In vivo pharmacokinetics and pharmacodynamics of a new triazole, voriconazole, in a murine candidiasis model

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.

Preclinical Pharmacokinetic/Pharmacodynamic Studies and Clinical Trials in the Drug Development Process of EMA-Approved Antifungal Agents: A Review

Antifungal drug development is essential as invasive fungal disease is still associated with a very high mortality rate and the emergence of resistant species in the last decade. In Europe, the European Medical Agency (EMA) approves antifungals and publishes the European Public Assessment Report (EPAR) including the information leading up to the authorisation. We looked at EMA-approved antifungals and their reports within the last 23 years. We focused primarily on the role of pharmacokinetic/pharmacodynamic indices in antifungal development and the level of information depicted in their corresponding report. Furthermore, we investigated guidelines applicable to the development process at the time and compared the content with a focus on pharmacokinetic/pharmacodynamic studies and preclinical requirements. Since 2000, six new antifungal substances have been authorised. Most were authorised for treatment of Candida infections or Aspergillus infections but also included rarer pathogens. Pharmacokinetic/pharmacodynamic indices were scarcely investigated and/or mentioned in the report. Current antifungal EMA guidelines started emphasising investigating pharmacokinetic/pharmacodynamic indices in 2010 and then again in 2016. It remains to be seen how this translates into the authorisation process for new antifungals.

Optimization of Voriconazole Dosing Regimens Against Aspergillus Species and Candida Species in Pediatric Patients After Hematopoietic Cell Transplantation: A Theoretical Study Based on Pharmacokinetic/Pharmacodynamic Analysis

This study aimed to optimize the dosing regimens of voriconazole (VRC) for pediatric patients after hematopoietic cell transplantation with different cytochrome P450 (CYP) 2C19 phenotypes and body weights, based on pharmacokinetic (PK)/pharmacodynamic (PD) analysis. The PK parameters of VRC were derived from previous literature. Combined with key factors affecting VRC, patients were categorized into 9 subgroups based on different CYP2C19 phenotypes (poor metabolizer/intermediate metabolizer, normal metabolizer, and rapid metabolizer/ultrarapid metabolizer) and typical body weights (15, 40, and 65 kg). Monte Carlo simulation was used to investigate dosing regimens for different groups. The area under the 24-hour free drug concentration-time curve to the minimum inhibitory concentration (MIC) > 25 was used as the target value for effective treatment. The probability of target achievement and the cumulative fraction of response were determined on the basis of the assumed MICs and MICs distribution frequency of Aspergillus species and Candida species. When the MIC was ≤1 mg/L, 4 mg/kg every 12 hours was sufficient for optimal effects in groups 1-3 and groups 5 and 6; however, 6 mg/kg every 12 hours was required for group 4, and 8 mg/kg every 12 hours was required for groups 7-9. In empirical treatment, lower (2-6 mg/kg every 12 hours) and higher (6-12 mg/kg every 12 hours) dosing regimens were recommended for Candida spp. and Aspergillus spp., respectively. Our findings will assist in selecting appropriate dosing regimens of VRC for pediatric patients after hematopoietic cell transplantation with different CYP2C19 phenotypes and body weights. Clinically, it is better to continuously adjust the dosing on the basis of the therapeutic drug monitoring.

A pH-tuned chitosan-PLGA nanocarrier for fluconazole delivery reduces toxicity and improves efficacy against resistant Candida

Fluconazole (FLZ) is a broad-spectrum antifungal used against Candida infections. Candida auris displays resistance to FLZ. Drug nanocarriers composed of natural (chitosan, C) or synthetic polymers (polylactide co-glycolide, PLGA) show improved drug characteristics, efficacy and reduction in toxicity. Here, C-PLGA nanoparticles (110 nm) were synthesized by coacervation method and loaded with FLZ, achieving ~8-wt% drug loading. The nanoformulation displayed pH-tuned slow sustained drug release (83 %) up to 5 d, at pH 4, while 34 % release occurred at pH 7.0. Fluorescent-tagged C-PLGA-NPs were localized on the Candida cell wall/membrane as seen by confocal microscopy. This resulted in ~1.9-fold reduced efflux of R6G dye as compared to bare drug treatment in Candida albicans and resistant C. auris. The nanoformulation showed a significant 16- and 64-fold (p < 0.0001) enhanced antifungal activity (MIC 5 and 2.5 μg/ml) against C. albicans and C. auris, respectively, as compared to FLZ. The nanoformulation showed highly effective antifungal activity in-vivo against C. albicans and C. auris. Moreover, the nephrotoxicity and hepatotoxicity was negligible. Thus, PLGA NPs-mediated fluconazole delivery can contribute to increased drug efficacy and to reduce the problem of fungal resistance.

The Safety, Toleration, and Pharmacokinetics of Two Intravenous Voriconazole Formulations in Healthy Chinese Volunteers After Increasing Dose Administrations

Sulfobutyl ether-beta-cyclodextrin sodium salt contained in the marketed intravenous voriconazole injection as a solubilizer may cause harmful accumulations. This study aimed to evaluate the safety, tolerability, and pharmacokinetics (PKs) of two intravenous voriconazole formulations containing excipients from different manufacturers using increasing dose administrations in healthy Chinese volunteers. A randomized, double-blind, placebo-controlled trial was conducted in three cohorts with 42 healthy Chinese volunteers. Each cohort of 14 volunteers was allocated in proportion (8:4:2) to test the formulation, reference voriconazole, or placebo successively by single-dose then multiple-dose administrations of 3, 4, and 6 mg/kg. Forty-one volunteers completed all drug administrations. The pharmacokinetics of test formulations are characterized by high interindividual variability (coefficient of variance of C_max up to 68.0%, AUC_0-τ up to 70.2%, and nonlinear PKs with a regression coefficient of C_max  = 1.31 and AUC_0-τ  = 1.75 in a single dose). In the steady state, R_Auc of the test drug versus reference drug of the 3, 4, and 6 mg/kg dose group were 5.2 and 5.3, 5.6 and 6.3, and 5.8 and 5.5, respectively, and Rc_max were 2.5 and 2.7, 2.6 and 3.1, and 2.8 and 2.6, respectively. Eighty-three adverse events with 37 transient visual disturbances were mild. PKs with high interindividual variability, nonlinear characteristics, and significant dose-dependent accumulation were comparable between the two formulations. Overall, the safety of the test formulation was acceptable.

Pharmacokinetic/Pharmacodynamic Target Attainment of Different Antifungal Agents in De-escalation Treatment in Critically Ill Patients: a Step toward Dose Optimization Using Monte Carlo Simulation

Differences in pharmacokinetics/pharmacodynamics (PK/PD) target attainment are rarely considered when antifungals are switched in critically ill patients. This study intends to explore whether the antifungal de-escalation treatment strategy and the new intermittent dosing strategy of echinocandins in critically ill patients are able to achieve the corresponding PK/PD targets. The published population PK models of antifungals in critically ill patients and a public data set from the MIMIC-III database (n = 662) were employed to evaluate PK/PD target attainment of different dosing regimens of antifungals. Cumulative fraction of response (CFR) was calculated for each dosing regimen. Most guideline-recommended dosing regimens of fluconazole and voriconazole could achieve target exposure as de-escalation treatment in critically ill patients. For initial echinocandin treatment, achievement of the target exposure decreased as body weight increased, and the intermittent dosing strategy had a slightly higher CFR value in most simulations compared to conventional dosing strategy. For Candida albicans and Candida glabrata infection, caspofungin at the lowest dose achieved a CFR of >90%, while micafungin or anidulafungin required almost the highest doses simulated in this study to achieve the same effect. None of the echinocandins other than 150 mg every 24 h (q24h) or 200 mg q48h of caspofungin achieved the target CFR for Candida parapsilosis infection. These findings support the guideline-recommended dose of triazoles for antifungal de-escalation treatment and confirm the insufficient dosage of echinocandins in critically ill patients, indicating that a dosing regimen based on body weight or intermittent dosing of echinocandins may be required.

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.

Recent Advances in Therapeutic Drug Monitoring of Voriconazole, Mycophenolic Acid, and Vancomycin: A Literature Review of Pediatric Studies

The review includes studies dated 2011-2021 presenting the newest information on voriconazole (VCZ), mycophenolic acid (MPA), and vancomycin (VAN) therapeutic drug monitoring (TDM) in children. The need of TDM in pediatric patients has been emphasized by providing the information on the differences in the drugs pharmacokinetics. TDM of VCZ should be mandatory for all pediatric patients with invasive fungal infections (IFIs). Wide inter- and intrapatient variability in VCZ pharmacokinetics cause achieving and maintaining therapeutic concentration during therapy challenging in this population. Demonstrated studies showed, in most cases, VCZ plasma concentrations to be subtherapeutic, despite the updated dosages recommendations. Only repeated TDM can predict drug exposure and individualizing dosing in antifungal therapy in children. In children treated with mycophenolate mofetil (MMF), similarly as in adult patients, the role of TDM for MMF active form, MPA, has not been well established and is undergoing continued debate. Studies on the MPA TDM have been carried out in children after renal transplantation, other organ transplantation such as heart, liver, or intestine, in children after hematopoietic stem cell transplantation or cord blood transplantation, and in children with lupus, nephrotic syndrome, Henoch-Schönlein purpura, and other autoimmune diseases. MPA TDM is based on the area under the concentration-time curve; however, the proposed values differ according to the treatment indication, and other approaches such as pharmacodynamic and pharmacogenetic biomarkers have been proposed. VAN is a bactericidal agent that requires TDM to prevent an acute kidney disease. The particular group of patients is the pediatric one. For this group, the general recommendations of the dosing may not be valid due to the change of the elimination rate and volume of distribution between the subjects. The other factor is the variability among patients that concerns the free fraction of the drug. It may be caused by both the patients' population and sample preconditioning. Although VCZ, MMF, and VAN have been applied in pediatric patients for many years, there are still few issues to be solve regarding TDM of these drugs to ensure safe and effective treatment. Except for pharmacokinetic approach, pharmacodynamics and pharmacogenetics have been more often proposed for TDM.

Predicting the Outcome of Voriconazole Individualized Medication Using Integrated Pharmacokinetic/Pharmacodynamic Model

Therapeutic drug monitoring is considered to be an effective tool for the individualized use of voriconazole. However, drug concentration measurement alone doesn’t take into account the susceptibility of the infecting microorganisms to the drug. Linking pharmacodynamic data with the pharmacokinetic profile of individuals is expected to be an effective method to predict the probability of a certain therapeutic outcome. The objective of this study was to individualize voriconazole regimens by integrating individual pharmacokinetic parameters and pathogen susceptibility data through Monte Carlo simulations The individual pharmacokinetic parameters of 35 hospitalized patients who received voriconazole were calculated based on a validated population pharmacokinetic model. The area under the concentration-time curve for free drug/minimal inhibitory concentration (fAUC_ss/MIC) > 25 was selected as the pharmacokinetic/pharmacodynamic (PK/PD) parameter predicting the efficacy of voriconazole. The cumulative fraction of response (CFR) of the target value was assessed. To verify this conclusion, a logistic regression analysis was used to explore the relationship between actual clinical efficiency and the CFR value. For the 35 patients, the area under the free drug concentration-time curve (fAUC_ss) was calculated to be 34.90 ± 21.67 mgh/L. According to the dualistic logistic regression analysis, the minimal inhibitory concentration (MIC) value of different kinds of fungi had a great influence on the effectiveness of clinical treatment. It also showed that the actual clinical efficacy and the CFR value of fAUC_ss/MIC had a high degree of consistency. The results suggest that it is feasible to individualize voriconazole dosing and predict clinical outcomes through the integration of data on pharmacokinetics and antifungal susceptibility.

Plausible drug interaction between cyclophosphamide and voriconazole via inhibition of CYP2B6

The inhibitory activities of eight cytochrome P450 (CYP) isoenzymes for representative or suspected inhibitors of CYPs, including pesticides, were evaluated simultaneously using an in vitro cocktail incubation method to demonstrate the importance of systematic evaluation of CYP inhibitory risks in drug interaction (DI). Potent inhibition of CYP2B6 was noticeable for some azoles, including voriconazole. When voriconazole and cyclophosphamide were co-administered in mice, cyclophosphamide-induced alopecia and leukopenia were significantly suppressed by approximately 50% with increased blood concentrations of cyclophosphamide. The formation of an active metabolite of cyclophosphamide was suppressed effectively by voriconazole in the mouse liver microsomes. Surveys of adverse event reporting databases in Japan (JADER) and the U.S. (FAERS) showed that the proportional reporting ratios of neutropenia, hemorrhagic cystitis, and alopecia for cyclophosphamide, which is principally activated by CYP2B6 in humans, were mostly reduced, or tended to be reduced when azoles, including voriconazole, were prescribed in combination. It is highly likely that DIs between cyclophosphamide and azoles occur in the clinical setting. This study also suggests that more proper consideration of CYP2B6-mediated DIs is warranted. The combination of the in vitro cocktail method and a survey of adverse event reporting databases was a useful method to comprehensively detect pharmacokinetic DIs.

Contribution of Population Pharmacokinetics of Glycopeptides and Antifungals to Dosage Adaptation in Paediatric Onco-hematological Malignancies: A Review

The response to medications in children differs not only in comparison to adults but also between children of the different age groups and according to the disease. This is true for anti-infectives that are widely prescribed in children with malignancy. In the absence of pharmacokinetic/pharmacodynamic paediatric studies, dosage is frequently based on protocols adapted to adults. After a short presentation of the drugs, we reviewed the population pharmacokinetic studies available for glycopeptides (vancomycin and teicoplanin, n = 5) and antifungals (voriconazole, posaconazole, and amphotericin B, n = 9) currently administered in children with onco-hematological malignancies. For each of them, we reported the main study characteristics including identified covariates affecting pharmacokinetics and proposed paediatric dosage recommendations. This review highlighted the very limited amount of data available, the lack of consensus regarding PK/PD targets used for dosing optimization and regarding dosage recommendations when available. Additional PK studies are urgently needed in this specific patient population. In addition to pharmacokinetics, efficacy may be altered in immunocompromised patients and prospective clinical evaluation of new dosage regimen should be provided as they are missing in most cases.

The Role of New Posaconazole Formulations in the Treatment of Candida albicans Infections: Data from an In Vitro Pharmacokinetic-Pharmacodynamic Model

Posaconazole is more active than fluconazole against Candida albicans in vitro and is approved for the treatment of oropharyngeal candidiasis but not for that of invasive candidiasis (IC). Here, we explored the efficacy of posaconazole against C. albicans in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model of IC and determined the probability of pharmacodynamic target attainment for the oral solution and intravenous (i.v.)/tablet formulations. Three clinical C. albicans isolates (posaconazole MICs, 0.008 to 0.25 mg/liter) were studied in the in vitro PK/PD dilution model simulating steady-state posaconazole PK. The in vitro exposure-effect relationship, area under the 24-h free drug concentration curve (fAUC_0-24)/MIC, was described and compared with in vivo outcome in animals with IC. PK/PD susceptibility breakpoints and trough levels required for optimal treatment were determined for EUCAST and CLSI 24-h/48-h (CLSI24h/CLSI48h) methods using the fAUC_0-24/MIC associated with half-maximal activity (EI₅₀) and Monte Carlo simulation analysis for oral solution (400 mg every 12 hours [q12h]) and i.v./tablet formulations (300 mg q24h). The in vitro mean (95% confidence interval [CI]) EI₅₀ was 330 (183 to 597) fAUC_0-24/MIC for CLSI24h and 169 (92 to 310) for EUCAST/CLSI48h methods, which are close to the near-stasis in vivo effect. The probability of target attainment for EI₅₀ was estimated; for the wild-type isolates (MIC ≤ 0.06 mg/liter), it was low for the oral solution and higher than 95% for the i.v./tablet formulations for the EUCAST/CLSI48h methods but not for the CLSI 24-h method. Non-wild-type isolates with EUCAST/CLSI48h MICs of 0.125 and 0.25 mg/liter would require trough levels of >1.2 and >2.4 mg/liter, respectively. Posaconazole i.v./tablet formulations may have a role in the therapy of invasive infections by wild-type C. albicans isolates, provided that a steady state is reached quickly. A PK/PD susceptibility breakpoint at the epidemiological cutoff (ECV/ECOFF) of 0.06 mg/liter was determined.

Does DDI-Predictor Help Pharmacists to Detect Drug-Drug Interactions and Resolve Medication Issues More Effectively?

The characterization of drug-drug interactions (DDIs) may require the use of several different tools, such as the thesaurus issued by our national health agency (i.e., ANSM), the metabolic pathways table from the Geneva University Hospital (GUH), and DDI-Predictor (DDI-P). We sought to (i) compare the three tools’ respective abilities to detect DDIs in routine clinical practice and (ii) measure the pharmacist intervention rate (PIR) and physician acceptance rate (PAR) associated with the use of DDI-P. The three tools’ respective DDI detection rates (in %) were measured. The PIRs and PARs were compared by using the area under the curve ratio given by DDI-P (R_AUC) and applying a chi-squared test. The DDI detection rates differed significantly: 40.0%, 76.5%, and 85.2% for ANSM (The National Agency for the Safety of Medicines and Health Products), GUH and DDI-P, respectively (p < 0.0001). The PIR differed significantly according to the DDI-P’s R_AUC: 90.0%, 44.2% and 75.0% for R_AUC ≤ 0.5; R_AUC 0.5–2 and R_AUC > 2, respectively (p < 0.001). The overall PAR was 85.1% and did not appear to depend on the R_AUC category (p = 0.729). Our results showed that more pharmacist interventions were issued when details of the strength of the DDI were available. The three tools can be used in a complementary manner, with a view to refining medication adjustments.

Model-Informed Drug Development for Anti-Infectives: State of the Art and Future

Model-informed drug development (MIDD) has a long and rich history in infectious diseases. This review describes foundational principles of translational anti-infective pharmacology, including choice of appropriate measures of exposure and pharmacodynamic (PD) measures, patient subpopulations, and drug-drug interactions. Examples are presented for state-of-the-art, empiric, mechanistic, interdisciplinary, and real-world evidence MIDD applications in the development of antibacterials (review of minimum inhibitory concentration-based models, mechanism-based pharmacokinetic/PD (PK/PD) models, PK/PD models of resistance, and immune response), antifungals, antivirals, drugs for the treatment of global health infectious diseases, and medical countermeasures. The degree of adoption of MIDD practices across the infectious diseases field is also summarized. The future application of MIDD in infectious diseases will progress along two planes; "depth" and "breadth" of MIDD methods. "MIDD depth" refers to deeper incorporation of the specific pathogen biology and intrinsic and acquired-resistance mechanisms; host factors, such as immunologic response and infection site, to enable deeper interrogation of pharmacological impact on pathogen clearance; clinical outcome and emergence of resistance from a pathogen; and patient and population perspective. In particular, improved early assessment of the emergence of resistance potential will become a greater focus in MIDD, as this is poorly mitigated by current development approaches. "MIDD breadth" refers to greater adoption of model-centered approaches to anti-infective development. Specifically, this means how various MIDD approaches and translational tools can be integrated or connected in a systematic way that supports decision making by key stakeholders (sponsors, regulators, and payers) across the entire development pathway.

Pharmacokinetics of voriconazole after a single intramuscular injection in large falcons (Falco spp.)

Voriconazole is one of the main azoles used to treat invasive aspergillosis in falconry raptors and birds. Despite the fact that there are studies for oral and intravenous use of voriconazole in birds, there are none for its effect after intramuscular use. Empirical use of intramuscular voriconazole in falcons, indicated quicker therapy response than the oral one. Aim of this study is to evaluate the in vivo pharmacokinetic disposition of injectable voriconazole after a single intramuscular injection in large falcons (i.e., Gyrfalcons, Saker falcons, Peregrine falcons). No clinical side effects were observed in the falcons. Absorption of voriconazole was rapid (0.5-2 hours) and reached a plasma level (>1 μg/ml) which is above the minimal inhibitory concentration (MIC) for all known Aspergillus strains. This level was maintained for 16 to 20 hours, thus indicating that a single injection of 12.5 mg/kg is not enough if T > MIC is taken into consideration. On a newer aspect, according to the AUC24 unbound: MIC parameter would be indicated that this dose would be rather sufficient for most Aspergillus strains.

ERG11 Polymorphism in Voriconazole-Resistant Candida tropicalis: Weak Role of ERG11 Expression, Ergosterol Content, and Membrane Permeability

Mutations in ERG11 were detected by gene sequencing and amino acid alignment in 18 Candida tropicalis strains with different degrees of sensitivity to voriconazole (VRC). ERG11 expression, sterol content, and membrane permeability were also evaluated. We report three missense mutations in ERG11 that resulted in resistance to VRC. The transcriptional levels of ERG11 as well as the ergosterol content and membrane permeability demonstrated no correlation to only a slight correlation with the obtained MIC values, but the data did suggest a tendency toward such a correlation.

Pharmacokinetic/Pharmacodynamic Analysis of Voriconazole Against Candida spp. and Aspergillus spp. in Allogeneic Stem Cell Transplant Recipients

BACKGROUND

To evaluate the adequacy of different dosing regimens of voriconazole for the prophylaxis of invasive candidiasis and aspergillosis in adult allogeneic stem cell transplant recipients by means of population pharmacokinetic (PK) modelling and simulation.

METHODS

Allogeneic stem cell transplant recipients receiving voriconazole were included in this observational study. A population PK model was developed. Three oral voriconazole-dosing regimens were simulated: 200, 300, and 400 mg twice daily. The pharmacodynamic target was defined as fAUC0-24/0.7. A probability of target attainment ≥90% was considered optimal. The cumulative fraction of response was defined as the fraction of patients achieving the pharmacodynamic target when a population of simulated patients is matched with a simulated population of different Candida spp. and Aspergillus spp. The percentage of patients with trough plasma concentrations at steady state (Ctrough) within the reference range (1-5.5 mg/L) was also calculated.

RESULTS

A 2-compartment PK model was developed using data from 40 patients, which contributed 237 voriconazole plasma samples, including trough and maximum concentrations. Voriconazole 200, 300, and 400 mg twice daily achieved probability of target attainment ≥90% for minimal inhibitory concentration values ≤0.25, ≤0.38, and ≤0.50 mg/L, respectively. The cumulative fraction of response for A. niger, A. versicolor, and A. flavus increased >10% when increasing voriconazole dose from 200 to 400 mg twice daily (from 72.5% to 89.5% for A. niger; from 77.7% to 88.7% for A. versicolor; and from 82.4% to 94.9% for A flavus). The percentage of patients with Ctrough within the reference range increased 15% when voriconazole dose was increased from 200 to 300 mg twice daily.

CONCLUSIONS

The PK simulations in this study suggest that transplant recipients on voriconazole prophylaxis against invasive candidiasis or aspergillosis are likely to achieve the target concentrations associated with the desired treatment outcomes if the maintenance dose is 200 mg twice daily. However, Aspergillus spp. with high minimal inhibitory concentrations could require higher maintenance doses.

Synthesis, Spectroscopic, Thermal and Catalytic Properties of Four New Metal (II) Complexes with Selected N- and O-Donor Ligands

Four solid compounds with formulae: Co(OAc)₂(Im)·H₂O (I), Ni(OAc)₂(Im)_1.5·2H₂O (II), Cu₂(OAc)₄(Im) (III) and Zn(OAc)₂(Im)·H₂O (IV) (where: Im = 1H-Imidazole) were prepared and characterized by chemical and elemental analysis, powder X-ray diffraction patterns and FTIR spectroscopy. Catalytic properties of each complex for styrene oxidation reaction were investigated. Furthermore, thermal properties of compounds were studied using the TG-DTG and DSC techniques under dry air atmosphere. Additionally, volatile thermal decomposition and fragmentation products were also investigated using the TG-FTIR spectra in air.

From bench to bedside: Perspectives on the utility of pharmacokinetics/pharmacodynamics in predicting the efficacy of antifungals in invasive candidiasis

The aim of this perspective is to give an overlook on the utility of pharmacokinetics/pharmacodynamics (PK/PD) in predicting the efficacy of antifungals in invasive candidiasis. Overall, from the available literature it appears that bridging data of PK/PD of antifungals from the laboratory to the clinic for the treatment of invasive candidiasis are feasible only partially. Fluconazole is the only antifungal agent having the pharmacodynamic threshold of efficacy identified in experimental animal models convincingly validated in the clinical setting of invasive candidiasis as well. Conversely, for voriconazole and posaconazole data on this topic are very limited. For the echinocandins, robust PK/PD identified in the laboratory represented the rationale for defining differential clinical breakpoints of echinocandins against different species of Candida by the regulatory agencies. However, translation of the findings in the clinical setting provided conflicting results. Data on PK/PD of amphotericin B and flucytosine in models of invasive candidiasis are quite limited, and clinical studies assessing the role of drug exposure on efficacy are currently lacking. The expectation is that prospective studies could test more and more frequently the validity of experimental PK/PD data of antifungals in the clinical setting of invasive candidiasis. The findings could represent a step forward in addressing adequate antifungal stewardship programmes.

Toward Harmonization of Voriconazole CLSI and EUCAST Breakpoints for Candida albicans Using a Validated In Vitro Pharmacokinetic/Pharmacodynamic Model

CLSI and EUCAST susceptibility breakpoints for voriconazole and Candida albicans differ by one dilution (≤0.125 and ≤0.06 mg/liter, respectively) whereas the epidemiological cutoff values for EUCAST (ECOFF) and CLSI (ECV) are the same (0.03 mg/liter). We therefore determined the pharmacokinetic/pharmacodynamic (PK/PD) breakpoints of voriconazole against C. albicans for both methodologies with an in vitro PK/PD model, which was validated using existing animal PK/PD data. Four clinical wild-type and non-wild-type C. albicans isolates (voriconazole MICs, 0.008 to 0.125 mg/liter) were tested in an in vitro PK/PD model. For validation purposes, mouse PK were simulated and in vitro PD were compared with in vivo outcomes. Human PK were simulated, and the exposure-effect relationship area under the concentration-time curve for the free, unbound fraction of a drug from 0 to 24 h (fAUC_0-24)/MIC was described for EUCAST and CLSI 24/48-h methods. PK/PD breakpoints were determined using the fAUC_0-24/MIC associated with half-maximal activity (EI₅₀) and Monte Carlo simulation analysis. The in vitro 24-h PD EI₅₀ values of voriconazole against C. albicans were 2.5 to 5 (1.5 to 17) fAUC/MIC. However, the 72-h PD were higher at 133 (51 to 347) fAUC/MIC for EUCAST and 94 (35 to 252) fAUC/MIC for CLSI. The mean (95% confidence interval) probability of target attainment (PTA) was 100% (95 to 100%), 97% (72 to 100%), 83% (35 to 99%), and 49% (8 to 91%) for EUCAST and 100% (97 to 100%), 99% (85 to 100%), 91% (52 to 100%), and 68% (17 to 96%) for CLSI for MICs of 0.03, 0.06, 0.125, and 0.25 mg/liter, respectively. Significantly, >95% PTA values were found for EUCAST/CLSI MICs of ≤0.03 mg/liter. For MICs of 0.06 to 0.125 mg/liter, trough levels 1 to 4 mg/liter would be required to attain the PK/PD target. A PK/PD breakpoint of C. albicans voriconazole at the ECOFF/ECV of 0.03 mg/liter was determined for both the EUCAST and CLSI methods, indicating the need for breakpoint harmonization for the reference methodologies.

Extrapolating Antifungal Animal Data to Humans - Is it reliable?

PURPOSE OF REVIEW

This article aimed to review animal models of antifungals and identifies human literature to assess if the extrapolation of results is reliable.

RECENT FINDINGS

Animal studies have helped identify AUC/MIC targets for new drugs and formulations such as isavuconazole and delayed release posaconazole that have translated to successful outcomes in humans. Models have also been influential in the identification of possible combination therapies for the treatment of aspergillosis, such as voriconazole and echinocandins. However, challenges are endured with animal models when it comes to replicating the pharmacokinetics of humans which has been exemplified with the newest itraconazole formulation. Additionally, animal models have displayed a survival benefit with the use of iron chelators and amphotericin for mucormycosis which was not demonstrated in humans.

SUMMARY

Animal models have been a staple in the development and optimization of antifungal agents. They afford the ability to investigate uncommon diseases, such as invasive fungal infections, that would otherwise take years and many resources to complete. Although there are many benefits of animal models there are also shortcomings. This is why the reliability of extrapolating data from animal models to humans is often scrutinized.

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.

Population Pharmacokinetics of Voriconazole and Optimization of Dosage Regimens Based on Monte Carlo Simulation in Patients With Liver Cirrhosis

Because voriconazole metabolism is highly influenced by liver function, the dose regimen of voriconazole should be carefully assessed in patients with liver cirrhosis. We aimed to identify significant factors associated with plasma concentrations. Blood samples were collected from patients with liver cirrhosis who received voriconazole, and voriconazole concentrations were determined. One-compartment model with first-order absorption and elimination appropriately characterized the in vivo process of voriconazole. The typical population value of voriconazole clearance (CL) was 1.45 L/h and the volume of distribution (V) was 132.12 L. The covariate analysis identified that CYP2C19 gene phenotype and Child-Pugh classification were strongly associated with CL and body weight had a significant influence on V. The results of the Monte Carlo simulation suggested that CYP2C19 gene phenotype was a critical factor for determining voriconazole dosage in patients with liver cirrhosis. The extensive metabolizer patients with Aspergillus fumigatus infections could be treated effectively with a recommended dose of 75 mg twice daily in mild to moderate liver cirrhosis and 100 mg once daily in moderate severe liver cirrhosis. However, the recommended dosage for Candida albicans infections patients was not achieved in present study.

Model-based Voriconazole Dose Optimization in Chinese Adult Patients With Hematologic Malignancies

PURPOSE

The objective of this study was to characterize the population pharmacokinetics of voriconazole and to identify factors that significantly affect pharmacokinetic parameters and to further investigate optimal dosage regimens in Chinese adult patients with hematologic malignancies.

METHODS

A prospective population pharmacokinetic analysis was performed on 186 concentration measurements obtained from 41 adult patients with hematologic malignancies. All enrolled patients were treated with voriconazole for diagnosed or suspected invasive fungal diseases. Oral voriconazole was routinely administered at a maintenance dose of 200 mg q12h. Serial blood samples were collected after steady-state of each patient. Monte Carlo simulation was applied to optimize dosage strategies.

FINDINGS

A one-compartment model with first-order absorption and elimination adequately described the data. The typical voriconazole clearance was 4.18 L/h, the volume of distribution was 88.9 L, and the absorption rate constant was 0.729 h^-1. Clearance and steady-state exposure (AUC_0-12) were found to be significantly associated with age and CYP2C19 phenotype. The average AUC_0-12 of elderly patients (aged 60-90 years) was 2.1 times higher than that of relative younger patients (aged 18-59 years). The average AUC_0-12 of poor metabolizers (PMs) was approximately 2.5 and 1.8 times higher than that of extensive and intermediate metabolizers (IMs), respectively. Considering both efficacy and tolerability, dosage regimens of 100 and 50 mg orally administered every 12 hours were recommended for elderly IMs and PMs, respectively.

IMPLICATIONS

A population pharmacokinetic model for voriconazole in Chinese adult patients with hematologic malignancies was successfully developed and could well capture voriconazole's pharmacokinetic characteristics. Age and CYP2C19 phenotype were found to significantly influence voriconazole clearance and should be taken into consideration clinically for dose optimization. The optimal dosage strategies in specific clinical scenarios were proposed in this study based on model simulation. Because of the high incidence of mutant CYP2C19*2 and *3 alleles, genetic testing seems to be necessary for Asian elderly patients when voriconazole treatment is initiated.

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.

Are In Vitro Susceptibilities to Azole Antifungals Predictive of Clinical Outcome in the Treatment of Candidemia?

The purpose of this review is to critically analyze published data evaluating the impact of azole pharmacokinetic and pharmacodynamic parameters, MICs, and Candida species on clinical outcomes in patients with candidemia. Clinical breakpoints (CBPs) for fluconazole and voriconazole, which are used to determine susceptibility, have been defined by the Clinical and Laboratory Standards Institute (CLSI) for Candida species. Studies evaluating the relationship between treatment efficacy and in vitro susceptibility, as well as the pharmacodynamic targets, have been conducted in patients treated with fluconazole for candidemia; however, for species other than Candida albicans and Candida glabrata, and for other forms of invasive candidiasis, data remain limited and randomized trials are not available. Limited data evaluating these relationships with voriconazole are available. While pharmacodynamic targets for posaconazole and isavuconazole have been proposed based upon studies conducted in murine models, CBPs have not been established by CLSI. Fluconazole remains an important antifungal agent for the treatment of candidemia, and data supporting its use based on in vitro susceptibility are growing, particularly for C. albicans and C. glabrata Further investigation is needed to establish the roles of voriconazole, posaconazole, and isavuconazole in the treatment of candidemia and for all agents in the treatment of other forms of invasive candidiasis.

Optimization of Voriconazole Therapy for the Treatment of Invasive Fungal Infections in Adults

Therapeutic concentrations of voriconazole in invasive fungal infections (IFIs) are ensured using a drug monitoring approach, which relies on attainment of steady-state pharmacokinetics. For voriconazole, time to reach steady state can vary from 5-7 days, not optimal for critically ill patients. We developed a population pharmacokinetic/pharmacodynamic model-based approach to predict doses that can maximize the net benefit (probability of efficacy-probability of adverse events) and ensure therapeutic concentrations, early on during treatment. The label-recommended 200 mg voriconazole dose resulted in attainment of targeted concentrations in ≥80% patients in the case of Candida spp. infections, as compared to only 40-50% patients, with net benefit ranging from 5.8-61.8%, in the case of Aspergillus spp. infections. Voriconazole doses of 300-600 mg were found to maximize the net benefit up to 51-66.7%, depending on the clinical phenotype (due to CYP2C19 status and pantoprazole use) of the patient and type of Aspergillus infection.

Comparative Study of Ocular Pharmacokinetics of Gatifloxacin Between Continuous Lavage and Hourly Topical Instillation in Rabbits

PURPOSE

To investigate the ocular pharmacokinetics and distribution of gatifloxacin between continuous lavage through the Morgan lens and repeated topical drop instillation in rabbits.

METHODS

Thirty-six healthy rabbits were randomly divided into 2 groups, and 0.3% gatifloxacin ophthalmic solution was instilled by continuous lavage using the Morgan lens onto the left eyes at 15 mL/h (or 50 μL of the same solution repeatedly administered topically every hour). The animals were killed at 2, 4, 8, and 12 hours in the Morgan lens group or at 12 and 24 hours in the topical instillation group. Aqueous humor specimens were collected from the anterior chamber first, and other ocular tissues and plasma were collected subsequently. Pharmacokinetic and pharmacodynamic indices, other than the minimum inhibitory concentration (MIC), were used as therapeutic parameters in ocular tissues.

RESULTS

The highest concentration was found in the corneas in both groups. With continuous lavage, gatifloxacin reached an efficacious high concentration in 4 hours in the cornea, which is equivalent to about 23 times the concentration reached in the same tissue by hourly topical instillation for 12 to 24 hours. Using historic data as references, C/MIC90 was 105 (>10) and AUC0-t/MIC90 was 194 h (>125) in the cornea in the continuous lavage group at 4 hours, whereas these values were 5 and 73 hours for the topical hourly instillation group.

CONCLUSIONS

Compared with hourly topical instillation, continuous lavage through the Morgan lens could achieve significantly higher concentrations in ocular tissues within a short period, especially in the cornea. Continuous lavage may be a much more efficient way to treat recalcitrant corneal infections.

Application of different pharmacokinetic models to describe and predict pharmacokinetics of voriconazole in magellanic penguins following oral administration

Aspergillosis is a condition causing serious morbidity and mortality in captive penguins and other bird species. It can be treated with antifungal drugs, such as voriconazole. However, the pharmacokinetics of voriconazole are variable between different animal and bird species. Therefore, the pharmacokinetics of voriconazole were investigated in this study in Magellanic penguins. Pharmacokinetic models were constructed and applied to predict the pharmacokinetics of voriconazole during long-term treatment in Magellanic penguins, since the voriconazole treatment duration in chronic aspergillosis cases can last up to several months. Plasma voriconazole concentration-time data from adult Magellanic penguins (Spheniscus magellanicus; n = 15) following a single oral (PO) dose of either 2.5 mg/kg or 5 mg/kg in a herring in three separate study periods 7-12 months apart were collected. Mean plasma voriconazole concentrations were above the targeted MIC for Aspergillus fumigatus for 2 hr following a single 2.5 mg/kg voriconazole dose while the plasma concentrations exceeded the MIC for least 24 hr following a 5 mg/kg dose. Nonlinear mixed-effects modeling was used to fit two pharmacokinetic models, one with first-order and another with saturable elimination, to the single-dose data. Fits were good for both, as long as dose was included as a covariate for the first-order model so that clearance was lower and the half-life longer for animals receiving the 5 mg/kg dose. Although the single-dose data suggested saturated elimination at higher concentrations, the model with saturable elimination did not predict plasma voriconazole concentrations well for a clinical aspergillosis case receiving long-term treatment, possibly because of induction of metabolizing enzymes with chronic exposure. Pharmacokinetic models should accurately predict plasma drug concentrations for different dosage regimens in order to be applicable in the field. Future studies should focus on determining clearance at steady-state to be able to refine the pharmacokinetic models presented here and improve model performance for long-term oral voriconazole administration in Magellanic penguins.

Comparison of the Ocular Penetration and Pharmacokinetics Between Natamycin and Voriconazole After Topical Instillation in Rabbits

PURPOSE

To investigate the ocular penetration of natamycin (NAT) and voriconazole (VRC) after topical instillation in New Zealand white rabbits using simplified liquid chromatography-tandem mass spectrometry (LC-MS/MS) and high-performance liquid chromatography.

METHODS

Seventy-eight healthy rabbits were randomly divided into 3 groups. In the first 2 groups, 72 rabbits were used for single-dose testing (36 for NAT, 36 for VRC), in which 50 μL of 5.0% NAT or 1.0% VRC was instilled into the rabbits' left eyes. In the 3rd group, 6 rabbits were used for repeated-dose testing in which 50 μL of 5.0% NAT was instilled into their left eyes 12 times (once per hour) during the daytime. These animals were sacrificed immediately to collect their aqueous humors and corneas.

RESULTS

After a single topical instillation, the highest concentrations in the cornea and aqueous humor for VRC were 34.1 μg/g and 14.7 μg/mL, respectively. The permeability ratios of aqueous/cornea were from 0.1 to 1.26. The highest concentrations in cornea and aqueous humor for NAT were 299.3 ng/g and 27.1 ng/mL, respectively. The permeability ratios of aqueous/cornea were from 0.02 to 0.23. In the repeated-dose group, the NAT concentrations in the cornea and aqueous humor were 10,569 ng/g and 54.4 ng/mL, respectively. The permeability ratio was as low as 0.0051.

CONCLUSION

The better corneal penetration of VRC suggests that it is more suitable for deep corneal fungal infections than NAT via topical ocular administration.

In Vivo Pharmacokinetics and Pharmacodynamics of APX001 against Candida spp. in a Neutropenic Disseminated Candidiasis Mouse Model

APX001 is the prodrug of APX001A, which is a first-in-class small molecule with a unique mechanism of action that inhibits the fungal enzyme Gwt1 in the glycosylphosphatidylinositol (GPI) biosynthesis pathway. The goal of the present study was to determine which pharmacokinetic/pharmacodynamic (PK/PD) index and magnitude best correlated with efficacy in the murine disseminated candidiasis model for Candida albicans (n = 5), C. glabrata (n = 5), and C. auris (n = 4). MIC values ranged from 0.002 to 0.03 mg/liter for C. albicans, from 0.008 to 0.06 mg/liter for C. glabrata, and from 0.004 to 0.03 mg/liter for C. auris Plasma APX001A pharmacokinetic measurements were performed in mice after oral administration of 4, 16, 64, and 256 mg/kg of body weight APX001. Single-dose pharmacokinetic studies exhibited maximum plasma concentration (C_max) values of 0.46 to 15.6 mg/liter, area under the concentration-time curve (AUC) from time zero to infinity (AUC_0-inf) values of 0.87 to 70.0 mg · h/liter, and half-lives of 1.40 to 2.75 h. A neutropenic murine disseminated candidiasis model was utilized for all treatment studies, and drug dosing was by the oral route. Dose fractionation was performed against C. albicans K1, with total doses ranging from 4 to 1,024 mg/kg/day of APX001 fractionated into regimens of dosing every 3, 6, 8, and 12 h for a 24-h treatment duration. Nonlinear regression analysis was used to determine which PK/PD index best correlated with efficacy on the basis of the reduction in the number of CFU/kidney at 24 h. The 24-h free-drug AUC/MIC ratio (fAUC_0-24/MIC) was the PK/PD index that best correlated with efficacy (coefficient of determination [R²] = 0.88). Treatment studies with the remaining strains utilized regimens of 1 to 256 mg/kg of APX001 administered every 6 h for a 24-h duration with C. albicans and a 96-h study duration with C. glabrata and C. auris The dose required to achieve 50% of the maximum effect (ED₅₀) and stasis fAUC/MIC targets were as follows: for C. albicans, 3.67 ± 3.19 and 20.60 ± 6.50, respectively; for C. glabrata, 0.38 ± 0.21 and 1.31 ± 0.27, respectively; and for C. auris, 7.14 ± 4.54 and 14.67 ± 8.30, respectively. The present studies demonstrated in vitro and in vivo APX001A and APX001 potency, respectively, against C. albicans, C. glabrata, and C. auris. These results have potential relevance for clinical dose selection and evaluation of susceptibility breakpoints. The identification of a lower AUC/MIC ratio target for C. glabrata suggests that species-specific susceptibility breakpoints should be explored.

Pharmacodynamic studies of voriconazole: informing the clinical management of invasive fungal infections

INTRODUCTION

Voriconazole is a broad-spectrum antifungal agent commonly used to treat invasive fungal infections (IFI), including aspergillosis, candidiasis, Scedosporium infection, and Fusarium infection. IFI often occur in immunocompromised patients, leading to increased morbidity and mortality.

AREAS COVERED

The objective of this review is to summarize the pharmacodynamic properties of voriconazole and to provide considerations for potential optimal dosing strategies. Studies have demonstrated superior clinical response when an AUC/MIC >25 or Cmin/MIC >1 is attained in adult patients, correlating to a trough concentration range as narrow as 2-4.5 mg/L; however, these targets are poorly established in the pediatric population. Topics in this discussion include voriconazole use in multiple age groups, predisposing patient factors for IFI, and considerations for clinicians managing IFI. Expert commentary: The relationship between voriconazole dosing and exposure is not well defined due to the large inter- and intra-subject variability. Development of comprehensive decision support tools for individualizing dosing, particularly in children who require higher dosing, will help to increase the probability of achieving therapeutic efficacy and decrease sub-therapeutic dosing and adverse events.

Virulence and antifungal therapy of murine disseminated infection by Rhodotorula mucilaginosa

Rhodotorula infections have emerged in recent years causing mainly fungemia associated to high mortality. We have evaluated the in vitro activity of nine antifungal drugs against four clinical strains of Rhodotorula mucilaginosa, being amphotericin B, voriconazole and posaconazole the most active compounds. The experimental virulence of this fungus and the efficacy of the three mentioned drugs were evaluated in disseminated infections in neutropenic mice. Infection resulted in a high fungal load in all the organs studied without evident particular tropism. All treated animals showed reduced burden respect to the control in a strain dependent manner being voriconazole slightly superior to posaconazole and amphotericin B.

Experiment design for nonparametric models based on minimizing Bayes Risk: application to voriconazole¹

An experimental design approach is presented for individualized therapy in the special case where the prior information is specified by a nonparametric (NP) population model. Here, a NP model refers to a discrete probability model characterized by a finite set of support points and their associated weights. An important question arises as to how to best design experiments for this type of model. Many experimental design methods are based on Fisher information or other approaches originally developed for parametric models. While such approaches have been used with some success across various applications, it is interesting to note that they largely fail to address the fundamentally discrete nature of the NP model. Specifically, the problem of identifying an individual from a NP prior is more naturally treated as a problem of classification, i.e., to find a support point that best matches the patient's behavior. This paper studies the discrete nature of the NP experiment design problem from a classification point of view. Several new insights are provided including the use of Bayes Risk as an information measure, and new alternative methods for experiment design. One particular method, denoted as MMopt (multiple-model optimal), will be examined in detail and shown to require minimal computation while having distinct advantages compared to existing approaches. Several simulated examples, including a case study involving oral voriconazole in children, are given to demonstrate the usefulness of MMopt in pharmacokinetics applications.

Antifungal pharmacodynamics: Latin America's perspective

The current increment of invasive fungal infections and the availability of new broad-spectrum antifungal agents has increased the use of these agents by non-expert practitioners, without an impact on mortality. To improve efficacy while minimizing prescription errors and to reduce the high monetary cost to the health systems, the principles of pharmacokinetics (PK) and pharmacodynamics (PD) are necessary. A systematic review of the PD of antifungals agents was performed aiming at the practicing physician without expertise in this field. The initial section of this review focuses on the general concepts of antimicrobial PD. In vitro studies, fungal susceptibility and antifungal serum concentrations are related with different doses and dosing schedules, determining the PD indices and the magnitude required to obtain a specific outcome. Herein the PD of the most used antifungal drug classes in Latin America (polyenes, azoles, and echinocandins) is discussed.

Exploring interactions between pathogens and the Drosophila gut

Gastrointestinal infection can provoke substantial disturbance at both a local as well as at a systemic level and may evolve into a chronic disease state. Our growing knowledge of gut-pathogen interactions has been based to a large extent on the use of genetically tractable model hosts such as the fruit fly Drosophila melanogaster. In this review we will summarise the growing literature and critically address the advantages and disadvantages of using this model to extrapolate results from studying pathogen virulence and intestinal responses to humans.

Pharmacodynamics for antifungal drug development: an approach for acceleration, risk minimization and demonstration of causality

The treatment of invasive fungal diseases constitutes a significant unmet medical need. There are relatively few antifungal agents in clinical development and a paucity of novel targets. Morbidity and mortality remain high and clinical outcomes are compromised by submaximal efficacy, emergence of drug resistance and drug-related toxicity. Thus, new antifungal agents are urgently required. A deep understanding of exposure-response relationships underpins the development of safe and effective clinical regimens of any therapeutic agent. Pharmacokinetics (PK) and pharmacodynamics (PD) is increasingly recognized as a vital tool in the development of new antimicrobial agents and maximizes the probability that the right dose will be studied the first time. There is currently no information or agreement as to what constitutes an adequate PK/PD package for the development of a new antifungal agent. This review provides a summary of the achievements of antifungal PK/PD for the treatment of invasive candidiasis, invasive aspergillosis and cryptococcal meningoencephalitis, and outlines the necessary components of a PK/PD package for a new antifungal agent. Such information is critical for the accelerated and efficient development of new agents and enables improved clinical outcomes to be secured.

Pharmacokinetic/pharmacodynamic analysis of voriconazole against Candida spp. and Aspergillus spp. in children, adolescents and adults by Monte Carlo simulation

The objective of this study was to investigate the cumulative fraction of response of various voriconazole dosing regimens against six Candida and six Aspergillus spp. in immunocompromised children, immunocompromised adolescents, and adults. Using pharmacokinetic parameters and pharmacodynamic data, 5000-subject Monte Carlo simulations (MCSs) were conducted to evaluate the ability of simulated dosing strategies in terms of fAUC/MIC targets of voriconazole. According to the results of the MCSs, current voriconazole dosage regimens were all effective for children, adolescents and adults against Candida albicans, Candida parapsilosis and Candida orthopsilosis. For adults, dosing regimens of 4 mg/kg intravenous every 12 h (q12h) and 300 mg orally q12h were sufficient to treat fungal infections by six Candida spp. (C. albicans, C. parapsilosis, Candida tropicalis, Candida glabrata, Candida krusei and C. orthopsilosis) and five Aspergillus spp. (Aspergillus fumigatus, Aspergillus flavus, Aspergillus terreus, Aspergillus niger and Aspergillus nidulans). However, high doses should be recommended for children and adolescents in order to achieve better clinical efficacy against A. fumigatus and A. nidulans. The current voriconazole dosage regimens were all ineffective against A. niger for children and adolescents. All voriconazole dosage regimens were not optimal against Aspergillus versicolor. This is the first study to evaluate clinical therapy of various voriconazole dosing regimens against Candida and Aspergillus spp. infections in children, adolescents and adults using MCS. The pharmacokinetic/pharmacodynamic-based dosing strategy provided a theoretical rationale for identifying optimal voriconazole dosage regimens in children, adolescents and adults in order to maximise clinical response and minimise the probability of exposure-related toxicity.

Voriconazole pharmacokinetics following HSCT: results from the BMT CTN 0101 trial

BACKGROUND

Voriconazole is a first-line agent for the prevention and treatment of a number of invasive fungal diseases. Relatively little is known about the relationship between drug exposure and the prevention of invasive fungal infections.

PATIENTS AND METHODS

A pharmacokinetic-pharmacodynamic substudy was performed as part of the BMT CTN 0101 trial, which was a randomized clinical trial comparing voriconazole with fluconazole for the prevention of invasive fungal infections in HSCT recipients. A previously described population pharmacokinetic model was used to calculate the maximum a posteriori Bayesian estimates for 187 patients. Drug exposure in each patient was quantified in terms of the average AUC and average trough concentrations. The relationship between drug exposure and the probability of breakthrough infection was investigated using logistic regression. AUC and trough concentrations in patients with and without breakthrough infection were compared.

RESULTS

Pharmacokinetic data from each patient were readily described using the maximum a posteriori Bayesian estimates. There were only five patients that had a breakthrough infection while receiving voriconazole in the first 100 days post-HSCT. For these patients, there was no statistically significant relationship between the average AUC or average trough concentration and the probability of breakthrough infection [OR (95% CI) 1.026 (0.956-1.102) and 1.108 (0.475-2.581), respectively]. P value for these estimates was 0.474 and 0.813, respectively.

CONCLUSIONS

Given the very small number of proven/probable infections, it was difficult to identify any differences in drug exposure in HSCT recipients with and without breakthrough fungal infections.

In Vivo Synergy of Amphotericin B plus Posaconazole in Murine Aspergillosis

Aspergillus fumigatus is the main mold causing invasive fungal infection that shows high mortality rates. Therapeutic failure and the increase in drug resistance make it necessary to explore alternative treatments for this infection. We have evaluated the efficacy of amphotericin B at 0.8 mg/kg or 0.3 mg/kg of body weight combined with 40 mg/kg of posaconazole against three A. fumigatus isolates in a murine model of disseminated infection. The combination of the polyene and the azole led to a greater increase in survival and a significantly greater reduction in tissue burden than monotherapies.

Response of a clinical Escherichia coli strain to repeated cefquinome exposure in a piglet tissue-cage model

BACKGROUND

In order to provide some basis for effective dosage regimens that optimize efficacy with respect to bacteriological and clinical cures, the in vivo activity of cefquinome against a clinical Escherichia coli (E.coli) strain (the minimum inhibitory concentration value for this strain equals to the MIC90 value of 0.25 μg/ml for 210 E.coli strains isolated from pigs) was investigated by using a piglet tissue-cage infection model. The aim was to elucidate the pharmacokinetic/pharmacodynamics (PK/PD) index associated with cefquinome efficacy, and then to identify the magnitude of the PK/PD parameter required for different degree of efficacy in clinical treatment.

RESULTS

Tissue-cage infection model was established in piglets, and then the animals received intramuscular injection of cefquinome twice a day for 3 days to create a range of different drug exposures. The tissue-cage fluid was collected at 1, 3, 6, 9 and 12 h after every drug administration for drug concentrationdetermination and bacteria counting. Different cefquinome regimens produced different percentages of time during that drug concentrations exceeded the MIC (%T > MIC), ranging from 0% to 100%. Cefquinome administration at 0.2, 0.4, 0.6, 0.8, 1, 2 and 4 mg/kg reduced the bacterial count (log10 CFU/mL) in tissue-cage fluid by -1.00 ± 0.32, -1.83 ± 0.08, -2.33 ± 0.04, -2.96 ± 0.16, -2.99 ± 0.16, -2.93 ± 0.11, -3.43 ± 0.18, respectively. The correlation coefficient of the PK/PD index with antibacterial effect of the drug was 0.90 for %T > MIC, 0.62 for AUC0-12/MIC, and 0.61 for Cmax/MIC, suggesting the most important PK/PD parameter was %T > MIC. A inhibitory form of sigmoid maximum effect (Emax) model was used to estimate %T > MIC, and the respective values required for continuous 1/6-log drop, 1/3-log drop and 1/2-log drop of the clinical E.coli count during each 12 h treatment period were 3.97%, 17.08% and 52.68%.

CONCLUSIONS

The data derived from this study showed that cefquinome exhibited time-dependent killing profile. And from the results of the present study, it can be assumed that when %T > MIC reached 52.68%, cefquinome could be expected to be effective against a clinical E.coli strain for which the MIC value is below 0.128 μg/ml (3-log drop of bacteria count can be achieved after six successive administrations for 3 days).