Pharmacokinetics of mycophenolic acid and external evaluation of two limited sampling strategies of drug exposure in patients with juvenile systematic lupus erythematosus.

INTRODUCTION: Mycophenolate mofetil (MMF), a pro-drug of mycophenolic acid (MPA), has become a major therapeutic option in juvenile systemic lupus erythematosus (jSLE). Monitoring MPA exposure using area under curve (AUC) has proved its value to increase efficacy and safety in solid organ transplantation both in children and adults, but additional data are required in patients with autoimmune diseases. In order to facilitate MMF therapeutic drug monitoring (TDM) in children, Bayesian estimators (BE) of MPA AUC0-12 h using limited sampling strategies (LSS) have been developed. Our aim was to conduct an external validation of these LSS using rich pharmacokinetics and compare their predictive performance. METHODS: Pharmacokinetic blood samples were collected from jSLE treated by MMF and MPA plasma concentrations were determined using high-performance liquid chromatography system with ultraviolet detection (HPLC-UV). Individual AUC0-12 h at steady state was calculated using the trapezoid rule and compared with two LSS: (1) ISBA, a two-stage Bayesian approach developed for jSLE and (2) ADAPT, a non-linear mixed effects model with a parametric maximum likelihood approach developed with data from renal transplanted adults. RESULTS: We received 41 rich pediatric PK at steady state from jSLE and calculated individual AUC0-12 h. The external validation MPA AUC0-12 h was conducted by selecting the concentration-time points adapted to ISBA and ADAPT: (1) ISBA showed good accuracy (bias: - 0.8 mg h/L), (2) ADAPT resulted in a bias of 6.7 mg L/h. The corresponding relative root mean square prediction error (RSME) was 23% and 43% respectively. CONCLUSION: According to our external validation of two LSS of drug exposure, the ISBA model is recommended for Bayesian estimation of MPA AUC0-12 h in jSLE. In the literature focusing on MMF TDM, an efficacy cut-off for MPA AUC0-12 h between 30 and 45 mg h/L is proposed in jSLE but this requires additional validation.

Serum Creatinine and Serum Cystatin C are Both Relevant Renal Markers to Estimate Vancomycin Clearance in Critically Ill Neonates.

Purpose: Serum creatinine (SCr) is used as a marker of kidney function to guide dosing of renally eliminated drugs. Serum Cystatin C (S-CysC) has been suggested as a more reliable kidney marker than SCr in adults and children. Purpose of this study was to investigate S-CysC as alternative renal marker to SCr for estimating vancomycin clearance in neonates undergoing intensive care. Methods: Vancomycin pharmacokinetics (PK), SCr and S-CysC data were collected in patients undergoing vancomycin treatment in the neonatal intensive care unit of Robert Debré Hospital - Paris. A population PK analysis was performed utilizing routine therapeutic drug monitoring samples. S-CysC and SCr were compared as covariates on vancomycin clearance using stepwise covariate modeling (forward inclusion [p < 0.05] and backward elimination [p < 0.01]). Model performance was evaluated by graphical and statistical criteria. Results: A total of 108 vancomycin concentrations from 66 patients (postmenstrual age [PMA] of 26-46 weeks) were modeled with an allometric one-compartment model. The median (range) values for SCr and S-CysC were 41 (12-153) µmol/l and 1.43 (0.95-2.83) mg/l, respectively. Following stepwise covariate model building, SCr was retained as single marker of kidney function (after accounting for weight and PMA) in the final model. Compared to the final model based on SCr, the alternative model based on S-CysC showed very similar performance (e.g. BIC of 578.3 vs. 576.4) but included one additional covariate: impact of mechanical ventilation on vancomycin clearance, in addition to the effects of size and maturation. Conclusion: ill neonates. However, if using S-CysC for this purpose mechanical ventilation needs to be taken into account.

Reporting of offspring data in diabetes, HIV infection and hypertension trials during pregnancy: a systematic review.

BACKGROUND: Clinical trials are conducted during pregnancy to evaluate benefits and risks of medicines for mother and child. The safety of maternal treatments is a key issue for healthcare professionals and parents. OBJECTIVE: To analyse offspring data reported in clinical trials in pregnant women with diabetes, HIV infection or hypertension (three of the most common diseases in women of childbearing potential) and either treated prior to pregnancy for these chronic diseases or diagnosed and treated during pregnancy. METHODS: PubMed and Embase (1 January 1997 to 31 December 2017) were searched for drug trials in pregnant women with diabetes, HIV infection or hypertension. Titles and abstracts were screened, followed by a full-text review of eligible articles. Inclusion criteria were interventional clinical trials in pregnant women treated with medication and full text in English. Trial characteristics, maternal and offspring data were extracted. Data were summarised by disease and study. Twelve key items were considered for the offspring. RESULTS: Overall, 196 articles reporting 132 clinical trials (diabetes n=55; HIV n=59; hypertension n=18) were included. Key offspring data were frequently not reported, for example, number of births (diabetes: 22/55, 40%; HIV: 14/59, 24%; hypertension: 10/18, 56%). Congenital malformations were often not reported with sufficient detail (diabetes: 40/55, 73%; HIV: 39/59, 66%; hypertension: 17/18, 94%). Similar observations were made for other key items (eg, fetal losses, neonatal deaths). CONCLUSION: Under-reporting of key data for the offspring was frequent in publications of clinical trials in pregnant women with diabetes, HIV infection or hypertension making the assessment of the benefit-risk ratio of treatment options during pregnancy difficult. TRIAL REGISTRATION NUMBER: CRD42017057024.

Body Surface Area-Based Dosing Regimen of Caspofungin in Children: a Population Pharmacokinetics Confirmatory Study.

We evaluated the population pharmacokinetics of caspofungin in children (2 to 12 years of age). The real-world data from 48 children were best fit by a two-compartment model with first-order elimination. Subsequent covariate analysis demonstrated that body surface area had a significant correlation with caspofungin pharmacokinetics, compared to body weight. The population pharmacokinetics of caspofungin confirmed that adjustment of caspofungin dosage based on body surface area is most appropriate for pediatric use.

Population pharmacokinetics and dosing optimization of teicoplanin in children with malignant haematological disease.

AIM: Children with haematological malignancy represent an identified subgroup of the paediatric population with specific pharmacokinetic parameters. In these patients, inadequate empirical antibacterial therapy may result in infection-related morbidity and increased mortality, making optimization of the dosing regimen essential. As paediatric data are limited, our aim was to evaluate the population pharmacokinetics of teicoplanin in order to define the appropriate dosing regimen in this high risk population. METHODS: The current dose of teicoplanin was evaluated in children with haematological malignancy. Population pharmacokinetics of teicoplanin were analyzed using nonmem software. The dosing regimen was optimized based on the final model. RESULTS: Eighty-five children (age range 0.5 to 16.9 years) were included. Therapeutic drug monitoring and opportunistic samples (n = 143) were available for analysis. With the current recommended dose of 10 mg kg(-1) day(-1) , 41 children (48%) had sub-therapeutic steady-state trough concentrations (Css,min <10 mg l(-1) ). A two compartment pharmacokinetic model with first order elimination was developed. Systematic covariate analysis identified that bodyweight (size) and creatinine clearance significantly influenced teicoplanin clearance. The model was validated internally. Its predictive performance was further confirmed in an external validation. In order to reach the target AUC of 750 mg l(-1) h 18 mg kg(-1) was required for infants, 14 mg kg(-1) for children and 12 mg kg(-1) for adolescents. A patient-tailored dose regimen was further developed and reduced variability in AUC and Css,min values compared with the mg kg(-1) basis dose, making the modelling approach an important tool for dosing individualization. CONCLUSIONS: This first population pharmacokinetic study of teicoplanin in children with haematological malignancy provided evidence-based support to individualize teicoplanin therapy in this vulnerable population.

Population pharmacokinetics and dosing optimization of vancomycin in children with malignant hematological disease.

An increase in vancomycin dose has been proposed in adults with malignant hematological disease. As pediatric data are limited, our aim was to evaluate the population pharmacokinetics of vancomycin in order to define the appropriate dosing regimen in children with malignant hematological disease. Vancomycin concentrations were collected prospectively during therapeutic monitoring. Population pharmacokinetic analysis was performed using NONMEM software. Seventy children (age range, 0.3 to 17.7 years) were included. With the current recommended dosing regimen of 40 to 60 mg/kg/day, 53 children (76%) had subtherapeutic steady-state trough concentrations (Css/min of <10 mg/liter). A one-compartment model with first-order elimination was developed. Systematic covariate analysis identified that weight significantly influenced clearance (CL) and volume of distribution (V) with power functions of 0.677 for CL and 0.838 for V. Vancomycin CL also significantly increased with increases in creatinine clearance and seemed to be higher in children with malignant hematological disease than in the general pediatric population. The model was validated internally. Its predictive performance was further confirmed in an external validation by Bayesian estimation. A patient-tailored dosing regimen was developed based on the final pharmacokinetic model and showed that a higher proportion of patients reached the target Css/min than with the traditional mg/kg-basis dose (60% versus 49%) and that the risks associated with underdosing or overdosing were reduced. This is the first population pharmacokinetic study of vancomycin in children with malignant hematological disease. An optimized dosing regimen, taking into account patient weight, creatinine clearance, and susceptibility of the pathogens involved, could routinely be used to individualize vancomycin therapy in this vulnerable population.

External Evaluation of Population Pharmacokinetic Models of Vancomycin in Neonates: The transferability of published models to different clinical settings.

BACKGROUND: Vancomycin is one of the most evaluated antibiotics in neonates using modeling and simulation approaches. However no clear consensus on optimal dosing has been achieved. The objective of the present study was to perform an external evaluation of published models, in order to test their predictive performances in an independent dataset and to identify the possible study-related factors influencing the transferability of pharmacokinetic models to different clinical settings. METHOD: Published neonatal vancomycin pharmacokinetic models were screened from the literature. The predictive performance of 6 models was evaluated using an independent dataset (112 concentrations from 78 neonates). The evaluation procedures used simulation-based diagnostics (visual predictive check [VPC] and normalized prediction distribution errors [NPDE]). RESULTS: Differences in predictive performances of models for vancomycin pharmacokinetics in neonates were found. The mean of NPDE for 6 evaluated models were 1.35, -0.22, -0.36, 0.24, 0.66, 0.48, respectively. These differences were explained, at least partly, by taking into account the method used to measure serum creatinine concentrations. The adult conversion factor of 1.3 (enzymatic to Jaffé) was tested with an improvement in the VPC and NPDE, but it still need to be evaluated and validated in neonates. Differences were also identified between analytical methods for vancomycin. CONCLUSION: The importance of analytical techniques for serum creatinine concentrations and vancomycin as a predictor of vancomycin concentrations in neonates has been confirmed. Dosage individualisation of vancomycin in neonates should consider not only patients' characteristics and clinical conditions, but also the methods used to measure serum creatinine and vancomycin.

Determinants of mercaptopurine toxicity in paediatric acute lymphoblastic leukemia maintenance therapy.

AIMS: 6-mercaptopurine (6-MP) is used in the treatment of childhood acute lymphoblastic leukaemia (ALL). Its red blood cell (RBC) metabolite concentrations (6-thioguanine [6-TGN] and 6-methylmercaptopurine nucleotides [6-MMPN]) are related to drug response. We investigated the impact of non-genetic covariates and pharmacogenetic polymorphisms affecting thiopurine methyltransferase (TPMT) and inosine triphosphate pyrophosphatase (ITPA) on 6-MP metabolism and response. METHODS: Sixty-six children with ALL treated according to EORTC 58951 protocol were included in this study. Six patients had a heterozygous genotype for the most common TPMT polymorphisms, nine for ITPA 94 C > A and 17 for ITPA IVS2+21 A > C. 6-MP metabolites concentrations were analyzed by mixed model analysis. RESULTS: During maintenance, steady-state RBC 6-TGN concentrations were lower in patients aged 6 years or younger (493 pmol/8 × 10(8) RBC) than in older children (600 pmol/8 × 10(8) RBC). 6-MMPN concentrations were low in patients with TPMT variant/wild-type ITPA (1862 pmol/8 × 10(8) RBC), intermediate in wild-type patients and high (16468 pmol/8 × 10(8) RBC) in patients wild-type TPMT/variant ITPA. A 6-MMPN threshold of 5000 pmol/8 × 10(8) RBC was associated with an increased risk of hepatotoxicity. CONCLUSION: In this study, age and both TPMT and ITPA genotypes influenced 6-MP metabolism. High 6-MMPN was associated with hepatotoxicity. These pharmacological tools should be used to monitor ALL treatment in children.

Population pharmacokinetics of ganciclovir following administration of valganciclovir in paediatric renal transplant patients.

OBJECTIVE: To develop a population pharmacokinetic model for valganciclovir in paediatric renal transplant recipients, identify covariates that explain variability, and determine valganciclovir dosage regimens for cytomegalovirus (CMV) prophylaxis in children. METHODS: The pharmacokinetics of valganciclovir were described with plasma concentrations from 22 patients (age range 3-17 years) 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 a bootstrap and visual predictive check. The dosage regimens of valganciclovir for CMV prophylaxis in children were simulated using the final model. RESULTS: The mean population pharmacokinetic parameters were apparent systemic clearance (CL) 10.1L/h, apparent central volume of distribution 5.2 L, apparent peripheral volume of distribution 30.7 L, inter-tissue clearance 3.97 L/h, absorption rate constant 0.369 h-1 and lag-time 0.743 h. The covariate analysis identified creatinine clearance (CL(CR)) and bodyweight (WT) as individual factors influencing the apparent oral clearance: CL= 8.04 x (CL(CR)/89)(2.93) + 3.62 x (WT/28) L/h. The results of the simulation showed that for a typical patient (WT 28 kg and CL(CR) 89 mL/min), an area under the plasma concentration-time curve of 43 +/- 10.6 mg x h/mL will be achieved with valganciclovir 500 mg once daily. CONCLUSION: The dosage regimens of valganciclovir for CMV prophylaxis have been defined using the final population pharmacokinetic model based on WT and CLCR for paediatric renal transplantation patients.

A limited sampling strategy to estimate individual pharmacokinetic parameters of methotrexate in children with acute lymphoblastic leukemia.

PURPOSE: The objectives of this study were to characterize the population pharmacokinetics of MTX in patients with acute lymphoblastic leukemia (ALL) with ages ranging from 2 to 16 years and to propose a limited sampling strategy to estimate individual pharmacokinetic parameters. METHODS: Seventy-nine children were enrolled in this study; they received 1-4 courses of chemotherapy. MTX was administered at a dose of 5 g/m2. MTX population parameters were estimated from 61 patients (231 courses; age range: 2-16 years). The data were analyzed by nonlinear mixed-effect modeling with use of a two-compartment structural model. The interoccasion variability was taken into account in the model. Eighteen additional patients (70 courses) were used to evaluate the predictive performances of the Bayesian approach and to devise a limited sampling strategy. RESULTS: The following population parameters were obtained: total clearance (CL) = 8.8 l/h (inter-individual variability: 43%), initial volume of distribution (V1) = 17.3 l (48%), k12 = 0.0225 h(-1) (41%), and k21 = 0.0629 h(-1) (24%). The inter-individual variability in the initial volume of distribution was partially explained by the fact that this parameter was weight-dependent. Intercourse variability was limited, with a mean variation of 13.2%. The protocol involving two sampling times, 24 and 48 h after the beginning of infusion, allows precise and accurate determination of individual pharmacokinetic parameters and consequently, it was possible to predict the time at which the MTX concentration reached the predicted threshold (0.2 microM) below which the administration of folinic acid could be stopped. CONCLUSION: The results of this study combine the relationships between the pharmacokinetic parameters of MTX and patient covariates that may be useful for dose adjustment, with a convenient sampling procedure that may aid in optimizing pediatric patient care.

Pharmacokinetics of ganciclovir in pediatric renal transplant recipients.

Ganciclovir (GCV) is effective in preventing and treating cytomegalovirus (CMV) infection in solid organ transplant recipients. The aims of the present study were to determine the pharmacokinetics of GCV administered intravenously (IV) and orally (p.o.) as pre-emptive anti-CMV therapy in pediatric renal transplant recipients and to monitor trough levels and side-effects during pre-emptive therapy. Eleven pediatric renal transplant recipients (aged 11.0+/-3.9 years) were included. The diagnosis of CMV infection, based on two positive pp-65 CMV blood antigen tests at 1 week apart, was made at 39+/-12 days post renal transplantation. They received IV GCV at a dose of 5.0+/-0.3 mg/kg per 12 h for 15 days, followed by GCV p.o. at a dose of 46.7+/-8.2 mg/kg per 12 h for 3 months. Pharmacokinetics (PK) were studied at steady state and GCV plasma concentrations were measured by high-performance liquid chromatography. After IV GCV administration, PK parameters were: C(0)=0.84+/-0.66 microg/ml; C(max)=11.77+/-2.82 microg/ml; AUC(0-12 h)=42.29+/-17.57 microg/ml per hour; Cl=0.13+/-0.05 l/h per kg. After p.o. GCV administration, PK parameters were: C(0)=1.08+/-0.68 microg/ml; C(max)=2.70+/-1.07 microg/ml; AUC(0-12 h)=18.97+/-9.36 microg/ml per hour; Cl/F=2.97+/-1.42 l/h per kg. Bioavailability (F) was 4.9+/-1.2%. Pre-dose concentrations (C(0)) measured under p.o. GCV (n=51) were 1.29+/-0.80 microg/ml (8 C(0) values were below 0.5 microg/ml). Pp-65 CMV blood antigen tests became negative after 16+/-11 days of treatment. GCV was well tolerated. Because of the limited bioavailability, the recommended high doses of p.o. GCV (50 mg/kg per 12 h) were administered and were associated with trough levels over 0.5 microg/ml. In 1 patient who received an erroneously low dosage p.o., CMV resistance to GCV appeared, requiring foscarnet.