Serum ganciclovir drug exposure in children receiving standard ganciclovir dosing

Intravenous ganciclovir (GCV) is used for the treatment of cytomegalovirus (CMV) infection in immunocompromised children. Although the therapeutic target for treatment is unclear, studies have shown a serum area under the concentration-time curve (AUC24h) ≥40 mg/L·h correlates with effective CMV prevention. This study aimed to externally validate existing GCV population pharmacokinetic (PopPK) models and develop a model if needed and evaluate the serum AUC24h achieved with standard GCV dosing and propose an optimized dosing strategy for immunocompromised children. Ganciclovir drug monitoring data from two pediatric hospitals were retrospectively collected, and published pediatric PopPK models were externally validated. The population AUC24h with standard GCV dosing (5 mg/kg twice daily) was calculated, and an optimized dosing strategy was determined using Monte Carlo simulations to achieve an AUC24h between 40 and 100 mg/L·h. Overall, 161 samples from 23 children with a median (range) age of 9.0 years (0.4-17.0) and weight of 28.2 kg (5.6-73.3) were analyzed. Transferability of published pediatric PopPK models was limited. Thus, a one-compartment model with first-order absorption and elimination with weight and serum creatinine as covariates was developed. The median (5th-95th percentiles) steady state AUC24h with standard dosing was 38.3 mg/L·h (24.8-329.2) with 13 children having an AUC24h <40 mg/L·h, particularly those aged <4 years (8/13). An optimized simulated GCV dosing regimen, ranging from 2 to 13 mg/kg twice daily for children with normal renal function, achieved 61%-78% probability of target attainment. Standard GCV dosing likely results in inadequate drug exposure in more than half of the children, particularly those aged <4 years. An optimized dosing regimen has been proposed for clinical validation.

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.

Pharmacokinetic and Pharmacodynamic Assessment of Valganciclovir in Infants With Congenital Cytomegalovirus Infection

BACKGROUND

Valganciclovir (VGCV) is administered at a dose of 16 mg/kg 2 times daily for 6 months to treat symptomatic congenital cytomegalovirus (CMV) infections. During the treatment period, approximately 20% of the patients developed grade 3 or higher neutropenia. Currently, information on the pharmacokinetics and pharmacodynamics of ganciclovir, an active metabolite of VGCV, in infants is limited. In the current study, the relationship between ganciclovir concentration and neutropenia was investigated, and a population pharmacokinetic (PPK) model of ganciclovir in infants with symptomatic congenital CMV infection was developed.

METHODS

Japanese infants who were prescribed oral VGCV for symptomatic congenital CMV infections between July 2017 and January 2021 were included. The relationship between the observed trough ganciclovir concentrations and neutrophil counts was examined. PPK analysis was performed to evaluate the covariates affecting the pharmacokinetics of ganciclovir.

RESULTS

Twenty-seven ganciclovir serum samples from 8 patients were analyzed. A moderate negative correlation was observed between the observed trough ganciclovir concentration and neutrophil count. PPK model analysis showed that postmenstrual age (PMA) affected the total body clearance of ganciclovir after correcting for the empirical allometric scaling of body weight. Based on PMA and body weight, a nomogram to achieve the target area under the concentration-time curve from 0 to 24 hours of 40-60 mcg·h·mL-1 of ganciclovir was calculated.

CONCLUSIONS

The relationship between neutrophil count and ganciclovir trough concentration in infants was clarified. The PPK model showed that the dose of VGCV should be reduced in patients with a low PMA to achieve target exposure.

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.

Population Pharmacokinetics of Ganciclovir in Allogeneic Hematopoietic Stem Cell Transplant Patients

Treatment of cytomegalovirus (CMV) infection in allogeneic hematopoietic stem cell transplantation (alloHCT) patients with ganciclovir is complicated by toxicity and resistance. This study aimed to develop an intravenous ganciclovir population pharmacokinetic model for post-alloHCT patients and to determine dosing regimens likely to achieve suggested therapeutic exposure targets. We performed a prospective observational single-center pharmacokinetic study in adult alloHCT patients requiring treatment with intravenous ganciclovir for CMV viremia or disease. Samples were analyzed using a validated ultraperformance liquid chromatography method. Population pharmacokinetic analysis and Monte Carlo simulations (n = 1000) were performed using Pmetrics for R. Twenty patients aged 18 to 69 years were included in the study. A 2-compartment model with linear elimination from the central compartment and between occasion variability best described the data. Incorporating creatinine clearance (CLCR) estimated by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation and presence of continuous renal replacement therapy as covariates for ganciclovir clearance improved the model. Compared to current dosing recommendations, simulations demonstrated loading doses were required to achieve a target AUC24 of 80 to 120 mg.h/L on day 1 of induction therapy. Increased individualization of post-loading induction and maintenance doses based on CLCR is required to achieve the suggested exposures for efficacy (AUC24 >80/>40 mg.h/L for induction/maintenance) while remaining below the exposure thresholds for toxicity (AUC24 <120/<60 mg.h/L for induction/maintenance). Intravenous ganciclovir dosing in alloHCT patients can be guided by CLCR estimated by CKD-EPI. Incorporation of loading doses into induction dosing regimens should be considered for timely achievement of currently suggested exposures.

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.

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 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.

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.

Pilot Study of Model-Based Dosage Individualization of Ganciclovir in Neonates and Young Infants with Congenital Cytomegalovirus Infection

Newborns with congenital cytomegalovirus (CMV) infection are at high risk for developing permanent sequelae. Intravenous ganciclovir therapy is frequently used for the treatment of congenital CMV infection. A target area under the concentration-time curve from 0 to 24 h (AUC_0-24) of 40 to 50 μg · h/ml is recommended. The standard dose has resulted in a large variability in ganciclovir exposure in newborns, indicating the unmet need of dosage individualization for this vulnerable population, but the implementation of this strategy remains challenging in clinical practice. We aim to evaluate the clinical utility of model-based dosage individualization of ganciclovir in newborns using an opportunistic sampling approach. The predictive performance of a published ganciclovir population pharmacokinetic model was evaluated using an independent patient cohort. The individual dose was adjusted based on the target AUC_0-24 to ensure its efficacy. A total of 26 newborns with congenital CMV infection were included in the present study. Only 11 (42.3%) patients achieved the target AUC_0-24 after being given the standard dose. For all the subtherapeutic patients (achieving <80% of the target AUC) (n = 5), a model-based dosage adjustment was performed using the Bayesian estimation method combined with the opportunistic sampling strategy. The adjusted doses were increased by 28.6% to 60.0% in these five patients, and all adapted AUC_0-24 values achieved the target (range, 48.6 to 66.1 μg · h/ml). The clinical utility of model-based dosing individualization of ganciclovir was demonstrated in newborns with congenital CMV infection. The population pharmacokinetic model combined with the opportunistic sampling strategy provides a clinically feasible method to adapt the ganciclovir dose in neonatal clinical practice. (This study has been registered at ClinicalTrials.gov under registration no. NCT03113344.).

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.

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

AIM

Our aims were to quantify ganciclovir pharmacokinetics in paediatric and adult kidney, liver and lung transplant patients taking a range of valganciclovir doses to prevent herpes virus infections, including a 450 mg regimen, and to identify sources of pharmacokinetic variability.

METHOD

Plasma samples were collected at 2, 4, 8 and 12 weeks post-transplant and at 4, 6, 8 and 12 months post-transplant in subjects prescribed longer courses. Ganciclovir was measured by liquid chromatography/ultraviolet detection. Non-linear mixed effects modelling was used to analyze the concentration-time data and evaluate demographic and transplant-related covariates.

RESULTS

A two compartment model with first order absorption best described the data. Given the range of body sizes, clearance and volume of distribution terms were scaled using standard weight-based allometric exponents. Creatinine clearance was included on apparent oral clearance. Final estimates in a standard 70 kg individual for apparent oral clearance, central volume of distribution, intercompartmental clearance and peripheral volume of distribution were 14.5 l h(-1) , 87.5 l, 4.80 l h(-1) and 42.6 l, respectively. The median terminal half-life for kidney, liver and lung transplant recipients was 9.4, 9.5 and 8.2 h, respectively. Median exposure (i.e. AUC(0,∞) in subjects taking valganciclovir 900 mg or 450 mg once daily was 57.4 and 34.3 μg ml(-1)  h, respectively.

CONCLUSION

Allometric scaling allowed simultaneous analysis of data from children and adults. Ganciclovir pharmacokinetics were similar among kidney, liver and lung transplant recipients. Ganciclovir exposure after valganciclovir 450 mg once daily may be suboptimal in some individuals and requires evaluation along with virologic outcomes data.

Valganciclovir dosing using area under the curve calculations in pediatric solid organ transplant recipients

Pediatric valganciclovir dosing recommendations have not been extensively validated for prevention or treatment for CMV infection. As such, we performed a pharmacokinetic study to compare different valganciclovir dosing regimens and the potential benefits of individualized dose adjustments in children following organ transplantation. Ganciclovir AUCs were calculated from four plasma drug levels in pediatric SOT recipients aged six months through three yr receiving valganciclovir suspension by mouth. Of the 28 ganciclovir AUC calculations performed, 11 (39%) were outside the therapeutic target range of 40-60 mcg h/L leading to a valganciclovir dose adjustment. Current manufacturer-recommended dosing based on BSA and CrCl was estimated to result in therapeutic AUCs in fewer patients than the simple weight-based formula used in our institution (4 vs. 13; p = 0.017). An AUC calculation using only the two- and five-h measurements was strongly correlated with the AUC using all four time measurements (R(2) = 0.846; p < 0.001). A simple weight-based dosing approach gives a higher probability for therapeutic AUCs compared to the manufacturer-recommended dosing in pediatric transplant patients aged six months through three yr with normal renal function. An AUC calculated using two sample times might allow for fewer blood draws in the future.

Pharmacokinetics of ganciclovir and valganciclovir in the adult horse

Equine herpes myeloencephalopathy, resulting from equine herpes virus type 1 (EHV-1) infection, is associated with substantial morbidity and mortality in the horse. As compared to other antiviral drugs, such as acyclovir, ganciclovir has enhanced potency against EHV-1. This study investigated the pharmacokinetics of ganciclovir and its oral prodrug, valganciclovir, in six adult horses in a randomized cross-over design. Ganciclovir sodium was administered intravenously as a slow bolus at a dose of 2.5 mg/kg, and valganciclovir was administered orally at a dose of 1800 mg per horse. Intravenously administered ganciclovir disposition was best described by a three-compartment model with a prolonged terminal half-life of 72 ± 9 h. Following the oral administration of valganciclovir, the mean observed maximum serum ganciclovir concentration was 0.58 ± 0.37 μg/mL, and bioavailability of ganciclovir from oral valganciclovir was 41 ± 20%. Superposition predicted that oral dosing of 1800-mg valganciclovir two times daily would fail to produce and maintain effective plasma concentrations of ganciclovir. However, superposition suggested that i.v. administration of ganciclovir at 2.5 mg/kg every 8 h for 24 h followed by maintenance dosing of 2.5 mg/kg every 12 h would maintain effective ganciclovir serum concentrations in most horses throughout the dosing interval.

Adaptive trials in paediatric development: dealing with heterogeneity and uncertainty in pharmacokinetic differences in children

AIMS

To assess whether an adaptive design in early clinical trials based on the paradigm of variable dosing and controlled exposure can provide better dosing recommendations compared with the standard fixed dose approach.

METHODS

In a clinical trial simulation setting, a paediatric study was simulated using a pharmacokinetic model previously developed for abacavir. Plasma concentrations following the current recommended dose (8 mg kg⁻¹) were taken at standard sampling times, exposures (AUC) were calculated and doses individually adapted to reach the target exposure (i.e. effective exposure in adults). A second round of simulations followed with the adapted doses, and the resulting concentrations were fitted again with the same model. Exposure distributions in both conditions (i.e. fixed dose and controlled exposure) were compared with the target exposure.

RESULTS

The AUC distribution after the current dose resulted in a median exposure of 6.43 mg h l⁻¹ (90th percentile 3.13-10.67 mg h l⁻¹). A total of 61 of 128 subjects showed AUC values either too low or to high compared with the target exposure. After dose adjustment, the median exposure was 6.94 mg h l⁻¹ (5.57-8.25 mg h l⁻¹), and only 14 subjects deviated from the target range.

CONCLUSIONS

Adaptive randomization can be used to optimize dosing regimens in early paediatric clinical trials. The randomization of patients to target exposure rather than dose increases the probability of demonstrating efficacy (i.e. study power) compared with dose-controlled trials. Furthermore, it contributes to further understanding of the role of dose on the total heterogeneity in clinical response.

24 weeks of valganciclovir prophylaxis in children after renal transplantation: a 4-year experience

BACKGROUND

Cytomegalovirus (CMV) is the most common opportunistic infection after solid-organ transplant. Valganciclovir prophylaxis significantly reduces disease, but limited data are available on its use in children. Recently, an increase in delayed-onset CMV disease has been noted with some arguing that longer prophylaxis may decrease late-onset disease.

METHODS

Single-center, retrospective analysis of pediatric renal transplant patients receiving 24 weeks valganciclovir prophylaxis (15 mg/kg/day, maximum 900 mg/day) from January 2004 to December 2008, aiming to measure the incidence of CMV disease and toxicity of valganciclovir.

RESULTS

We enrolled 111 patients, 60% males, 46% African Americans, and median age at transplant 14.5 years (range 1.4-20.4 years). Sixty-nine percent of donors and 44% of recipients were seropositive pretransplant. Median duration of valganciclovir use was 5.9 months (range 0.5-24 months). CMV viremia and disease occurred in 27% and 4.5%, respectively. All patients with disease presented after prophylaxis ended and all were D+/R-. Thymoglobulin use (P = 0.04) and positive donor CMV status (P = 0.02) were associated with a higher risk of CMV viremia. Twenty-four percent had hematologic toxicity directly associated with valganciclovir.

CONCLUSIONS

Valganciclovir use in children was effective as prophylaxis against CMV disease; no children at our institution developed disease while on therapy. Our regimen of 24 weeks of prophylaxis was associated with a lower rate of late-onset disease than previous reports with 12-week regimens. Further controlled studies should be considered to compare longer versus shorter periods of prophylaxis and dose reductions and their impact on prevention of late-onset disease, resistance, cost, and toxicity.

Principles of therapeutic drug monitoring

Therapeutic drug monitoring (TDM) is central to optimize drug efficacy in children, because the pharmacokinetics and pharmacodynamics of most drugs differ greatly between children and adults. Many factors should be analyzed to implement TDM in the pediatric population, including a validated pharmacological parameter and an analytical method adapted to children as limited sampling volumes and high sensitivity are required. The use of population approaches, new analytical methods such as saliva and dried blood spots, and pharmacodynamic monitoring give attractive options to improve TDM, individualize therapy in order to optimize efficacy and reduce adverse drug reactions.

Population pharmacokinetics and Bayesian estimator of mycophenolic acid in children with idiopathic nephrotic syndrome

AIMS

To develop a population pharmacokinetic model for mycophenolic acid (MPA) in children with idiopathic nephrotic syndrome (INS) treated with mycophenolate mofetil (MMF), identify covariates that explain variability and determine the Bayesian estimator of the area under the concentration-time curve over 12 h (AUC(0-12)).

METHODS

The pharmacokinetic model of MMF was described from 23 patients aged 7.4 +/- 3.9 years (range 2.9-14.9) using nonlinear mixed-effects modelling (NONMEM) software. A two-compartment model with lag-time and first-order absorption and elimination was developed. The final model was validated using visual predictive check. Bayesian estimator was validated using circular permutation method.

RESULTS

The population pharmacokinetic parameters were apparent oral clearance 9.7 l h(-1), apparent central volume of distribution 22.3 l, apparent peripheral volume of distribution 250 l, inter-compartment clearance 18.8 l h(-1), absorption rate constant 5.16 h(-1), lag time 0.215 h. The covariate analysis identified body weight and serum albumin as individual factors influencing the apparent oral clearance. Accurate Bayesian estimation of AUC(0-12) was obtained using the combination of three MPA concentrations measured just before (T(0)), 1 and 4 h (T(1) and T(4)) after drug intake with a small error of 0.298 microg h(-1) ml(-1) between estimated and reference AUC(0-12).

CONCLUSIONS

The population pharmacokinetic model of MPA was developed in children with INS. A three-point (T(0), T(1) and T(4)h) Bayesian estimator of AUC(0-12) was developed and might be used to investigate the relation between MPA pharmacokinetic and pharmacodynamics in children with INS and determine if there is any indication to monitor MPA exposure in order to improve patient outcome based on individual AUC-controlled MMF dosing.

Valganciclovir: recent progress

In 2001 valganciclovir was approved by the FDA for treatment of HIV associated retinitis and in 2003 for prevention of post transplant CMV. This review provides an update on the status of its use and areas of controversy: How long should prophylaxis be given?; What is the appropriate dose for prophylaxis?; Can it be used in children, and at what dose?; Can it be used to treat CMV disease? The question of optimal dosing will probably not be settled as the sample size for controlled trials would be prohibitive. Other trials clearly show that extended therapy provides added benefit, the drug is safe and an appropriate dose has been identified in children and oral therapy of CMV disease is effective.