A Population Pharmacokinetic Model of Valproic Acid in Pediatric Patients with Epilepsy: A Non-Linear Pharmacokinetic Model Based on Protein-Binding Saturation

Population pharmacokinetics of valproic acid in children with epilepsy: Implications for dose tailoring when switching from oral syrup to sustained-release tablets

Significant pharmacokinetic (PK) differences exist between different forms of valproic acid (VPA), such as syrup and sustained-release (SR) tablets. This study aimed to develop a population pharmacokinetic (PopPK) model for VPA in children with epilepsy and offer dose adjustment recommendation for switching dosage forms as needed. The study collected 1411 VPA steady-state trough concentrations (Ctrough) from 617 children with epilepsy. Using NONMEM software, a PopPK model was developed, employing a stepwise approach to identify possible variables such as demographic information and concomitant medications. The final model underwent internal and external evaluation via graphical and statistical methods. Moreover, Monte Carlo simulations were used to generate a dose tailoring strategy for typical patients weighting 20-50 kg. As a result, the PK characteristics of VPA were described using a one-compartment model with first-order absorption. The absorption rate constant (ka) was set at 2.64 and 0.46 h-1 for syrup and SR tablets. Body weight and sex were identified as significant factors affecting VPA's pharmacokinetics. The final PopPK model demonstrated acceptable prediction performance and stability during internal and external evaluation. For children taking syrup, a daily dose of 25 mg/kg resulted in the highest probability of achieving the desired target Ctrough, while a dose of 20 mg/kg/day was appropriate for those taking SR tablets. In conclusion, we established a PopPK model for VPA in children with epilepsy to tailor VPA dosage when switching between syrup and SR tablets, aiming to improve plasma VPA concentrations fluctuations.

Predictors of valproic acid steady-state serum levels in adult and pediatric psychiatric inpatients: a comparative analysis

RATIONALE

Valproic acid (VPA) is commonly used as a second-line mood stabilizer or augmentative agent in severe mental illnesses. However, population pharmacokinetic studies specific to psychiatric populations are limited, and clinical predictors for the precision application of VPA remain undefined.

OBJECTIVES

To identify steady-state serum VPA level predictors in pediatric/adolescent and adult psychiatric inpatients.

METHODS

We analyzed data from 634 patients and 1,068 steady-state therapeutic drug monitoring (TDM) data points recorded from 2015 to 2021. Steady-state VPA levels were obtained after tapering during each hospitalization episode. Electronic patient records were screened for routine clinical parameters and co-medication. Generalized additive mixed models were employed to identify independent predictors.

RESULTS

Most TDM episodes involved patients with psychotic disorders, including schizophrenia (29.2%) and schizoaffective disorder (17.3%). Polypharmacy was common, with the most frequent combinations being VPA + quetiapine and VPA + promethazine. Age was significantly associated with VPA levels, with pediatric/adolescent patients (< 18 years) demonstrating higher dose-adjusted serum levels of VPA (β = 7.6±2.34, p < 0.001) after accounting for BMI. Women tended to have higher adjusted VPA serum levels than men (β = 5.08±1.62, p < 0.001). The formulation of VPA (Immediate-release vs. extended-release) showed no association with VPA levels. Co-administration of diazepam exhibited a dose-dependent decrease in VPA levels (F = 15.7, p < 0.001), suggesting a potential pharmacokinetic interaction.

CONCLUSIONS

This study highlights the utility of population-specific pharmacokinetic data for VPA in psychiatric populations. Age, gender, and co-administration of diazepam were identified as predictors of VPA levels. Further research is warranted to establish additional predictors and optimize the precision application of VPA in psychiatric patients.

Nanomedicine revolutionizes epilepsy treatment: overcoming therapeutic hurdles with nanoscale solutions

INTRODUCTION

Epilepsy, a prevalent neurodegenerative disorder, profoundly impacts the physical and mental well-being of millions globally. Historically, antiseizure drugs (ASDs) have been the primary treatment modality. However, despite the introduction of novel ASDs in recent decades, a significant proportion of patients still experiences uncontrolled seizures.

AREAS COVERED

The rapid advancement of nanomedicine in recent years has enabled precise targeting of the brain, thereby enhancing therapeutic efficacy for brain diseases, including epilepsy.

EXPERT OPINION

Nanomedicine holds immense promise in epilepsy treatment, including but not limited to enhancing drug solubility and stability, improving drug across blood-brain barrier, overcoming resistance, and reducing side effects, potentially revolutionizing clinical management. This paper provides a comprehensive overview of current epilepsy treatment modalities and highlights recent advancements in nanomedicine-based drug delivery systems for epilepsy control. We discuss the diverse strategies used in developing novel nanotherapies, their mechanisms of action, and the potential advantages they offer compared to traditional treatment methods.

Pharmacokinetic profiles and egg residue patterns of levamisole in laying hens at two dosing rates and two routes of administration

The levamisole maximum residue limit for edible fat, kidney, and muscle of chickens is 0.01 mg/kg. However, no maximum residue limit has been established for eggs. In the present study, the pharmacokinetic profile and levamisole residue in the eggs from laying hens were investigated using ultra-performance liquid chromatography-tandem mass spectrometry. A single dose of levamisole (30 mg/kg) was administered via the intramuscular or oral route, and an additional egg residue study was performed with 300 or 600 mg/kg commercial LEV drug (30 or 60 mg/kg as levamisole) orally. The limit of quantification was 0.0056 μg/mL and 0.0015 mg/kg for plasma and eggs, respectively. The plasma concentration was below the limit of quantification 10 and 12 h after intramuscular and oral administration, respectively. The half-life of the absorption phase was comparable between the intramuscular and oral routes, which was approximately 1 h, and the mean maximum concentration value was significantly higher in intramuscular (2.29 ± 0.30 μg/mL) than in oral (1.45 ± 0.38 μg/mL) route. The relative oral bioavailability after intramuscular administration was 92.3%. In the egg residue study, dose-dependent area under concentration and maximum concentration were observed after single oral administration of 30 and 60 mg/kg egg residue, and the calculated withdrawal period for both 30 and 60 mg/kg groups based on the positive list system standard (0.01 mg/kg) was 7 d after the treatment.

Modeling the protein binding non-linearity in population pharmacokinetic model of valproic acid in children with epilepsy: a systematic evaluation study

Background: Several studies have investigated the population pharmacokinetics (popPK) of valproic acid (VPA) in children with epilepsy. However, the predictive performance of these models in the extrapolation to other clinical environments has not been studied. Hence, this study evaluated the predictive abilities of pediatric popPK models of VPA and identified the potential effects of protein binding modeling strategies. Methods: A dataset of 255 trough concentrations in 202 children with epilepsy was analyzed to assess the predictive performance of qualified models, following literature review. The evaluation of external predictive ability was conducted by prediction- and simulation-based diagnostics as well as Bayesian forecasting. Furthermore, five popPK models with different protein binding modeling strategies were developed to investigate the discrepancy among the one-binding site model, Langmuir equation, dose-dependent maximum effect model, linear non-saturable binding equation and the simple exponent model on model predictive ability. Results: Ten popPK models were identified in the literature. Co-medication, body weight, daily dose, and age were the four most commonly involved covariates influencing VPA clearance. The model proposed by Serrano et al. showed the best performance with a median prediction error (MDPE) of 1.40%, median absolute prediction error (MAPE) of 17.38%, and percentages of PE within 20% (F20, 55.69%) and 30% (F30, 76.47%). However, all models performed inadequately in terms of the simulation-based normalized prediction distribution error, indicating unsatisfactory normality. Bayesian forecasting enhanced predictive performance, as prior observations were available. More prior observations are needed for model predictability to reach a stable state. The linear non-saturable binding equation had a higher predictive value than other protein binding models. Conclusion: The predictive abilities of most popPK models of VPA in children with epilepsy were unsatisfactory. The linear non-saturable binding equation is more suitable for modeling non-linearity. Moreover, Bayesian forecasting with prior observations improved model fitness.

Joint use of population pharmacokinetics and machine learning for optimizing antiepileptic treatment in pediatric population

Purpose

Unpredictable drug efficacy and safety of combined antiepileptic therapy is a major challenge during pharmacotherapy decisions in everyday clinical practice. The aim of this study was to describe the pharmacokinetics of valproic acid (VA), lamotrigine (LTG), and levetiracetam (LEV) in a pediatric population using nonlinear mixed-effect modeling, while machine learning (ML) algorithms were applied to identify any relationships among the plasma levels of the three medications and patients' characteristics, as well as to develop a predictive model for epileptic seizures.

Methods

The study included 71 pediatric patients of both genders, aged 2-18 years, on combined antiepileptic therapy. Population pharmacokinetic (PopPK) models were developed separately for VA, LTG, and LEV. Based on the estimated pharmacokinetic parameters and the patients' characteristics, three ML approaches were applied (principal component analysis, factor analysis of mixed data, and random forest). PopPK models and ML models were developed, allowing for greater insight into the treatment of children on antiepileptic treatment.

Results

Results from the PopPK model showed that the kinetics of LEV, LTG, and VA were best described by a one compartment model with first-order absorption and elimination kinetics. Reliance on random forest model is a compelling vision that shows high prediction ability for all cases. The main factor that can affect antiepileptic activity is antiepileptic drug levels, followed by body weight, while gender is irrelevant. According to our study, children's age is positively associated with LTG levels, negatively with LEV and without the influence of VA.

Conclusion

The application of PopPK and ML models may be useful to improve epilepsy management in vulnerable pediatric population during the period of growth and development.

Handling Delayed or Missed Dose of Antiseizure Medications: A Model-Informed Individual Remedial Dosing

BACKGROUND AND OBJECTIVES

Delayed or missed antiseizure medications (ASMs) doses are common during long-term or lifelong antiepilepsy treatment. This study aims to explore optimal individualized remedial dosing regimens for delayed or missed doses of 11 commonly used ASMs.

METHODS

To explore remedial dosing regimens, Monte Carlo simulation was used based on previously identified and published population pharmacokinetic models. Six remedial strategies for delayed or missed doses were investigated. The deviation time outside the individual therapeutic range was used to evaluate each remedial regimen. The influences of patients' demographics, concomitant medication, and scheduled dosing intervals on remedial regimens were assessed. RxODE and Shiny in R were used to perform Monte Carlo simulation and recommend individual remedial regimens.

RESULTS

The recommended remedial regimens were highly correlated with delayed time, scheduled dosing interval, and half-life of the ASM. Moreover, the optimal remedial regimens for pediatric and adult patients were different. The renal function, along with concomitant medication that affects the clearance of the ASM, may also influence the remedial regimens. A web-based dashboard was developed to provide individualized remedial regimens for the delayed or missed dose, and a user-defined module with all parameters that could be defined flexibly by the user was also built.

DISCUSSION

Monte Carlo simulation based on population pharmacokinetic models may provide a rational approach to propose remedial regimens for delayed or missed doses of ASMs in pediatric and adult patients with epilepsy.

Population pharmacokinetics of ruxolitinib in children with hemophagocytic lymphohistiocytosis: focus on the drug-drug interactions

PURPOSE

The optimal dose regimen of ruxolitinib (RUX) in children with hemophagocytic lymphohistiocytosis (HLH) remains to be determined. The aim was to develop and verify a population pharmacokinetic (PPK) model, and then provide references for the optimization of dose regimen of RUX in children with HLH.

METHODS

A total of 189 RUX concentrations from 32 children were included. The PPK model was established using the nonlinear mixed-effects model approach. Predictive performance and stability of the final PPK model were evaluated. The exposure of RUX in different clinical scenarios was simulated through Monte Carlo simulations.

RESULTS

A one-compartment model with first-order absorption and linear elimination was identified to describe the disposition of RUX. The absorption rate constant (K_a) in the final PPK model was 1.05 h^-1, and the apparent clearance (CL/F) and volume of distribution (V/F) were 9.80 L/h and 30.6 L, respectively. Coadministration with triazoles (TZS) and azithromycin (AZM) resulted in approximately 31.0% and 32.4% reductions in the CL/F of RUX, respectively. Multiple evaluation procedures showed satisfactory predictive performance and stability of the final model. Monte Carlo simulations showed that the exposure of RUX was significantly affected by the coadministration with TZS and/or AZM under different clinical scenarios.

CONCLUSION

For the first time, a PPK model of RUX in children with HLH was developed and evaluated. The coadministration with TZS and/or AZM were found to reduce the clearance of RUX in children. These findings could provide new insights for the precise treatment of RUX in children with HLH.

Developmental Population Pharmacokinetics-Pharmacodynamics of Meropenem in Chinese Neonates and Young Infants: Dosing Recommendations for Late-Onset Sepsis

The pharmacokinetic (PK) studies of meropenem in Chinese newborns with late-onset sepsis (LOS) are still lacking. Causative pathogens of LOS and their susceptibility patterns in China differ from the data abroad. We, therefore, conducted a developmental population pharmacokinetic−pharmacodynamic analysis in Chinese newborns with the goal to optimize meropenem dosing regimens for LOS therapy. An opportunistic sampling strategy was used to collect meropenem samples, followed by model building and validation. A Monte Carlo simulation was performed to show the probability of target attainment (PTA) for various dosages. The information from 78 newborns (postmenstrual age: 27.4−46.1 weeks) was compiled and had a good fit to a 1-compartment model that had first order elimination. The median (range) values of estimated weight−normalized volume of distribution (V)and clearance (CL) were 0.60 (0.51−0.69) L/kg and 0.16 (0.04−0.51) L/h/kg, respectively. Covariate analysis revealed that postnatal age (PNA), gestational age (GA) and current weight (CW) were the most important factors in describing meropenem PK. Simulation results showed for LOS with a minimal inhibitory concentration (MIC) of 8 mg/L, the doses of 30 mg/kg 3 times daily (TID) as a 1-h infusion for newborns with GA ≤ 37 weeks and 40 mg/kg TID as a 3-h infusion for those with GA > 37 weeks were optimal, with PTA of 71.71% and 75.08%, respectively. In conclusion, we proposed an evidence-based dosing regimen of meropenem for LOS in Chinese newborns by using the population pharmacokinetic−pharmacodynamic analysis, based on domestic common pathogens and their susceptibility patterns.

Understanding inter-individual variability in pharmacokinetics/pharmacodynamics of aripiprazole in children with tic disorders: Individualized administration based on physiological development and CYP2D6 genotypes

Objective: This study aims to develop a combined population pharmacokinetic (PPK) model for aripiprazole (ARI) and its main active metabolite dehydroaripiprazole (DARI) in pediatric patients with tic disorders (TD), to investigate the inter-individual variability caused by physiological and genetic factors in pharmacokinetics of ARI and optimize the dosing regimens for pediatric patients. Methods: A prospective PPK research was performed in Chinese children with TD. Totally 84 patients aged 4.83-17.33 years were obtained for the pharmacokinetic analysis. 27 CYP2D6 and ABCB1 gene alleles were detected. Moreover, the clinical efficacy was evaluated according to reduction rate of Yale Global Tic Severity Scale (YGTSS) score at the 12th week comparing with the baseline. Monte Carlo simulations were used to evaluate and optimize dosing regimens. Results: The PPK model was established to predict the concentrations of ARI and DARI. Body weight and CYP2D6 genotype were the significant covariates affecting the clearance of ARI. The DARI/ARI metabolic ratios (MRs) of AUC24h, Cmin and Cmax at the steady state of results were ultra-rapid metabolizers (UMs) > normal metabolizers (NMs) > intermediated metabolizers (IMs). MRs could be used to distinguish UMs or IMs from other patients. The best predictor of clinical efficacy for TD was the trough concentration of ARI and the cut-off point was 101.636 ng/ml. Conclusion: The pharmacokinetics of ARI and DARI in pediatric TD were significantly influenced by body weight and CYP2D6 genotype. Individualized dosing regimens were recommended for pediatric patients with TD to ensure clinical efficacy.

Pharmacogenetics-based population pharmacokinetic analysis and dose optimization of valproic acid in Chinese southern children with epilepsy: Effect of ABCB1 gene polymorphism

Objective: The aim of this study was to establish a population pharmacokinetic (PPK) model of valproic acid (VPA) in pediatric patients with epilepsy in southern China, and provide guidance for individualized medication of VPA therapy. Methods: A total of 376 VPA steady-state trough concentrations were collected from 103 epileptic pediatric patients. The PPK parameter values for VPA were calculated by using the nonlinear mixed-effects modeling (NONMEM) method, and a one-compartment model with first-order absorption and elimination processes was applied. Covariates included demographic information, concomitant medications and selected gene polymorphisms. Goodness-of-fit (GOF), bootstrap analysis, and visual predictive check (VPC) were used for model evaluation. In addition, we used Monte Carlo simulations to propose dose recommendations for different subgroup patients. Results: A significant effect of the patient age and ABCB1 genotypes was observed on the VPA oral clearance (CL/F) in the final PPK model. Compared with patients with the ABCB1 rs3789243 AA genotype, CL/F in patients with GG and AG genotypes was increased by 8% and reduced by 4.7%, respectively. The GOF plots indicated the satisfactory predictive performance of the final model, and the evaluation by bootstrap and VPC showed that a stable model had been developed. A table of individualized dosing regimens involving age and ABCB1 genotype was constructed based on the final PPK model. Conclusion: This study quantitatively investigated the effects of patient age and ABCB1 rs3789243 variants on the pharmacokinetic variability of VPA. The PPK models could be beneficial to individual dose optimization in epileptic children on VPA therapy.

Clinical Pharmacokinetic Monitoring of Free Valproic Acid Levels: A Systematic Review

BACKGROUND

Current guidelines recommend therapeutic drug monitoring as a critical component of valproic acid (VPA) therapy. Due to high protein binding, the active unbound (free) portion of VPA can be misrepresented by total VPA serum levels in certain clinical scenarios. Monitoring free VPA serum levels may be warranted when assessing the clinical response to VPA therapy.

OBJECTIVES

The aims were to conduct a systematic review to identify a therapeutic range for free VPA serum levels; to explore the correlation of free VPA serum levels with clinical toxicity and therapeutic benefit; and to examine predictors of discordance between free and total VPA levels.

METHODS

Medline, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), PsycINFO, BIOSIS Previews, and Cumulative Index to Nursing and Allied Health Literature (CINAHL) were searched from the time of database inception to June 20, 2021. Randomized controlled trials and observational studies that evaluated any patient receiving VPA with free VPA level monitoring were included.

RESULTS

Of 189 citations, we identified 27 relevant studies, which included 14 observational studies, two case series, and 11 case reports. Three studies provided a therapeutic range for free VPA levels between 20 and 410 μmol/L. Two studies suggested the occurrence of hyperammonemia and thrombocytopenia at free VPA serum levels above 60 µmol/L and 103.3 µmol/L, respectively. Two studies suggested an upper limit for neurotoxicity at free VPA serum levels of 70 µmol/L and 207.9 µmol/L. Hypoalbuminemia was identified as a predictor of therapeutic discordance.

CONCLUSIONS

This review demonstrates a paucity of data informing the clinical utility of free VPA serum levels. Further high-quality trials are needed to validate an optimal therapeutic range for free VPA levels.

Population Pharmacokinetic Analysis and Dosing Optimization of Sirolimus in Children With Tuberous Sclerosis Complex

Sirolimus is confirmed to be effective in the treatment of tuberous sclerosis complex (TSC) and related disorders. The study aims to establish a population pharmacokinetic model of oral sirolimus for children with TSC and provide an evidence-based approach for individualization of sirolimus dosing in the pediatric population. A total of 64 children were recruited in this multicenter, retrospective pharmacokinetic study. Whole-blood concentrations of sirolimus, demographic, and clinical information were collected and analyzed using a nonlinear mixed-effects population modeling method. The final model was internally and externally validated. Then Monte Carlo simulations were performed to evaluate and optimize the dosing regimens. In addition, the efficacy and safety of sirolimus therapy was assessed retrospectively in patients with epilepsy or cardiac rhabdomyomas associated with TSC. Finally, the sirolimus pharmacokinetic profile was described by a 1-compartment model with first-order absorption and elimination along with body weight and total daily dose as significant covariates. The typical population parameter estimates of apparent volume of distribution and apparent clearance were 69.48 L and 2.79 L/h, respectively. Simulations demonstrated that dosage regimens stratified by body surface area may be more appropriate for children with TSC. These findings could be used to inform individualized dosing strategies of sirolimus for pediatric patients with TSC.

Published population pharmacokinetic models of valproic acid in adult patients: a systematic review and external validation in a Chinese sample of inpatients with bipolar disorder

BACKGROUND

This study reviewed all published valproic acid (VPA) population pharmacokinetic (PPK) models in adult patients and assessed them using external validation methods to determine predictive performance.

METHODS

Thirteen published PPK models (labeled with letters A to M) not restricted to children were identified in PubMed, Embase, and Web of Science databases. They were evaluated in a sample totaling 411 serum concentrations from 146 adult inpatients diagnosed with bipolar disorder in a Chinese hospital. Serum concentrations of VPA were analyzed by validated ultra-performance liquid chromatography-tandem mass spectrometry. Performance was assessed by 4 tests (prediction-based diagnostics, visual predictive checks, normalized prediction distribution error, and Bayesian forecasting).

RESULTS

Models K and L, developed in large samples of Chinese and Thai patients, showed good performance in our Chinese dataset. Models H and J demonstrated good performance in Tests 2 and 3 of the 4 tests, respectively. Another 7 models exhibited intermediate performance. The models with the worst performance, F and M, could not be improved by Bayesian forecasting.

CONCLUSION

In our validation study the most important factors contributing to good performance were absence of children, Asian ethnicity, one-compartment models and inclusion of body weight and VPA dose in previously published models.

Population Pharmacokinetics of Valproic Acid in Pediatric and Adult Caucasian Patients

(1) Background: The aim of this study was to explore the valproic acid (VPA) pharmacokinetic characteristics in a large population of pediatric and adult Caucasian patients and to establish a robust population pharmacokinetic (PopPK) model. (2) Methods: A total of 2527 serum VPA samples collected from 1204 patients included in a therapeutic drug monitoring program were retrospectively analyzed. Patients were randomly assigned to either a model development group or an external evaluation group. PopPK analysis was performed on 1751 samples from 776 patients with NONMEM using a nonlinear mixed-effect modelling approach. The influence of demographic, anthropometric, treatment and comedication variables on the apparent clearance (CL/F) of VPA was studied. The bootstrap method was used to evaluate the final model internally. External evaluation was carried out using 776 VPA serum samples from 368 patients. (3) Results: A one-compartment model with first-order absorption and elimination successfully described the data. The final model included total body weight, age and comedication with phenytoin, phenobarbital and carbamazepine with a significant impact on VPA elimination. Internal and external evaluations demonstrated the good predictability of the model. (4) Conclusions: A PopPK model of VPA in Caucasian patients was successfully established, which will be helpful for model-informed precision dosing approaches in clinical patient care.

Population Pharmacokinetic Analysis of Dexmedetomidine in Children using Real World Data from Electronic Health Records and Remnant Specimens

AIM

Our objectives were to perform a population pharmacokinetic analysis of dexmedetomidine in children using remnant specimens and electronic health records (EHRs) and explore the impact of patient's characteristics and pharmacogenetics on dexmedetomidine clearance.

METHODS

Dexmedetomidine dosing and patient data were gathered from EHRs and combined with opportunistically sampled remnant specimens. Population pharmacokinetic models were developed using nonlinear mixed-effects modeling. Stage one developed a model without genotype variables; Stage two added pharmacogenetic effects.

RESULTS

Our final study population included 354 post-cardiac surgery patients age 0 to 22 years (median 16 months). The data were best described with a two-compartment model with allometric scaling for weight and Hill maturation function for age. Population parameter estimates and 95% confidence intervals were 27.3 L/hr (24.0 - 31.1 L/hr) for total clearance (CL), 161 L (139 - 187 L) for central compartment volume of distribution (V₁ ), 26.0 L/hr (22.5 - 30.0 L/hr) for intercompartmental clearance (Q), and 7903 L (5617 - 11119 L) for peripheral compartment volume of distribution (V₂ ). The estimate for postmenstrual age when 50% of adult clearance is achieved was 42.0 weeks (41.5 - 42.5 weeks) and the Hill coefficient estimate was 7.04 (6.99 - 7.08). Genotype was not statistically or clinically significant.

CONCLUSION

Our study demonstrates the use of real-world EHR data and remnant specimens to perform a population PK analysis and investigate covariate effects in a large pediatric population. Weight and age were important predictors of clearance. We did not find evidence for pharmacogenetic effects of UGT1A4 or UGT2B10 genotype or CYP2A6 risk score.

Effect of CYP2C19 polymorphisms on serum valproic level acid in Chinese Han patients with schizophrenia

Valproic acid is an anticonvulsant, which is also widely used for treating psychiatric disorders. Some clinical trials have demonstrated benefits of valproic acid augmentation therapy in schizophrenia. Interindividual variability in valproic acid dose and serum concentration may reflect functional consequences of genetic polymorphisms in genes encoding drug-metabolizing enzymes. The aim of this study was to determine the relationship between serum concentrations of valproic acid and single nucleotide polymorphisms of the cytochrome P450 (CYP) 2C19 gene in patients with schizophrenia. All patients had been receiving fixed dose of valproic acid for at least 2 weeks. The daily doses were 0.5–1.5 g. No other drugs except olanzapine were coadministered. Serum concentrations of valproic acid were measured using the ultra-high performance liquid chromatography method with mass-spectrometric detection. The CYP2C19 (CYP2C19*2 G681A rs4244285 and CYP2C19*3 G636A rs4986893) genotypes were identified by real-time PCR analyses. The mean concentration/dose ratios of valproic acid were significantly higher in patients with CYP2C19 *1/*2 genotype (P < 0.01) or CYP2C19 *2/*3 genotype (P < 0.01) than in those with CYP2C12 *1/*1 genotype. The mean concentration/dose ratios of valproic acid were significantly higher in patients with 1 (P < 0.01) or 2 (P < 0.01) mutated alleles for CYP2C19 than in those without mutated alleles. And the post hoc analysis revealed that the result has acceptable statistical (power (1 – β) = 0.8486 at type I  level of 0.05) to support the observed significant associations for CYP2C19 SNPs and serum C/D ratios of valproic acid. The findings of this study suggest that the genetic polymorphisms of CYP2C19 significantly affect the steady-state serum concentrations of valproic acid in Chinese Han population. The determination of the CYP2C19 genotypes may be useful for dosing adjustment in schizophrenia patients on valproic acid therapy.

Valproic acid autoinduction: a case-based review

Although valproic acid (VPA) induces the metabolism of multiple other drugs, the clinical reports of VPA autoinduction are rare. A comprehensive literature search yielded only one published case series, which provided the rationale to conduct a review of the published cases along with a new case of VPA autoinduction. Although there may be myriad of reasons for lack of published cases of VPA autoinduction, potential underreporting may be one of the core reasons. Lack of understanding into the highly complex metabolism of VPA may also make it difficult to recognize and report VPA autoinduction. However, it is important to mention that in addition to autoinduction increased elimination of VPA may be mediated by several pharmacokinetic (PK) factors, such as drug interactions, genetic polymorphisms of metabolic enzymes, and protein displacement reactions. As VPA is metabolized by multiple metabolic pathways, the risk for drug interactions is relatively high. There is also a growing evidence for high genetic inducibility of some enzymes involved in VPA metabolism. Protein displacement reactions with VPA increase the biologically active and readily metabolizable free fraction and pose a diagnostic challenge as they are usually not requested by most clinicians. Thus, monitoring of free fraction with total VPA levels may prevent clinically serious outcomes and optimize VPA treatment in clinically challenging patients. This case-based review compares the clinical data from three published cases and a new case of VPA autoinduction to enhance clinicians' awareness of this relatively rare but clinically relevant phenomenon along with a discussion of potential underlying mechanisms.

Clinical utiliy of a model-based piperacillin dose in neonates with early-onset sepsis

AIMS

Early-onset sepsis (EOS) is a common disease in neonates with a high morbidity and mortality rate. Piperacillin/tazobactam has been used extensively and empirically for EOS treatment without clinically validated dosing regimens, although the population pharmacokinetics (PPK) of piperacillin in neonates has been reported. Therefore, we wanted to study the effectiveness and tolerance of a PPK model-based dosing regimen of piperacillin/tazobactam in EOS patients.

METHODS

A prospective, single-centre, phase II clinical study of piperacillin/tazobactam in neonates with EOS was conducted. The dosing regimen (90 mg·kg^-1 , q8h) was determined based on a previous piperacillin PPK model in young infants using NONMEM v7.4. The pharmacodynamics (PD) target (70%fT > MIC, free drug concentration above MIC during 70% of the dosing interval) attainment was calculated using NONMEM combined with an opportunistic sampling design. The clinical treatment data were collected.

RESULTS

A total of 52 neonates were screened and 49 neonates completed their piperacillin/tazobactam treatment course and were included in this analysis. The median (range) values of postmenstrual age were 33.57 (range 26.14-41.29) weeks. Forty-seven (96%) neonates reached their PD target. Eight (16%) neonates experienced treatment failure clinically. The mean (SD, range) duration of treatment and length of hospitalization were 100.1 (62.2, 36.2-305.8) hours and 31 (30, 5-123) days. There were no obvious adverse events and no infection-related deaths occurred in the first month of life.

CONCLUSIONS

A model-based dosing regimen of piperacillin/tazobactam was evaluated clinically, was tolerated well and was determined to be effective for EOS treatment.

Population pharmacokinetics-pharmacodynamics of ceftazidime in neonates and young infants: Dosing optimization for neonatal sepsis

Ceftazidime is a third-generation cephalosporin with high activity against many pathogens. But the ambiguity and diversity of the dosing regimens in neonates and young infants impair access to effective treatment. Thus, we conducted a population pharmacokinetic study of ceftazidime in this vulnerable population and recommended a model-based dosage regimen to optimize sepsis therapy. Totally 146 neonates and young infants (gestational age (GA): 36-43.4 weeks, postnatal age (PNA): 1-81 days, current weight (CW): 900-4500 g) were enrolled based on inclusion and exclusion criteria. Ceftazidime bloods samples (203) were obtained using the opportunistic sampling strategy and determined by the high-performance liquid chromatography. The population pharmacokinetic-pharmacodynamic analysis was conducted by nonlinear mixed effects model (NONMEM). A one-compartment model with first-order elimination best described the pharmacokinetic data. Covariate analysis showed the significance of GA, PNA, and CW on developmental pharmacokinetics. Monte Carlo simulation was performed based on above covariates and minimum inhibitory concentration (MIC). In the newborns with PNA ≤ 3 days (MIC=8 mg/L), the dose regimen was 25 mg/kg twice daily (BID). For the newborns with PNA > 3 days (MIC=16 mg/L), the optimal dose was 30 mg/kg three times daily (TID) for those with GA ≤ 37 weeks and 40 mg/kg TID for those with GA > 37 weeks. Overall, on the basis of the developmental population pharmacokinetic-pharmacodynamic analysis covering the whole range of neonates and young infants, the evidence-based ceftazidime dosage regimens were proposed to optimize neonatal early-onset and late-onset sepsis therapy.

Estrogen profile- and pharmacogenetics-based lamotrigine dosing regimen optimization: Recommendations for pregnant women with epilepsy

During pregnancy, various physiological changes occur that can alter the pharmacokinetics of antiepileptic drugs, such as lamotrigine (LTG). Anticipating the change in LTG dose required to achieve a pre-pregnancy target concentration is challenging. This study aimed to develop a refined population pharmacokinetic (PopPK) model of LTG in pregnant women with epilepsy (WWE) to identify factors explaining the variability in pharmacokinetics and to establish a model-informed individualized dosing regimen. On that basis, a coarsened model containing only clinical variables was also developed to examine its predictive performance compared to the refined model. In total, 322 concentration-time points from 51 pregnant WWE treated with LTG were employed to establish a refined PopPK model that included endogenous estrogen profiles, variants of candidate genes encoding LTG-metabolizing enzymes and -transporter proteins, and other clinical variables and a coarsened model that included only clinical variables, respectively. Data from an additional 11 patients were used for external validation of these two models. A nonlinear mixed-effect modeling approach was used for PopPK analysis of LTG. The standard goodness-of-fit method, bootstrap, normalized prediction distribution errors and external evaluation were adopted to estimate the stability and predictive performance of the candidate models. Akaike information criterion (AIC) was used to compare the goodness of fit between these two models. A lower AIC indicates a better fit of the data and the preferred model. Recommended dosing regimens for pregnant WWE were selected using Monte Carlo simulation based on the established optimal model. In the refined PopPK model, the population mean of apparent LTG clearance (CL/F) in pregnant WWE was estimated to be 2.82 L/h, with an inter-individual variability of 23.6%. PopPK analysis indicated that changes in estrogen profile during pregnancy were the predominant reason for the significant variations in LTG-CL/F. Up to the 3rd trimester, the concentration accumulation effect of E2 increased LTG-CL/F by 5.109 L/h from baseline levels. Contrary to effect of E2, E3 as the main circulating estrogen in pregnancy with a peak value of 34.41 ng/mL is 1000-fold higher than that in non-pregnancy reduced LTG-CL/F by 1.413 L/h. In addition, the UGT2B7 rs4356975 C > T and ABCB1 rs1128503 A > G variants may contribute to a better understanding of the inter-individual variability in LTG-CL/F. LTG-CL/F was 1.66-fold higher in UGT2B7 rs4356975 CT or TT genotype carriers than in CC genotype carriers. In contrast, ABCB1 rs1128503 GG genotype carriers had only 71.9% of the LTG-CL/F of AA or AG genotype carriers. In the coarsened PopPK model, the gestational age was a promising predictor of changes in LTG-CL/F. When comparing these two models, the refined PopPK model was favored over the coarsened PopPK model (AIC = -30.899 vs. -20.017). Monte Carlo simulation based on optimal PopPK model revealed that the LTG dosage administered to carriers of the UGT2B7 rs4356975 CT or TT genotype required a 33-50% increase to reach the pre-pregnancy target concentration, and carriers of the ABCB1 rs1128503 GG genotype required a 33-66% lower dose of LTG than carriers of the ABCB1 rs1128503 AA or AG genotype. Changes in estrogen profile during pregnancy was a better predictor of variations in LTG-CL/F than gestational age. The developed model based on estrogen profile and pharmacogenetics can serve as a foundation for further optimization of dosing regimens of LTG in pregnant WWE.

Population Pharmacokinetics of Lithium in Young Pediatric Patients With Intellectual Disability

Background: Lithium is a well-established treatment for bipolar disorders and has been shown to be neuroprotective, and thus low doses might be useful for the treatment of childhood brain injury and neurological sequelae. However, pharmacokinetic (PK) data in children are limited. This study was to investigate the PKs after oral administration of low-dose lithium carbonate in young children with intellectual disability.

Methods: Fifty-two children with intellectual disability aged 4–10 years old were enrolled. A series of blood samples were collected after a single-dose administration of lithium carbonate. The serum lithium concentration was measured using a validated ion chromatography assay, and the PK concentration data were modeled using a nonlinear mixed effect model in the NONMEM program.

Results: The lithium concentration over time was adequately described by a two-compartment disposition, with a transient absorption and first-order elimination process. The inclusion of body weight as an allometric factor significantly improved the model fit, but age and gender were not associated with the PKs of lithium. The clearance, central volume, inter-compartmental clearance, and peripheral volume estimates from the final population PK model were 0.98 L/h, 13.1 L, 0.84 L/h, and 8.2 L for children with a body weight of 20 kg. The model evaluation suggested that there is no obvious discrepancy between the observations and predictions in the proposed model. A visual predictive check demonstrated the good predictive performance of the final model.

Conclusions: The lithium PK properties in young children were similar to those in older children and adults. The proposed model can be used for further PK/PD analysis to optimize the dosage regimen of lithium in children.

Determination of vancomycin exposure target and individualised dosing recommendations for neonates: model-informed precision dosing

INTRODUCTION

Few studies incorporating population pharmacokinetic/pharmacodynamic (Pop-PK/PD) modelling have been conducted to quantify the exposure target of vancomycin in neonates. A retrospective observational cohort study was undertaken in neonates to determine this target and dosing recommendations (chictr.org.cn, ChiCTR1900027919).

METHODS

A Pop-PK model was developed to estimate PK parameters. Causalities between acute kidney injury (AKI) occurrence and vancomycin use were verified using Naranjo criteria. Thresholds of vancomycin exposure in predicting AKI or efficacy were identified via classification and regression tree analysis. Associations between exposure thresholds and clinical outcomes, including AKI and efficacy, were analysed by logistic regression. Dosing recommendations were designed using Monte Carlo simulations based on the optimised exposure target.

RESULTS

Pop-PK modelling included 182 neonates with 411 observations. On covariate analysis, neonatal physiological maturation, renal function and concomitant use of vasoactive agents (VAS) significantly affected vancomycin PK. Seven cases of vancomycin-induced AKI were detected. Area under the concentration-time curve from 0-24 hours (AUC_0-24) ≥ 485 mg•h/L was an independent risk factor for AKI after adjusting for VAS co-administration. The clinical efficacy of vancomycin was analysed in 42 patients with blood culture-proven staphylococcal sepsis. AUC_0-24 to minimum inhibitory concentration (AUC_0-24/MIC) ≥ 234 was the only significant predictor of clinical effectiveness. Monte Carlo simulations indicated that regimens in Neonatal Formulary 7 and Red Book (2018) were unsuitable for all neonates.

CONCLUSION

An AUC_0-24 of 240-480 (assuming MIC = 1 mg/L) is a recommended exposure target of vancomycin in neonates. Model-informed dosing regimens are valuable in clinical practice.

Population pharmacokinetics of unbound valproic acid in pediatric epilepsy patients in China: a protein binding model

PURPOSE

The purpose of this study was to establish a protein binding model of unbound valproic acid (VPA) based on Chinese pediatric patients with epilepsy and provide a reference for clinical medication.

METHODS

A total of 313 patients were included and both their total and unbound VPA concentrations (375 pairs of concentrations) were measured. NONMEM software was used for population pharmacokinetic modeling. The stepwise method was used to screen the potential covariates. Goodness-of-fit plot, bootstrap, and visual predictive check were used for model evaluation. In addition, dose recommendations for typical patients aged 0 to 16 years were proposed by Monte Carlo simulations.

RESULTS

A one-compartment model of first-order absorption and first-order elimination was used to describe the pharmacokinetic characteristics of unbound VPA, and the linear non-saturable binding equation was introduced to describe the protein binding. Body weight, age-based maturation, and co-medicated with lamotrigine could affect the CL/F of unbound and bound VPA. Model evaluation showed satisfactory robustness of the final model. The dosing regimens for children aged 0 to 16 years were proposed based on the final established model.

CONCLUSION

We developed a population pharmacokinetic model of unbound and bound VPA that took account of protein binding. The VPA dosing regimen in pediatric patients with epilepsy needs to be optimized by the body weight, age, and co-medications.

Population Pharmacokinetics Modeling of Vancomycin Among Chinese Infants With Normal and Augmented Renal Function

There have been good amounts of population pharmacokinetics (PPK) models of vancomycin for Chinese pediatric patients, but none of them had a special focus on modeling infant population with different levels of renal function. Since renal function variability is prominent among infant population and the clearance (CL) of vancomycin is heavily related to renal excretion, it is important to establish precise PPK models based on individual renal function levels. We employed a PPK approach to develop three models of vancomycin in parallel for Chinese pediatric patients with normal renal function [estimated glomerular filtration rate (eGFR) between 30 and 86 ml/min/1.73 m², Model 1], with augmented renal function (eGFR ≥ 86 ml/min/1.73 m², Model 2), or with all levels of renal function (Model 3). Three one-compartment models with first-order elimination kinetics were established. The predictive ability of Model 1 and Model 2 among each certain population is comparable with that of Model 3 with no statistical difference. Our study revealed that among the infant population with augmented renal function, only body weight was included as a covariate, which indicated that for an infant whose eGFR ≥ 86 ml/min/1.73 m², taking blood sample is not compulsory for predicting vancomycin blood concentration, which avoids unnecessary injury to vulnerable infants.

Population Pharmacokinetic Study of Vancomycin in Chinese Pediatric Patients with Hematological Malignancies

STUDY OBJECTIVES

Vancomycin is a primary antibiotic for the treatment of severe infections in children with malignant hematological disease. However, precise dosing of vancomycin is difficult in children because of high interindividual variability and limited data of pharmacokinetic profiles. The present study aims to develop a population pharmacokinetic (PPK) model for vancomycin in Chinese pediatric patients with hematological malignancies.

DESIGN

This was a retrospective pharmacokinetic study.

SETTING

The setting for this study was a tertiary-care children's hospital.

PATIENTS

This study included 92 pediatric patients with hematological malignancies who received vancomycin and experienced therapeutic drug monitoring from February 2017 to December 2018.

MEASUREMENTS AND MAIN RESULTS

A PPK model was generated with a nonlinear mixed effects model. In addition, required doses to achieve target therapeutic concentrations were simulated based on the final model. A one-compartment model with first-order elimination fit the concentration data best. Actual body weight (BW) and glomerular filtration rate (GFR) were the significant influential factors on the clearance (CL) of vancomycin. The final PPK model for CL was CL (L/h) = 4.18  × GFR / 145 0.741 × BW / 25 K , K =  BW - 0.856 / BW - 0.856 + 6 . 53 - 0.856 , and the volume of distribution was 22.3 L. The model proved to be robust and reliable. Reference dosing regimens were proposed based on the final model.

CONCLUSIONS

A PPK model of vancomycin was established for Chinese pediatric patients with hematological malignancies using a nonlinear mixed effects model, which provided a reference for the clinical application of vancomycin.

Remedial dosing recommendations for delayed or missed doses of valproic acid in patients with epilepsy based on Monte Carlo simulations

OBJECTIVE

Delayed or missed doses are unavoidable in the pharmacotherapy of epilepsy and significantly compromise the efficacy of antiepileptic drug treatment. An inappropriate remedial regimen can cause seizure relapse or serious adverse events. This study investigated the effect of delayed or missed doses on the pharmacokinetics (PK) of valproic acid (VPA) in patients with epilepsy and established remedial dosing recommendations for nonadherent patients.

METHODS

Monte Carlo simulations are based on all previous population pharmacokinetic models for pediatric, adult and elderly patients with epilepsy. The following four remedial strategies were investigated for each delayed dose: A) A partial dose or a regular dose is taken immediately; a regular dose is taken at the next scheduled time. B) The delayed dose was administered immediately, followed by a partial dose at the next scheduled time. C) The delayed dose and a partial dose are taken; the next scheduled time is skipped, and the regular regimen is resumed. D) Double doses are taken when missed one dose or two doses, and the regular regimen at the subsequent scheduled time is resumed.

RESULTS

The recommended remedial dose was related to the delay duration and daily dose. Remedial dosing strategies A and B were almost equivalent, whereas Strategy C was recommended when the delayed dose was close to the next scheduled dose. Strategy D was only suggested for delayed two doses.

CONCLUSION

Simulations provide quantitative insight into the remedial regimens for nonadherent patients, and clinicians should select the optimal regimen for each patient based on the individual's status.

Predictive ability of published population pharmacokinetic models of valproic acid in Thai manic patients

WHAT IS KNOWN AND OBJECTIVE

Population pharmacokinetic (PopPK) models of valproic acid (VPA) have been developed to aid individualized drug dosing, but most of these have been based on the treatment of epileptic patients and recent evidence shows that VPA clearance (CL_VPA ) in manic patients differs from that in epileptic patients. In the light of this, the predictive ability of selected VPA PopPK models based on epileptic patients was assessed to determine whether they could be used with patients with mania.

METHODS

VPA PopPK models that were based on the treatment of epileptic patients and developed using a non-linear mixed-effect approach with a one-compartment structure were selected and used to predict the VPA concentrations of a validation data set. The mean absolute prediction error (MAPE) and root mean square error (RMSE) were used to assess the accuracy and precision of the model.

RESULTS

The validation data set consisted of 235 Thai manic patients with a mean age of 39.6 years and a mean weight of 62.8 kg. Five models were selected to predict VPA concentrations in patients suffering from mania, and these were labelled A, C, E, F and G. The results showed that all models sufficiently predicted VPA concentrations in patients with mania, and of the models studied, G provided the most accurate and precise predictions, with MAPE and RMSE of 23% and 29.75, respectively.

WHAT IS NEW AND CONCLUSION

VPA PopPK models developed using patients with epilepsy can also be used for individualized dosing of patients with mania, but before implementation, the accuracy of these models' predictions should be assessed in the target population.

Impact of gender, albumin, and CYP2C19 polymorphisms on valproic acid in Chinese patients: a population pharmacokinetic model

OBJECTIVE

This prospective study aimed to establish the valproic acid (VPA) population pharmacokinetic model in Chinese patients and realise personalised medication on the basis of population pharmacokinetics.

METHODS

The patients' clinical information and VPA plasma concentrations were collected from The General Hospital of Taiyuan Iron & Steel (Group) Corporation (TISCO). Nonlinear mixed-effect modelling was used to build the population pharmacokinetic model. To characterise the pharmacokinetic data, a one-compartment pharmacokinetic model with first-order absorption and elimination was used. The first-order conditional estimation with η-ε interaction was applied throughout the model-developing procedure. The absorption rate constant (Ka) was fixed at 2.38 hour^-1, and the impact of covariates on clearance and apparent volume of distribution were also explored. Medical records of 60 inpatients were reviewed prospectively and the objective function value (OFV) of the base model and final model were 851.813 and 817.622, respectively.

RESULTS

Gender was identified as the covariate that had a significant impact on the volume of distribution, and albumin and CYP2C19 genotypes influenced clearance.

CONCLUSION

Bootstrap and VPC indicated that a reliable model had been developed that was based on the simulation results, and a simple-to-use dosage regimen table was created to guide clinicians for VPA drug dosing.

Population pharmacokinetic study of caffeine citrate in Chinese premature infants with apnea

WHAT IS KNOWN AND OBJECTIVES

Caffeine citrate is a commonly used methylxanthine for pharmacologic treatment of apnea of prematurity. The aim of this study was to develop and verify a population pharmacokinetic (PPK) model, which can provide a reference for individualized caffeine citrate treatment of apnea in Chinese premature infants.

METHODS

A total of 88 serum concentration measurements from 46 preterm patients (median gestational age 29 weeks) were retrospectively collected and the relevant clinical data of patients were recorded. The PPK analysis was performed by non-linear mixed-effect modelling method using NONMEM. Allometric scaling was applied in the PPK analysis, and the final model was evaluated by graphic and statistical methods, including goodness-of-fit plots, normalized prediction distribution errors plots and bootstrap procedures.

RESULTS

A one-compartment model with first-order elimination was successfully fitted to the data. The typical scaled values for the parameters clearance and volume of distribution (V) were 0.268 L/h and 109 L per 70 kg, respectively. The weight at the time of blood collection (CW) and post-natal age were identified as important predictors for pharmacokinetic parameters of caffeine. The evaluation process showed good stability and predictability of the final PPK model.

WHAT IS NEW AND CONCLUSION

This is a complete PPK study of caffeine citrate in Chinese premature infants with apnea, which complements caffeine pharmacokinetic data of the premature from China. A final PPK model was developed which may serve as a beneficial tool for the use of caffeine citrate in the treatment of apnea in Chinese preterm infants.

Population Pharmacokinetics and Pharmacodynamics of Norvancomycin in Children With Malignant Hematological Disease

Knowledge of pharmacokinetic (PK) behavior of norvancomycin (NVCM) in pediatric patients is lacking, which leads to empirical therapy in clinical practice. This study developed a population PK model of children aged 0-15 years; 112 opportunistic samples in total from 90 children were analyzed. The stability and prediction of the final model were evaluated by goodness-of-fit plots, nonparametric bootstrap, visual predictive check, and normalized prediction distribution errors. The PKs of NVCM in children was described by a 2-compartment model with first-order elimination along with body weight and estimated glomerular filtration rate as significant covariates on clearance. The population typical values of the PK parameters were as follows: clearance 0.12 L/kg/h, central compartment distribution volume 0.17 L/kg, peripheral compartment distribution volume 0.38 L/kg, and intercompartmental clearance 0.35 L/kg/h. Logistic analysis showed that the ratio of area under the concentration-time curve over 24 hours (AUC_0-24 ) to minimum inhibitory concentration (MIC) had the strongest correlation with clinical efficacy, and at least 80% clinical efficiency could be achieved when AUC_0-24 /MIC ≥ 221.06 was defined as the target. Monte Carlo simulation results suggested that a higher dose was required for this pediatric population in order to reach the target. The dosing regimen was optimized based on the final model. A population PK model of NVCM was first characterized in children with hematologic malignancy, and an evidence-based approach for NVCM dosage individualization was provided.

Population pharmacokinetic and pharmacogenetics of imatinib in Chinese patients with chronic myeloid leukemia

Aim: This study aimed to establish a population pharmacokinetic (PPK) model in Chinese patients with chronic myeloid leukemia, and to quantify the effects of pharmacogenetics on pharmacokinetic parameters of imatinib. Methods: A total of 229 plasma concentrations from 170 patients were analyzed. Nonlinear mixed effect model was used to establish the PPK model. Results: A one-compartment model with first-order absorption and first-order elimination adequately describes imatinib pharmacokinetics. Actual bodyweight shows slight effect on the estimated apparent clearance (CL/F) of imatinib in this study population. The final PPK model is: Ka (1/h) = 0.329; CL/F (l/h) = 9.25 × (actual bodyweight/70)0.228; V/F(l) = 222. Conclusion: Actual bodyweight has a slight effect on CL/F. Demographics, physiopathology and pharmacogenetics covariates have no significant effects on imatinib pharmacokinetics.

Pharmacokinetic considerations for anti-epileptic drugs in children

INTRODUCTION

Epilepsy is a chronic and debilitating neurological disease, with a peak of incidence in the first years of life. Today, the vast armamentarium of antiepileptic drugs (AEDs) available make even more challenging to select the most appropriate AED and establish the most effective dosing regimen. In fact, AEDs pharmacokinetics is under the influence of important age-related factors which cannot be ignored. Areas covered: Physiological changes occurring during development age (different body composition, immature metabolic patterns, reduced renal activity) can significantly modify the pharmacokinetic profile of AEDs (adsorption, volume of distribution, half-life, clearance), leading to an altered treatment response. We reviewed the main pharmacokinetic characteristics of AEDs used in children, focusing on age-related factors which are of relevance when treating this patient population. Expert opinion: To deal with this pharmacokinetic variability, physicians have at their disposal two tools: 1) therapeutic drug concentration monitoring, which may help to set the optimal therapeutic regimen for each patient and to monitor eventual fluctuation, and 2) the use of extended-release drug formulations, when available. In the next future, the development of 'ad-hoc' electronic dashboard systems will represent relevant decision-support tools making the AED therapy even more individualized and precise, especially in children.

Population Pharmacokinetics and Dosing Optimization of Amoxicillin in Neonates and Young Infants

Amoxicillin is widely used to treat bacterial infections in neonates. However, considerable intercenter variability in dosage regimens of antibiotics exists in clinical practice. The pharmacokinetics of amoxicillin has been described in only a few preterm neonates. Thus, we aimed to evaluate the population pharmacokinetics of amoxicillin through a large sample size covering the entire age range of neonates and young infants and to establish evidence-based dosage regimens based on developmental pharmacokinetics-pharmacodynamics. This is a prospective, multicenter, pharmacokinetic study using an opportunistic sampling design. Amoxicillin plasma concentrations were determined using high-performance liquid chromatography. Population pharmacokinetic analysis was performed using NONMEM. A total of 224 pharmacokinetic samples from 187 newborns (postmenstrual age range, 28.4 to 46.3 weeks) were available for analysis. A two-compartment model with first-order elimination was used to describe population pharmacokinetics. Covariate analysis showed that current weight, postnatal age, and gestational age were significant covariates. The final model was further validated for predictive performance in an independent cohort of patients. Monte Carlo simulation demonstrated that for early-onset sepsis, the currently used dosage regimen (25 mg/kg twice daily [BID]) resulted in 99.0% of premature neonates and 87.3% of term neonates achieving the pharmacodynamic target (percent time above MIC), using a MIC breakpoint of 1 mg/liter. For late-onset sepsis, 86.1% of premature neonates treated with 25 mg/kg three times a day (TID) and 79.0% of term neonates receiving 25 mg/kg four times a day (QID) reached the pharmacodynamic target, using a MIC breakpoint of 2 mg/liter. The population pharmacokinetics of amoxicillin was assessed in neonates and young infants. A dosage regimen was established based on developmental pharmacokinetics-pharmacodynamics.

Pharmacokinetic evaluation of vigabatrin dose for the treatment of refractory focal seizures in children using adult and pediatric data

Vigabatrin is indicated as adjunctive therapy for refractory focal seizures. For children, European recommendations indicate maintenance doses varying from 30 to 100 mg/kg/day for this indication. Since cumulated dose was associated with retinal toxicity, it is essential to administrate the lowest effective dose to patients. This work was conducted with the purpose to determine the pediatric doses of vigabatrin that allow a similar exposure than effective doses in adults (2-3 g/day) through a pharmacokinetic (PK) study, using both pediatric and adult data. For this study, we focused on the active S(+) enantiomer of vigabatrin. First, the adult effective exposition range of vigabatrin-S was determined from an adult PK model. Then, this same model was scaled to the pediatric population using allometry and maturation principles to account for growth and development. The ability of the model to predict pediatric data was assessed by comparing population predictions with observed pediatric data. Finally, the extrapolated pediatric model was used to simulate pediatric expositions which were compared to the adult exposition range (36.5-77.9 mg.h/L). From those simulations, we determined that, for children aged between 3 months and 18 years, doses between 40 and 50 mg/kg/day allow vigabatrin-S expositions similar to those found in adults at the recommended posology. We proposed those doses as optimal maintenance doses that may be increased, if necessary, by slow titration.

Population pharmacokinetics of valproic acid in epileptic children: Effects of clinical and genetic factors

Valproic acid (VPA) is a first-line anti-epileptic drug that is used in the treatment of generalized and partial seizures. Gene variants had been proved to influence the pharmacokinetics (PK) of VPA and contribute to its inter-individual variability (IIV). The aim of this study was to systematically investigate the effects of candidate gene variants (CYPs, UGTs, ABC transporters, and nuclear receptors) on VPA PK in Chinese children with epilepsy. A total of 1065 VPA serum trough concentrations at steady state were collected from 264 epileptic pediatric patients aged 3 months to 16 years. The population pharmacokinetic (PPK) model was developed using a nonlinear mixed effects modelling (NONMEM) approach. For the final PPK model, the oral clearance (CL/F) of VPA was estimated to be 0.259 L/h with IIV of 13.3%. The estimates generated by NONMEM indicated that the VPA CL/F was significantly influenced by patient body weight (increased by an exponent of 0.662), co-administration with carbamazepine (increased CL/F by 22%), and daily dose of VPA (increased by an exponent of 0.22). CL/F in patients with the LEPR rs1137101 variant (668 AG and GG genotypes) was much lower than in patients with the AA genotype (17.8% and 22.6% lower, respectively). However, none of the CYPs or UGTs gene variants was found to influence the PK of VPA in this study. Evaluation by bootstrap and normalized prediction distribution error (NPDE) showed that the final model was stable. The predictive performance was evaluated by goodness-of-fit (GOF) plots and visual predictive checks (VPC), and the results indicated satisfactory precision. Our model suggests a correlation between VPA CL/F and LEPR rs1137101 variants, which might be beneficial in the context of individual dose optimization.

Population Pharmacokinetics of Vancomycin in Chinese ICU Neonates: Initial Dosage Recommendations

The main goal of our study was to characterize the population pharmacokinetics of vancomycin in critically ill Chinese neonates to develop a pharmacokinetic model and investigate factors that have significant influences on the pharmacokinetics of vancomycin in this population. The study population consisted of 80 neonates in the neonatal intensive care unit (ICU) from which 165 trough and peak concentrations of vancomycin were obtained. Nonlinear mixed effect modeling was used to develop a population pharmacokinetic model for vancomycin. The stability and predictive ability of the final model were evaluated based on diagnostic plots, normalized prediction distribution errors and the bootstrap method. Serum creatinine (Scr) and body weight were significant covariates on the clearance of vancomycin. The average clearance was 0.309 L/h for a neonate with Scr of 23.3 μmol/L and body weight of 2.9 kg. No obvious ethnic differences in the clearance of vancomycin were found relative to the earlier studies of Caucasian neonates. Moreover, the established model indicated that in patients with a greater renal clearance status, especially Scr < 15 μmol/L, current guideline recommendations would likely not achieve therapeutic area under the concentration-time curve over 24 h/minimum inhibitory concentration (AUC24h/MIC) ≥ 400. The exceptions to this are British National Formulary (2016-2017), Blue Book (2016) and Neofax (2017). Recommended dose regimens for neonates with different Scr levels and postmenstrual ages were estimated based on Monte Carlo simulations and the established model. These findings will be valuable for developing individualized dosage regimens in the neonatal ICU setting.

A population pharmacokinetic model taking into account protein binding for the sustained-release granule formulation of valproic acid in children with epilepsy

PURPOSE

The objective of this work was to develop a population pharmacokinetic model for a prolonged-release granule formulation of valproic acid (VPA) in children with epilepsy and to determine the doses providing a VPA trough concentration (C_trough) within the target range (50-100 mg/L).

METHODS

Ninety-eight children (1-17.6 years, 325 plasma samples) were included in the study. The model was built with NONMEM 7.3. The probability to obtain C_trough between 50 and 100 mg/L was determined by the Monte Carlo simulations for doses of 20, 30, 40, and 60 mg/kg/day and body weights between 10 and 70 kg.

RESULTS

A one compartment model, with first-order absorption and flip-flop parameterization and linear elimination, but taking protein binding into account, was used to describe the data. Typical values for unbound VPA clearance and distribution volume were 6.24 L/h/70 kg and 130 L/h/70 kg respectively. Both parameters were related to body weight via allometric models. The highest probability to obtain a C_trough within the target range for 10-kg children was obtained with a 40 mg/kg daily dose, whereas daily doses of 30 and 20 mg/kg were found appropriate for 20 to 30- and ≥ 40-kg children respectively. However, for these same doses, the exposure to unbound VPA could differ by 40%.

CONCLUSIONS

If the present study supports the current dose recommendations of 20-30 mg/kg/day, except for children under 20 kg, who may need higher doses, it also highlights the need for further research on the pharmacokinetics/pharmacodynamic profile of unbound VPA.

A systematic review of population pharmacokinetics of valproic acid

AIMS

Population pharmacokinetics is an essential tool that helps guide individualized dosing regimens. The aims of this systematic review are to provide knowledge concerning population pharmacokinetics of valproic acid (VPA) and to identify factors influencing VPA pharmacokinetic variability.

METHODS

PubMed and Embase databases were systematically searched from inception to June, 2017. Relevant articles from reference lists were also included. All population pharmacokinetic studies of VPA conducted in humans and that employed a nonlinear mixed effect modelling approach were included in this review.

RESULTS

Twenty-six studies were included in this review. Most studies characterized VPA pharmacokinetics as a one-compartment model. Three studies reported a two-compartment model. Body weight, dose and age were significant predictors for VPA volume of distribution (V_d ). The estimated V_d for one-compartment models ranged from 8.4 to 23.3 l. For two-compartment models, peripheral volumes of distribution ranged from 4.08 to 42.1 l. Frequently reported significant predictors for VPA clearance (CL_VPA ) included body weight, VPA dose, concomitant medications, gender and age. The estimated CL_VPA ranged from 0.206 to 1.154 l h^-1 and the inter-individual variability ranged from 13.40 to 35.90%. Two studies reported population pharmacokinetics/pharmacodynamics of VPA in patients with epilepsy. Seventeen studies evaluated the performance of their final models.

CONCLUSIONS

Significant predictors influencing VPA pharmacokinetics as well as model methodologies are highlighted in this review. For clinical application, CL_VPA could be predicted using body weight, VPA dose, concomitant medications, gender or age. For future research, there is a knowledge gap regarding population pharmacokinetics/pharmacodynamics of VPA in a population other than epileptic patients.

Population Pharmacokinetics of High-Dose Methotrexate in Patients With Primary Central Nervous System Lymphoma

The intra- and inter-individual variances of methotrexate (MTX) pharmacokinetics are extremely large, and the pharmacokinetic property of MTX in patients with primary central nervous system lymphoma (PCNSL) is unestablished. A total of 701 MTX plasma concentrations from 98 patients with PCNSL under high-dose MTX therapy were used to develop the population pharmacokinetic (popPK) model of MTX by using the nonlinear mixed-effects modeling method. A 2-compartment model was employed to describe the pharmacokinetic property of MTX. In the final popPK model, inclusion of serum creatinine and body surface area significantly reduced objective function value for clearance over the base model (p <0.001), and inclusion of age significantly reduced objective function value for distribution volume of central compartment (V_c) over the base model (p <0.001). In the final popPK model, the inter-individual clearance = 6.67 × (SCR/68.1)^-0.48 × (BSA/1.75)^1.17; V_c = 24.46 × (age/57.16)^0.81. The precision of all parameters was acceptable (relative standard error <28.61%). Bootstrap and visual predictive check results indicated that the final popPK model was stable with acceptable predictive ability. The popPK model may be useful for personalized medication in PCNSL patients under high-dose MTX therapy. Further studies are warranted to confirm the results.

Population pharmacokinetics of arginine glutamate in healthy Chinese volunteers

1. The present study developed population pharmacokinetic models of arginine and glutamate in healthy Chinese volunteers. Two nonlinear mixed-effect models were developed using NONMEM® software (ICON Development Solutions, Ellicott City, MD) to describe the pharmacokinetic properties and to assess the relevant parameters as well as the inter-individual variability. The potential covariates were screened using stepwise approach and the stability and predictive capability of the models were performed using bootstrap and visual predictive check. 2. The concentration time curves of arginine and glutamate were best described by a first-order elimination two-compartment model and a nonlinear elimination one-compartment model, respectively. The final parameter estimation of arginine for CL was 44.1 L/h. Q, V₁ and V₂ were 23 L/h, 20.3 L and 46 L, respectively. The final parameter estimation of glutamate for V_max and K_m were 18.8 mg/h and 77.2 mg/L, respectively. V for low dose and high dose was 23.1 L and 36.3 L, respectively. 3. For arginine, weight was significant covariate on the apparent distribution volume of peripheral compartment. The gain in weight remarkably increases V_2. For glutamate, dose as a significant covariate on the apparent distribution volume was included, subjects received high dose (20 g) have remarkably higher V compared to subjects received low dose (10 g).