Extrapolation of Efficacy from Adults to Pediatric Patients of Drugs for Treatment of Partial Onset Seizures: A Regulatory Perspective.

The US Food and Drug Administration (FDA) has concluded that the efficacy of drugs approved for the treatment of partial onset seizures (POS) in adults can be extrapolated to pediatric patients 1 month of age and above and that independent efficacy trials in this pediatric population are no longer needed. This paper focuses on the dosing, pharmacokinetic (PK), exposure-response, and clinical information that were leveraged from the approved drugs for the treatment of POS to conduct analyses that supported extrapolation of efficacy in pediatric patients. Clinical data from trials for eight drugs (levetiracetam, oxcarbazepine, topiramate, lamotrigine, gabapentin, perampanel, tiagabine, and vigabatrin) approved in both adults and pediatric patients for the treatment of POS were analyzed. Comparisons of exposures at approved doses, placebo response, and model-based exposure-response relationships were performed. Based on disease similarity, similar response to intervention, and similar exposure-response relationships in adults and pediatric patients, it was concluded that extrapolation of efficacy in pediatric patients aged 1 month and above is acceptable. PK analysis to determine pediatric dose and regimens that provide drug exposure similar to that known to be effective in adult patients with POS will be required, along with long-term open-label safety data in pediatric patients.

Approaches to Dose Finding in Neonates, Illustrating the Variability between Neonatal Drug Development Programs.

Drug dosing in neonates should be based on integrated knowledge concerning the disease to be treated, the physiological characteristics of the neonate, and the pharmacokinetics (PK) and pharmacodynamics (PD) of a given drug. It is critically important that all sources of information be leveraged to optimize dose selection for neonates. Sources may include data from adult studies, pediatric studies, non-clinical (juvenile) animal models, in vitro studies, and in silico models. Depending on the drug development program, each of these modalities could be used to varying degrees and with varying levels of confidence to guide dosing. This paper aims to illustrate the variability between neonatal drug development programs for neonatal diseases that are similar to those seen in other populations (meropenem), neonatal diseases related but not similar to pediatric or adult populations (clopidogrel, thyroid hormone), and diseases unique to neonates (caffeine, surfactant). Extrapolation of efficacy from older children or adults to neonates is infrequently used. Even if a disease process is similar between neonates and children or adults, such as with anti-infectives, additional dosing and safety information will be necessary for labeling, recognizing that dosing in neonates is confounded by maturational PK in addition to body size.

Extrapolation of Adult Efficacy to Pediatric Patients With Chemotherapy-Induced Nausea and Vomiting.

Chemotherapy-induced nausea and vomiting (CINV) is a common treatment-related adverse event that negatively impacts the quality of life of cancer patients. During pediatric drug development, extrapolation of efficacy from adult to pediatric populations is a pathway that can minimize the exposure of children to unnecessary clinical trials, improve efficiency, and increase the likelihood of success in obtaining a pediatric indication. The acceptability of the use of extrapolation depends on a series of evidence-based assumptions regarding the similarity of disease, response to intervention, and exposure-response relationships between adult and pediatric patients. This study evaluated publicly available summaries of data submitted to the US Food and Drug Administration for drugs approved for CINV to assess the feasibility of extrapolation for future development programs. Extracted data included trial design, emetogenic potential of chemotherapy, primary end points, participant enrollment criteria, and antiemetic pharmacokinetics. Adult and pediatric clinical trial designs for assessment of efficacy and safety shared key design elements. Antiemetic drugs found to be efficacious in adults were also efficacious in pediatric patients. Systemic drug concentrations at approved doses were similar for ondansetron, granisetron, and aprepitant, but an exposure-response analysis of palonosetron in children suggested that higher palonosetron systemic exposure is necessary for the prevention of CINV in the pediatric population. For 5-hydroxytryptamine-3 and neurokinin-1 receptor antagonist antiemetic drugs, efficacy in adults predicts efficacy in children, supporting the extrapolation of effectiveness of an antiemetic product in children from adequate and well-controlled studies in adult patients with CINV.

Model-Informed Drug Discovery and Development: Current Industry Good Practice and Regulatory Expectations and Future Perspectives.

Good practices around model-informed drug discovery and development (MID3) aim to improve the implementation, standardization, and acceptance of these approaches within drug development and regulatory review. A survey targeted to clinical pharmacology and pharmacometric colleagues across industry, the US Food and Drug Administration (FDA), and the European Medicines Agency (EMA) was conducted to understand current and future roles of MID3. The documented standards were generally affirmed as a "good match" to current industry practice and regulatory expectations, with some identified gaps that are discussed. All have seen at least a "modest" step forward in MID3 implementation associated with greater organizational awareness and share the expectation for a future wider use and impact. The priority within organizations was identified as a limitation with respect to the future of MID3. Finally, potential solutions, including a global overarching MID3 regulatory guideline, to facilitate greater acceptance by industry and regulatory decision makers are discussed.

Exposure Matching for Extrapolation of Efficacy in Pediatric Drug Development.

During drug development, matching adult systemic exposures of drugs is a common approach for dose selection in pediatric patients when efficacy is partially or fully extrapolated. This is a systematic review of approaches used for matching adult systemic exposures as the basis for dose selection in pediatric trials submitted to the US Food and Drug Administration (FDA) between 1998 and 2012. The trial design of pediatric pharmacokinetic (PK) studies and the pediatric and adult systemic exposure data were obtained from FDA publicly available databases containing reviews of pediatric trials. Exposure-matching approaches that were used as the basis for pediatric dose selection were reviewed. The PK data from the adult and pediatric populations were used to quantify exposure agreement between the 2 patient populations. The main measures were the pediatric PK studies' trial design elements and drug systemic exposures (adult and pediatric). There were 31 products (86 trials) with full or partial extrapolation of efficacy with an available PK assessment. Pediatric exposures had a range of mean Cmax and AUC ratios (pediatric/adult) of 0.63 to 4.19 and 0.36 to 3.60, respectively. Seven of the 86 trials (8.1%) had a predefined acceptance boundary used to match adult exposures. The key PK parameter was consistently predefined for antiviral and anti-infective products. Approaches to match exposure in children and adults varied across products. A consistent approach for systemic exposure matching and evaluating pediatric PK studies is needed to guide future pediatric trials.

Role of Quantitative Clinical Pharmacology in Pediatric Approval and Labeling.

Dose selection is one of the key decisions made during drug development in pediatrics. There are regulatory initiatives that promote the use of model-based drug development in pediatrics. Pharmacometrics or quantitative clinical pharmacology enables development of models that can describe factors affecting pharmacokinetics and/or pharmacodynamics in pediatric patients. This manuscript describes some examples in which pharmacometric analysis was used to support approval and labeling in pediatrics. In particular, the role of pharmacokinetic (PK) comparison of pediatric PK to adults and utilization of dose/exposure-response analysis for dose selection are highlighted. Dose selection for esomeprazole in pediatrics was based on PK matching to adults, whereas for adalimumab, exposure-response, PK, efficacy, and safety data together were useful to recommend doses for pediatric Crohn's disease. For vigabatrin, demonstration of similar dose-response between pediatrics and adults allowed for selection of a pediatric dose. Based on model-based pharmacokinetic simulations and safety data from darunavir pediatric clinical studies with a twice-daily regimen, different once-daily dosing regimens for treatment-naïve human immunodeficiency virus 1-infected pediatric subjects 3 to <12 years of age were evaluated. The role of physiologically based pharmacokinetic modeling (PBPK) in predicting pediatric PK is rapidly evolving. However, regulatory review experiences and an understanding of the state of science indicate that there is a lack of established predictive performance of PBPK in pediatric PK prediction. Moving forward, pharmacometrics will continue to play a key role in pediatric drug development contributing toward decisions pertaining to dose selection, trial designs, and assessing disease similarity to adults to support extrapolation of efficacy.

The IQ-CSRC prospective clinical Phase 1 study: "Can early QT assessment using exposure response analysis replace the thorough QT study?".

A collaboration between the Consortium for Innovation and Quality in Pharmaceutical Development and the Cardiac Safety Research Consortium has been formed to design a clinical study in healthy subjects demonstrating that the thorough QT (TQT) study can be replaced by robust ECG monitoring and exposure-response (ER) analysis of data generated from First-in-Man single ascending dose (SAD) studies. Six marketed drugs with well-characterized QTc effects were identified in discussions with FDA; five have caused QT prolongation above the threshold of regulatory concern. Twenty healthy subjects will be enrolled in a randomized, placebo-controlled study designed with the intent to have similar power to exclude small QTc effects as a SAD study. Two doses (low and high) of each drug will be given on separate, consecutive days to 9 subjects. Six subjects will receive placebo. Data will be analyzed using linear mixed-effects ER models. Criteria for QT-positive drugs will be the demonstration of an upper bound (UB) of the 2-sided 90% confidence interval (CI) of the projected QTc effect at the peak plasma level of the lower dose above the threshold of regulatory concern (currently 10 ms) and a positive slope of ER relationship. The criterion for QT-negative drug will be an UB of the CI of the projected QTc effect of the higher dose <10 ms. It is expected that a successful outcome in this study will provide evidence supporting replacement of the TQT study with ECG assessments in standard early clinical development studies for a new chemical entity.

Adolescent dosing and labeling since the Food and Drug Administration Amendments Act of 2007.

IMPORTANCE: During pediatric drug development, dedicated pharmacokinetic studies are generally performed in all relevant age groups to support dose selection for subsequent efficacy trials. To our knowledge, no previous assessments regarding the need for an intensive pharmacokinetic study in adolescents have been performed. OBJECTIVES: To compare U.S. Food and Drug Administration (FDA)-approved adult and adolescent drug dosing and to assess the utility of allometric scaling for the prediction of drug clearance in the adolescent population. DESIGN: Adult and adolescent dosing and drug clearance data were obtained from FDA-approved drug labels and publicly available databases containing reviews of pediatric trials submitted to the FDA. Dosing information was compared for products with concordant indications for adolescent and adult patients. Adolescent drug clearance was predicted from adult pharmacokinetic data by using allometric scaling and compared with observed values. MAIN OUTCOMES AND MEASURES: Adolescent and adult dosing information and drug clearance. RESULTS: There were 126 unique products with pediatric studies submitted to the FDA since the FDA Amendments Act of 2007, of which 92 had at least 1 adolescent indication concordant with an adult indication. Of these 92 products, 87 (94.5%) have equivalent dosing for adults and adolescent patients. For 18 of these 92 products, a minimum weight or body surface area threshold is recommended for adolescents to receive adult dosing. Allometric scaling predicted adolescent drug clearance with an overall mean absolute percentage error of 17.0%. CONCLUSIONS AND RELEVANCE: Approved adult and adolescent drug dosing is equivalent for 94.5% of products with an adolescent indication studied since the FDA Amendments Act of 2007. Allometric scaling may be a useful tool to avoid unnecessary dedicated pharmacokinetic studies in the adolescent population during pediatric drug development, although each development program in adolescents requires a full discussion of drug dosing with the FDA.

Knowledge management for efficient quantitative analyses during regulatory reviews.

Knowledge management comprises the strategies and methods employed to generate and leverage knowledge within an organization. This report outlines the activities within the Division of Pharmacometrics at the US FDA to effectively manage knowledge with the ultimate goal of improving drug development and advancing public health. The infrastructure required for pharmacometric knowledge management includes provisions for data standards, queryable databases, libraries of modeling tools, archiving of analysis results and reporting templates for effective communication. Two examples of knowledge management systems developed within the Division of Pharmacometrics are used to illustrate these principles. The benefits of sound knowledge management include increased productivity, allowing reviewers to focus on research questions spanning new drug applications, such as improved trial design and biomarker development. The future of knowledge management depends on the collaboration between the FDA and industry to implement data and model standards to enhance sharing and dissemination of knowledge.

Impact of pharmacometric analyses on new drug approval and labelling decisions: a review of 198 submissions between 2000 and 2008.

Pharmacometric analyses have become an increasingly important component of New Drug Application (NDA) and Biological License Application (BLA) submissions to the US FDA to support drug approval, labelling and trial design decisions. Pharmacometrics is defined as a science that quantifies drug, disease and trial information to aid drug development, therapeutic decisions and/or regulatory decisions. In this report, we present the results of a survey evaluating the impact of pharmacometric analyses on regulatory decisions for 198 submissions during the period from 2000 to 2008. Pharmacometric review of NDAs included independent, quantitative analyses by FDA pharmacometricians, even when such analysis was not conducted by the sponsor, as well as evaluation of the sponsor's report. During 2000-2008, the number of reviews with pharmacometric analyses increased dramatically and the number of reviews with an impact on approval and labelling also increased in a similar fashion. We also present the impact of pharmacometric analyses on selection of paediatric dosing regimens, approval of regimens that had not been directly studied in clinical trials and provision of evidence of effectiveness to support a single pivotal trial. Case studies are presented to better illustrate the role of pharmacometric analyses in regulatory decision making.

Efficacy of pulmonary insulin delivery in diabetic rats: use of a model-based approach in the evaluation of insulin powder formulations.

The potential of N-trimethyl chitosan (TMC) with two degrees of quaternization (DQ), TMC20 (DQ 20%, as a mucoadhesive) and TMC60 (DQ 60%, as a mucoadhesive and a permeation enhancer), and dextran (as a non-mucoadhesive and non-permeation enhancer) microparticles as carriers for pulmonary delivery of insulin was studied in diabetic rats. The impact of the powder formulation on insulin bioavailability and its pharmacological effect was evaluated using a population pharmacokinetic-pharmacodynamic (PKPD) model. Insulin-loaded microparticles were prepared by a supercritical fluid (SCF) drying technique. They had a median volume diameter and median volume aerodynamic diameter of about 6-10 microm and 4 microm, respectively. The PK of insulin in the diabetic rats was analyzed by a one-compartment disposition model and the PD was described by the minimal model of glucose disappearance. The bioavailability of the pulmonarily administered dextran-, TMC20- and TMC60-insulin microparticles relative to subcutaneously (SC) administered insulin, was 0.48, 0.59 and 0.95, respectively. Histological examinations of the rats' lungs did not show any local adverse reactions after single administration of insulin powders. The pharmacodynamic model could describe the insulin-glucose relationship and pharmacodynamic efficiency of insulin formulations, which was about 0.6(*)10(-5) ml/microU, irrespective of the formulations. The current findings suggest that TMC microparticles are a promising vehicle for pulmonary delivery of insulin.

Use of oral glucose minimal model-derived index of insulin sensitivity in subjects with early type 1 diabetes mellitus.

Insulin resistance plays an important role during various stages of the type 1 diabetes mellitus disease process. Unfortunately, many of the techniques used to measure insulin sensitivity are experimentally laborious and time-consuming and are thus impractical for larger clinical and population studies. Therefore, in this study, we obtain estimates of insulin sensitivity from a simpler experiment, the oral glucose tolerance test (OGTT), and compare them with those from a frequently sampled intravenous glucose tolerance test (FSIGT) in a population of subjects defined as having early type 1 diabetes mellitus (abnormal 2-hour glucose on OGTT) and a group of healthy controls. A total of 19 subjects were studied. Eight antibody-positive first- or second-degree relatives of patients with type 1 diabetes mellitus and 11 healthy controls underwent both a 3-hour OGTT and an insulin-modified FSIGT on separate days. Indices of insulin sensitivity (SI) were estimated from the recently derived oral glucose minimal model and the original minimal model of glucose kinetics for the OGTT and FSIGT, respectively. Estimates of SI from the OGTT correlated closely with those from the FSIGT in both early type 1 diabetes mellitus (rs=0.76, P = .04) and healthy control (rs = 0.67, P = .03) populations. This preliminary study demonstrates the usefulness of OGTT-derived estimates of insulin sensitivity in an early type 1 diabetes mellitus population. Given the simplicity of the OGTT relative to the traditional methods of measuring SI, the oral glucose minimal model may be appropriate for large population studies and clinical trials.

Population approaches to estimate minimal model indexes of insulin sensitivity and glucose effectiveness using full and reduced sampling schedules.

The intravenous glucose tolerance test (IVGTT) interpreted with the minimal model provides individual indexes of insulin sensitivity (S(I)) and glucose effectiveness (S(G)). In population studies, the traditional approach, the standard two-stage (STS) method, fails to account for uncertainty in individual estimates, resulting in an overestimation of between-subject variability. Furthermore, in the presence of reduced sampling and/or insulin resistance, individual estimates may be unobtainable, biasing population information. Therefore, we investigated the use of two population approaches, the iterative two-stage (ITS) method and nonlinear mixed-effects modeling (NM), in a population (n = 235) of insulin-sensitive and insulin-resistant subjects under full (FSS, 33 samples) and reduced [RSS(240-min), 13 samples and RSS(180-min), 12 samples] IVGTT sampling schedules. All three population methods gave similar results with the FSS. Using RSS(240), the three methods gave similar results for S(I), but S(G) population means were overestimated. With RSS(180), S(I) and S(G) population means were higher for all three methods compared with their FSS counterparts. NM estimated similar between-subject variability (19% S(G), 53% S(I)) with RSS(180), whereas ITS showed regression to the mean for S(G) (0.01% S(G), 56% S(I)) and STS provided larger population variability in S(I) (29% S(G), 91% S(I)). NM provided individual estimates for all subjects, whereas the two-stage methods failed in 16-18% of the subjects using RSS(180) and 6-14% using RSS(240). We conclude that population approaches, specifically NM, are useful in studies with a sparsely sampled IVGTT ( approximately 12 samples) of short duration ( approximately 3 h) and when individual parameter estimates in all subjects are desired.

Paradoxical role of cytochrome P450 3A in the bioactivation and clinical effects of levo-alpha-acetylmethadol: importance of clinical investigations to validate in vitro drug metabolism studies.

OBJECTIVE: Levo-alpha-acetylmethadol (LAAM, levacetylmethadol) is a long-acting opioid agonist used for the prevention of opioid withdrawal. LAAM undergoes sequential N-demethylation to norLAAM and dinorLAAM, which are more potent and longer-acting than LAAM. Hepatic and intestinal microsomal N-demethylation in vitro is catalysed mainly by cytochrome P450 (CYP) 3A4; however, the role of CYP3A in LAAM disposition in humans in vivo is unknown. This investigation tested the hypothesis that CYP3A induction (or inhibition) would increase (or decrease) LAAM metabolism and bioactivation and, thus, clinical effects. It also related changes in LAAM disposition during enzyme inhibition or induction to any changes in pharmacological effect. METHODS: Healthy volunteers (n = 13) completed the three-way, randomised, balanced crossover study. Subjects received oral LAAM (0.25 mg/kg) after CYP3A induction (rifampicin [rifampin]), inhibition (troleandomycin) or nothing (controls). Plasma and urine LAAM, norLAAM and dinorLAAM were determined by electrospray high-performance liquid chromatography/mass spectrometry (HPLC/MS). Dark-adapted pupil diameter change from baseline (miosis) was the LAAM effect measure. Results were analysed by noncompartmental methods and by a combined pharmacokinetic/pharmacodynamic model. RESULTS: Compared with controls, CYP3A induction (or inhibition) decreased (or increased) plasma LAAM concentrations and mean area under the plasma concentration-time curve from time zero to infinity (AUC(infinity) 199 +/- 91 [control] versus 11.3 +/- 4.0 [rifampicin] and 731 +/- 229 ng . h/mL [troleandomycin]; p < 0.05), and increased (or decreased) median formation clearances of norLAAM (1740 versus 14 100 and 302 mL/h/kg; p < 0.05) and dinorLAAM (636 versus 7840 and 173 mL/h/kg; p < 0.05). Surprisingly, however, CYP3A induction (or inhibition) decreased (or increased) mean plasma metabolite AUC from 0 to 96 hours (AUC(96)) [norLAAM + dinorLAAM] (859 +/- 241 versus 107 +/- 48 and 1185 +/- 179 ng . h/mL; p < 0.05) and clinical effects (mean miosis AUC(96) 128 +/- 40 versus 22.5 +/- 14.9 and 178 +/- 81 mm . h; p < 0.05). Clinical effects were best correlated with plasma norLAAM concentrations. CONCLUSION: CYP3A mediates human LAAM N-demethylation and bioactivation to norLAAM and dinorLAAM in vivo. Paradoxically, however, CYP3A induction decreased and inhibition increased LAAM active metabolite concentrations and clinical effects. This suggests a CYP3A-mediated metabolic pathway leading to inactive metabolites, which predominates over CYP3A-dependent bioactivation. These results highlight the need for clinical investigations to validate in vitro drug metabolism studies.

Integrated model of hepatic and peripheral glucose regulation for estimation of endogenous glucose production during the hot IVGTT.

We have developed a new model to describe endogenous glucose kinetics during a labeled (hot) intravenous glucose tolerance test (IVGTT) to derive a time profile of endogenous glucose production (EGP). We reanalyzed data from a previously published study (P. Vicini, J. J. Zachwieja, K. E. Yarasheski, D. M. Bier, A. Caumo, and C. Cobelli. Am J Physiol Endocrinol Metab 276: E285-E294, 1999), in which insulin-modified [6,6-2H2]glucose-labeled IVGTTs (0.33 g/kg glucose) were performed in 10 normal subjects. In addition, a second tracer ([U-13C]glucose) was infused in a variable rate to clamp the endogenous glucose tracer-to-tracee ratio (TTR). Our new model describing endogenous glucose kinetics was incorporated into the two-compartment hot minimal-model structure. The model gave estimates of glucose effectiveness [1.54 +/- 0.31 (SE) ml x kg(-1) x min(-1)], insulin sensitivity (37.74 +/- 5.23 10(4) dl x kg(-1) x min(-1) x microU(-1) x ml), and a new parameter describing the sensitivity of EGP to the inhibitory effect of insulin (IC50 = 0.0195 +/- 0.0046 min(-1)). The model additionally provided an estimate of the time course of EGP showing almost immediate inhibition, followed by a secondary inhibitory effect caused by infusion of insulin, and a large overshoot as EGP returns to its basal value. Our estimates show very good agreement with those obtained via deconvolution and the model-independent TTR clamp technique. These results suggest that the new integrated model can serve as a simple one-step approach to obtain metabolic indexes while also providing a parametric description of EGP.