Stephanie Läer

Population Pharmacokinetic Studies in Pediatrics: Issues in Design and Analysis

The current review addresses the following 3 frequently encountered challenges in the design and analysis of population pharmacokinetic studies in pediatrics: (1) body size adjustments during the development of pharmacostatistical models, (2) design and validation of limited sampling strategies, and (3) the integration of historical priors in data analysis and trial simulation. Size adjustments with empiric approaches based on body weight or body surface area have frequently proven as a pragmatic tool to overcome large size differences in a pediatric study population. Allometric size adjustments, however, provide a more mechanistic, physiologically based approach that, if used a priori, allows delineation of the effect of size from that of other covariates that show a high degree of collinearity. The frequent lack of dense data sets in pediatric clinical pharmacology because of ethical and logistic constraints in study design can be overcome with the application of D-optimality-based limited sampling schemes in combination with Bayesian and nonlinear mixed-effects modeling approaches. Empirically based dose selection and clinical trial designs for pediatric clinical pharmacology studies can be improved by applying clinical trial simulation techniques, especially if they integrate adult and pediatric in vitro and/or in vivo data as historic priors. Although integration of these concepts and techniques in population pharmacokinetic analyses is not only limited to pediatric research, their application allows researchers to overcome some major hurdles frequently encountered in pharmacokinetic studies in pediatrics and, thus, provides the basis for additional clinical pharmacology research in this previously insufficiently studied fraction of the general population.

Physiologically Based Pharmacokinetic (PBPK) Modeling in Children

This review summarizes the present status of physiologically based pharmacokinetic (PBPK) modeling and simulation (M&S) and its application in support of pediatric drug research. We address the reasons that PBPK is suited to the current needs of pediatric drug development and pharmacotherapy in light of the evolution in pediatric PBPK methodologies and approaches, which were originally developed for the purpose of toxicologic evaluation. Also discussed is the current degree of confidence in using PBPK to support pediatric drug development and registration and the key factors essential for robust results and broader adoption of pediatric PBPK M&S.

Physiologically based pharmacokinetic modeling: methodology, applications, and limitations with a focus on its role in pediatric drug development.

The concept of physiologically based pharmacokinetic (PBPK) modeling was introduced years ago, but it has not been practiced significantly. However, interest in and implementation of this modeling technique have grown, as evidenced by the increased number of publications in this field. This paper demonstrates briefly the methodology, applications, and limitations of PBPK modeling with special attention given to discuss the use of PBPK models in pediatric drug development and some examples described in detail. Although PBPK models do have some limitations, the potential benefit from PBPK modeling technique is huge. PBPK models can be applied to investigate drug pharmacokinetics under different physiological and pathological conditions or in different age groups, to support decision-making during drug discovery, to provide, perhaps most important, data that can save time and resources, especially in early drug development phases and in pediatric clinical trials, and potentially to help clinical trials become more “confirmatory” rather than “exploratory”.

The In Silico Child: Using Simulation to Guide Pediatric Drug Development and Manage Pediatric Pharmacotherapy

Significant gains have been made in the appreciation of pediatrics as an important population in which rationale pharmacotherapy guidance is warranted but often currently lacking. Although the regulatory framework for major improvements in pediatric drug development was implemented in Europe a decade later than the United States, recent efforts, including the 2007 “Better Medicines for Children” initiative, indicate that the awareness of this problem is indeed a global phenomenon. Nevertheless, there still remains a gap between the awareness and the implementation of rationale and scientifically based drug development and applied pharmacotherapy in children. Specifically, a vision of how best to move from empiricism toward a plan that incorporates biologic knowledge about the maturation of physiologic processes as well as the drug‐ and disease‐specific knowledge generated from drug development and applied pharmacotherapy in adults must evolve from the present intentions. Modeling and simulation approaches can facilitate such a vision that ultimately should provide benefit to pediatric patients. Although recent examples of pediatric in silico approaches are compelling, their ultimate value may be in the identification of data and studies that better guide drug therapy and in the education of pediatric caregivers to the principles of clinical pharmacology that underlie optimal pharmacotherapeutic decisions in children.

N-Terminal pro-brain natriuretic peptide: normal ranges in the pediatric population including method comparison and interlaboratory variability

Abstract The aim of the present study was the investigation of N-terminal pro-brain natriuretic peptide (NT-proBNP) in the pediatric population. This is essential for adequate monitoring and classification of pediatric patients with heart disease, but no consistent data are available yet. In addition, the comparability of two commercially available NT-proBNP assays and the inter-laboratory variability for the most suitable one were assessed. For this purpose, 408 subjects (1–29years) were included. NT-proBNP was determined with a non-competitive electrochemiluminescent immunoassay (Roche NT-proBNP; n=402) and a competitive enzyme-immunoassay (Biomedica NT-proBNP; n=402). Inter-laboratory variability was evaluated for the Roche assay by stepwise inclusion of four and 11 centers throughout Germany, respectively. Roche NT-proBNP ranged from 5.0 to 391.5ng/L, with higher values for younger children. The 97.5th (75th) percentile curve ranged from 319.9ng/L (231.2 ng/L, 1–3years) to 114.9ng/L (53.3 ng/L, 18years). In contrast, Biomedica NT-proBNP ranged from 253.7 to 7602.8 ng/L, with no significant age dependency. The mean difference between the assays was 1649.7ng/L (95% confidence interval 1546.3–1753.1ng/L). Inter-laboratory variability ranged from 6.5% to 3.8%, covering a range from 51.3 to 6618.1ng/L. The assay seems to influence the interpretation of resulting NT-proBNP values and therefore has to be chosen carefully. For the monitoring and classification of pediatric patients with congenital heart disease, age-based NT-proBNP values should be used.

Plasma Concentrations of N-Terminal Brain Natriuretic Peptide in Healthy Children, Adolescents, and Young Adults: Effect of Age and Gender

Children with congenital heart disease need adequate diagnostic classification regarding their cardiovascular status (CVS). N-terminal brain natriuretic peptide (N-BNP) plasma concentration indicates dysfunction of the cardiovascular system and guides decisions concerning treatment and prognosis. Reference values are established for adults, with age-dependent increasing values and higher values in women. To avoid misclassification concerning the CVS, a large group of healthy children and adolescents can be used show the relationship between gender, age, and N-BNP and these can serve as reference values. N-BNP was measured in 434 healthy subjects (240 female and 194 male) with ages ranging from 0 to 32 years without any cardiovascular disease or renal or hepatic impairment. Measurements were performed with an electrochemiluminescence immunoassay from Roche Diagnostics. Mean N-BNP decreased from 12.6 fmol/ml (0–9 years; n = 79) to 9.41 fmol/ml (10–14 years; n = 154) and in adolescents from 6.1 (15–19 years; n = 99) to 4.8 fmol/ml (>19 years; n = 102) in adults (p < 0.05). Mean N-BNP concerning gender did not differ in any age group younger than 19 years. In contrast, the adult female group had 78% higher N-BNP compared to the male group (p < 0.05). There was a significant peak in N-BNP at the age of 12–14 years. This study shows that reference values for N-BNP differed profoundly in children compared to adults and were up to 260% higher in children without any gender difference. Therefore, these reference values will help to avoid CVS misclassification in children for the biomarker N-BNP.

Off-label drug use among hospitalised children: identifying areas with the highest need for research

Objective of the study To analyse the off-label use of drugs on a paediatric ward in Germany, and to identify domains of pharmacotherapy with the highest need for research concerning off-label use in children. Setting A prospective observational study was conducted on a paediatric ward in Duesseldorf in Germany between January and June 2006. Method Data about patients, diagnoses and prescribed drugs were collected from the prescription records and the discharge letters. Diagnoses were classified in groups by means of the International Classification of Diseases. Drugs were grouped according to the Anatomical Therapeutic Chemical Classification system. We compared the off-label prescriptions with those on the list of paediatric needs and priority list established by the European Medicines Agency (EMEA). Main outcome measure Off-label use was defined due to age, indication, route of application and dose. Results The study included 417 patients. We analysed 1,812 prescriptions representing 211 different drugs. In total, 253 patients (61%) received at least one off-label prescription. Of all analysed prescriptions, 553 (31%) were off-label. The percentage of off-label prescriptions among the five most frequently prescribed drug groups were as follows: 60% cardiovascular drugs (CV: 129/216), 42% anti-infectives (AI: 190/449), 30% drugs for respiratory system (RS: 100/335), 25% drugs for alimentary tract and metabolism (AM: 67/269) and 3% analgesics and antipyretics (AA: 8/264); with 17 drugs, the cardiovascular drugs also showed the highest number of different off-label prescribed drugs due to age: AI: 14; AM: 11; RS: 5; AA: 1. In addition, there was a nearly complete overlap between the identified off-label prescriptions in cardiovascular drugs and those listed by the EMEA to be prioritized for urgent research in Europe. ConclusionCardiovascular drugs are a domain of pharmacotherapy, with a large need for research in paediatrics. The results of our study can guide the researcher to future trials on off-label prescriptions such as cardiovascular drugs, especially due to the fact that the identified off-label prescribed drugs in this group are also mentioned by the EMEA to be prioritized for paediatric research.

Receptor mechanisms involved in the 5‐HT‐induced inotropic action in the rat isolated atrium

1 The effects of 5‐hydroxytryptamine (5‐HT) in rat cardiac preparations were studied. 5‐HT up to 10 μM failed to affect contractility in papillary muscles. However, in electrically driven (1 Hz) left atria 5‐HT exerted a positive inotropic effect that started at 1 μM and attained its maximum at 10 μM (312±50% of predrug value, n=8). 2 5‐HT 10 μM stimulated the content of inositol‐1,4,5‐trisphosphate but not of cyclic AMP in rat left atria. 3 Plasma and serum levels of 5‐HT amounted to about 0.3 μM and 15 μM, respectively. 4 The selective 5‐HT4 receptor antagonists GR 125487 (10 nM and 1 μM) and SB 203186 (1 μM) did not attenuate the positive inotropic effect of 5‐HT in rat left atria. In contrast, the 5‐HT2 receptor antagonist ketanserin (5 nM, 50 nM, 1 μM) resulted in a concentration‐dependent diminution of the positive inotropic effect of 5‐HT in rat left atria. 5 Reverse transcriptase polymerase chain reaction with specific primers detected mRNA of the 5‐HT2A receptor in rat atria and ventricles, while expression of the 5‐HT4 receptor was confined to atria. 6 It is suggested that the positive inotropic effect of 5‐HT in electrically driven rat left atria is mediated by ketanserin‐sensitive 5‐HT2A receptors and not through 5‐HT4 receptors.

Levels of brain natriuretic peptide in children with right ventricular overload due to congenital cardiac disease.

OBJECTIVE To evaluate the role of the concentration of brain natriuretic peptide in the plasma, and its correlation with haemodynamic right ventricular parameters, in children with overload of the right ventricle due to congenital cardiac disease. METHODS We studied 31 children, with a mean age of 4.8 years, with volume or pressure overload of the right ventricle caused by congenital cardiac disease. Of the patients, 19 had undergone surgical biventricular correction of tetralogy of Fallot, 11 with pulmonary stenosis and 8 with pulmonary atresia, and 12 patients were studied prior to operations, 7 with atrial septal defects and 5 with anomalous pulmonary venous connections. We measured brain natriuretic peptide using Triage(R), from Biosite, United States of America. We determined end-diastolic pressures of the right ventricle, and the peak ratio of right to left ventricular pressures, by cardiac catheterization and correlated them with concentrations of brain natriuretic peptide in the plasma. RESULTS The mean concentrations of brain natriuretic peptide were 87.7, with a range from 5 to 316, picograms per millilitre. Mean end-diastolic pressure in the right ventricle was 5.6, with a range from 2 to 10, millimetres of mercury, and the mean ratio of right to left ventricular pressure was 0.56, with a range from 0.24 to 1.03. There was a positive correlation between the concentrations of brain natriuretic peptide and the ratio of right to left ventricular pressure (r equal to 0.7844, p less than 0.0001) in all patients. These positive correlations remained when the children with tetralogy of Fallot, and those with atrial septal defects or anomalous pulmonary venous connection, were analysed as separate groups. We also found a weak correlation was shown between end-diastolic right ventricular pressure and concentrations of brain natriuretic peptide in the plasma (r equal to 0.5947, p equal to 0.0004). CONCLUSION There is a significant correlation between right ventricular haemodynamic parameters and concentrations of brain natriuretic peptide in the plasma of children with right ventricular overload due to different types of congenital cardiac disease. The monitoring of brain natriuretic peptide may provide a non-invasive and safe quantitative follow up of the right ventricular pressure and volume overload in these patients.

Utility of N-terminal brain natriuretic peptide plasma concentrations in comparison to lactate and troponin in children with congenital heart disease following open-heart surgery

We conducted a prospective study in a pediatric cardiac intensive care unit in order to determine the diagnostic value of N-terminal brain natriuretic peptide (N-BNP) plasma concentration in the perioperative care of children with congenital heart disease (CHD). N-BNP plasma concentrations were determined by using a validated enzyme immunoassay. We measured N-BNP the day before surgery and up to 15 days postoperatively in 23 children (age range, 0.25–11 years) undergoing cardiac surgery due to various CHDs. Supply and duration of catecholamines, vasodilators, and respiratory therapy were determined and correlated to N-BNP. In addition, troponin T (TnT) and arterial Lactat (aL) concentrations were measured simultaneously. We found a significant correlation between preoperative and maximal N-BNP levels and dosage of vasodilators (r = 0.41, p < 0.02 and r = 0.83, p < 0.01, respectively). Maximal TnT and aL levels were not correlated to dosage of vasodilators. The dosage and duration of catecholamines, the duration of respiratory therapy, and the plasma concentration of TnT and aL were not correlated to pre- or perioperative N-BNP. Maximal TnT and aL levels were correlated to duration (r = 0.53, p < 0.01 and r = 0.48, p < 0.02) and dosage (r = 0.52, p < 0.02 and r = 0.60, p < 0.01) of catecholamines and duration of respiratory therapy (r = 0.57, p < 0.01 and r = 0.50, p < 0.02). As recent studies show, N-BNP appears to be a powerful neurohumoral indicator of ventricular function and prognosis for guiding therapy in the outpatient department or for discriminating cardiac from noncardiac symptoms. In contrast, the value of N-BNP for guiding perioperative therapy in pediatric cardiac intensive care units is limited.