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

Development and validation of a clinical risk score nomogram for predicting voriconazole trough concentration above 5 mg/L: a retrospective cohort study

The therapeutic range of voriconazole (VRC) is narrow, this study aimed to explore factors influencing VRC plasma concentrations > 5 mg/L and to construct a clinical risk score nomogram prediction model. Clinical data from 221 patients with VRC prophylaxis and treatment were retrospectively analyzed. The patients were randomly divided into a training cohort and a validation cohort at a 7:3 ratio. Univariate and binary logistic regression analysis was used to select independent risk factors for VRC plasma concentration above the high limit (5 mg/L). Four indicators including age, weight, CYP2C19 genotype, and albumin were selected to construct the nomogram prediction model. The area under the curve values of the training cohort and the validation cohort were 0.841 and 0.802, respectively. The decision curve analysis suggests that the nomogram model had good clinical applicability. In conclusion, the nomogram provides a reference for early screening and intervention in a high-risk population.

Successful Treatment of Disseminated Fusariosis in a 15-Month-Old Boy With Refractory Acute Lymphoblastic Leukemia Using High-Dose Voriconazole

BACKGROUND

Infections due to rare molds, such as Fusarium spp., cause severe and difficult-to-control diseases with increasing frequency. Data on fusariosis in children and on the use of voriconazole (VCZ), considered a drug of choice, are scarce in infants and children <2 years of age.

CASE PRESENTATION

We present the first, to our knowledge, pediatric case of disseminated mycosis due to Fusarium musae in a 15-month-old boy with relapsed/refractory acute lymphoblastic leukemia, diagnostics and outcome. Herein, at this severely immunocompromised patient, after prompt diagnosis, disseminated fusariosis was successfully treated with high-dose VCZ at a final dose of 15 mg/kg of body weight twice a day. This occurred by achieving adequate drug exposures as determined by drug susceptibility testing and followed by therapeutic drug monitoring without observed toxicity.

CONCLUSIONS

Appropriate diagnostic approach and timely administration of optimal antifungal therapy with VCZ were important for the successful treatment of disseminated fusariosis. Therapeutic drug monitoring, especially in <2-year-old children, is necessary to achieve sufficient drug exposure for optimal therapeutic response without toxicity.

Mycophenolate Metabolite Trough Concentrations Are Not Well Correlated With Dosing or Adverse Outcomes in Pediatric Heart Transplant Recipients

OBJECTIVE

Although mycophenolate metabolite trough concentrations in serum are routinely obtained for pediatric orthotopic heart transplant (OHT) recipients, limited data support this practice. We sought to investigate the relationship of mycophenolic acid (MPA) and MPA glucuronide (MPAG) serum concentrations to dosing and adverse outcomes among pediatric OHT patients.

METHODS

This retrospective study included OHT recipients ages 0 to 21 years who received mycophenolate mofetil (MMF) with MPA and MPAG serum trough concentration monitoring. The primary outcome was the relationship between MPA and MPAG serum concentrations and dosing. Secondary outcomes included the relationship of adverse outcomes to either MPA and MPAG concentrations or dosing.

RESULTS

A total of 98 patients with 1287 MPA and MPAG trough serum concentrations (each) were included. The median initial MMF dose was 40.3 mg/kg/day (IQR, 35.12-51.83) and 1164.4 mg/m2/day (IQR, 1080.77-1206.86). There was no correlation between either MPA or MPAG serum concentrations and mg/kg dosing, or mg/m2 dosing. When comparing the adverse effect of bone marrow suppression with no adverse effect, the median MPA serum trough concentration was 2 (IQR, 1.1-3.2) versus 1.6 (IQR, 0.8-2.5), p = 0.003. When comparing the adverse effect of infection with no adverse effect, median MPA serum trough concentration was 0.9 (IQR, 0.49-1.7) versus 1.6 (IQR, 0.8-2.5), p < 0.001. The clinical utility of this finding is of uncertain benefit. There was no association between MPAG serum concentrations and any adverse outcome (p = 0.053).

CONCLUSIONS

We did not identify a correlation between mycophenolate serum trough concentrations and either adverse outcomes or dosing. Based on these results, we discourage routine monitoring of mycophenolate trough concentrations.

Development of an on-site therapeutic drug monitoring method using a portable spectrometer

We report on the development of an on-site therapeutic drug monitoring (TDM) method for vancomycin (VCM) utilizing a portable spectrometer and commercially available immunoturbidimetric assay reagents designed for automated clinical chemistry analyzers. The method enables the quantification of VCM in plasma samples within 10 min, with a good correlation between the measured values and the theoretical values (r2 = 0.995). The intra and inter-day precisions were found to be below 12.5% and 17.7%, respectively. Moreover, we established a correlation between the quantitative values using this method and those measured through HPLC-UV and automated clinical chemistry analyzers, showing good reliability (R2 = 0.970 and 0.951, respectively). This method allows anyone to rapidly perform TDM at the bedside and is expected to be used to evaluate appropriate drug therapy.

Navigating fungal infections and antifungal stewardship: drug resistance, susceptibility testing, therapeutic drug monitoring and future directions

Antifungal stewardship refers to the rational use of antifungal agents. Historically, in some instances, the misuse or overuse of antifungal agents has predisposed patients to an elevated risk of systemic side-effects and treatment resistance, as well as increased healthcare costs. Superficial mycoses, such as onychomycosis, are sometimes treated without any diagnostic testing and is associated with a high likelihood of self-diagnosis and self-treatment, potentially leading to the emergence of resistance against commonly used antifungals like terbinafine. Practitioners need to ensure that a proper clinical diagnosis is backed up by appropriate testing. This may include the traditional light microscopy and culture; additionally, molecular techniques (such as polymerase chain reaction, terbinafine gene mutational analysis) and antifungal susceptibility testing are considerations as appropriate. The choice of antifungal agent should be guided by what is the standard of care in the location where the clinician practices as well as more broadly state and national prescription patterns. Recently, reports of treatment resistance concerning both superficial and deep fungal infections have added another layer of difficulty to clinical practice. This review aims to explore the phenomenon of antifungal drug resistance, and highlights the importance of adopting antifungal stewardship programs. We provide an overview of treatment resistance and mechanisms of resistance reported thus far in dermatophytes. Challenges of performing antifungal susceptibility testing and therapeutic drug monitoring are discussed, as well as principles, recommendations and future directions of antifungal stewardship programs.

Body Surface Area-Based Dosing of Mycophenolate Mofetil in Pediatric Hematopoietic Stem Cell Transplant Recipients: A Prospective Population Pharmacokinetic Study

Mycophenolate mofetil (MMF) is commonly used for acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (HSCT). However, limited population pharmacokinetic (PPK) data are available for pediatric HSCT patients. This study aimed to develop a PPK model and recommend optimal oral MMF dosage in pediatric HSCT patients. This prospective study involved pediatric HSCT patients at a tertiary academic institution. Patients received oral MMF 15-20 mg/kg twice daily for aGVHD prophylaxis and treatment. The PPK analysis was conducted using a nonlinear mixed-effects modeling method. Simulation was performed considering different body surface areas (BSAs) (0.5 m2, 1.0 m2, 1.5 m2) and dosing (400 mg/m2, 600 mg/m2, 900 mg/m2 twice daily). Based on the simulation, an optimal dosage of oral MMF was suggested. A total of 20 patients and 80 samples were included in the PPK model development. A one-compartment model with first-order absorption adequately described the pharmacokinetics of mycophenolic acid (MPA). BSA was a statistically significant covariate on Vd/F. Simulation suggested the optimal dosage of oral MMF as 900 mg/m2 twice daily, respectively. A reliable PPK model was developed with good predictive performance. This model-informed optimal MMF dosage in pediatric HSCT patients can provide valuable dosing guidance in real-world clinical practice.

Comparison of ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and enzyme-multiplied immunoassay technique (EMIT) for quantification of voriconazole plasma concentration from Chinese patients

Introduction

Voriconazole (VRZ) is the recommended standard treatment for life-threatening invasive aspergillosis. The plasma concentration of VRZ should be determined to optimise treatment results and reduce side effects. This study aimed to compare the correlation and concordance of ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and enzyme-multiplied immunoassay technique (EMIT) to determine VRZ plasma concentration in clinical practice.

Methods

An isotopically labelled internal standard UPLC-MS/MS method was established, validated, and subsequently applied to determine VRZ concentration. The UPLC-MS/MS method was also compared with a commercial EMIT method regarding results correlation and concordance.

Results

The calibration curve of UPLC-MS/MS was linear from 0.1 to 10 mg/L, the inter- and intra-day relative standard deviations (RSDs), and the stability of quality control samples were less than 15 %, satisfying the Bioanalytical Method Validation Guidelines. A total of 122 plasma samples were collected and analyzed using both methods. UPLC-MS/MS and EMIT showed a high correlation (r = 0.9534), and Bland-Altman analysis indicated a mean absolute bias of 1.035 mg/L and an average bias of 27.56 % between UPLC-MS/MS and EMIT. The paired Wilcoxon test and Bland-Altman analysis revealed poor consistency between the two methods. Furthermore, we compared the effects of different methods in clinical applications. Two threshold values for treatment efficacy (1.0 mg/L) and safety (5.5 mg/L) were established, and considerable discordance was observed between the original EMIT and UPLC-MS/MS results at both thresholds (p < 0.05). Nevertheless, the adjusted EMIT results were not inconsistent with the UPLC-MS/MS results regarding the efficacy (p = 0.125) and safety (p = 1.0) thresholds.

Conclusions

The isotopically labelled internal standard UPLC-MS/MS method is established and well applied in the clinical setting. A strong correlation but discordance was found between UPLC-MS/MS and EMIT, indicating that switching from UPLC-MS/MS to EMIT was unsuitable. However, the adjusted EMIT results may serve as a reliable surrogate when UPLC-MS/MS results cannot be obtained when necessary.

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.

Recent drug development and treatments for fungal infections

Fungal infections are now becoming a hazard to individuals which has paved the way for research to expand the therapeutic options available. Recent advances in drug design and compound screening have also increased the pace of the development of antifungal drugs. Although several novel potential molecules are reported, those discoveries have yet to be translated from bench to bedside. Polyenes, azoles, echinocandins, and flucytosine are among the few antifungal agents that are available for the treatment of fungal infections, but such conventional therapies show certain limitations like toxicity, drug interactions, and the development of resistance which limits the utility of existing antifungals, contributing to significant mortality and morbidity. This review article focuses on the existing therapies, the challenges associated with them, and the development of new therapies, including the ongoing and recent clinical trials, for the treatment of fungal infections. Advancements in antifungal treatment: a graphical overview of drug development, adverse effects, and future prospects.

Pro-arrhythmic effect of escitalopram and citalopram at serum concentrations commonly observed in older patients - a study based on a cohort of 19,742 patients

BACKGROUND

For a decade, patients have been advised against using high citalopram- and escitalopram-doses due to risk for ventricular arrhythmia and cardiac arrest. Still, these drugs are widely used to treat depression and anxiety especially in older patients. It is unclear why they are cardiotoxic and at what serum concentrations patients are at risk for arrhythmias. Thus, how many patients that are at risk for iatrogenic cardiac arrest is unknown.

METHODS

We studied the arrhythmogenic effects of citalopram, escitalopram and their metabolites on human cardiomyocytes. Concentrations showing pro-arrhythmic activity were compared with observed drug and metabolite serum concentrations in a cohort of 19,742 patients (age 12-105 years) using escitalopram or citalopram in Norway (2010-2019). As arrhythmia-risk is related to maximum serum concentration, this was simulated for different age-groups from the escitalopram patient material.

FINDINGS

Therapeutic concentrations of both citalopram and escitalopram but not their metabolites showed pro-arrhythmic changes in the human cardiac action potential. Due to age-dependent reduction of drug clearance, the proportion of patients above threshold for arrhythmia-risk increased with age. 20% of patients >65 years were predicted to reach potentially pro-arrhythmic concentrations, following intake of 10 mg escitalopram.

INTERPRETATION

All patients that are using escitalopram or citalopram and have genetic disposition for acquired long-QT syndrome, are >65 years, are using additional pro-arrhythmic drugs or have predisposition for arrhythmias, should be monitored with therapeutic drug monitoring (TDM) to avoid exposure to potentially cardiotoxic concentrations. Serum concentrations should be kept below 100 nM, to reduce arrhythmia-risk.

FUNDING

This study was funded by The Research Council of Norway (project number: 324062).

Modeling and Simulation as a Tool to Assess Voriconazole Exposure in the Central Nervous System

Voriconazole is a triazole antifungal used empirically for the treatment of complicated meningitis associated with Cryptococcus neoformans. Biopsy studies show that the drug exhibits adequate brain penetration although levels of cerebral spinal fluid (CSF) are highly variable. Considering that CSF is one of the main surrogates for CNS exposure, the present work proposed the building of a population pharmacokinetic modeling (popPK) model able to describing the exposure achieved by voriconazole in the plasma, interstitial cerebral fluid and CSF of healthy and infected rats. The developed popPK model was described by four compartments, including total plasma, free brain and total CSF concentrations. The following PK parameters were determined: K_m = 4.76 mg/L, V_max = 1.06 mg/h, Q₁ = 2.69 L, Q_in = 0.81 h^-1 and Q_out = 0.63 h^-1. Infection was a covariate in the Michaelis-Menten constant (K_m) and intercompartmental clearance from the brain tissue compartment to central compartment (Q_out). Simulations performed with the popPK model to determine the probability of reaching the therapeutic target of fAUC > MIC showed that VRC has sufficient tissue exposure in the interstitial fluid and in the CSF for the treatment of fungal infections in these tissues at prevalent minimum inhibitory concentrations.

Higher Weight-Based Doses Are Required to Achieve and Maintain Therapeutic Voriconazole Serum Trough Concentrations in Children

OBJECTIVE

Children require weight-based voriconazole doses proportionately larger than adults to achieve therapeutic serum trough concentrations (1-6 mcg/mL). The objective of this quality improvement project was to determine the initial dose, proportion of patients achieving target concentrations with initial dosing, and subsequent therapeutic drug monitoring and dose modifications needed to achieve and maintain therapeutic voriconazole concentrations in children.

METHODS

This retrospective study evaluated children aged <18 years treated with voriconazole during the study period. Dosing and therapeutic drug monitoring (TDM) values were collected and compared by age. Data are presented as median (IQR), unless otherwise stated.

RESULTS

Fifty-nine patients, aged 10.4 (3.7-14.7) years and 49% female, met inclusion criteria; 42 had at least 1 steady-state voriconazole serum trough concentration measured. Twenty-one of 42 (50%) achieved the target concentration at the first steady-state measurement. An additional 13 of 42 (31%) achieved the target following 2 to 4 dose modifications. The dose required to first achieve a value in the target range was 22.3 (18.0-27.1) mg/kg/day in children aged <12 years and 12.0 (9.8-14.0) mg/kg/day in children aged ≥12 years. After reaching the target, 59% and 81% of repeated steady-state measurements were in the therapeutic range in patients aged <12 years and ≥12 years, respectively.

CONCLUSIONS

Reaching therapeutic voriconazole serum trough concentrations required doses larger than currently recommended by the American Academy of Pediatrics. Multiple dose adjustments and TDM measurements were required to achieve and maintain therapeutic voriconazole serum concentrations.

Effect of Meal Timings and Meal Content on the AUC0-12h of Mycophenolic Acid: A Simulation Study

Meal timings and content related to gallbladder emptying in the enterohepatic circulation are important for explaining the high variability in mycophenolic acid exposure. The limited sampling strategy (LSS) was established to estimate the area under the plasma concentration-time curve from time 0 to 12 hours (AUC_0-12h ) of mycophenolic acid in therapeutic drug monitoring. The aim of this study is to investigate the effect of meal timings and content on the AUC_0-12h of mycophenolic acid and to assess the influence of meals on LSS. A mycophenolic acid pharmacokinetic model with a mechanism-based enterohepatic circulation process was employed to perform simulations under various assumed meal scenarios. The simulations were compared to evaluate the effect of meal timings and meal content on mycophenolic acid AUC_0-12h . Monte Carlo simulations were performed using the meal parameter with the greatest impact on mycophenolic acid AUC_0-12h as a variable. The corresponding LSS equations were established, and the predictive performance was assessed. Both the meal timings and meal content affected the mycophenolic acid AUC_0-12h , and the postdose fasting period had the greatest impact. The predictive performance of the LSS is sensitive to the postdose fasting period. Therefore, meal timings may improve the estimation of mycophenolic acid AUC_0-12h and the efficacy of therapeutic drug monitoring.

Therapeutic drug monitoring (TDM) as intervention: A cross-sectional analysis of characteristics of 173 registered clinical trials

Background

To examine fundamental characteristics of clinical trials with therapeutic drug monitoring (TDM) as intervention on world major clinical trials registry platform.

Methods

Cross-sectional analysis of clinical trials with TDM as intervention that were registered on WHO International Clinical Trials Registry Platform (ICTRP) or ClinicalTrials.gov. Relevant trial entries registered before and on March 2nd, 2022 were downloaded, deduplicated, and reviewed. Recruit country, monetary source, start years, study design, medical conditions, involved drugs, outcome measure, and subject information were extracted and analyzed.

Results

Overall, 173 clinical trials were included in this study. Majority of the trials were conducted in several economically prosperous countries. The earliest initiated trials dates back to 2002. Most of the trials were funded by hospitals (36.4%). A higher proportion of trials were conducted within one country (86.1%), as phase Ⅳ (34.1%) interventional study (82.7%), randomized (52.6%), parallel assignment (53.8%) and open label (67.0%). The most concerned medical condition were infectious or parasitic disease and neoplasms, with the most monitored drugs were immunosuppressants and β-lactam antibacterials. Most of the trials enroll no more than 50 subjects (30.6%), with both gender (95.4%), and adults (67.0%).

Conclusion

The trials were mainly conducted in several economically prosperous countries. The number of registered trials had gradually increased during the past years. Novel biological drugs have increasingly become the research hotspot. We expect that with abundant financial support, more high-quality large-scale, multicenter randomized clinical trials (RCTs) are designed and implemented to promote the development of TDM in the future.