Beyond biomarkers: an opportunity to address the 'pharmacodynamic gap' in pediatric drug development

A New Framework to Implement Model-Informed Dosing in Clinical Guidelines: Piperacillin and Amikacin as Proof of Concept

Background: Modeling and simulation is increasingly used to study pediatric pharmacokinetics, but clinical implementation of age-appropriate doses lags behind. Therefore, we aimed to develop model-informed doses using published pharmacokinetic data and a decision framework to adjust dosing guidelines based on these doses, using piperacillin and amikacin in critically ill children as proof of concept.

Methods: Piperacillin and amikacin pharmacokinetic models in critically ill children were extracted from literature. Concentration-time profiles were simulated for various dosing regimens for a virtual PICU patient dataset, including the current DPF dose and doses proposed in the studied publications. Probability of target attainment (PTA) was compared between the different dosing regimens. Next, updated dosing recommendations for the DPF were proposed, and evaluated using a new framework based on PK study quality and benefit-risk analysis of clinical implementation.

Results: Three studies for piperacillin (critically ill children) and one for amikacin (critically ill pediatric burn patients) were included. Simulated concentration-time profiles were performed for a virtual dataset of 307 critically ill pediatric patients, age range 0.1–17.9 y. PTA for unbound piperacillin trough concentrations >16 mg/L was >90% only for continuous infusion regimens of 400 mg/kg/day vs. 9.7% for the current DPF dose (80 mg/kg/6 h, 30 min infusion). Amikacin PTA was >90% with 20 mg/kg/d, higher than the PTA of the DPF dose of 15 mg/kg/d (63.5%). Using our new decision framework, altered DPF doses were proposed for piperacillin (better PTA with loading dose plus continuous infusion), but not for amikacin (studied and target population were not comparable and risk for toxicity with higher dose).

Conclusions: We show the feasibility to develop model-informed dosing guidelines for clinical implementation using existing pharmacokinetic data. This approach could complement literature and consensus-based dosing guidelines for off-label drugs in the absence of stronger evidence to support pediatricians in daily practice.

Useful pharmacodynamic endpoints in children: selection, measurement, and next steps

Pharmacodynamic (PD) endpoints are essential for establishing the benefit-to-risk ratio for therapeutic interventions in children and neonates. This article discusses the selection of an appropriate measure of response, the PD endpoint, which is a critical methodological step in designing pediatric efficacy and safety studies. We provide an overview of existing guidance on the choice of PD endpoints in pediatric clinical research. We identified several considerations relevant to the selection and measurement of PD endpoints in pediatric clinical trials, including the use of biomarkers, modeling, compliance, scoring systems, and validated measurement tools. To be useful, PD endpoints in children need to be clinically relevant, responsive to both treatment and/or disease progression, reproducible, and reliable. In most pediatric disease areas, this requires significant validation efforts. We propose a minimal set of criteria for useful PD endpoint selection and measurement. We conclude that, given the current heterogeneity of pediatric PD endpoint definitions and measurements, both across and within defined disease areas, there is an acute need for internationally agreed, validated, and condition-specific pediatric PD endpoints that consider the needs of all stakeholders, including healthcare providers, policy makers, patients, and families.

The clinical translation gap in child health exercise research: a call for disruptive innovation

In children, levels of play, physical activity, and fitness are key indicators of health and disease and closely tied to optimal growth and development. Cardiopulmonary exercise testing (CPET) provides clinicians with biomarkers of disease and effectiveness of therapy, and researchers with novel insights into fundamental biological mechanisms reflecting an integrated physiological response that is hidden when the child is at rest. Yet the growth of clinical trials utilizing CPET in pediatrics remains stunted despite the current emphasis on preventative medicine and the growing recognition that therapies used in children should be clinically tested in children. There exists a translational gap between basic discovery and clinical application in this essential component of child health. To address this gap, the NIH provided funding through the Clinical and Translational Science Award (CTSA) program to convene a panel of experts. This report summarizes our major findings and outlines next steps necessary to enhance child health exercise medicine translational research. We present specific plans to bolster data interoperability, improve child health CPET reference values, stimulate formal training in exercise medicine for child health care professionals, and outline innovative approaches through which exercise medicine can become more accessible and advance therapeutics across the broad spectrum of child health.

Is indirect hyperbilirubinemia a useful biomarker of reduced propofol clearance in neonates?

AIM

Large interindividual variability in neonatal propofol clearance is documented which, in part, can be explained by postmenstrual age (PMA) and postnatal age (PNA). We aimed to document whether indirect bilirubin, instead of or in addition to PNA, could improve predictability of propofol clearance and serve as a useful biomarker of reduced propofol clearance in neonates.

METHODS

Indirect serum bilirubin was introduced as a dichotomous or continuous variable (both age-normalized) in a previously developed three-compartment pharmacokinetic model, based on 235 concentration-time points obtained in 25 neonates after single bolus administration of propofol. For pharmacokinetic analysis, nonlinear mixed effect modeling 6.2 was used.

RESULTS

The covariates PMA and PNA explained 67% of the interindividual variability compared with 45% in the model with PMA and bilirubin.

CONCLUSION

Age, reflected by PMA and PNA, is a more relevant clinical predictor of neonatal propofol clearance compared with PMA and raised indirect hyperbilirubinemia.

Clinical pharmacological studies in children: From exploratory towards confirmation driven methodology

Just like children are not small adults, pediatric studies are not just subgroup-adult studies. Clinical pharmacology aims to predict these effects based on drug, population and/or patient-specific pharmacokinetics (concentration-time profiles) and -dynamics (concentration-effect profile). The most essential characteristics of childhood are growth and maturation. Both phenomena are most prominent during infancy making the claim that “an infant is not just a small child” as relevant compared to the paradigm that “a child is not just a small adult”. From a clinical pharmacology perspective, the consequence of such a dynamic setting is extensive variability throughout childhood in both the pharmacokinetics and pharmacodynamics. Trial design probably has impact on recruitment to an even greater extent compared to adult studies. In general, if a study is designed well, with a clear clinical question with which parents and children can identify, they are likely to consider participation. Open communication with all stakeholders involved will most likely result in ethically correct, practically feasible, scientifically sound, and economical reasonable studies to provide children with the appropriate treatment. From an academic perspective, feasibility, relevance, applicability and costs of clinical pharmacological studies in children can be significantly improved by new sampling concepts (e.g., saliva, urine, dried spot blood) and the systematic introduction of already known information into the trial design through model based pediatric drug development, that mainly affect feasibility of pharmacokinetic studies. In contrast, for the pharmacodynamic part of pediatric studies, development and validation of population specific biomarkers or robust outcome variables is urgently needed.