Population pharmacokinetics of valganciclovir prophylaxis in paediatric and adult solid organ transplant recipients

Assessment of patients' characteristics associated with the efficacy and safety of oral valganciclovir treatment for infants with symptomatic congenital cytomegalovirus disease

INTRODUCTION

Insurance coverage for oral valganciclovir (VGCV) began in Japan in April 2023 on the basis of results, including our clinical trials for symptomatic congenital cytomegalovirus (CMV) disease. The VGCV treatment is available throughout Japan, so clinicians must consider the likelihood of hearing improvement and the possibility of neutropenia before dosing.

MATERIALS AND METHODS

We performed a substudy of an investigator-initiated, single-arm, prospective, multicenter, clinical trial in which 24 infants with symptomatic congenital CMV disease were orally administered 16 mg/kg VGCV twice daily for 6 months as an intervention. We examined the infants' baseline characteristics associated with improved hearing impairment or a severely reduced neutrophil count.

RESULTS

Of the 24 patients, 4 had normal hearing on assessment of their ear with the best hearing. Hearing impairment improved in 14 patients and did not respond to VGCV treatment in 6 patients at the 6-month hearing assessment. CMV DNA levels in plasma at baseline were higher in patients in whom hearing did not respond to treatment. A neutrophil count <500/mm3 occurred in 5 (21%) patients for the first 6 weeks and in 8 (33%) patients for the first 6 months. A neutrophil count at screening and the lowest neutrophil count over the 6 months showed the highest correlation (r = 0.477, p = 0.019).

CONCLUSIONS

Infants with a low plasma viral load at screening tend to have an improvement in hearing impairment. Clinicians should be aware of neutropenia during VGCV treatment particularly in patients with a low neutrophil count during screening.

Challenges for the improvement of valganciclovir prophylaxis in solid organ transplantation and the possible role of therapeutic drug monitoring in adults

Cytomegalovirus (CMV) infection frequently occurs after solid organ transplantation and is associated with an increased morbidity and mortality. Fortunately, the development of valganciclovir prophylaxis has lowered the incidence of CMV infection and its complications in immunosuppressed solid organ transplant recipients. However, breakthrough infections during valganciclovir prophylaxis and late CMV infection after cessation of valganciclovir prophylaxis still occur with the current prophylactic strategy. Additionally, valganciclovir resistance has emerged among CMV strains, which complicates the treatment of CMV infections. Furthermore, the use of valganciclovir is associated with myelotoxicity, which can lead to the premature withdrawal of prophylaxis. It is important to address these current issues in order to improve the standard care after solid organ transplantation. This paper will therefore discuss the clinical practice of valganciclovir prophylaxis, elaborate on its issues and suggest how to improve the current prophylactic strategy with a possible role for therapeutic drug monitoring.

Trough ganciclovir concentration as predictor of leukopenia in lung transplant recipients receiving valganciclovir prophylaxis

BACKGROUND

Valganciclovir is the first-line agent for Cytomegalovirus prophylaxis after lung transplantation. However, its use is associated with a relatively high risk of hematological toxicity. This study aimed to investigate the relationship between trough ganciclovir concentration and hematologic toxicity in lung transplantation patients receiving valganciclovir prophylaxis, and identify factors that affect ganciclovir pharmacokinetics in this population.

METHODS

This prospective observational study included 24 lung transplant patients receiving valganciclovir prophylaxis. The cutoff value of trough ganciclovir concentration was estimated using receiver operating characteristic analysis in leukopenia grade 3 and higher. Population pharmacokinetic analysis was performed using a nonlinear mixed-effects modeling program.

RESULTS

The trough ganciclovir concentration was significantly higher in the group with leukopenia grades 3 or higher than in the group with grades less than or equal to 2 (1605.7 ± 860.1 ng/mL [n = 3] vs. 380.5 ± 175.8 ng/mL (n = 21), p < .001). The cutoff value of trough ganciclovir concentration for predicting greater than or equal to grade 3 leukopenia was estimated as 872.0 ng/mL. Creatinine clearance and lung re-transplantation were found to have a significant impact on the total body clearance of valganciclovir. Ganciclovir clearance was decreased in patients with reduced creatine clearance or re-transplantation.

CONCLUSION

These results suggest that higher ganciclovir trough concentrations are associated with an increased risk of leukopenia grade 3 or higher, and that creatinine clearance and lung re-transplantation affected the pharmacokinetics of ganciclovir.

Optimizing ganciclovir and valganciclovir dosing regimens in pediatric patients with cytomegalovirus infection: a spotlight on therapeutic drug monitoring

INTRODUCTION

Infants and immunocompromised children with cytomegalovirus (CMV) infection have significant morbidity and mortality. Ganciclovir (GCV) and its oral prodrug valganciclovir (VGCV) are the major antiviral options of choice for the prophylaxis and treatment of CMV infection. However, with the currently recommended dosing regimens used in pediatric patients, large intra- and inter-individual variability of pharmacokinetic (PK) parameters and exposure are observed.

AREAS COVERED

This review describes the PK and pharmacodynamic (PD) characteristics of GCV and VGCV in pediatrics. Moreover, the role of therapeutic drug monitoring (TDM) and current clinical practice for GCV and VGCV dosing regimens optimization in pediatrics are discussed.

EXPERT OPINION

GCV/VGCV TDM has shown the potential value to improve the benefit/risk ratio in pediatrics when using the therapeutic ranges derived from adults. However, well-designed studies are required to evaluate the relationship of TDM with clinical outcomes. Furthermore, studies to explore the children-specific dose-response-effect relationships will be helpful to facilitate the TDM practice. In the clinical setting, optimal sampling methods such as limited sampling strategies for pediatrics can be used in TDM and intracellular ganciclovir triphosphate may be used as an alternative TDM marker.

Establishment and Evaluation of a Parametric Population Pharmacokinetic Model Repository for Ganciclovir and Valganciclovir

BACKGROUND

Ganciclovir and valganciclovir are used for prophylaxis and treatment of cytomegalovirus infection. However, there is great interindividual variability in ganciclovir's pharmacokinetics (PK), highlighting the importance of individualized dosing. To facilitate model-informed precision dosing (MIPD), this study aimed to establish a parametric model repository of ganciclovir and valganciclovir by summarizing existing population pharmacokinetic information and analyzing the sources of variability. (2) Methods: A total of four databases were searched for published population PK models. We replicated these models, evaluated the impact of covariates on clearance, calculated the probability of target attainment for each model based on a predetermined dosing regimen, and developed an area under the concentration-time curve (AUC) calculator using maximum a posteriori Bayesian estimation. (3) Results: A total of 16 models, one- or two-compartment models, were included. The most significant covariates were body size (weight and body surface area) and renal function. The results show that 5 mg/kg/12 h of ganciclovir could make the AUC_0-24h within 40-80 mg·h/L for 50.03% pediatrics but cause AUC_0-24h exceeding the exposure thresholds for toxicity (120 mg·h/L) in 51.24% adults. (4) Conclusions: Dosing regimens of ganciclovir and valganciclovir should be adjusted according to body size and renal function. This model repository has a broad range of potential applications in MIPD.

Limited Sampling Strategies to Predict Ganciclovir Exposure after Valganciclovir Administration and to Reduce Monitoring Constraints in Renal Transplant Children

Valganciclovir, the ganciclovir prodrug, is an antiviral agent used to prevent cytomegalovirus infection in renal transplant children. Therapeutic drug monitoring is still necessary to ensure optimal therapeutic area under the concentration-time curve from 0 to 24 h (AUC0-24) of 40 to 60 μg·h/mL since valganciclovir presents a high pharmacokinetic variability. To calculate ganciclovir AUC0-24 with the trapezoidal method, 7 samples are needed. The objective of this study was to develop and validate a reliable and clinically applicable limited sampling strategy (LSS) for individualizing valganciclovir dose in renal transplant children. Rich pharmacokinetic data from ganciclovir plasmatic dosages measured in renal transplant children who received valganciclovir to prevent cytomegalovirus infection at Robert Debré University Hospital were collected retrospectively. Ganciclovir AUC0-24s were calculated using the trapezoidal method. The LSS was developed using a multilinear regression approach to predict AUC0-24. The patients included were divided into two groups for model development (50 patients) and validation (30 patients). A total of 80 patients were included between February 2005 and November 2018. Multilinear regression models were developed on 50 pharmacokinetic profiles (50 patients) and validated with an independent group of 43 pharmacokinetic profiles (30 patients). Regressions based on samples collected at T1h-T4h-T8h, T2h-T4h-T8h, or T1h-T2h-T8h presented the best AUC0-24 predictive performances with an average difference between reference and predicted AUC0-24 of -0.27, 0.34, and -0.40 μg·h/mL, respectively. In conclusion, valganciclovir dosage adaptation was required in children to achieve the target AUC0-24. Three LSS models using three pharmacokinetic blood samples instead of seven will be useful for individualizing valganciclovir prophylaxis in renal transplant children.

Therapeutic Drug Monitoring of Ganciclovir: Where Are We?

BACKGROUND

Ganciclovir is the mainstay of therapy for the prophylaxis and treatment of Cytomegalovirus. However, therapy with this antiviral agent is hindered by side effects such as myelosuppression, which often leads to therapy cessation. Underdosing, as an attempt to prevent side effects, can lead to drug resistance and therapy failure. Therapeutic drug monitoring (TDM) has been used to overcome these problems. The purpose of this narrative review was to give an overview of ganciclovir TDM, available assays, population pharmacokinetic models, and discuss the current knowledge gaps.

METHODS

For this narrative review, a nonsystematic literature search was performed on the PubMed database in April 2021. The following search terms were used: ganciclovir, valganciclovir, pharmacokinetics, pharmacodynamics, population pharmacokinetics, therapeutic drug monitoring, bioassay, liquid chromatography coupled with tandem mass spectrometry, liquid chromatography, chromatography, spectrophotometry, and toxicity. In addition, the reference lists of the included articles were screened.

RESULTS

The most common bioanalysis method identified was liquid chromatography coupled with tandem mass spectrometry. There are different models presenting ganciclovir IC50; however, establishing a pharmacokinetic/pharmacodynamic target for ganciclovir based on preclinical data is difficult because there are no studies combining dynamic drug exposure in relation to inhibition of viral replication. The data on ganciclovir TDM show large interindividual variability, indicating that TDM may play a role in modifying the dose to reduce toxicity and prevent treatment failure related to low concentrations. The main hurdle for implementing TDM is the lack of robust data to define a therapeutic window.

CONCLUSIONS

Although the pharmacokinetics (PK) involved is relatively well-described, both the pharmacodynamics (PD) and pharmacokinetic/pharmacodynamic relationship are not. This is because the studies conducted to date have mainly focused on estimating ganciclovir exposure, and owing to the limited therapeutic options for CMV infections, future studies on ganciclovir are warranted.

Rapid determination of acyclovir, its main metabolite 9-carboxymethoxymethylguanine, ganciclovir and penciclovir in human serum by LC-MS/MS

A novel MS‐based analytical method for simultaneous analysis of the antiviral drugs acyclovir, its metabolite 9‐carboxymethoxymethylguanine, ganciclovir, and penciclovir in human serum is described. These antiviral drugs are active against herpes virus infections. Acyclovir and penciclovir are regarded as safe and effective medicines with mild side effects such as headache and gastrointestinal discomfort, and ganciclovir is regarded as more toxic and is known to cause, for example, bone marrow suppression. Acyclovir’s main metabolite 9‐carboxymethoxymethylguanine is a presumptive neurotoxin and should be monitored in patients with impaired renal function or in cases with neurotoxic symptoms. A sample was prepared using protein precipitation with 1% formic acid in methanol containing isotopically labeled internal standard. Chromatographic separation on a biphenyl column and mass spectrometric detection were performed in multiple reaction monitoring (MRM) mode on a Xevo TQ‐S micro with ESI in positive ion mode, within 3 min. Inter‐day assay accuracies for the quality controls varied between 95 and 104% and intra‐day assay between 93 and 105%. Inter‐day and intra‐day assay imprecision for the quality controls ranged between 1.4 and 4.2% and 1.7 and 6.5% respectively. The lower limit of quantification for all four substances was 0.156 μmol/L. It is an accurate and reproducible method for therapeutic drug monitoring.

Pharmacokinetics, Pharmacodynamics, and Therapeutic Drug Monitoring of Valganciclovir and Ganciclovir in Transplantation

Ganciclovir and valganciclovir are first choice drugs for the prevention and treatment of cytomegalovirus infection and disease in solid organ and stem cell transplant recipients. Only a few studies on the pharmacokinetics and exposure/efficacy or exposure/safety relationships of ganciclovir and valganciclovir in transplant recipients have been published so far, and there are still controversies about the exposure parameter to use for therapeutic drug monitoring (TDM). We performed an extensive literature review of the clinical pharmacokinetics data, the exposure/effect relationships in terms of efficacy and safety, and the available tools for valganciclovir and ganciclovir TDM in adults and pediatrics transplant recipients. The pharmacokinetics of ganciclovir and valganciclovir is well described in adults and children, and a high interindividual variability is commonly observed. In contrast, the drug pharmacodynamics has been poorly described in adults and barely in children. The average 24-hour area under the concentration-time curve (AUC_0-24h ) seems to be the best predictor of efficacy and toxicity. The benefit of TDM remains controversial in adult patients but should be considered in children due to higher interindividual variability and lower probability of target attainment. Several bayesian estimators based on limited sampling strategies have been developed with this aim and may be used in clinical practice for the AUC-based individual dose adjustment of ganciclovir and valganciclovir.

Thoroughly Validated Bayesian Estimator and Limited Sampling Strategy for Dose Individualization of Ganciclovir and Valganciclovir in Pediatric Transplant Recipients

BACKGROUND AND OBJECTIVE

Given a high pharmacokinetic inter-individual variability and a low exposure target achievement, ganciclovir (GCV) therapeutic drug monitoring is sometimes used in children. We aimed to develop and validate Bayesian estimators based on limited sampling strategies for the estimation of GCV area under the concentration-time curve from 0 to 24 h in pediatric transplant recipients treated with valganciclovir (VGCV) or GCV.

METHODS

Solid organ transplant or stem-cell transplant recipients who received GCV or VGCV and had available GCV concentrations per standard of care were retrospectively included in this study for pharmacokinetic modeling and development of Bayesian estimators using the iterative two-stage Bayesian method. Validation datasets included additional child recipients of a solid organ transplant or stem-cell transplant, and child recipients of a kidney or liver transplant enrolled in a previous study. Various combinations of three or two sampling times, applicable in clinical practice, were assessed based on the relative mean bias, standard deviation, and the root mean square error in a development dataset and three independent validation datasets.

RESULTS

In the development dataset, the mean bias/standard deviation/root mean square error for the 1 h/2 h/3 h and 1 h/3 h limited sampling strategies were - 1.4%/9.3%/9.1% and - 3.5%/12.2%/12.3%, respectively for GCV, while for VGCV, the mean bias/standard deviation/root mean square error for the 1 h/2 h/6 h and 1 h/6 h limited sampling strategies were 0.7%/13.5%/13.3% and - 0.1%/12.1%/11.8%, respectively. In the independent validation datasets, seven (13%) and five (14%) children would have had misclassifications of their exposure using these Bayesian estimators and limited sampling strategies for VGCV and GCV, respectively.

CONCLUSIONS

Three plasma samples collected at 1 h/2 h/3 h and 1 h/2 h/6 h post-dose for GCV and VGCV respectively, are sufficient to accurately determine GCV area under the concentration-time curve from 0 to 24 h for pharmacokinetic-enhanced therapeutic drug monitoring.

Population Pharmacokinetics of Intravenous Ganciclovir and Oral Valganciclovir in a Pediatric Population To Optimize Dosing Regimens

Ganciclovir is indicated for curative or preventive treatment of cytomegalovirus (CMV) infections. This study aimed to characterize ganciclovir pharmacokinetics, following intravenous ganciclovir and oral valganciclovir administration, to optimize dosing schemes. All children aged <18 years receiving ganciclovir or valganciclovir were included in this study. Pharmacokinetics were described using nonlinear mixed-effect modeling. Monte Carlo simulations were used to optimize the dosing regimen to maintain the area under the concentration-time curve (AUC) in the preventive or therapeutic target. Among the 105 children (374 concentration-time observations) included, 78 received intravenous (i.v.) ganciclovir, 19 received oral valganciclovir, and 6 received both drugs. A two-compartment model with first-order absorption for valganciclovir and first-order elimination best described the data. An allometric model was used to describe the bodyweight (BW) effect. Estimated glomerular filtration rate (eGFR) and medical status of critically ill children were significantly associated with ganciclovir elimination. Recommended doses were adapted for prophylactic treatment. To obtain a therapeutic exposure, doses should be increased to 40 mg/kg of body weight/day oral or 15 to 20 mg/kg/day i.v. in children with normal eGFR and to 56 mg/kg/day oral or 20 to 25 mg/kg/day i.v. in children with augmented eGFR. These doses should be prospectively confirmed, and therapeutic drug monitoring could be used to refine them individually. (This study has been registered at ClinicalTrials.gov under identifier NCT02539407.).

Population pharmacokinetics of ganciclovir and valganciclovir in paediatric solid organ and stem cell transplant recipients

AIMS

Ganciclovir (GCV) and its prodrug valganciclovir (VGCV) are first-line agents to prevent and treat cytomegalovirus in transplant recipients. There is high pharmacokinetic (PK) interindividual variability and PK data are scarce, especially in paediatric stem cell transplant (SCT) recipients. We sought to determine the optimal GCV and VGCV dosing in transplanted children.

METHODS

We conducted a single-centre retrospective population PK (POPPK) study of IV GCV and enteral VGCV in paediatric solid organ transplant (SOT) and SCT recipients. We included children who were transplanted and had available plasma GCV concentrations, done per standard of care. POPPK analysis was performed using a nonlinear mixed effects modelling approach with NONMEM. Optimal dosing was determined based on the achievement of the surrogate efficacy target: GCV 24 h area under the concentration-time curve (AUC_0-24h ) of 40-60 mg.h.L^-1 .

RESULTS

Fifty children with a median [range] age of 7.5 years [0.5-17.4] contributed 580 PK samples. A two-compartment model with first-order absorption with a lag time and first-order elimination fit the data well. Creatinine clearance and body weight (WT) were significant covariates for GCV clearance (CL); and WT for the volumes of distribution. IV GCV 15-20 mg.kg^-1 .day^-1 divided every 12 hours achieved the highest probability of target achievement (PTA) (33.0-33.8%). Enteral VGCV 30 and 40 mg.kg^-1 .day^-1 divided every 12 hours in children 0-<6 years, and 6-18 years, respectively, achieved the highest PTA (29.1-33.0%).

CONCLUSION

This is the first POPPK model developed in children with either SOT or SCT. Concentration target achievement was low, suggesting a potential benefit for therapeutic drug monitoring to ensure optimal exposure.

Valganciclovir-Ganciclovir Use and Systematic Therapeutic Drug Monitoring. An Invitation to Antiviral Stewardship

Valganciclovir (VGCV) and ganciclovir (GCV) doses must be adjusted according to indication, renal function and weight. No specific therapeutic exposure values have been established. We aimed to evaluate the adequacy of VGCV/GCV doses, to assess the interpatient variability in GCV serum levels, to identify predictive factors for this variability and to assess the clinical impact. This is a prospective study at a tertiary institution including hospitalized patients receiving VGCV/GCV prophylaxis or treatment. Adequacy of the antiviral dose was defined according to cytomegalovirus guidelines. Serum levels were determined using High-Performance Liquid Chromatography. Blood samples were drawn at least 3 days after antiviral initiation. Outcome was considered favorable if there was no evidence of cytomegalovirus infection during prophylaxis or when a clinical and microbiological resolution was attained within 21 days of treatment and no need for drug discontinuation due to toxicity. Seventy consecutive patients [74.3% male/median age: 59.2 years] were included. VGCV was used in 25 patients (35.7%) and GCV in 45 (64.3%). VGCV/GCV initial dosage was deemed adequate in 47/70 cases (67.1%), lower than recommended in 7/70 (10%) and higher in 16/70 (22.9%). Large inter-individual variability of serum levels was observed, with median trough levels of 2.3 mg/L and median peak levels of 7.8 mg/L. Inadequate dosing of VGCV/GCV and peak levels lower than 8.37 or greater than 11.86 mg/L were related to poor outcome. Further studies must be performed to confirm these results and to conclusively establish if VGCV/GCV therapeutic drug monitoring could be useful to improve outcomes in specific clinical situations.

Population Pharmacokinetics and Bayesian Estimation of the Area Under the Concentration-Time Curve for Ganciclovir in Adult Chinese Renal Allograft Recipients After Valganciclovir Administration

Valganciclovir (VGCV) is the prodrug of ganciclovir (GCV). The objective of this study was to establish a population pharmacokinetic model (PPK) of GCV to investigate the PK characteristics of GCV after administration of VGCV in adult Chinese renal allograft recipients. Seventy Chinese renal allograft recipients were given 450 mg (n = 41) or 900 mg (n = 29) VGCV daily. Blood samples were drawn 0-24 hours after 5 days' therapy, and GCV plasma levels were determined. The PPK model was constructed using nonlinear mixed-effects modeling, and the Bayesian estimation of AUC_0-24h was constructed for an individual patient based on limited plasma samples. The PK of GCV was best described by a 2-compartment model with a first-order absorption process. The CL/F, V₂ /F, Q/F, V₃ /F, K_a , and lag time of GCV were 15.8 ± 0.71 L/h, 10.9 ± 2.38 L, 3.98 ± 0.40 L/h, 167 ± 44.0 L, 0.23 ± 0.0078 1/h, and 0.93 ± 0.017 hours, respectively. Clearance of creatinine was found to have a significant impact on the CL/F of GCV (P < .01). Sampling strategies consisted of plasma concentrations 0 and 2 and 0, 2, and 4 hours after VGCV administration were shown to be suitable for the estimation of the GCV AUC_0-24h . The PPK model was acceptable and can describe the PK of GCV in Chinese renal transplant patients administered VGCV. The AUC_0-24h of GCV in Chinese renal transplant patients can be calculated by a limited sampling strategy method.

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

Purpose

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

Methods

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

Results

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

Conclusion

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

Electronic supplementary material

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

Population pharmacokinetics of ganciclovir after valganciclovir in renal transplant children

BACKGROUND

Valganciclovir, the ganciclovir prodrug, is an antiviral agent administered orally to prevent or treat cytomegalovirus infection in solid organ transplant recipients. Dosing regimen of valganciclovir is still controversial in children, as the number of patients reaching the Area Under the Curve at steady state (AUC_ss) target (40 - 60 mg.h/L) remains highly variable. The aim of this study was to determine the population pharmacokinetics of valganciclovir in paediatric renal transplant recipients and propose an appropriate dosing regimen.

METHODS

Renal transplant children who received valganciclovir to prevent or treat cytomegalovirus infection at Robert Debré University Hospital were included. Plasma ganciclovir concentrations were determined by high performance liquid chromatography and ultraviolet detection. Population pharmacokinetic analysis was performed with NONMEM software.

RESULTS

104 patients, aged 2 to 20 years, treated with valganciclovir administered at a mean dose of 17.3 ± 6.1 mg/kg to prevent and/or treat cytomegalovirus infection after renal transplantation were included. A total of 1212 samples were available. A two-compartment model with first-order elimination best fitted the data: ganciclovir clearance increased with body surface area, was 15% higher in boys and decreased with increasing creatinine concentration. Central volume of distribution increased with body surface area and was 14% higher in boys. According to the personalized dosing regimen, 65.7% and 65.4% of children were predicted to achieve the AUC_ss target for cytomegalovirus prophylaxis and treatment, respectively.

CONCLUSION

A new pharmacokinetic model was built allowing to propose individualised dose adapted to renal transplanted paediatric patients characteristics.

Ganciclovir

Ganciclovir is synthetic nucleoside analog of guanine closely related to acyclovir but has greater activity against cytomegalovirus. This comprehensive profile on ganciclovir starts with a description of the drug: nomenclature, formulae, chemical structure, elemental composition, and appearance. The uses and application of the drug are explained. The methods that were used for the preparation of ganciclovir are described and their respective schemes are outlined. The methods which were used for the physical characterization of the dug are: ionization constant, solubility, X-ray powder diffraction pattern, crystal structure, melting point, and differential scanning calorimetry. The chapter contains the spectra of the drug: ultraviolet spectrum, vibrational spectrum, nuclear magnetic resonance spectra, and the mass spectrum. The compendial methods of analysis of ganciclovir include the United States Pharmacopeia methods. Other methods of analysis that were reported in the literature include: high-performance liquid chromatography alone or with mass spectrometry, electrophoresis, spectrophotometry, voltammetry, chemiluminescence, and radioimmunoassay. Biological investigation on the drug includes: pharmacokinetics, metabolism, bioavailability, and biological analysis. Reviews on the methods used for preparation or for analysis of the drug are provided. The stability of the drug in various media and storage conditions is reported. More than 240 references are listed at the end of the chapter.

Feasibility and applicability of antimicrobial stewardship in immunocompromised patients

PURPOSE OF REVIEW

Antimicrobial stewardship is the primary intervention in the battle against antimicrobial resistance, but clinicians do not always apply many key antimicrobial stewardship principles to patients with significant immune defects due to lack of data and fear of bad outcomes. We review evidence regarding the application of stewardship principles to immunocompromised patients, with a focus on solid organ and hematopoietic stem cell transplant recipients.

RECENT FINDINGS

Antimicrobial stewardship programs (ASPs), targeting immunocompromised patient populations such as oncology and transplant, are gaining traction. Emerging literature suggests that several stewardship interventions can be adapted to immunocompromised hosts and improve antimicrobial utilization, but data supporting improved outcomes is very limited.

SUMMARY

The application of antimicrobial stewardship principles to immunocompromised patients is feasible, necessary, and urgent. As antimicrobial stewardship programs gain momentum across a diverse range of healthcare settings more immunocompromised patients will fall under their purview. It is imperative that centers applying antimicrobial stewardship principles share their experience and establish collaborative research efforts to advance our knowledge base in applying antimicrobial stewardship initiatives to immunocompromised host populations, both in terms of programmatic success and patient outcomes.

Successful treatment and FDG-PET/CT monitoring of HHV-6 encephalitis in a non-neutropenic patient: case report and literature review

Human herpesvirus (HHV)-6 reactivation is associated with severe forms of encephalitis among patients undergoing hematopoietic stem cell transplantation. Cases in non-neutropenic patients are uncommon. The efficacy of ganciclovir and other compounds that are used for the treatment of HHV-6 encephalitis remains suboptimal and linked to toxicity. Valganciclovir, the oral prodrug of ganciclovir, could be practical to treat outpatients, but it is not commonly used for severe cases. We report a case of HHV-6 encephalitis in a non-neutropenic patient successfully treated with valganciclovir and undergoing therapeutic drug monitoring in plasma and in the cerebrospinal fluid. Resolution of infectious foci was documented by cerebral MRI and F18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT). A review of the literature on HHV-6 encephalitis is also reported.

Valganciclovir Dosing for Cytomegalovirus Prophylaxis in Pediatric Solid-organ Transplant Recipients: A Prospective Pharmacokinetic Study

BACKGROUND

Valganciclovir is extensively used for prophylaxis and treatment of cytomegalovirus (CMV) infection in solid-organ transplant recipients. However, pharmacokinetic data in children are scarce, and the pediatric dosing regimen is uncertain. This study sought to prospectively evaluate the pharmacokinetic profile, the clinical efficacy and safety of oral valganciclovir in pediatric transplant recipients and compare different dosing regimens.

METHODS

The cohort included solid-organ transplant recipients treated with valganciclovir for CMV prophylaxis in 2014-2015 at a tertiary pediatric medical center. All received a weight-based once-daily oral dose of 17 mg/kg. Ganciclovir concentrations were measured and the area under the curve (AUC0-24) was calculated.

RESULTS

Thirteen children of median age 7.3 years (interquartile range, 2.2-11.6) were included. Median ganciclovir AUC0-24 was 21.0 mcg·h/mL (interquartile range, 17.1-39.8); 10 patients (77%) attained AUC0-24 <40 mcg·h/mL. Exposure to ganciclovir was about 2-fold lower in young children (<9 years old; P = 0.01) and children with low body surface area (BSA; <0.7 m; P = 0.006) than in their counterparts. Significantly lower doses were recommended with our weight-based protocol than with the manufacturer-recommended BSA- and glomerular filtration rate-based protocol (P = 0.002), reaching a 3-fold difference in infants. No evidence of CMV viremia or disease was observed while prophylaxis was given.

CONCLUSIONS

The weight-based regimen of 17 mg/kg/dose oral valganciclovir results in relatively low ganciclovir exposure, especially in young children with low BSA, yet showed satisfactory clinical efficacy for CMV prophylaxis. The manufacturer's dosing recommendation appears to result in supratherapeutic ganciclovir concentrations. Further studies are needed to establish target AUCs and valganciclovir dosing for CMV prophylaxis in pediatric transplant recipients.

Clinical pharmacokinetics and pharmacodynamics of ganciclovir and valganciclovir in children with cytomegalovirus infection

INTRODUCTION

Among infants and immunocompromised children cytomegalovirus (CMV) is associated with significant morbidity and mortality.

AREAS COVERED

This review describes the clinical pharmacokinetics and pharmacodynamics of ganciclovir and valganciclovir for the treatment and prevention of CMV infection in children.

EXPERT OPINION

A 24-h ganciclovir area under the concentration versus time curve (AUC₀₋₂₄) of 40 - 60 μg h/ml decreased the risk of CMV infection for adults undergoing CMV prophylaxis. For adults undergoing treatment for active CMV disease, a target AUC₀₋₁₂ of 40 - 60 μg h/ml has been suggested. The applicability of these targets to children remains uncertain; however, with the most sophisticated dosing regimens developed to date only 21% of patients are predicted to reach these targets. Moving forward, identification of optimal pediatric ganciclovir and valganciclovir dosing regimens may involve the use of an externally validated pediatric population pharmacokinetic model for empirical dosing, an optimal sampling strategy for collecting a minimal number of blood samples for each patient and Bayesian updating of the dosing regimen based on an individual patient's pharmacokinetic profile.