Population pharmacokinetics of micafungin in pediatric patients and implications for antifungal dosing

Pharmacokinetic evaluation of twice-a-week micafungin for prophylaxis of invasive fungal disease in children with acute lymphoblastic leukaemia: a prospective observational cohort study

OBJECTIVES

To determine the pharmacokinetics of twice-a-week micafungin prophylaxis in paediatric leukaemic patients to provide the rationale for this approach.

METHODS

Twice-a-week micafungin at a dose of 9 mg/kg (maximum 300 mg) was given during the leukaemic induction treatment with at least one pharmacokinetic assessment. Non-linear mixed-effects modelling was used for analysis. For model building, our paediatric data were strengthened with existing adult data. Monte Carlo simulations were performed with twice-a-week dosing regimens of 5, 7 and 9 mg/kg and flat dosing per weight band. Simulated paediatric exposures were compared with the exposure in adults after a once-daily 100 mg regimen.

RESULTS

Sixty-one paediatric patients were included with a median age and weight of 4.0 years (range 1.0-17) and 19.5 kg (range 8.60-182), respectively. A two-compartment model best fitted the data. CL and central Vd were lower (P < 0.01) in paediatric patients compared with adults. Predicted exposures (AUC0-168 h) for the 5, 7 and 9 mg/kg and flat dosing per weight band regimens exceeded the adult reference exposure.

CONCLUSIONS

All twice-a-week regimens appeared to result in adequate exposure for Candida therapy, with simulated exposures well above the adult reference exposure. These findings provide the rationale for the pharmacokinetic equivalence of twice-a-week and once-daily micafungin regimens. The greater micafungin exposures seem to be caused by a slower-than-anticipated CL in our paediatric leukaemic patients. The generalizability of our results for Aspergillus prophylaxis cannot be provided without assumptions on target concentrations and within-class identical efficacy.

Pharmacokinetic, efficacy, and safety considerations for the use of antifungal drugs in the neonatal population

INTRODUCTION

Invasive fungal infections are an important cause of morbidity and mortality in infants, particularly in extreme prematurity. Successful systemic treatment requires consideration of antifungal efficacy, safety, and pharmacokinetics, including optimization of dosing in this population.

AREAS COVERED

This review summarizes published pharmacokinetic data on four classes of antifungal agents used in the neonatal population. Alterations in absorption, distribution, drug metabolism and clearance in infants compared to adult populations are highlighted. Additionally, pharmacodynamics, safety, and therapeutic drug monitoring are discussed. Recent advancements in neonatal antifungal pharmacotherapies are examined, with emphasis on clinical application.

EXPERT OPINION

Over the last two decades, published studies have provided increased knowledge on pharmacokinetic considerations in the neonatal population. Future research should focus on filling in the knowledge gaps that remain regarding the benefits and risks of combination antifungal therapy, the rising use of micafungin for invasive candidiasis given its fungicidal activity against polyene and azole-resistant Candida species and its minimal adverse effect profile, and the need for pharmacokinetic and safety data of broad spectrum triazoles, like voriconazole and posaconazole, in infants. Furthermore, efforts should focus on well-designed trials, including population pharmacokinetic studies, to develop dosing recommendations with subsequent implementation into clinical practice.

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.

Population Pharmacokinetics of Anidulafungin in Critically Ill Patients

A two-compartment pharmacokinetic (PK) population model of anidulafungin was fitted to PK data from 23 critically ill patients (age, 65 years [range, 28 to 81 years]; total body weight [TBW], 75 kg [range, 54 to 168 kg]). TBW was associated with clearance and incorporated into a final population PK model. Simulations suggested that patients with higher TBWs had less-extensive MIC coverage. Dosage escalation may be warranted in patients with high TBWs to ensure optimal drug exposures for treatment of Candida albicans and Candida glabrata infections.

Clinical Pharmacokinetics and Pharmacodynamics of Micafungin

Micafungin is a selective inhibitor of the synthesis of fungal 1,3-β-d-glucan, an essential component of the fungal cell wall. It is available as a powder for infusion only and is registered for the treatment of invasive and esophageal candidiasis in addition to prophylaxis of Candida infections in both adults and children. Average exposure after a single intravenous 100 mg dose in healthy adults is 133 mg h/L. Both exposure and maximum plasma concentration show linear dose proportional pharmacokinetics (PK) over a 0.15–8 mg/kg dose range. In healthy adults, the clearance (CL) is 10.4 mL/h/kg and volume of distribution is 0.2 L/kg; both are independent of the dose. Micafungin is metabolized by arylsulfatase, catechol-O-methyltransferase, and several cytochrome P450 (CYP) isoenzymes (3A4, 1A2, 2B6 and 2C), but no dose adjustments are necessary in patients with (severe) hepatic dysfunction. Exposure to micafungin is lower in hematology patients, and is even further lowered in critically ill patients (including burn patients) compared with healthy volunteers, which might have consequences for treatment efficacy. In children, an increased CL has been reported: 40–80 mL/h/kg in premature neonates and 20 mL/h/kg in children >4 months of age. Therefore, relatively higher doses of 4–10 mg/kg in premature neonates and 2–4 mg/kg in children with invasive candidiasis are used. However, these higher CLs may also be explained by the eightfold higher free fraction of unbound micafungin in premature neonates, meaning that an augmented dose might not be required.

ESCMID-ECMM guideline: diagnosis and management of invasive aspergillosis in neonates and children

SCOPE

Presenting symptoms, distributions and patterns of diseases and vulnerability to invasive aspergillosis (IA) are similar between children and adults. However, differences exist in the epidemiology and underlying conditions, the usefulness of newer diagnostic tools, the pharmacology of antifungal agents and in the evidence from interventional phase 3 clinical trials. Therefore, the European Society for Clinical Microbiology and Infectious Diseases (ESCMID) and the European Confederation of Medical Mycology (ECMM) have developed a paediatric-specific guideline for the diagnosis and management of IA in neonates and children.

METHODS

Review and discussion of the scientific literature and grading of the available quality of evidence was performed by the paediatric subgroup of the ESCMID-ECMM-European Respiratory Society (ERS) Aspergillus disease guideline working group, which was assigned the mandate for the development of neonatal- and paediatric-specific recommendations.

QUESTIONS

Questions addressed by the guideline included the epidemiology of IA in neonates and children; which paediatric patients may benefit from antifungal prophylaxis; how to diagnose IA in neonates and children; which antifungal agents are available for use in neonates and children; which antifungal agents are suitable for prophylaxis and treatment of IA in neonates and children; what is the role of therapeutic drug monitoring of azole antifungals; and which management strategies are suitable to be used in paediatric patients. This guideline provides recommendations for the diagnosis, prevention and treatment of IA in the paediatric population, including neonates. The aim of this guideline is to facilitate optimal management of neonates and children at risk for or diagnosed with IA.

Overview of antifungal dosing in invasive candidiasis

In the past, most antifungal therapy dosing recommendations for invasive candidiasis followed a 'one-size fits all' approach with recommendations for lowering maintenance dosages for some antifungals in the setting of renal or hepatic impairment. A growing body of pharmacokinetic/pharmacodynamic research, however now points to a widespread 'silent epidemic' of antifungal underdosing for invasive candidiasis, especially among critically ill patients or special populations who have altered volume of distribution, protein binding and drug clearance. In this review, we explore how current adult dosing recommendations for antifungal therapy in invasive candidiasis have evolved, and special populations where new approaches to dose optimization or therapeutic drug monitoring may be needed, especially in light of increasing antifungal resistance among Candida spp.

Invasive Candidiasis in Infants and Children: Recent Advances in Epidemiology, Diagnosis, and Treatment

This paper reviews recent advances in three selected areas of pediatric invasive candidiasis: epidemiology, diagnosis, and treatment. Although the epidemiological trends of pediatric invasive candidiasis illustrate a declining incidence, this infection still carries a heavy burden of mortality and morbidity that warrants a high index of clinical suspicion, the need for rapid diagnostic systems, and the early initiation of antifungal therapy. The development of non-culture-based technologies, such as the T2Candida system and (1→3)-β-d-glucan detection assay, offers the potential for early laboratory detection of candidemia and CNS candidiasis, respectively. Among the complications of disseminated candidiasis in infants and children, hematogenous disseminated Candida meningoencephalitis (HCME) is an important cause of neurological morbidity. Detection of (1→3)-β-d-glucan in cerebrospinal fluid serves as an early diagnostic indicator and an important biomarker of therapeutic response. The recently reported pharmacokinetic data of liposomal amphotericin B in children demonstrate dose–exposure relationships similar to those in adults. The recently completed randomized clinical trial of micafungin versus deoxycholate amphotericin B in the treatment of neonatal candidemia provides further safety data for an echinocandin in this clinical setting.

Invasive Aspergillosis in Children: Update on Current Guidelines

Invasive aspergillosis (IA) is an important cause of infectious morbidity and mortality in immunocompromised paediatric patients. Despite improvements in diagnosis, prevention, and treatment, IA is still associated with high mortality rates. To address this issue, several international societies and organisations have proposed guidelines for the management of IA in the paediatric population. In this article, we review current recommendations of the Infectious Diseases Society of America, the European Conference on Infection in Leukaemia and the European Society of Clinical Microbiology and Infectious Diseases for the management and prevention of IA in children.

Invasive Candidiasis in pediatric patients at King Fahad Medical City in Central Saudi Arabia. A 5-year retrospective study

Objectives:

To identify predisposing factors, species distribution, antifungal susceptibility, and outcome.

Methods:

This study is a retrospective chart review that was conducted at a children’s hospital at King Fahad Medical City, Riyadh, Kingdom of Saudi Arabia. One hundred twenty-nine children with invasive candidiasis who were admitted between January 2010 and January 2015.

Results:

The statistical analysis results have revealed a group of risk factors; prematurity in 37 (28.7%) of patients, low birth weight in 42 (32.6%), central venous catheter in 59 (45.7%), malignancy in 21 (16.3%), immunotherapy in 20 (15.5%), and ventilator support in 60 (46.5%). More than 2-fold mortality rate in patients who had heart vegetation (odds ratio [OR]: 2.9) and patients who had Candida isolated from their blood were more than twice as likely to die as patients with Candida isolated from other sites (OR: 2.2). A total of 48.3% of patients on ventilator died versus 26.1% who were not on ventilator (p=0.009); and 43.8% of patients in the ICU died versus only 24.5% of patients who were not in the ICU (p=0.03). Candida parapsilosis exhibited the highest mortality rate (56.2%).

Conclusion:

Candida albicans is the most common isolate among all Candida species. Gender, low birth weight, prolonged ICU stay, presence of vegetation, positive blood culture, and mechanical ventilation as a strong predictive risk factors for death in children with invasive candidiasis, a finding that could be applied as prophylactic indicator in critically ill children especially neonates.

Population Pharmacokinetic Model and Meta-analysis of Outcomes of Amphotericin B Deoxycholate Use in Adults with Cryptococcal Meningitis

There is a limited understanding of the population pharmacokinetics (PK) and pharmacodynamics (PD) of amphotericin B deoxycholate (DAmB) for cryptococcal meningitis. A PK study was conducted in n = 42 patients receiving DAmB (1 mg/kg of body weight every 24 h [q24h]). A 2-compartment PK model was developed. Patient weight influenced clearance and volume in the final structural model. Monte Carlo simulations estimated drug exposure associated with various DAmB dosages. A search was conducted for trials reporting outcomes of treatment of cryptococcal meningitis patients with DAmB monotherapy, and a meta-analysis was performed. The PK parameter means (standard deviations) were as follows: clearance, 0.03 (0.01) × weight + 0.67 (0.01) liters/h; volume, 0.82 (0.80) × weight + 1.76 (1.29) liters; first-order rate constant from central compartment to peripheral compartment, 5.36 (6.67) h^-1; first-order rate constant from peripheral compartment to central compartment, 9.92 (12.27) h^-1 The meta-analysis suggested that the DAmB dosage explained most of the heterogeneity in cerebrospinal fluid (CSF) sterility outcomes but not in mortality outcomes. Simulations of values corresponding to the area under concentration-time curve from h 144 to h 168 (AUC_144-168) resulted in median (interquartile range) values of 5.83 mg · h/liter (4.66 to 8.55), 10.16 mg · h/liter (8.07 to 14.55), and 14.51 mg · h/liter (11.48 to 20.42) with dosages of 0.4, 0.7, and 1.0 mg/kg q24h, respectively. DAmB PK is described adequately by a linear model that incorporates weight with clearance and volume. Interpatient PK variability is modest and unlikely to be responsible for variability in clinical outcomes. There is discordance between the impact that drug exposure has on CSF sterility and its impact on mortality outcomes, which may be due to cerebral pathology not reflected in CSF fungal burden, in addition to clinical variables.

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.

Dose Reduction of Caspofungin in Intensive Care Unit Patients with Child Pugh B Will Result in Suboptimal Exposure

Background and Objectives

Caspofungin is an echinocandin antifungal agent used as first-line therapy for the treatment of invasive candidiasis. The maintenance dose is adapted to body weight (BW) or liver function (Child-Pugh score B or C). We aimed to study the pharmacokinetics of caspofungin and assess pharmacokinetic target attainment for various dosing strategies.

Methods

Caspofungin pharmacokinetic data from 21 intensive care unit (ICU) patients was available. A population pharmacokinetic model was developed. Various dosing regimens (loading dose/maintenance dose) were simulated: licensed regimens (I) 70/50 mg (for BW <80 kg) or 70/70 mg (for BW >80 kg); and (II) 70/35 mg (for Child-Pugh score B); and adapted regimens (III) 100/50 mg (for Child-Pugh score B); (IV) 100/70 mg; and (V) 100/100 mg. Target attainment based on a preclinical pharmacokinetic target for Candida albicans was assessed for relevant minimal inhibitory concentrations (MICs).

Results

A two-compartment model best fitted the data. Clearance was 0.55 L/h and the apparent volumes of distribution in the central and peripheral compartments were 8.9 and 5.0 L, respectively. The median area under the plasma concentration–time curve from time zero to 24 h on day 14 for regimens I–V were 105, 65, 93, 130, and 186 mg·h/L, respectively. Pharmacokinetic target attainment was 100 % (MIC 0.03 µg/mL) irrespective of dosing regimen but decreased to (I) 47 %, (II) 14 %, (III) 36 %, (IV) 69 %, and (V) 94 % for MIC 0.125 µg/mL.

Conclusion

The caspofungin maintenance dose should not be reduced in non-cirrhotic ICU patients based on the Child-Pugh score if this classification is driven by hypoalbuminemia as it results in significantly lower exposure. A higher maintenance dose of 70 mg in ICU patients results in target attainment of >90 % of the ICU patients with species with an MIC of up to 0.125 µg/mL.

Fractal Geometry-Based Decrease in Trimethoprim-Sulfamethoxazole Concentrations in Overweight and Obese People

Trimethoprim-sulfamethoxazole (TMP-SMX) is one of the most widely drugs on earth. The World Health Organization recommends it as an essential basic drug for all healthcare systems. Dosing is inconsistently based on weight, assuming linear relationships. Given that obesity is now a global "pandemic" it is vital that we evaluate the effect of obesity on trimethoprim-sulfamethoxazole concentrations. We conducted a prospective clinical experiment based on optimized design strategies and artificial intelligence algorithms and found that weight and body mass index (BMI) had a profound effect on drug clearance and volume of distribution, and followed nonlinear fractal geometry-based relationships. The findings were confirmed by demonstrating decreased TMP-SMX peak and area under the concentration-time curves in overweight patients based on standard regression statistics. The nonlinear relationships can now be used to identify new TMP-SMX doses in overweight and obese patients for each of the infections caused by the >60 pathogens for which the drug is indicated.

Pharmacokinetics and Safety of Micafungin in Infants Supported With Extracorporeal Membrane Oxygenation

BACKGROUND

Candida is a leading cause of infection in infants on extracorporeal membrane oxygenation (ECMO). Optimal micafungin dosing is unknown in this population because ECMO can alter drug pharmacokinetics (PK).

METHODS

To characterize micafungin pharmacokinetics and safety in infants on ECMO, we conducted an open-label pharmacokinetics trial. Infants on ECMO either received intravenous micafungin 4 mg/kg every 24 h for invasive candidiasis prophylaxis or 8 mg/kg every 24 h when a fungal infection was suspected or confirmed. We collected plasma samples after single and multiple micafungin doses. We defined the therapeutic target as the adult exposure associated with efficacy in phase III trials and the prophylactic target as one-half of the therapeutic target.

RESULTS

We enrolled 12 infants (124 samples) with a median age of 59 days. Using a 1-compartment model, median weight-normalized volume of distribution and clearance were 0.64 L/kg and 0.041 L/kg/h, respectively. Dose-exposure simulations revealed that doses of 2.5 and 5 mg/kg every 24 h matched exposure targets for prophylaxis and treatment of invasive candidiasis, respectively. We did not observe any drug-related adverse events.

CONCLUSIONS

In infants on ECMO, micafungin volume of distribution was higher and clearance was in the upper range of previously published values for infants not on ECMO. Based on these data, we recommend dosing of 2.5 and 5 mg/kg every 24 h for prophylaxis and treatment of invasive candidiasis, respectively, to match adult exposure proven effective against Candida spp.

Population pharmacokinetics and pharmacodynamics of teicoplanin in neonates: making better use of C-reactive protein to deliver individualized therapy

OBJECTIVES

There is uncertainty about the optimal teicoplanin regimens for neonates. The study aim was to determine the population pharmacokinetics (PK) of teicoplanin in neonates, evaluate currently recommended regimens and explore the exposure-effect relationships.

METHODS

An open-label PK study was conducted. Neonates from 26 to 44 weeks post-menstrual age were recruited (n = 18). The teicoplanin regimen was a 16 mg/kg loading dose, followed by 8 mg/kg once daily. Therapeutic drug monitoring and dose adjustment were not conducted. A standard two-compartment PK model was developed, followed by models that incorporated weight. A PK/pharmacodynamic (PD) model with C-reactive protein serial measurements as the PD input was fitted to the data. Monte Carlo simulations (n = 5000) were performed using Pmetrics. The AUCs at steady state and the proportion of patients achieving the recommended drug exposures (i.e. Cmin >15 mg/L) were determined. The study was registered in the European Clinical Trials Database Registry (EudraCT: 2012-005738-12).

RESULTS

The PK allometric model best accounted for the observed data. The PK parameters medians were: clearance = 0.435 × (weight/70)0.75 (L/h); volume = 0.765 (L); Kcp = 1.3 (h-1); and Kpc = 0.629 (h-1). The individual time-course of C-reactive protein was well described using the Bayesian posterior estimates for each patient. The simulated median AUC96-120 was 302.3 mg·h/L and the median Cmin at 120 h was 12.9 mg/L; 38.8% of patients attained a Cmin >15 mg/L by 120 h.

CONCLUSIONS

Teicoplanin population PK is highly variable in neonates, weight being the best descriptor of PK variability. A low percentage of neonates were able to achieve Cmin >15 mg/L. The routine use of therapeutic drug monitoring and improved knowledge on the PD of teicoplanin is required.

Single or 2-Dose Micafungin Regimen for Treatment of Invasive Candidiasis: Therapia Sterilisans Magna!

The time the earth takes to rotate its axis (the day) has dictated how often pharmaceutical compounds are dosed. The scientific link between the 2 events is materia medica arcana. As an example, in the treatment of invasive candidiasis, antifungal therapy with intravenous micafungin is dosed daily. A literature review revealed population pharmacokinetic analyses, in vivo pharmacokinetics/pharmacodynamics studies, and maximum-tolerated-dose studies of micafungin that examined optimal micafungin dosing strategies. The half-life of micafungin in patient blood was 14 hours in several studies, but was even longer in different organs, so that the concentration will persist above minimum inhibitory concentrations of Candida species for several days. Studies in mice and rabbits with persistent neutropenia and disseminated candidiasis, otherwise fatal, demonstrated that a single large dose of micafungin could clear disseminated candidiasis, even though the micafungin half-life in such animals is shorter than in humans. Human pharmacokinetics/pharmacodynamics studies confirmed this link between micafungin efficacy and the ratio of the area under the concentration-time curve, and the optimal exposures initially identified in neutropenic animals. Maximum tolerated dose studies have demonstrated safety of 900 mg administered daily for several weeks, whereas case reports demonstrate efficacy and safety of single 1400-mg doses. Thus, a single dose of micafungin, or 2 such doses within a few days of each other, is not only logical, but might even lead to faster clearance of Candida.

The Non-Linear Child: Ontogeny, Isoniazid Concentration, and NAT2 Genotype Modulate Enzyme Reaction Kinetics and Metabolism

N-acetyltransferase 2 (NAT2) catalyzes the acetylation of isoniazid to N-acetylisoniazid. NAT2 polymorphism explains 88% of isoniazid clearance variability in adults. We examined the effects of clinical and genetic factors on Michaelis-Menten reaction kinetic constants of maximum velocity (V_max) and affinity (K_m) in children 0–10 years old. We measured the rates of isoniazid elimination and N-acetylisoniazid production in the blood of 30 children. Since maturation effects could be non-linear, we utilized a pharmacometric approach and the artificial intelligence method, multivariate adaptive regression splines (MARS), to identify factors predicting NAT2 V_max and K_m by examining clinical, genetic, and laboratory factors in toto. Isoniazid concentration predicted both V_max and K_m and superseded the contribution of NAT2 genotype. Age non-linearly modified the NAT2 genotype contribution until maturation at ≥ 5.3 years. Thus, enzyme efficiency was constrained by substrate concentration, genes, and age. Since MARS output is in the form of basis functions and equations, it allows multiscale systems modeling from the level of cellular chemical reactions to whole body physiological parameters, by automatic selection of significant predictors by the algorithm.

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We identified the NAT2 K_m and V_max in children treated with isoniazid.

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Artificial intelligence (AI) algorithms were used to find predictors of K_m and V_max.

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Isoniazid concentration affected V_max and K_m, and superseded NAT2 genotype.

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Age non-linearly modified NAT2 genotype contribution until maturation at ≥ 5.3 years.

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AI output is in the form of equations that allow multiscale systems modeling.

The effects of maturation on drug metabolism have not been studied for the type phase II enzymes such as NAT2, which metabolizes the drug isoniazid. Genes have been found to control speed of isoniazid metabolism. Studies to characterize affinity and maximum velocity for isoniazid metabolism in people were last performed in two individuals' livers in the 1960s. We identified NAT2 affinity and maximum velocity in 30 tuberculosis children treated with isoniazid. Artificial intelligence methods found that metabolism was affected by the drug's concentration more than by genes, which were affected by age up to 5.3 years.

[Echinocandins: Applied pharmacology]

The echinocandins share pharmacodynamic properties, although there are some interesting differences in their pharmacokinetic behaviour in the clinical practice. They are not absorbed by the oral route. They have a somewhat special distribution in the organism, as some of them can reach high intracellular concentrations while, with some others, the concentration is reduced. They are highly bound to plasma proteins, thus it is recommended to administer a loading dose for anidulafungin and caspofungin, although this procedure is not yet clear with micafungin. Echinocandins are excreted via a non-microsomal metabolism, so the urinary concentration is very low. Some carrier proteins that take part in the biliary clearance process are probably involved in the interactions described with caspofungin and micafungin. These two drugs must be used with caution in patients with severely impaired hepatic function, while all of them can be used without special precautions when there is renal impairment or the patient requires renal replacement therapy.

Pediatric Invasive Aspergillosis

Invasive aspergillosis (IA) is a disease of increasing importance in pediatrics due to growth of the immunocompromised populations at risk and improvements in long-term survival for many of these groups. While general principles of diagnosis and therapy apply similarly across the age spectrum, there are unique considerations for clinicians who care for children and adolescents with IA. This review will highlight important differences in the epidemiology, clinical manifestations, diagnosis, and therapy of pediatric IA.

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.

Pediatric Invasive Candidiasis: Epidemiology and Diagnosis in Children

Pediatric patients present with differing underlying conditions and cytotoxic therapeutic protocols, so the differing epidemiology of invasive candidiasis in children versus adults is not surprising. Understanding the Candida species epidemiology is critical, as we often begin empiric therapy or therapy before antifungal susceptibilities are known. Reports with newer molecular diagnostic assays for invasive candidiasis are rare and require more study to develop firm pediatric-specific guidance. Antifungal treatment of pediatric candidiasis is reviewed in the context of larger epidemiologic studies and the few trials completed to date.

Clinical pharmacology of antifungal agents to overcome drug resistance in pediatric patients

INTRODUCTION

Antifungal resistance is an emerging problem that increases morbidity and mortality in immunosuppressed pediatric patients, who suffer from invasive fungal diseases. Optimal pharmacological management is critical for the successful treatment of invasive fungal infections by resistant strains.

AREAS COVERED

This paper reviews the mechanisms of resistance of different classes of antifungal agents and the current understanding of pediatric antifungal pharmacology for overcoming antifungal resistance in children based on laboratory and clinical studies in the English literature. The therapeutic choices against fungal pathogens with intrinsic or acquired resistance are further reviewed.

EXPERT OPINION

There is a paucity of data in the pediatric population regarding the epidemiology of the resistant organisms to different antifungal agents. It is also unknown if there are more prevalent molecular mechanisms that promote antifungal resistance. Selection and dosages of the most effective antifungal agent for overcoming the antifungal resistance is crucial. However, there are limited studies guiding the optimal dosage and duration of treatment for management of emergent antifungal resistance. Further studies are warranted to elucidate the optimal pharmacology of the current antifungal agents against resistant organisms and to advance the development of new antifungal agents.

Impact of special patient populations on the pharmacokinetics of echinocandins

Echinocandins belong to the class of antifungal agents. Currently, three echinocandin drugs are licensed for intravenous treatment of invasive fungal infections: anidulafungin, caspofungin and micafungin. While their antifungal activity overlaps, there are substantial differences in pharmacokinetics (PK). Numerous factors may account for variability in PK of echinocandins including age (pediatrics vs adults), body surface area and body composition (normal weight vs obesity), disease status (e.g., critically ill and burn patients) and organ dysfunction (kidney and liver impairment). Subsequent effects of altered exposure might impact efficacy and safety. Knowledge of PK behavior is crucial in optimal clinical utilization of echinocandin in a specific patient or patient population. This review provides up-to-date information on PK data of anidulafungin, caspofungin and micafungin in special patient populations. Patient populations addressed are neonates, children and adolescents, obese patients, patients with hepatic or renal impairment, critically ill patients (including burn patients) and patients with hematological diseases.

Advances in the treatment of invasive neonatal candidiasis

INTRODUCTION

Invasive candidiasis is responsible for ∼ 10% of nosocomial sepsis in very-low-birth-weight infants and is associated with substantial morbidity and mortality. Over the last two decades, the antifungal armamentarium against Candida spp. has increased; however, efficacy and safety studies in this population are lacking.

AREAS COVERED

We reviewed the medical literature and extracted information on clinical and observational studies evaluating the use of antifungal agents in neonates with invasive candidiasis.

EXPERT OPINION

Efficacy and safety data for antifungals in neonates are lacking, and the majority of studies conducted to date have concentrated on pharmacokinetic/pharmacodynamic evaluations. Unlike other anti-infective agents, efficacy data in the setting of neonatal candidiasis cannot be extrapolated from adult studies due to differences in the pathophysiology of the disease in this population relative to older children and adults. Data for amphotericin B deoxycholate, fluconazole, and micafungin suggest that these are the current agents of choice for this disease in neonates until data for newer antifungal agents become available. For prophylaxis, data from fluconazole randomized controlled trials will be submitted to the regulatory agencies for labeling. Ultimately, the field of therapeutics for neonatal candidiasis will require multidisciplinary collaboration given the numerous challenges associated with conducting clinical trials in neonates.

Population pharmacokinetics of micafungin and its metabolites M1 and M5 in children and adolescents

The aim of this analysis was to identify therapeutic micafungin regimens for children that produce the same micafungin exposures known to be effective for the prevention and treatment of Candida infections in adults. Pediatric pharmacokinetic data from 229 patients between the ages of 4 months and <17 years were obtained from four phase I and two phase III clinical trials. Population pharmacokinetic models were used to simulate the proportion of children who had a steady-state area under the concentration-time curve at 24 hours (AUC24) of micafungin within the 10th to 90th percentile range observed in a population of adults receiving a dose of micafungin with established efficacy for invasive candidiasis (100 mg/day), i.e., 75 to 139 μg·h/ml. Simulated pediatric dosages of 0.5 to 5 mg/kg of body weight/day were explored. A two-compartment model was used that incorporated body weight as a predefined covariate for allometric scaling of the pharmacokinetic parameters. During construction of the model, aspartate aminotransferase and total bilirubin were also identified as covariates that had a significant effect on micafungin clearance. A dose of 2 mg/kg resulted in the highest proportion of children within the predefined micafungin AUC24 target range for invasive candidiasis. Cutoffs of 40 or 50 kg for weight-based dosing resulted in heavier children being appropriately dosed. Thus, dose regimens of 1, 2, and 3 mg/kg/day micafungin are appropriate for the prevention of invasive candidiasis, the treatment of invasive candidiasis, and the treatment of esophageal candidiasis, respectively, in children aged 4 months to <17 years.

Pharmacokinetic and safety profiles of repeated-dose prophylactic micafungin in children and adolescents undergoing hematopoietic stem cell transplantation

Micafungin is a potent echinocandin antifungal that can be used for both prophylaxis and treatment of Candida infections. This open-label study assessed the pharmacokinetics and safety profile of prophylactic micafungin in children and adolescents (aged 4 mo to 16 y) undergoing hematopoietic stem cell transplantation. Patients received once-daily doses of either 1 or 1.5 mg/kg micafungin, based on their body weight, for 10 to 14 days. In total, 40 patients received micafungin. Area under the plasma micafungin concentration-time curve was highest in patients aged 6 to 11 years in the 1.5 mg/kg treatment group. Peak plasma micafungin concentration displayed no age-related differences, but was higher in the 1.5 mg/kg versus the 1 mg/kg group. Clearance at steady state by weight and volume of distribution by weight were considerably higher in patients aged 4 months to 5 years. Results from this study show that age and body weight affect micafungin pharmacokinetics in pediatric patients undergoing hematopoietic stem cell transplantation.

Subtherapeutic concentrations of first-line anti-TB drugs in South African children treated according to current guidelines: the PHATISA study

OBJECTIVES

There is a paucity of evidence regarding the optimal dosing of anti-TB drugs in children. The aim of this study was to identify the pharmacokinetic parameters of first-line anti-TB drugs and the concentrations achieved after implementation of the 2010 WHO-recommended paediatric dosages.

METHODS

We conducted a prospective, observational pharmacokinetic study in children 10 years old or younger who were on isoniazid, rifampicin, pyrazinamide and ethambutol therapy in Durban, KwaZulu-Natal, South Africa. Blood was collected at six timepoints over a 24 h period, chosen using optimal sampling theory. The drug concentrations were simultaneously modelled to identify the compartmental pharmacokinetics of each drug in each child, using the ADAPT program.

RESULTS

The best six sampling timepoints in children were identified as 0 (pre-dose) and 0.42, 1.76, 3.37, 10.31 and 24 h post-dose. Thirty-one children were recruited and blood was drawn at these timepoints. Rifampicin, ethambutol and pyrazinamide were best described using a one-compartment model, while isoniazid was best described with a two-compartment model. Only 2/31 (6%), 20/31 (65%), 17/31 (55%) and 2/13 (15%) of children attained the WHO 2 h target therapeutic concentrations of rifampicin, isoniazid, pyrazinamide and ethambutol, respectively. Moreover, only 24/31 (77%), 6/31 (19%) and 8/31 (26%) achieved the AUCs associated with an optimal clinical response to rifampicin, pyrazinamide and isoniazid, respectively. No single risk factor was significantly associated with below-normal drug levels.

CONCLUSIONS

The drug concentrations of all first-line anti-TB drugs were markedly below the target therapeutic concentrations in most South African children who received the revised WHO-recommended paediatric weight-based dosages.

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.

Population pharmacokinetics of teicoplanin in children

Teicoplanin is frequently administered to treat Gram-positive infections in pediatric patients. However, not enough is known about the pharmacokinetics (PK) of teicoplanin in children to justify the optimal dosing regimen. The aim of this study was to determine the population PK of teicoplanin in children and evaluate the current dosage regimens. A PK hospital-based study was conducted. Current dosage recommendations were used for children up to 16 years of age. Thirty-nine children were recruited. Serum samples were collected at the first dose interval (1, 3, 6, and 24 h) and at steady state. A standard 2-compartment PK model was developed, followed by structural models that incorporated weight. Weight was allowed to affect clearance (CL) using linear and allometric scaling terms. The linear model best accounted for the observed data and was subsequently chosen for Monte Carlo simulations. The PK parameter medians/means (standard deviation [SD]) were as follows: CL, [0.019/0.023 (0.01)] × weight liters/h/kg of body weight; volume, 2.282/4.138 liters (4.14 liters); first-order rate constant from the central to peripheral compartment (Kcp), 0.474/3.876 h(-1) (8.16 h(-1)); and first-order rate constant from peripheral to central compartment (Kpc), 0.292/3.994 h(-1) (8.93 h(-1)). The percentage of patients with a minimum concentration of drug in serum (Cmin) of <10 mg/liter was 53.85%. The median/mean (SD) total population area under the concentration-time curve (AUC) was 619/527.05 mg · h/liter (166.03 mg · h/liter). Based on Monte Carlo simulations, only 30.04% (median AUC, 507.04 mg · h/liter), 44.88% (494.1 mg · h/liter), and 60.54% (452.03 mg · h/liter) of patients weighing 50, 25, and 10 kg, respectively, attained trough concentrations of >10 mg/liter by day 4 of treatment. The teicoplanin population PK is highly variable in children, with a wider AUC distribution spread than for adults. Therapeutic drug monitoring should be a routine requirement to minimize suboptimal concentrations. (This trial has been registered in the European Clinical Trials Database Registry [EudraCT] under registration number 2012-005738-12.).

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.

Pharmacokinetic/pharmacodynamic modelling approaches in paediatric infectious diseases and immunology

Pharmacokinetic/pharmacodynamic (PKPD) modelling is used to describe and quantify dose-concentration-effect relationships. Within paediatric studies in infectious diseases and immunology these methods are often applied to developing guidance on appropriate dosing. In this paper, an introduction to the field of PKPD modelling is given, followed by a review of the PKPD studies that have been undertaken in paediatric infectious diseases and immunology. The main focus is on identifying the methodological approaches used to define the PKPD relationship in these studies. The major findings were that most studies of infectious diseases have developed a PK model and then used simulations to define a dose recommendation based on a pre-defined PD target, which may have been defined in adults or in vitro. For immunological studies much of the modelling has focused on either PK or PD, and since multiple drugs are usually used, delineating the relative contributions of each is challenging. The use of dynamical modelling of in vitro antibacterial studies, and paediatric HIV mechanistic PD models linked with the PK of all drugs, are emerging methods that should enhance PKPD-based recommendations in the future.

Considerations in the pharmacologic treatment and prevention of neonatal sepsis

The management of neonatal sepsis is challenging owing to complex developmental and environmental factors that contribute to inter-individual variability in the pharmacokinetics and pharmacodynamics of many antimicrobial agents. In this review, we describe (i) the changing epidemiology of early- and late-onset neonatal sepsis; (ii) the pharmacologic considerations that influence the safety and efficacy of antibacterials, antifungals, and immunomodulatory adjuvants; and (iii) the recommended dosing regimens for pharmacologic agents commonly used in the treatment and prevention of neonatal sepsis. Neonatal sepsis is marked by high morbidity and mortality, such that prompt initiation of antimicrobial therapy is essential following culture collection. Before culture results are available, combination therapy with ampicillin and an aminoglycoside is recommended. When meningitis is suspected, ampicillin and cefotaxime may be considered. Following identification of the causative organism and in vitro susceptibility testing, antimicrobial therapy may be narrowed to provide targeted coverage. Therapeutic drug monitoring should be considered for neonates receiving vancomycin or aminoglycoside therapies. For neonates with invasive fungal infections, the development of new antifungal agents has significantly improved therapeutic outcomes in recent years. Liposomal amphotericin B has been found to be safe and efficacious in patients with renal impairment or toxicity caused by conventional amphotericin B. Antifungal prophylaxis with fluconazole has also been reported to dramatically reduce rates of neonatal invasive fungal infections and to improve long-term neurodevelopmental outcomes among treated children. Additionally, several large multicenter studies are currently investigating the safety and efficacy of oral lactoferrin as an immunoprophylactic agent for the prevention of neonatal sepsis.

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.

Safety and pharmacokinetic profiles of repeated-dose micafungin in children and adolescents treated for invasive candidiasis

BACKGROUND

Micafungin is an echinocandin with proven efficacy against a broad range of fungal infections, including those caused by Candida spp.

OBJECTIVE

To evaluate the safety and pharmacokinetics of once-daily 3 mg/kg and 4.5 mg/kg micafungin in children with proven, probable or suspected invasive candidiasis.

METHODS

Micafungin safety and pharmacokinetics were assessed in 2 phase I, open-label, repeat-dose trials. In Study 2101, children aged 2-16 years were grouped by weight to receive 3 mg/kg (≥25 kg) or 4.5 mg/kg (<25 kg) intravenous micafungin for 10-14 days. In Study 2102, children aged 4 months to <2 years received 4.5 mg/kg micafungin. Study protocols were otherwise identical.

RESULTS

Safety was analyzed in 78 and 9 children in Studies 2101 and 2102, respectively. Although adverse events (AEs) were experienced by most children (2101: n=62; 2102: n=9), micafungin-related AEs were less common (2101: n=28; 2102: n=1), and the number of patients discontinuing due to AEs was low (2101: n=4; 2102: n=1). The most common micafungin-related AEs were infusion-associated symptoms, pyrexia and hypomagnesemia (Study 2101), and liver function abnormalities (Study 2102). The micafungin pharmacokinetic profile was similar to that seen in other studies conducted in children, but different than that observed in adults.

CONCLUSIONS

In this small cohort of children, once-daily doses of 3 mg/kg and 4.5 mg/kg micafungin were well tolerated. Pharmacokinetic data will be combined in a population pharmacokinetic analysis to support US dosing recommendations in children.

Antifungal therapy in children: an update

Invasive fungal infections are a common problem in children affected by primary or secondary immunodeficiencies. Thanks to an increased knowledge about their mechanisms of action and their pharmacokinetic and toxicity profiles, the use of these drugs in common and uncommon invasive infections in immunocompromised children has improved over the last decades. Choosing the most appropriate antifungal drug is a serious challenge for any clinician, also considering that, in most cases, therapy has to be started before cultures are available, the choice being driven by clinical symptoms and statistical criteria only. In this study, we performed a systematic review of literature, providing antifungal treatment recommendations for paediatric patients which can help clinicians find the most suitable treatment for each specific case. Principal antifungal drugs-ranging from first-generation antimycotics to the latest molecules-are classified according to their targets, and of each group, the pharmacokinetic profile, clinical indications and side effects are extensively described.

Weight drives caspofungin pharmacokinetic variability in overweight and obese people: fractal power signatures beyond two-thirds or three-fourths

Echinocandins, such as caspofungin, are commonly used to treat candidemia and aspergillosis. Success rates for candidemia treatment are approximately 70%. Dose optimization may further help improve these success rates, given that the microbial effect of these agents is concentration dependent. There are conflicting data as regards the effect of weight and/or obesity on caspofungin drug concentrations. We designed a prospective study to evaluate the population pharmacokinetics of caspofungin in adults with a weight difference range of 100 kg. Caspofungin pharmacokinetics were best described using a two-compartment pharmacokinetic model. There were 18 subjects studied, of whom half were women. The central volume was typically 4.2 liters but increased by a factor of (weight/53.6)(3/4). The peripheral compartment volume was typically 2.53 liters but increased by a factor of (weight/53.6)(3/2), an unusual power law signature. Similarly, the 3/4 power law best described the relationship between weight and systemic clearance for persons weighing >66.3 kg, whereas intercompartmental clearance was best described by the 3/2 power signature. There are two implications of our findings. First, lower caspofungin area-under-the-concentration-time curves are achieved in obese persons than thinner ones. This suggests that dose optimization in heavier patients may improve clinical success rates. Second, the 3/2 exponent is unusual in fractal geometry-based scaling and warrants further study. Moreover, this suggests that use of a "floating" instead of a fixed exponent may be more useful in studies where weight is under investigation as a potential cause of pharmacokinetic variability within adult patients. (This study protocol was registered at www.clinicaltrials.gov under registration number NCT01062165.).