Dosing in Children: A Critical Review of the Pharmacokinetic Allometric Scaling and Modelling Approaches in Paediatric Drug Development and Clinical Settings

Personalized metabolic whole-body models for newborns and infants predict growth and biomarkers of inherited metabolic diseases

Comprehensive whole-body models (WBMs) accounting for organ-specific dynamics have been developed to simulate adult metabolism, but such models do not exist for infants. Here, we present a resource of 360 organ-resolved, sex-specific models of newborn and infant metabolism (infant-WBMs) spanning the first 180 days of life. These infant-WBMs were parameterized to represent the distinct metabolic characteristics of newborns and infants, including nutrition, energy requirements, and thermoregulation. We demonstrate that the predicted infant growth was consistent with the recommendation by the World Health Organization. We assessed the infant-WBMs' reliability and capabilities for personalization by simulating 10,000 newborns based on their blood metabolome and birth weight. Furthermore, the infant-WBMs accurately predicted changes in known biomarkers over time and metabolic responses to treatment strategies for inherited metabolic diseases. The infant-WBM resource holds promise for personalized medicine, as the infant-WBMs could be a first step to digital metabolic twins for newborn and infant metabolism.

Utility of life stage-specific chemical risk assessments based on New Approach Methodologies (NAMs)

The safety assessments for chemicals targeted for use or expected to be exposed to specific life stages, including infancy, childhood, pregnancy and lactation, and geriatrics, need to account for extrapolation of data from healthy adults to these populations to assess their human health risk. However, often adequate and relevant toxicity or pharmacokinetic (PK) data of chemicals in specific life stages are not available. For such chemicals, New Approach Methodologies (NAMs), such as physiologically based pharmacokinetic (PBPK) modeling, biologically based dose response (BBDR) modeling, in vitro to in vivo extrapolation (IVIVE), etc. can be used to understand the variability of exposure and effects of chemicals in specific life stages and assess their associated risk. A life stage specific PBPK model incorporates the physiological and biochemical changes associated with each life stage and simulates their impact on the absorption, distribution, metabolism, and elimination (ADME) of these chemicals. In our review, we summarize the parameterization of life stage models based on New Approach Methodologies (NAMs) and discuss case studies that highlight the utility of a life stage based PBPK modeling for risk assessment. In addition, we discuss the utility of artificial intelligence (AI)/machine learning (ML) and other computational models, such as those based on in vitro data, as tools for estimation of relevant physiological or physicochemical parameters and selection of model. We also discuss existing gaps in the available toxicological datasets and current challenges that need to be overcome to expand the utility of NAMs for life stage-specific chemical risk assessment.

Confirming the Suitability of a Gentamicin Dosing Strategy in Neonates Using the Population Pharmacokinetic Approach with Truncated Sampling Duration

(1) Background: Gentamicin is known to be nephrotoxic and ototoxic. Although gentamicin dosage guidelines have been established for preterm and term neonates, reports do show attainment of recommended peak concentrations but toxic gentamicin concentrations are common in this age group. (2) Methods: This was a prospective, observational study conducted in Namibia with 52 neonates. A dose of 5 mg/kg gentamicin was administered over 3-5 s every 24 h in combination with benzylpenicillin 100,000 IU/kg/12 h or ampicillin 50 mg/kg/8 h. Two blood samples were collected from each participant using a truncated pharmacokinetic sampling schedule. (3) Results: The one-compartment linear pharmacokinetic model best described the data. Birthweight, postnatal age, and white blood cell count were predictive of clearance (CL), while birthweight was predictive of volume (V). For the typical neonate (median weight 1.57 kg, median postnatal age 4 days (0.011 years), median log-transformed WBC of 2.39), predicted CL and V were 0.069 L/h and 0.417 L, respectively-similar to literature values. Simulated gentamicin concentrations varied with respect to postnatal age and bodyweight. (4) Conclusions: A 5 mg/kg/24 h dosage regimen yielded simulated gentamicin concentrations with respect to age and birthweight similar to those previously reported in the literature to be safe and efficacious, confirming its appropriateness.

The One Pill Can Kill Myth

ABSTRACT

"One Pill Can Kill" is a meme originating in the 1990s. This construct lists pharmaceuticals that have the alleged potential for fatality after the ingestion of a single pill by a toddler. However, its foundation is fundamentally flawed because it contravenes a basic principle of pediatric pharmacology, allometric scaling. Other than opioids, there are no literature examples of one pill killing a toddler. The negative outcome of the one pill can kill construct is inappropriate management manifested by over-referral of young children by poison centers to emergency departments for care, overly prolonged emergency department observation and needless hospital admissions. A more accurate construct is that one pill of anything other than opioids will not kill anybody with the caveat being that we are referring to regulated pharmaceuticals.

Animal-to-Human Dose Translation of ANTHRASIL for Treatment of Inhalational Anthrax in Healthy Adults, Obese Adults, and Pediatric Subjects

Anthrax Immune Globulin Intravenous (AIGIV [ANTHRASIL]), was developed for the treatment of toxemia associated with inhalational anthrax. It is a plasma product collected from individuals vaccinated with anthrax vaccine and contains antitoxin IgG antibodies against Bacillus anthracis protective antigen. A pharmacokinetic (PK) and exposure-response model was constructed to assess the PKs of AIGIV in anthrax-free and anthrax-exposed rabbits, non-human primates and anthrax-free humans, as well as the relationship between AIGIV exposure and survival from anthrax, based on available preclinical/clinical studies. The potential effect of anthrax on the PKs of AIGIV was evaluated and estimates of survival odds following administration of AIGIV protective doses with and without antibiotic co-treatment were established. As the developed PK model can simulate exposure of AIGIV in any species for any dosing scenario, the relationship between the predicted area under the concentration curve of AIGIV in humans and the probability of survival observed in preclinical studies was explored. Based on the simulation results, the intravenous administration of 420 U (units of potency as measured by validated Toxin Neutralization Assay) of AIGIV is expected to result in a > 80% probability of survival in more than 90% of the human population. Additional simulations suggest that exposure levels were similar in healthy and obese humans, and exposure in pediatrics is expected to be up to approximately seven-fold higher than in healthy adults, allowing for doses in pediatric populations that ranged from one to seven vials. Overall, the optimal human dose was justified based on the PK/pharmacodynamic (PD) properties of AIGIV in animals and model-based translation of PK/PD to predict human exposure and efficacy.

Physiologically Based Pharmacokinetic Modeling in Neonates: Current Status and Future Perspectives

Rational drug use in special populations is a clinical problem that doctors and pharma-cists must consider seriously. Neonates are the most physiologically immature and vulnerable to drug dosing. There is a pronounced difference in the anatomical and physiological profiles be-tween neonates and older people, affecting the absorption, distribution, metabolism, and excretion of drugs in vivo, ultimately leading to changes in drug concentration. Thus, dose adjustments in neonates are necessary to achieve adequate therapeutic concentrations and avoid drug toxicity. Over the past few decades, modeling and simulation techniques, especially physiologically based pharmacokinetic (PBPK) modeling, have been increasingly used in pediatric drug development and clinical therapy. This rigorously designed and verified model can effectively compensate for the deficiencies of clinical trials in neonates, provide a valuable reference for clinical research design, and even replace some clinical trials to predict drug plasma concentrations in newborns. This review introduces previous findings regarding age-dependent physiological changes and pathological factors affecting neonatal pharmacokinetics, along with their research means. The application of PBPK modeling in neonatal pharmacokinetic studies of various medications is also reviewed. Based on this, we propose future perspectives on neonatal PBPK modeling and hope for its broader application.

Opportunities and challenges of pharmacovigilance in special populations: a narrative review of the literature

The relatively new discipline of pharmacovigilance (PV) aims to monitor the safety of drugs throughout their evolution and is essential to discovering new drug risks. Due to their specific and complex physiology, children, pregnant women, and elderly adults are more prone to adverse drug reactions (ADRs). Additionally, the lack of clinical trial data exacerbates the challenges faced with pharmacotherapy in these populations. Elderly patients tend to have multiple comorbidities often requiring more extensive medication, which adds additional challenges for healthcare professionals (HCPs) in delivering safe and effective pharmacotherapy. Clinical trials often have inherent limitations, including insufficient sample size and limited duration of research; as some ADRs are attributed to long-term use of a drug, these may go undetected during the course of the trial. Therefore, the implementation of PV is key to insuring the safe and effective use of drugs in special populations. We conducted a thorough review of the scientific literature on PV systems across the European Union, the United States, and China. Our review focused on basic physiological characteristics, drug use, and PV for specific populations (children, pregnant women, and the elderly). This article aims to provide a reference for the development of follow-up policies and improvement of existing policies as well as provide insight into drug safety with respect to patients of special populations.

Application of Allometric Scaling and Salisbury Rule for the Prediction of Antimalarial Drugs for First-in-Pediatric Dose Selection

BACKGROUND

In pediatric drug development, the selection of first-in-pediatric dose is of immense importance. Generally, the pharmacokinetic information and a safe and efficacious dose of a drug in adults are already known and this information can then be used to select first-in-pediatric dose. The objective of this study was to predict the pediatric dose of antimalarial drugs and compare the predicted dose with the recommended dose.

METHODS

In this study, two simple methods to project a first-in-pediatric dose to initiate a clinical trial for antimalarial drugs were evaluated. These two methods were Salisbury Rule and allometric scaling. The predicted doses of antimalarial drugs by the two methods were compared with the observed doses recommended by the World Health Organization (WHO) or the US Food and Drug Administration (FDA).

RESULTS

In this study, 15 antimalarial drugs with 88 observations (different body weight groups) were evaluated. From allometric scaling, all 88 observations were within 0.5-1.5-fold and 0.7-1.3-fold prediction error. From Salisbury Rule, all 88 observations were within 0.5-1.5-fold and 86 observations were within 0.7-1.3-fold prediction error.

CONCLUSIONS

The proposed methods are simple and quite accurate in their predictive power. These methods can be developed on a spreadsheet or a calculator in a very short period of time and are applicable to first-in-pediatric clinical trials or even in a clinical setting.

Allometric Scaling of Testosterone Enanthate Pharmacokinetics to Adolescent Hypogonadal Males (IM and SC Administration)

Context

Intramuscular (IM) testosterone enanthate (TE) and testosterone pellets were US Food and Drug Administration approved before 1962 for pediatric use but not studied in controlled trials in adolescents.

Objective

An analysis using nonlinear mixed effect (NLME) modeling was designed to evaluate the adult pharmacokinetics (PK) of subcutaneous (SC) and IM TE. This model was used to simulate SC and IM TE administration in adolescents of different weight groups.

Methods

Data from adult male patients in a phase 2 trial were used to characterize the PK of TE using population PK modeling for SC and IM administration: Allometry was used to scale PK parameters from the adult model to simulate adolescent (aged 12 to < 18 years) serum testosterone levels at body weights of 30, 40, 50, and 60 kg after weekly, every-other-week (EOW), and monthly SC and IM administration of 12.5, 25, 50, 75, and 100 mg TE regimens.

Results

The final data set included 714 samples from 15 patients receiving 100 mg SC TE and 123 samples from 10 patients receiving 200 mg IM TE. In simulated populations, average serum concentration SC:IM ratios were 0.783, 0.776, and 0.757 at steady state for weekly, EOW, and monthly dosing groups, respectively. Simulated regimens of 12.5 mg SC TE monthly produced serum testosterone levels representative of early puberty and simulated pubertal stage progression following multiple subsequent testosterone dose increases.

Conclusion

SC TE administration achieved a testosterone exposure-response relationship similar to IM TE in simulated adolescent hypogonadal males, which may reduce size of fluctuations in serum T and related symptoms.

Estimation of Pediatric Dosage of Antimalarial Drugs, Using Pharmacokinetic and Physiological Approach

Most of the individuals who die of malaria in sub-Saharan Africa are children. It is, therefore, important for this age group to have access to the right treatment and correct dose. Artemether-lumefantrine is one of the fixed dose combination therapies that was approved by the World Health Organization to treat malaria. However, the current recommended dose has been reported to cause underexposure or overexposure in some children. The aim of this article was, therefore, to estimate the doses that can mimic adult exposure. The availability of more and reliable pharmacokinetic data is essential to accurately estimate appropriate dosage regimens. The doses in this study were estimated using the physiological information from children and some pharmacokinetic data from adults due to the lack of pediatric pharmacokinetic data in the literature. Depending on the approach that was used to calculate the dose, the results showed that some children were underexposed, and others were overexposed. This can lead to treatment failure, toxicity, and even death. Therefore, when designing a dosage regimen, it is important to know and include the distinctions in physiology at various phases of development that influence the pharmacokinetics of various drugs in order to estimate the dose in young children. The physiology at each time point during the growth of a child may influence how the drug is absorbed, gets distributed, metabolized, and eliminated. From the results, there is a very clear need to conduct a clinical study to further verify if the suggested (i.e., 0.34 mg/kg for artemether and 6 mg/kg for lumefantrine) doses could be clinically efficacious.

Precision sirolimus dosing in children: The potential for model-informed dosing and novel drug monitoring

The mTOR inhibitor sirolimus is prescribed to treat children with varying diseases, ranging from vascular anomalies to sporadic lymphangioleiomyomatosis to transplantation (solid organ or hematopoietic cell). Precision dosing of sirolimus using therapeutic drug monitoring (TDM) of sirolimus concentrations in whole blood drawn at the trough (before the next dose) time-point is the current standard of care. For sirolimus, trough concentrations are only modestly correlated with the area under the curve, with R 2 values ranging from 0.52 to 0.84. Thus, it should not be surprising, even with the use of sirolimus TDM, that patients treated with sirolimus have variable pharmacokinetics, toxicity, and effectiveness. Model-informed precision dosing (MIPD) will be beneficial and should be implemented. The data do not suggest dried blood spots point-of-care sampling of sirolimus concentrations for precision dosing of sirolimus. Future research on precision dosing of sirolimus should focus on pharmacogenomic and pharmacometabolomic tools to predict sirolimus pharmacokinetics and wearables for point-of-care quantitation and MIPD.

Impact of Drug Exposure on Resistance Selection Following Artemether-Lumefantrine Treatment for Malaria in Children With and Without HIV in Uganda

Artemisinin-based combination therapies (ACTs) are the primary treatment for malaria. It is essential to characterize the pharmacokinetics (PKs) and pharmacodynamics (PDs) of ACTs in vulnerable populations at risk of suboptimal dosing. We developed a population PK/PD model using data from our previous study of artemether-lumefantrine in HIV-uninfected and HIV-infected children living in a high-transmission region of Uganda. HIV-infected children were on efavirenz-, nevirapine-, or lopinavir-ritonavir-based antiretroviral regimens, with daily trimethoprim-sulfamethoxazole prophylaxis. We assessed selection for resistance in two key parasite transporters, pfcrt and pfmdr1, over 42-day follow-up and incorporated genotyping into a time-to-event model to ascertain how resistance genotype in relation to drug exposure impacts recurrence risk. Two hundred seventy-seven children contributed 364 episodes to the model (186 HIV-uninfected and 178 HIV-infected), with recurrent microscopy-detectable parasitemia detected in 176 episodes by day 42. The final model was a two-compartment model with first-order absorption and an estimated age effect on bioavailability. Systemic lumefantrine exposure was highest with lopinavir-ritonavir, lowest with efavirenz, and equivalent with nevirapine and HIV-uninfected children. HIV status and lumefantrine concentration were significant factors associated with recurrence risk. Significant selection was demonstrated for pfmdr1 N86 and pfcrt K76 in recurrent infections, with no evidence of selection for pfmdr1 Y184F. Less sensitive parasites were able to tolerate lumefantrine concentrations ~ 3.5-fold higher than more sensitive parasites. This is the first population PK model of lumefantrine in HIV-infected children and demonstrates selection for reduced lumefantrine susceptibility, a concern as we confront the threat to ACTs posed by emerging artemisinin resistance in Africa.

Innovations in Pediatric Therapeutics Development: Principles for the Use of Bridging Biomarkers in Pediatric Extrapolation

Even with recent substantive improvements in health care in pediatric populations, considerable need remains for additional safe and effective interventions for the prevention and treatment of diseases in children. The approval of prescription drugs and biological products for use in pediatric settings, as in adults, requires demonstration of substantial evidence of effectiveness and favorable benefit-to-risk. For diseases primarily affecting children, such evidence predominantly would be obtained in the pediatric setting. However, for conditions affecting both adults and children, pediatric extrapolation uses scientific evidence in adults to enable more efficiently obtaining a reliable evaluation of an intervention's effects in pediatric populations. Bridging biomarkers potentially have an integral role in pediatric extrapolation. In a setting where an intervention reliably has been established to be safe and effective in adults, and where there is substantive evidence that disease processes in pediatric and adult settings are biologically similar, a 'bridging biomarker' should satisfy three additional criteria: effects on the bridging biomarker should capture effects on the principal causal pathway through which the disease process meaningfully influences 'feels, functions, survives' measures; secondly, the experimental intervention should not have important unintended effects on 'feels, functions, survives' measures not captured by the bridging biomarker; and thirdly, in statistical analyses in adults, the intervention's net effect on 'feels, functions, survives' measures should be consistent with what would be predicted by its level of effect on the bridging biomarker. A validated bridging biomarker has considerable potential utility, since an intervention's efficacy could be extrapolated from adult to pediatric populations if evidence in children establishes the intervention not only to be safe but also to have substantive effects on that bridging biomarker. Proper use of bridging biomarkers could increase availability of reliably evaluated therapies approved for use in pediatric settings, enabling children and their caregivers to make informed choices about health care.

A pediatric quantitative systems pharmacology model of neurofilament trafficking in spinal muscular atrophy treated with the antisense oligonucleotide nusinersen

Phosphorylated neurofilament heavy subunit (pNfH) has been recently identified as a promising biomarker of disease onset and treatment efficacy in spinal muscular atrophy (SMA). This study introduces a quantitative systems pharmacology model representing the SMA pediatric scenario in the age range of 0-20 years with and without treatment with the antisense oligonucleotide nusinersen. Physiological changes typical of the pediatric age and the contribution of SMA and its treatment to the peripheral pNfH levels were included in the model by extending the equations of a previously developed mathematical model describing the neurofilament trafficking in healthy adults. All model parameters were estimated by fitting data from clinical trials that enrolled SMA patients treated with nusinersen. The data from the control group of the study was employed to build an in silico population of untreated subjects, and the parameters related to the treatment were estimated by fitting individual pNfH time series of SMA patients followed during the treatment. The final model reproduces well the pNfH levels in the presence of SMA in both the treated and untreated conditions. The results were validated by comparing model predictions with the data obtained from an additional cohort of SMA patients. The reported good predictive model performance makes it a valuable tool for investigating pNfH as a biomarker of disease progression and treatment response in SMA and for the in silico evaluation of novel treatment protocols.

A Simple Method for the Prediction of Therapeutic Proteins (Monoclonal and Polyclonal Antibodies and Non-Antibody Proteins) for First-in-Pediatric Dose Selection: Application of Salisbury Rule

In order to conduct a pediatric clinical trial, it is important to optimize pediatric dose as accurately as possible. In this study, a simple weight-based method known as ‘Salisbury Rule’ was used to predict pediatric dose for therapeutic proteins and was then compared with the observed pediatric dose. The observed dose was obtained mainly from the FDA package insert and if dosing information was not available from the FDA package insert then the observed dose was based on the dose given to an age group in a particular study. It was noted that the recommended doses of most of the therapeutic proteins were extrapolated to pediatrics from adult dose based on per kilogram (kg) body weight basis. Since it is widely believed that pediatric dose should be selected based on the pediatric clearance (CL), a CL based pediatric dose was projected from the following equation: Dose in children = Adult dose × (Observed CL in children/Observed adult CL). In this study, this dose was also considered observed pediatric dose for comparison. A ±30% prediction error (predicted vs. observed) was considered acceptable. There were 21 monoclonal antibodies, 5 polyclonal antibodies in children ≥ 2 years of age, 4 polyclonal antibodies in preterm and term neonates, and 11 therapeutic proteins (non-antibodies) in the study. In children < 30 kg body weight, the predicted doses were within 0.5−1.5-fold prediction error for 87% (monoclonal antibody), 100% (polyclonal antibody), and 92% (non-antibodies) observations. In children > 30 kg body weight, the predicted doses were within 0.5−1.5-fold prediction error for 96% (monoclonal antibody), 100% (polyclonal antibody), and 100% (non-antibodies) observations. The Salisbury Rule mimics more to CL-based dose rather than per kg body weight-based extrapolated dose from adults. The Salisbury Rule for the pediatric dose prediction can be used to select first-in-children dose in pediatric clinical trials and may be in clinical settings.

Use of Antibiotics in Preterm Newborns

Due to complex maturational and physiological changes that characterize neonates and affect their response to pharmacological treatments, neonatal pharmacology is different from children and adults and deserves particular attention. Although preterms are usually considered part of the neonatal population, they have physiological and pharmacological hallmarks different from full-terms and, therefore, need specific considerations. Antibiotics are widely used among preterms. In fact, during their stay in neonatal intensive care units (NICUs), invasive procedures, including central catheters for parental nutrition and ventilators for respiratory support, are often sources of microbes and require antimicrobial treatments. Unfortunately, the majority of drugs administered to neonates are off-label due to the lack of clinical studies conducted on this special population. In fact, physiological and ethical concerns represent a huge limit in performing pharmacokinetic (PK) studies on these subjects, since they limit the number and volume of blood sampling. Therapeutic drug monitoring (TDM) is a useful tool that allows dose adjustments aiming to fit plasma concentrations within the therapeutic range and to reach specific drug target attainment. In this review of the last ten years’ literature, we performed Pubmed research aiming to summarize the PK aspects for the most used antibiotics in preterms.

Population pharmacokinetics and clinical outcomes of polymyxin B in paediatric patients with multidrug-resistant Gram-negative bacterial infections

BACKGROUND

Current polymyxin B dosing in children relies on scant data.

OBJECTIVES

To build a population pharmacokinetic (PK) model for polymyxin B in paediatric patients and assess the likely appropriateness of different dosages.

METHODS

A total of 19 paediatric patients were enrolled to receive intravenous polymyxin B (1.33-2.53 mg/kg/day), and the median age was 12.5 (range 3.2-17.8) years. Serial plasma samples were collected at steady-state and modelled by population PK analysis. Clinical efficacy and nephrotoxicity of polymyxin B treatment were also assessed.

RESULTS

PK data were adequately described by a two-compartment model with first-order elimination, and weight was a significant covariate of polymyxin B clearance. Clinical success occurred in 14 of 19 patients (73.7%) and only one patient developed acute kidney injury. The 28 day mortality was 10.5% (2/19). The steady-state polymyxin B exposure was 36.97 ± 9.84 mg·h/L, lower than the therapeutic exposure of 50-100 mg·h/L. With the AUC24h/MIC target of 50, the dosage of 1.5-3.0 mg/kg/day had a probability of target attainments over 90% when MICs were <0.5 mg/L.

CONCLUSIONS

Dose adjustment of polymyxin B needs to consider the MIC of infecting pathogens. Current polymyxin B dosing for paediatric patients may be acceptable when MICs are <0.5 mg/L.

A General Biphasic Bodyweight Model for Scaling Basal Metabolic Rate, Glomerular Filtration Rate, and Drug Clearance from Birth to Adulthood

The objective of this study is to propose a unified, continuous, and bodyweight-only equation to quantify the changes of human basal metabolic rate (BMR), glomerular filtration rate (GFR), and drug clearance (CL) from infancy to adulthood. The BMR datasets were retrieved from a comprehensive historical database of male and female subjects (0.02 to 64 years). The CL datasets for 17 drugs and the GFR dataset were generated from published maturation and growth models with reported parameter values. A statistical approach was used to simulate the model-generated CL and GFR data for a hypothetical population with 26 age groups (from 0 to 20 years). A biphasic equation with two power-law functions of bodyweight was proposed and evaluated as a general model using nonlinear regression and dimensionless analysis. All datasets universally reveal biphasic curves with two distinct linear segments on log-log plots. The biphasic equation consists of two reciprocal allometric terms that asymptotically determine the overall curvature. The fitting results show a superlinear scaling phase (asymptotic exponent >1; ca. 1.5-3.5) and a sublinear scaling phase (asymptotic exponent <1; ca. 0.5-0.7), which are separated at the phase transition bodyweight ranging from 5 to 20 kg with a mean value of 10 kg (corresponding to 1 year of age). The dimensionless analysis generalizes and offers quantitative realization of the maturation and growth process. In conclusion, the proposed mixed-allometry equation is a generic model that quantitatively describes the phase transition in the human maturation process of diverse human functions.

Population pharmacokinetic analysis of sildenafil in term and preterm infants with pulmonary arterial hypertension

Sildenafil is widely used off-label in pediatric patients with pulmonary arterial hypertension (PAH). This study was conducted to characterize the pharmacokinetics (PK) of sildenafil in term and preterm neonates with PAH, by developing a population PK model, and to suggest appropriate doses to achieve clinically effective concentrations. A population PK modelling analysis was performed using sildenafil and its metabolite N-desmethyl sildenafil (DMS) concentration data from 19 neonates with PAH, whose gestational ages ranged 24–41 weeks. They received sildenafil orally at a dose of 0.5–0.75 mg/kg, four times a day. To investigate the appropriate sildenafil dose, simulations were conducted according to body weight which was significant covariate for sildenafil clearance. A one-compartment model with first-order absorption adequately described the PKs of sildenafil and DMS. Sildenafil clearance was expected to increase rapidly with increasing body weight. In the simulation, sildenafil doses > 1 mg/kg was required to achieve and maintain target concentrations of sildenafil and to expect timely clinical effects in term and preterm infants. These results could be utilized for the safer and more effective use of sildenafil in term and preterm infants.

DEVELOPMENT OF A PARENTAL ATTITUDE SCALE FOR RATIONAL DRUG USE

Objective: The aim of this study is to develop a valid and reliable measurement tool to identify parental attitudes towards rational drug use. Methods: The sample of methodological study included 517 parents. “The Parent Information Form” and the “Parental Attitude Scale for Rational Drug Use (PASRDU)” were used to collect data. In the assessment of the data, validity and reliability analyses were applied. Results: In the study, CVI was calculated as 0.71. For the exploratory factor analysis KMO score was 0.86, and Bartlett's test was x2=7.559.22 in the study. For the confirmatory factor analysis, X2/Sd was measured at 3.47, GFI at 0.94, AGFI at 0.93, CFI at 0.92, RMSEA at 0.06 and SRMR at 0.06, and the scale structure was approved according to these findings. Consequently, the scale was formed of 40 items and 2 sub-scales. The Cronbach's Alpha value of the scale was 0.88. Item-total correlation values were 0.32-0.61, and test-retest value was r = 0.85. Conlusion: Validity and reliability analyses conducted during the process of scale development showed that PASRDU is a valid and reliable scale which finds out parents’ attitudes towards rational drug use. It is also useful for nurses to use within the safety criteria of drugs. This scale enables the nurse to determine the lack of rational drug use and provide training and consultancy on this subject. This scale can be used in primary and preventive health services.

Population Pharmacokinetic Modeling and Simulation of TQ-B3101 to Inform Dosing in Pediatric Patients With Solid Tumors

Background: TQ-B3101 is a novel kinase inhibitor currently in development for the treatment of advanced malignant solid tumor and relapsed or refractory ALK-positive anaplastic large cell lymphoma.

Methods: A population pharmacokinetic model was developed using data collected from a Phase 1 study and a Phase 2 study to characterize the pharmacokinetic of TQ-B3101 and its active metabolite (TQ-B3101M). The final model was used to optimize dosing of TQ-B3101 for pediatric patients (6-<18 years) with anaplastic large cell lymphoma.

Results: The pharmacokinetic of TQ-B3101 and TQ-B3101M was adequately described by a 1-compartment model with first-order absorption and elimination for parent drug coupled with a 2-compartment model with time-dependent clearance for the metabolite. The clearance of TQ-B3101M decreased over time with a maximum fractional reduction of 0.41. The estimated apparent clearance and apparent volume of distribution of TQ-B3101 were 2850 L/h and 4200 L, respectively. The elimination half-life of TQ-B3101 was 1.0 h. The distribution and elimination half-lives of TQ-B3101M at steady state were 4.9 and 39.4 h, respectively. The projected exposure of TQ-B3101M in virtual pediatric population following the body surface area tiered dosing regimen was similar to that in children pediatric patients after the recommended pediatric dose of crizotinib (280 mg/m2 twice daily), an analog of TQ-B3101M.

Conclusion: A population pharmacokinetic model was developed to provide optimal dose of regimen for further development of TQ-B3101 in pediatric patients with anaplastic large cell lymphoma.

Pediatric pharmacokinetic considerations and implications for drug dosing

Optimizing the dosing of medicines for pediatric patients in routine clinical practice and determining the dose for clinical trials is still a challenging task. Children differ from adults in their response to drugs due to inherent differences in pharmacokinetics and/or pharmacodynamics, and responses may also vary among pediatric patients of different ages. However, the greatest disparities compared to adult pharmacokinetic profiles are observed in children below 2 years of age. The maturation of the liver and the kidneys, as well as the variation in body composition, are considered to be the main sources of pharmacokinetic variability. Hence, besides specific pharmacodynamic features, understanding age-related changes in drug absorption, distribution, and elimination is fundamental for optimizing drug efficacy and avoiding toxicity. This paper summarizes the pharmacokinetic changes throughout the childhood, along with the effect of developmental changes on drug dosage calculation. In clinical practice, age and body weight-based dosing regimens are usually used. In spite of dosing recommendations based on age and/or body weight, variabilities in pharmacokinetics and pharmacodynamic response remain, implying a need to monitor patients and optimize the dosing regimen according to physiological characteristics, disease characteristics and therapy.

Population pharmacokinetics of clonazepam in saliva and plasma: Steps towards noninvasive pharmacokinetic studies in vulnerable populations

AIM

Traditional studies focusing on the relationship between pharmacokinetics (PK) and pharmacodynamics necessitate blood draws, which are too invasive for children or other vulnerable populations. A potential solution is to use noninvasive sampling matrices, such as saliva. The aim of this study was to develop a population PK model describing the relationship between plasma and saliva clonazepam kinetics and assess whether the model can be used to determine trough plasma concentrations based on saliva samples.

METHODS

Twenty healthy subjects, aged 18-30, were recruited and administered 0.5 or 1 mg of clonazepam solution. Paired plasma and saliva samples were obtained until 48 hours post-dose. A population pharmacokinetic model was developed describing the PK of clonazepam in plasma and the relationship between plasma and saliva concentrations. Bayesian maximum a posteriori optimization was applied to estimate the predictive accuracy of the model.

RESULTS

A two-compartment distribution model best characterized clonazepam plasma kinetics with a mixture component on the absorption rate constants. Oral administration of the clonazepam solution caused contamination of the saliva compartment during the first 4 hours post-dose, after which the concentrations were driven by the plasma concentrations. Simulations demonstrated that the lower and upper limits of agreements between true and predicted plasma concentrations were -28% to 36% with one saliva sample. Increasing the number of saliva samples improved these limits to -18% to 17%.

CONCLUSION

The developed model described the salivary and plasma kinetics of clonazepam, and could predict steady-state trough plasma concentrations based on saliva concentrations with acceptable accuracy.

Pharmacokinetics of Vancomycin in Critically Ill Children: A Systematic Review

Background and Objective

Vancomycin is often used in the ICU for the treatment of Gram-positive bacterial infection. In critically ill children, there are pathophysiologic changes that affect the pharmacokinetics of vancomycin. A systematic review of vancomycin pharmacokinetics and pharmacodynamics in critically ill children was performed.

Methods

Pharmacokinetic studies of vancomycin in critically ill children published up to May 2021 were included in the review provided they included children aged > 1 month. Studies including neonates were excluded. A search was performed using the PubMed, Scopus, and Google Scholar databases. The Risk of Bias Assessment Tool for Systematic Reviews (ROBIS) was used to check for quality and reduce bias. Data on study characteristics, patient demographics, clinical parameters, pharmacokinetic parameters, outcomes, and study limitations were collected.

Results

Thirteen studies were included in this review. A wide variety of dosing and sampling strategies were used in the studies. Methods for estimating vancomycin pharmacokinetics, especially the area under the curve over 24 h, varied. Vancomycin doses of 20–60 mg/kg were given daily. This resulted in high variability in pharmacokinetic parameters. Vancomycin trough level was less than 15 μg/mL in most of the studies. Vancomycin clearance ranged from 0.05 to 0.38 L/h/kg. Volume of distribution ranged from 0.1 to 1.16 L/kg. Half-life was between 2.4 and 23.6 h. Patients in the study receiving continuous vancomycin infusion had AUC₂₄ < 400 µg·h/mL.

Conclusion

There is large variability in the pharmacokinetics of vancomycin among critically ill patients. Studies to assess the factors responsible for this variability in vancomycin pharmacokinetics are needed.

Validation of the Lusaka Formula: A Novel Formula for Weight Estimation in Children Presenting for Surgery in Zambia

BACKGROUND

In children, the use of actual weight or predicted weight from various estimation methods is essential to reduce harm associated with dosing errors. This study aimed to validate the new locally derived Lusaka formula on an independent cohort of children undergoing surgery at the University Teaching Hospital in Lusaka, Zambia, to compare the Lusaka formula's performance to commonly used weight prediction tools and to assess the nutritional status of this population.

METHODS

The Lusaka formula (weight = [age in months/2] + 3.5 if under 1 year; weight = 2×[age in years] + 7 if older than 1 year) was derived from a previously published data set. We aimed to validate this formula in a new data set. Weights, heights, and ages of 330 children up to 14 years were measured before surgery. Accuracy was examined by comparing the (1) mean percentage error and (2) the percentage of actual weights that fell between 10% and 20% of the estimated weight for the Lusaka formula, and for other existing tools. World Health Organization (WHO) growth charts, mid upper arm circumference (MUAC), and body mass index (BMI) were used to assess nutritional status.

RESULTS

The Lusaka formula had similar precision to the Broselow tape: 160 (48.5%) vs 158 (51.6%) children were within 10% of the estimated weight, 241 (73.0%) vs 245 (79.5%) children were within 20% of the estimated weight. The Lusaka formula slightly underestimated weight (mean bias, -0.5 kg) in contrast to all other predictive tools, which overestimated on average. Twenty-two percent of children had moderate or severe chronic malnutrition (stunting) and 4.7% of children had moderate or severe acute malnutrition (wasting).

CONCLUSIONS

The Lusaka formula is comparable to, or better than, other age-based weight prediction tools in children presenting for surgery at the University Teaching Hospital in Lusaka, Zambia, and has the advantage that it covers a wider age range than tools with comparable accuracy. In this population, commonly used aged-based prediction tools significantly overestimate weights.

Effect of Intrinsic and Extrinsic Factors on the Pharmacokinetics of Antibody-Drug Conjugates (ADCs)

Antibody–drug conjugates (ADCs) are complex molecules wherein a monoclonal antibody is linked to a biologically active drug (a small molecule), forming a conjugate. Initially, most of the ADCs were developed and are being developed for the treatment of cancer; however, with time, it has been realized that ADCs can also be developed to manage or cure other diseases. Pharmacokinetics (PK) plays an important role in modern-day drug development and the knowledge of PK is crucial in designing a safe and efficacious dose to treat a wide variety of diseases. There are several factors that can alter the PK of a drug; as a result, one has to adjust the dose in a patient population. These factors can be termed ‘intrinsic’ or ‘extrinsic’. For small molecules, the impact of both intrinsic and extrinsic factors is well established. The impact of age, gender, disease states such as renal and hepatic impairment, drug–drug interaction, food, and in many cases alcohol on the PK of small molecules are well known. On the other hand, for macromolecules, the impact of these factors is not well established. Since the ADCs are a combination product of a monoclonal antibody linked to a small molecule, both the small molecule and the monoclonal antibody of the ADCs may be subjected to many intrinsic and extrinsic factors. This review summarizes the impact of intrinsic and extrinsic factors on the PK of ADCs and the payloads.

Wide size dispersion and use of body composition and maturation improves the reliability of allometric exponent estimates

To evaluate study designs and the influence of dispersion of body size, body composition and maturation of clearance or reliable estimation of allometric exponents. Non-linear mixed effects modeling and parametric bootstrap were employed to assess how the study sample size, number of observations per subject, between subject variability (BSV) and dispersion of size distribution affected estimation bias and uncertainty of allometric exponents. The role of covariate model misspecification was investigated using a large data set ranging from neonates to adults. A decrease in study sample size, number of observations per subject, an increase in BSV and a decrease in dispersion of size distribution, increased the uncertainty of allometric exponent estimates. Studies conducted only in adults with drugs exhibiting normal (30%) BSV in clearance may need to include at least 1000 subjects to be able to distinguish between allometric exponents of 2/3 and 1. Nevertheless, studies including both children and adults can distinguish these exponents with only 100 subjects. A marked bias of 45% (95%CI 41-49%) in the estimate of the allometric exponent of clearance was obtained when maturation and body composition were ignored in infants. A wide dispersion of body size (e.g. infants, children and adults) is required to reliably estimate allometric exponents. Ignoring differences in body composition and maturation of clearance may bias the exponent for clearance. Therefore, pharmacometricians should avoid estimating allometric exponent parameters without suitable designs and covariate models. Instead, they are encouraged to rely on the well-developed theory and evidence that clearance and volume parameters in humans scale with theory-based exponents.

Pharmacokinetics of Intravenous Paracetamol (Acetaminophen) and Ductus Arteriosus Closure After Premature Birth

In preterm infants, a high risk of hemodynamically significant patent ductus arteriosus (PDA) exists and its persistence is associated with an increased risk of severe morbidity. Current pharmacological options include ibuprofen or indomethacin. However, treatment by indomethacin or ibuprofen of a large PDA was shown to reduce early pulmonary hemorrhage and later medical treatment but had no effect on neonatal death or morbidity. Early prophylactic treatment of ductus arteriosus by paracetamol seems to be an attractive opportunity to reduce life-threatening morbidity. However, there are currently no data regarding the pharmacokinetics (PK) and pharmacodynamics of paracetamol in preterm neonates in this potential new indication. In this study, we aimed to develop a population PK model for paracetamol and investigate the relationship between paracetamol exposure levels and time to contraction of the ductus. Data were modeled using Monolix software. A one-compartment model adequately described the paracetamol concentration-time course. A Weibull model adequately described the time to contraction of the ductus. Our results suggest that the dosage used in this study (i.e., first day 42.5 mg/kg, then 30 mg/kg/day) allows for reaching the maximum inhibition response from paracetamol regarding the time to close the ductus. However, this study pointed out a lower effect of paracetamol on extremely preterm neonates (below 27 weeks). Therefore, a dose-finding study focusing specifically on extremely preterm neonates with treatment efficacy and toxicity is strongly needed.

Neural-ODE for pharmacokinetics modeling and its advantage to alternative machine learning models in predicting new dosing regimens

Forecasting pharmacokinetics (PK) for individual patients is a fundamental problem in clinical pharmacology. One key challenge is that PK models constructed using data from one dosing regimen must predict PK data for different dosing regimen(s). We propose a deep learning approach based on neural ordinary differential equations (neural-ODE) and tested its generalizability against a variety of alternative models. Specifically, we used the PK data from two different treatment regimens of trastuzumab emtansine. The models performed similarly when the training and the test sets come from the same dosing regimen. However, for predicting a new treatment regimen, the neural-ODE model showed substantially better performance. To date, neural-ODE is the most accurate PK model in predicting untested treatment regimens. This study represents the first time neural-ODE has been applied to PK modeling and the results suggest it is a widely applicable algorithm with the potential to impact future studies.

mRNA therapy restores euglycemia and prevents liver tumors in murine model of glycogen storage disease

Glycogen Storage Disease 1a (GSD1a) is a rare, inherited metabolic disorder caused by deficiency of glucose 6-phosphatase (G6Pase-α). G6Pase-α is critical for maintaining interprandial euglycemia. GSD1a patients exhibit life-threatening hypoglycemia and long-term liver complications including hepatocellular adenomas (HCAs) and carcinomas (HCCs). There is no treatment for GSD1a and the current standard-of-care for managing hypoglycemia (Glycosade®/modified cornstarch) fails to prevent HCA/HCC risk. Therapeutic modalities such as enzyme replacement therapy and gene therapy are not ideal options for patients due to challenges in drug-delivery, efficacy, and safety. To develop a new treatment for GSD1a capable of addressing both the life-threatening hypoglycemia and HCA/HCC risk, we encapsulated engineered mRNAs encoding human G6Pase-α in lipid nanoparticles. We demonstrate the efficacy and safety of our approach in a preclinical murine model that phenotypically resembles the human condition, thus presenting a potential therapy that could have a significant therapeutic impact on the treatment of GSD1a.

Clinical Pharmacology of Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are biopharmaceutical products where a monoclonal antibody is linked to a biologically active drug (a small molecule) forming a conjugate. Since the approval of first ADC (Gemtuzumab ozogamicin (trade name: Mylotarg)) for the treatment of CD33-positive acute myelogenous leukemia, several ADCs have been developed for the treatment of cancer. The goal of an ADC as a cancer agent is to release the cytotoxic drug to kill the tumor cells without harming the normal or healthy cells. With time, it is being realized that ADCS can also be used to manage or cure other diseases such as inflammatory diseases, atherosclerosis, and bacteremia and some research in this direction is ongoing. The focus of this review is on the clinical pharmacology aspects of ADC development. From the selection of an appropriate antibody to the finished product, the entire process of the development of an ADC is a difficult and challenging task. Clinical pharmacology is one of the most important tools of drug development since this tool helps in finding the optimum dose of a product, thus preserving the safety and efficacy of the product in a patient population. Unlike other small or large molecules where only one moiety and/or metabolite(s) is generally measured for the pharmacokinetic profiling, there are several moieties that need to be measured for characterizing the PK profiles of an ADC. Therefore, knowledge and understanding of clinical pharmacology of ADCs is vital for the selection of a safe and efficacious dose in a patient population.

Estimation of Ontogeny Functions for Renal Transporters Using a Combined Population Pharmacokinetic and Physiology-Based Pharmacokinetic Approach: Application to OAT1,3

To date, information on the ontogeny of renal transporters is limited. Here, we propose to estimate the in vivo functional ontogeny of transporters using a combined population pharmacokinetic (popPK) and physiology-based pharmacokinetic (PBPK) modeling approach called popPBPK. Clavulanic acid and amoxicillin were used as probes for glomerular filtration, combined glomerular filtration, and active secretion through OAT1,3, respectively. The predictive value of the estimated OAT1,3 ontogeny function was assessed by PBPK predictions of renal clearance (CL_R) of other OAT1,3 substrates: cefazolin and piperacillin. Individual CL_Rpost-hoc values, obtained from a published popPK model on the concomitant use of clavulanic acid and amoxicillin in critically ill children between 1 month and 15 years, were used as dependent variables in the popPBPK analysis. CL_R was re-parameterized according to PBPK principles, resulting in the estimation of OAT1,3-mediated intrinsic clearance (CL_{int,OAT1,3,invivo}) and its ontogeny. CL_{int,OAT1,3,invivo} ontogeny was described by a sigmoidal function, reaching half of adult level around 7 months of age, comparable to findings based on renal transporter-specific protein expression data. PBPK-based CL_R predictions including this ontogeny function were reasonably accurate for piperacillin in a similar age range (2.5 months–15 years) as well as for cefazolin in neonates as compared to published data (%RMSPE of 21.2 and 22.8%, respectively and %PE within ±50%). Using this novel approach, we estimated an in vivo functional ontogeny profile for CL_{int,OAT1,3,invivo} that yields accurate CL_R predictions for different OAT1,3 substrates across different ages. This approach deserves further study on functional ontogeny of other transporters.

Allometric Optimization of Enrofloxacin Dosage in Growing Male Turkeys: Empirical Evidence for Improved Internal Exposure

Rapid weight gain in turkeys causes a major change in the pharmacokinetics of drugs, leading to age-dependent variability in the internal exposure and, possibly, treatment failure and/or selection for antimicrobial resistance in young individuals. The aim of the study was to investigate whether a non-linear dosing protocol that accounts for the previously established allometric relation between enrofloxacin clearance and body weight (BW) may optimize the internal exposure to enrofloxacin in growing male turkeys. Enrofloxacin was administered four times, between the age of 5 and 16.5 weeks, when the turkeys’ BW increased from 1.47 to 14.92 kg. Enrofloxacin was given intravenously (i.v.) or orally at the dose calculated as follows: Dose = 30 × BW^0.59. After i.v. administration, the internal exposure to the drug—quantified as the area under the concentration–time curve (AUC)—was showing little age-related variation. The coefficient of variation (CV) for AUC in all individuals (15.7%) was only slightly higher than within the age groups (5.4–13.7%). After oral drug administration, CV for AUC in all individuals (22.1%) was similar as within the age groups (8.7–32.2%). These results show that intra-species allometric scaling may be efficiently implemented in the non-linear approach to enrofloxacin dosage in turkeys in order to obtain a precise internal exposure for the optimal antimicrobial effect.

Population Pharmacokinetics of Tapentadol in Children from Birth to <18 Years Old

OBJECTIVE

The main aim of this analysis was to characterize the pharmacokinetics (PK) of tapentadol in pediatric patients from birth to <18 years old who experience acute pain, requiring treatment with an opioid analgesic.

PATIENTS AND METHODS

Data from four clinical trials and 148 pediatric patients who received a single dose of tapentadol oral or intravenous solution were included. Population PK analysis was performed to determine the contribution of size-related (bodyweight) and function-related (maturation) factors to the changes in oral bioavailability (F), volume of distribution (V), and clearance (CL) with age. Simulations were carried out to compare pediatric exposures to reference adult values.

RESULTS

A one-compartment model with allometric scaling on disposition parameters (using theoretical or estimated exponents) and maturation functions on CL and F best described tapentadol PK. The estimated allometric exponents for CL (0.603) and V (0.820) differed slightly from the theoretical values of 0.75 for CL and 1 for V. A maximum in CL/F was observed at about 2-3 years when expressed on a bodyweight basis. Results for younger children as well as the F estimate were sensitive to the scaling approach, but CL/F and V/F as a function of age for the two scaling approaches led to similar curves within the bioequivalence range except below 5 weeks of age. Model-based simulations indicated that the doses used in the included clinical trials lead to exposures within the lower half of the targeted adult exposure.

CONCLUSION

The development of tapentadol is one of the first examples following a systematic approach for analgesic drug development for children. Our analysis enabled a full characterization and robust understanding of tapentadol PK in children from birth to <18 years, including preterm infants, and showed the importance of evaluating the sensitivity of the inferences of the PK parameters to the selected scaling approach.

Extrapolation of Drug Clearance in Children ≤ 2 Years of Age from Empirical Models Using Data from Children (> 2 Years) and Adults

BACKGROUND

The application of modeling and simulation approaches in clinical pharmacology studies has gained momentum over the last 20 years.

OBJECTIVES

The objective of this study was to develop six empirical models from clearance data obtained from children aged > 2 years and adults to evaluate the suitability of the models to predict drug clearance in children aged ≤ 2 years (preterm, term, and infants).

METHODS

Ten drugs were included in this study and administered intravenously: alfentanil, amikacin, busulfan, cefetamet, meperidine, oxycodone, propofol, sufentanil, theophylline, and tobramycin. These drugs were selected according to the availability of individual subjects' weight, age, and clearance data (concentration-time data for these drugs were not available to the author). The chosen drugs are eliminated by extensive metabolism by either the renal route or both the renal and hepatic routes. The six empirical models were (1) age and body weight-dependent sigmoidal maximum possible effect (E_max) maturation model, (2) body weight-dependent sigmoidal E_max model, (3) uridine 5'-diphospho [body weight-dependent allometric exponent model (BDE)], (4) age-dependent allometric exponent model (ADE), (5) a semi-physiological model, and (6) an allometric model developed from children aged > 2 years to adults. The model-predicted clearance values were compared with observed clearance values in an individual child. In this analysis, a prediction error of ≤ 50% for mean or individual clearance values was considered acceptable.

RESULTS

Across all age groups and the ten drugs, data for 282 children were compared between observed and model-predicted clearance values. The validation data consisted of 33 observations (sum of different age groups for ten drugs). Only three of the six models (body weight-dependent sigmoidal E_max model, ADE, and semi-physiological model) provided reasonably accurate predictions of clearance (> 80% observation with ≤ 50% prediction error) in children aged ≤ 2 years. In most instances, individual predicted clearance values were erratic (as indicated by % error) and were not in agreement with the observed clearance values.

CONCLUSIONS

The study indicated that simple empirical models can provide more accurate results than complex empirical models.

The Predictive Value of Glomerular Filtration Rate-Based Scaling of Pediatric Clearance and Doses for Drugs Eliminated by Glomerular Filtration with Varying Protein-Binding Properties

INTRODUCTION

For drugs eliminated by glomerular filtration (GF), clearance (CL) is determined by GF rate (GFR) and the unbound fraction of the drug. When predicting CL of GF-eliminated drugs in children, instead of physiologically based pharmacokinetic (PBPK) methods that consider changes in both GFR and protein binding, empiric bodyweight-based methods are often used. In this article, we explore the predictive value of scaling using a GFR function, and compare the results with linear and allometric scaling methods for drugs with different protein-binding properties.

METHODS

First, different GFR maturation functions were compared to identify the GFR function that would yield the most accurate GFR predictions across the pediatric age range compared with published pediatric inulin/mannitol CL values. Subsequently, the accuracy of pediatric CL scaling using this GFR maturation function was assessed and compared with PBPK CL predictions for hypothetical drugs binding, to varying extents, to serum albumin or α-acid glycoprotein across the pediatric age range. Additionally, empiric bodyweight-based methods were assessed.

RESULTS

The published GFR maturation functions yielded comparable maturation profiles, with the function reported by Salem et al. leading to the most accurate predictions. On the basis of this function, GFR-based scaling yields reasonably accurate (percentage prediction error ≤ 50%) pediatric CL values for all drugs, except for some drugs highly bound to AGP in neonates. Overall, this method was more accurate than linear or 0.75 allometric bodyweight-based scaling.

CONCLUSION

When scaling CL and dose by GFR function, maturational changes in plasma protein concentrations impact GF minimally, making this method a superior alternative to empiric bodyweight-based scaling.

Optimizing Estimated Glomerular Filtration Rate to Support Adult to Pediatric Pharmacokinetic Bridging Studies in Patients with Cystic Fibrosis

BACKGROUND

The estimated glomerular filtration rate (eGFR) is often used to model drug clearance (CL) and scale doses across age and body size. Over their lifetime, patients with cystic fibrosis (CF) receive repeated courses of tobramycin, an antibiotic with eGFR-dependent CL, for the treatment of pulmonary exacerbations. Tobramycin population pharmacokinetic (PK) modeling can be used to decipher the best approach to define eGFR for pediatric bridging studies.

METHODS

Inpatients with CF who received intravenous tobramycin between 1 January 2006 and 30 May 2018 were eligible for inclusion. Encounters without tobramycin concentration measurement or missing covariate data were excluded. Population PK analysis was performed using NONMEM.Covariate models were built  following identification of the base model, with specific emphasis on the effect of different methods of estimating renal function as a covariate of tobramycin CL.

RESULTS

A total of 296 CF patients contributed 1029 care encounters (420 pediatric, 609 adult) and 4352 tobramycin concentrations to this analysis. The median (minimum, maximum) age at encounter was 19 years (0.2, 60), with serum creatinine of 0.60 mg/dL (0.10, 3.41). A two-compartment model best described the observed data, with height and eGFR as significant covariates of tobramycin CL. eGFR was best modeled using a combination of the modified Schwartz and Chronic Kidney Disease Epidemiology Collaboration (CKDEPI) equations expressed in absolute units.

CONCLUSIONS

The CKDEPI equation bridges PK data generated in adults to adolescents with CF better than the current regulatory standard. The eGFR should be expressed in absolute units (mL/min) for PK analyses.

Physiologically based pharmacokinetic-pharmacodynamic evaluation of meropenem plus fosfomycin in paediatrics

AIMS

The objective of the current study was to evaluate paediatric dosing regimens for meropenem plus fosfomycin that generate sufficient coverage against multidrug-resistant bacteria.

METHODS

The physiologically based pharmacokinetic (PBPK) models of meropenem and fosfomycin were developed from previously published pharmacokinetic studies in five populations: healthy subjects of Japanese origin, and healthy adults, geriatric, paediatric and renally impaired of primarily Caucasian origins. Pharmacodynamic (PD) analyses were carried out by evaluating dosing regimens that achieved a ≥90% joint probability of target attainment (PTA), which was defined as the minimum of the marginal probabilities to achieve the target PD index of each antibiotic. For meropenem, the percentage of time over a 24-hour period wherein the free drug concentration was above the minimum inhibitory concentration (fT > MIC) of at least 40% was its PD target. The fosfomycin PD index was described by fAUC/MIC of at least 40.8.

RESULTS

For coadministration consisting of 20 mg/kg meropenem q8h as a 3-hour infusion and 35 mg/kg fosfomycin q8h also as a 3-hour infusion in a virtual paediatric population between 1 month and 12 years of age with normal renal function and a corresponding body weight between 3 and 50 kg, a joint PTA ≥ 90% is achieved at MICs of 16 and 64 mg/L for meropenem and fosfomycin coadministration, respectively, against Klebsiella pneumoniae and Pseudomonas aeruginosa.

CONCLUSION

The current study identified potentially effective paediatric dosing regimens for meropenem plus fosfomycin coadministration against multidrug-resistant bacteria.

State-of-the-Art Review on Physiologically Based Pharmacokinetic Modeling in Pediatric Drug Development

Physiologically based pharmacokinetic modeling and simulation is an important tool for predicting the pharmacokinetics, pharmacodynamics, and safety of drugs in pediatrics. Physiologically based pharmacokinetic modeling is applied in pediatric drug development for first-time-in-pediatric dose selection, simulation-based trial design, correlation with target organ toxicities, risk assessment by investigating possible drug-drug interactions, real-time assessment of pharmacokinetic-safety relationships, and assessment of non-systemic biodistribution targets. This review summarizes the details of a physiologically based pharmacokinetic modeling approach in pediatric drug research, emphasizing reports on pediatric physiologically based pharmacokinetic models of individual drugs. We also compare and contrast the strategies employed by various researchers in pediatric physiologically based pharmacokinetic modeling and provide a comprehensive overview of physiologically based pharmacokinetic modeling strategies and approaches in pediatrics. We discuss the impact of physiologically based pharmacokinetic models on regulatory reviews and product labels in the field of pediatric pharmacotherapy. Additionally, we examine in detail the current limitations and future directions of physiologically based pharmacokinetic modeling in pediatrics with regard to the ability to predict plasma concentrations and pharmacokinetic parameters. Despite the skepticism and concern in the pediatric community about the reliability of physiologically based pharmacokinetic models, there is substantial evidence that pediatric physiologically based pharmacokinetic models have been used successfully to predict differences in pharmacokinetics between adults and children for several drugs. It is obvious that the use of physiologically based pharmacokinetic modeling to support various stages of pediatric drug development is highly attractive and will rapidly increase, provided the robustness and reliability of these techniques are well established.

Pharmacokinetic-Pharmacodynamic Modeling in Pediatric Drug Development, and the Importance of Standardized Scaling of Clearance

Pharmacokinetic/pharmacodynamic (PKPD) modeling is important in the design and conduct of clinical pharmacology research in children. During drug development, PKPD modeling and simulation should underpin rational trial design and facilitate extrapolation to investigate efficacy and safety. The application of PKPD modeling to optimize dosing recommendations and therapeutic drug monitoring is also increasing, and PKPD model-based dose individualization will become a core feature of personalized medicine. Following extensive progress on pediatric PK modeling, a greater emphasis now needs to be placed on PD modeling to understand age-related changes in drug effects. This paper discusses the principles of PKPD modeling in the context of pediatric drug development, summarizing how important PK parameters, such as clearance (CL), are scaled with size and age, and highlights a standardized method for CL scaling in children. One standard scaling method would facilitate comparison of PK parameters across multiple studies, thus increasing the utility of existing PK models and facilitating optimal design of new studies.

The influence of age and body weight gain on enrofloxacin pharmacokinetics in turkeys-Allometric approach to dose optimization

Enrofloxacin is a concentration-dependent antimicrobial used in bacterial infections in poultry. During a few months of a turkey's life, pharmacokinetics of drugs undergoes substantial changes which may compromise their efficacy due to variability in internal exposure (measured by area under the concentration-time curve, AUC). The aim of this study was to describe the effects of age on the pharmacokinetics of a single intravenous (i.v.) and oral administration of enrofloxacin at a dose of 10 mg/kg to turkeys. It was found that during a 2.5-month-long period of growth from 1.4 to 14.6 kg, the AUC after i.v. administration increased almost threefold due to a significant decrease in the body clearance (from a mean of 0.76-0.28 L hr^-1  kg^-1 ). Over the same period, the mean elimination half-life was prolonged from 2.65 to 7.03 hr. Oral administration resulted in a similar trend in pharmacokinetic parameters. For both routes, formation of the major metabolite, ciprofloxacin, was marginal. Protein binding was not age-dependent and never exceeded 50%. Body clearance, volume of distribution and elimination half-life were subjected to an allometric analysis and a novel, nonlinear dosage protocol has been proposed to improve the internal exposure to the drug in different age groups of turkeys.

Population Pharmacokinetic/Pharmacodynamic Modeling of Methylprednisolone in Neonates Undergoing Cardiopulmonary Bypass

Methylprednisolone is used in neonates to modulate cardiopulmonary bypass (CPB)–induced inflammation, but optimal dosing and exposure are unknown. We used plasma methylprednisolone and interleukin (IL)‐6 and IL‐10 concentrations from neonates enrolled in a randomized trial comparing one vs. two doses of methylprednisolone to develop indirect response population pharmacokinetic/pharmacodynamic models characterizing the exposure–response relationships. We applied the models to simulate methylprednisolone dosages resulting in the desired IL‐6 and ‐10 exposures, known mediators of CPB‐induced inflammation. A total of 64 neonates (median weight 3.2 kg, range 2.2–4.3) contributed 290 plasma methylprednisolone concentrations (range 1.07–12,700 ng/mL) and IL‐6 (0–681 pg/mL) and IL‐10 (0.1–1125 pg/mL). Methylprednisolone plasma exposure following a single 10 mg/kg intravenous dose inhibited IL‐6 and stimulated IL‐10 production when compared with placebo. Higher (30 mg/kg) or more frequent (twice) dosing did not confer additional benefit. Clinical efficacy studies are needed to evaluate the effect of optimized dosing on outcomes.

The Path to Perfect Pediatric Posology - Drug Development in Pediatrics

Reluctance to enroll pediatric subjects in clinical trials has left gaps in information about dosing, safety, and efficacy of medications. Pharmacotherapeutic information for pediatric patients may be available for only a small range of ages and may be deficient, as children respond differently as they grow and mature from prematurity to adolescence. Current regulations, however, require early planning for the participation of children in drug development, as pediatric plans must be submitted at the end of phase 1 (European Union) or the end of phase 2 (United States). These plans are extensive, outlining planned studies, subjects to be enrolled, dose and dosage form justification, planned observations, and statistical analysis as well as planned modeling, simulation, and extrapolation analyses. The extent to which efficacy information in adults can be extrapolated to children depends on how similar the disease is in adults and each of the 5 pediatric age groups. Extrapolation may not be possible for conditions that do not occur in adults, requiring a complete development plan in adults, or extrapolation may be complete because of similar pathology and response to treatment. Pharmacokinetic and safety information cannot be extrapolated and must be collected in children of all ages, unless a waiver is granted. Physiologically based pharmacokinetic modeling, optimal design, population pharmacokinetics, and scavenged samples are all examples of new methodologies being used to study pediatric therapeutics. Clinicaltrials.gov and EU Clinical Trials registry are good sources of results of pediatric trials, although sponsors are also working toward prompt publication of study results in peer-reviewed journals.

Population pharmacokinetic modeling to facilitate dose selection of tapentadol in the pediatric population

OBJECTIVE

The main aim of this analysis was to characterize the pharmacokinetics (PK) of the strong analgesic tapentadol in 2-year-old to <18-year-old patients with acute pain and to inform the optimal dosing strategy for a confirmatory efficacy trial in this patient population.

METHODS

The analysis dataset included tapentadol concentrations obtained from 92 pediatric patients receiving a single tapentadol oral solution (OS) dose of 1.0 mg/kg bodyweight in two single-dose PK clinical trials. Population PK analysis was performed using nonlinear mixed effects modeling. Simulations were performed to identify tapentadol OS doses in pediatric subjects (2 to <18 years) that would produce exposures similar to those in adults receiving safe and efficacious doses of tapentadol IR (50-100 mg every 4 hrs).

RESULTS

Tapentadol PK in children aged from 2 to <18 years was best described by a one-compartment model. Mean population apparent clearance and apparent volume of distribution for a typical subject weighing 45 kg were 170 L/h and 685 L, respectively. Clearance, expressed in bodyweight units as L/h/kg, decreased with increasing age whereas total clearance (L/h) increased with increasing age. Model-based simulations suggested that a tapentadol OS dose of 1.25 mg/kg to children and adolescents aged 2 to <18 years would result in efficacious tapentadol exposures similar to those in adults receiving tapentadol immediate release 50-100 mg every 4 hrs. The proposed tapentadol OS dose was subsequently applied in a confirmatory efficacy trial in 2 to <18-year-old patients suffering from acute postsurgical pain.

CONCLUSION

This analysis provides an example of a model-based approach for a dose recommendation to be used in an efficacy trial in the pediatric population. Uniform dosing based on bodyweight was proposed for the treatment of acute pain in children aged from 2 to <18 years.

Population pharmacokinetics of piperacillin in febrile children receiving cancer chemotherapy: the impact of body weight and target on an optimal dosing regimen

BACKGROUND

The β-lactam antibiotic piperacillin (in combination with tazobactam) is commonly chosen for empirical treatment of suspected bacterial infections. However, pharmacokinetic variability among patient populations and across ages leads to uncertainty when selecting a dosing regimen to achieve an appropriate pharmacodynamic target.

OBJECTIVES

To guide dosing by establishing a population pharmacokinetic model for unbound piperacillin in febrile children receiving cancer chemotherapy, and to assess pharmacokinetic/pharmacodynamic target attainment (100% fT > 1×MIC and 50% fT > 4×MIC) and resultant exposure, across body weights.

METHODS

Forty-three children admitted for 89 febrile episodes contributed 482 samples to the pharmacokinetic analysis. The typical doses required for target attainment were compared for various dosing regimens, in particular prolonged infusions, across MICs and body weights.

RESULTS

A two-compartment model with inter-fever-episode variability in CL, and body weight included through allometry, described the data. A high CL of 15.4 L/h (70 kg) combined with high glomerular filtration rate (GFR) values indicated rapid elimination and hyperfiltration. The target of 50% fT > 4×MIC was achieved for an MIC of 4.0 mg/L in a typical patient with extended infusions of 2-3 (q6h) or 3-4 (q8h) h, at or below the standard adult dose (75 and 100 mg/kg/dose for q6h and q8h, respectively). Higher doses or continuous infusion were needed to achieve 100% fT > 1×MIC due to the rapid piperacillin elimination.

CONCLUSIONS

The licensed dose for children with febrile neutropenia (80 mg/kg q6h as a 30 min infusion) performs poorly for attainment of fT>MIC pharmacokinetic/pharmacodynamic targets. Given the population pharmacokinetic profile, feasible dosing regimens with reasonable exposure are continuous infusion (100% fT > 1×MIC) or prolonged infusions (50% fT > 4×MIC).