two decades, knowledge of the pharmacokinetics and pharmacodynamics of antifungal agents for infants and children remains incomplete. This review summarizes the pharmacology and clinical utility of currently available antifungal agents and discusses the opportunities and challenges for future research.

Therapeutic drug monitoring (TDM) of antifungal agents: guidelines from the British Society for Medical Mycology

The burden of human disease related to medically important fungal pathogens is substantial. An improved understanding of antifungal pharmacology and antifungal pharmacokinetics-pharmacodynamics has resulted in therapeutic drug monitoring (TDM) becoming a valuable adjunct to the routine administration of some antifungal agents. TDM may increase the probability of a successful outcome, prevent drug-related toxicity and potentially prevent the emergence of antifungal drug resistance. Much of the evidence that supports TDM is circumstantial. This document reviews the available literature and provides a series of recommendations for TDM of antifungal agents.