What is the best size predictor for dose in the obese child?

Tofacitinib pharmacokinetics in children and adolescents with juvenile idiopathic arthritis

These analyses characterized tofacitinib pharmacokinetics (PKs) in children and adolescents with juvenile idiopathic arthritis (JIA). Data were pooled from phase I (NCT01513902), phase III (NCT02592434), and open-label, long-term extension (NCT01500551) studies of tofacitinib tablet/solution (weight-based doses administered twice daily [b.i.d.]) in patients with JIA aged 2 to less than 18 years. Population PK modeling used a nonlinear mixed-effects approach, with covariates identified using stepwise forward-inclusion backward-deletion procedures. Simulations were performed to derive dosing recommendations for children and adolescents with JIA. Two hundred forty-six pediatric patients were included in the population PK model. A one-compartment model with first-order elimination and absorption with body weight as a covariate for oral clearance and apparent volume of distribution sufficiently described the data. Oral solution was associated with comparable average concentration (Cavg) and slightly higher (113.9%) maximum concentration (Cmax) versus tablet, which was confirmed by a subsequent randomized, open-label, bioavailability study conducted in healthy adult participants (n = 12) by demonstrating adjusted geometric mean ratios (90% confidence interval) between oral solution and tablet of 1.04 (1.00-1.09) and 1.10 (1.00-1.21) for area under the curve extrapolated to infinity and Cmax, respectively (NCT04111614). A dosing regimen of 3.2 mg b.i.d. solution in patients 10 to less than 20 kg, 4 mg b.i.d. solution in patients 20 to less than 40 kg, and 5 mg b.i.d. tablet/solution in patients greater than or equal to 40 kg, irrespective of age, was proposed to achieve constant Cavg across weight groups. In summary, population PK characterization informed a simplified tofacitinib dosing regimen that has been implemented in pediatric patients with JIA.

Dabigatran pharmacokinetic-pharmacodynamic in sheep: Informing dose for anticoagulation during cardiopulmonary bypass

BACKGROUND

The effect of the anticoagulant, dabigatran, and its antagonist, idarucizumab, on coagulation remains poorly quantified. There are few pharmacokinetic-pharmacodynamic data available to determine dabigatran dose in humans or animals undergoing cardiopulmonary bypass.

METHODS

Five sheep were given intravenous dabigatran 4 mg/kg. Blood samples were collected for thromboelastometric reaction time (R-time) and drug assay at 5, 15, 30, 60, 120, 240, 480 min, and 24 h. Plasma dabigatran concentrations and R-times were analyzed using an integrated pharmacokinetic-pharmacodynamic model using non-linear mixed effects. The impact of idarucizumab 15 mg/kg administered 120 min after dabigatran 4 mg/kg and its effect on R-time was observed.

RESULTS

A 2-compartment model described dabigatran pharmacokinetics with a clearance (CL 0.0453 L/min/70 kg), intercompartment clearance (Q 0.268 L/min/70 kg), central volume of distribution (V1 2.94 L/70 kg), peripheral volume of distribution (V2 9.51 L/70 kg). The effect compartment model estimates for a sigmoid EMAX model using Reaction time had an effect site concentration (Ce50 64.2 mg/L) eliciting half of the maximal effect (EMAX 180 min). The plasma-effect compartment equilibration half time (T1/2keo) was 1.04 min. Idarucizumab 15 mg/kg reduced R-time by approximately 5 min.

CONCLUSIONS

Dabigatran reversibly binds to the active site on the thrombin molecule, preventing activation of coagulation factors. The pharmacologic target concentration strategy uses pharmacokinetic-pharmacodynamic information to inform dose. A loading dose of dabigatran 0.25 mg/kg followed by a maintenance infusion of dabigatran 0.0175 mg/kg/min for 30 min and a subsequent infusion dabigatran 0.0075 mg/kg/min achieves a steady state target concentration of 5 mg/L in a sheep model.

Preliminary pharmacokinetics and patient experience of jet-injected dexmedetomidine in healthy adults

Jet injection is a drug delivery system without a needle. A compressed liquid drug formulation pierces the skin, depositing the drug into the subcutaneous or intramuscular tissues. We investigated the pharmacokinetics and patient experience of dexmedetomidine administered using jet injection in six healthy adult study participants. This needleless jet injection device was used to administer dexmedetomidine 0.5 μg/kg to the subcutaneous tissues overlying the deltoid muscle. Serum concentrations of dexmedetomidine were assayed at approximately 5 minutes, 15 minutes, 30 minutes, 1 hour and 4 hours after administration. Pharmacokinetic interrogation of concentration time profiles estimated an absorption half time for jet-injected dexmedetomidine of 21 minutes (coefficient of variation 69.4%) with a relative bioavailability assumed unity. In our samples the measured median peak (range) concentration was 0.164 μg/l (0.011-0.325 μg/l), observed in the sample taken at a median (range) of 13.5 minutes (11-30 minutes). The Richmond agitation sedation scale was used to assess the sedative effect, and scored 0 (alert and calm) or -1 (drowsy) in all participants. Five of the six participants stated they would prefer jet injection to needle injection in the future and one had no preference. The findings suggest that the use of a larger dose (>2 μg/kg) would be required to achieve the clinically relevant target concentration of 1 μg/l necessary to achieve deeper sedation (Richmond agitation sedation scale ≤3).

Pharmacokinetics and Proposed Dosing of Levetiracetam in Children With Obesity

OBJECTIVE

Characterize levetiracetam pharmacokinetics (PK) in children with obesity to inform dosing.

METHODS

Children 2 to <21 years old receiving standard of care oral levetiracetam across two opportunistic studies provided blood samples. Levetiracetam plasma PK data were analyzed with a nonlinear mixed-effects modeling approach. Indirect measures for body size and covariates were tested for model inclusion. Individual empirical Bayesian estimates using the final model parameters were compared by obesity status. Monte Carlo simulation using total body weight was performed in children with normal estimated glomerular filtration rate to identify dosing for children with obesity that resulted in comparable exposures to normal weight adults and children after receiving label dosing.

RESULTS

The population PK model was developed from 341 plasma concentrations from 169 children. A 1-compartment model best fit the data with fat-free mass as a significant covariate. Compared with children with normal weight, children with obesity had significantly lower body weight-normalized clearance (median [range], 4.77 [1.49-10.44] and 3.71 [0.86-13.55] L/h/70 kg, respectively). After label dosing with the oral formulation in children with obesity 4 to <16 years old, maximum and minimum steady-state concentrations were higher (25% and 41%, respectively [oral solution] and 27% and 19%, respectively [tablet]) compared with children with normal weight. Comparable exposures between children with and without obesity were achieved with weight-tiered dosing regimens of <75 kg or ≥75 kg.

CONCLUSIONS

Weight-tiered dosing for levetiracetam oral solution and tablets for children with obesity 4 to <16 years old results in more comparable exposures to children of normal weight.

Modeling adult COX-2 cerebrospinal fluid pharmacokinetics to inform pediatric investigation

AIM

Hysteresis is reported between plasma concentration and analgesic effect from nonsteroidal anti-inflammatory drugs. It is possible that the temporal delay between plasma and CSF nonsteroidal anti-inflammatory drugs mirrors this hysteresis. The temporal relationship between plasma and CSF concentrations of COX-inhibitors (celecoxib, rofecoxib, valdecoxib) has been described. The purpose of this secondary data analysis was to develop a compartmental model for plasma and CSF disposition of these COX-2 inhibitors.

METHODS

Plasma and CSF concentration-time profiles and protein binding data in 10 adult volunteers given oral celecoxib 200 mg, valdecoxib 40 mg and rofecoxib 50 mg were available for study. Nonlinear mixed effects models with a single plasma compartment were used to link a single CSF compartment with a transfer factor and an equilibration rate constant (Keq). To enable predictive modeling in pediatrics, celecoxib pharmacokinetics were standardized using allometry.

RESULTS

Movement of all three unbound plasma COX-2 drugs into CSF was characterized by a common equilibration half-time (T_1/2 keq) of 0.84 h. Influx was faster than efflux and a transfer scaling factor of 2.01 was required to describe conditions at steady-state. Estimated celecoxib clearance was 49 (95% CI 34-80) L/h/70 kg and the volume of distribution was 346 (95% CI 237-468) L/70 kg. The celecoxib absorption half-time was 0.35 h with a lag time of 0.62 h. Simulations predicted a 70-kg adult given oral celecoxib 200 mg with maintenance 100 mg twice daily would have a mean steady-state total (bound and unbound) plasma concentration of 174 μg L^-1 and CSF concentration of 1.1 μg L^-1 . A child (e.g., 25 kg, typically 7 years) given oral celecoxib 6 mg kg^-1 with maintenance of 3 mg kg^-1 twice daily would have 282 and 1.7 μg L^-1 mean plasma and CSF concentrations, respectively.

CONCLUSIONS

Transfer of unbound COX-2 inhibitors from plasma to CSF compartment can be described with a delayed effect model using an equilibration rate constant to collapse observed hysteresis. An additional transfer factor was required to account for passage across the blood-brain barrier. Use of a target concentration strategy for dose and consequent plasma (total and unbound) and CSF concentration prediction could be used to inform pediatric clinical studies.

Perioperative Acetaminophen Dosing in Obese Children

Acetaminophen is a commonly used perioperative analgesic drug in children. The use of a preoperative loading dose achieves a target concentration of 10 mg/L associated with a target analgesic effect that is 2.6 pain units (visual analogue scale 1–10). Postoperative maintenance dosing is used to keep this effect at a steady-state concentration. The loading dose in children is commonly prescribed per kilogram. That dose is consistent with the linear relationship between the volume of distribution and total body weight. Total body weight is made up of both fat and fat-free mass. The fat mass has little influence on the volume of distribution of acetaminophen but fat mass should be considered for maintenance dosing that is determined by clearance. The relationship between the pharmacokinetic parameter, clearance, and size is not linear. A number of size metrics (e.g., fat-free and normal fat mass, ideal body weight and lean body weight) have been proposed to scale clearance and all consequent dosing schedules recognize curvilinear relationships between clearance and size. This relationship can be described using allometric theory. Fat mass also has an indirect influence on clearance that is independent of its effects due to increased body mass. Normal fat mass, used in conjunction with allometry, has proven a useful size metric for acetaminophen; it is calculated using fat-free mass and a fraction (Ffat) of the additional mass contributing to total body weight. However, the Ffat for acetaminophen is large (Ffat = 0.82), pharmacokinetic and pharmacodynamic parameter variability high, and the concentration–response slope gentle at the target concentration. Consequently, total body weight with allometry is acceptable for the calculation of maintenance dose. The dose of acetaminophen is tempered by concerns about adverse effects, notably hepatotoxicity associated with use after 2–3 days at doses greater than 90 mg/kg/day.

Population Pharmacokinetic Model for Unbound Concentrations of Daptomycin in Patients with MRSA Including Patients Undergoing Hemodialysis

BACKGROUND AND OBJECTIVE

Unbound daptomycin concentrations are responsible for pharmacologically beneficial and adverse effects, although most previous reports have been limited to the use of total concentrations. We developed a population pharmacokinetic model to predict both total and unbound daptomycin concentrations.

METHODS

Clinical data were collected from 58 patients with methicillin-resistant Staphylococcus aureus including patients undergoing hemodialysis. A total of 339 serum total and 329 unbound daptomycin concentrations were used for model construction.

RESULTS

Total and unbound daptomycin concentration was explained by a model that assumed first-order distribution with two compartments, and first-order elimination. Normal fat body mass was identified as covariates. Renal function was incorporated as a linear function of renal clearance and independent non-renal clearance. The unbound fraction was estimated to be 0.066 with a standard albumin of 45 g/L and standard creatinine clearance of 100 mL/min. Simulated unbound daptomycin concentration was compared with minimum inhibitory concentration as a measure of clinical effectiveness and exposure-level-related induction of creatine phosphokinase elevation. The recommended doses were 4 mg/kg for patients with severe renal function [creatinine clearance (CLcr) ≤ 30 mL/min] and 6 mg/kg for patients with mild to moderate renal function (CLcr > 30 and ≤ 60 mL/min). A simulation indicated that dose adjusted by body weight and renal function improved target attainment.

CONCLUSIONS

This population pharmacokinetics model for unbound daptomycin could help clinicians to select the appropriate dose regimen for patients undergoing daptomycin treatment and reduce associated adverse effects.

Considerations for Intravenous Anesthesia Dose in Obese Children: Understanding PKPD

The intravenous induction or loading dose in children is commonly prescribed per kilogram. That dose recognizes the linear relationship between volume of distribution and total body weight. Total body weight comprises both fat and fat-free mass. Fat mass influences the volume of distribution and the use of total body weight fails to recognize the impact of fat mass on pharmacokinetics in children. Size metrics alternative to total body mass (e.g., fat-free and normal fat mass, ideal body weight and lean body weight) have been proposed to scale pharmacokinetic parameters (clearance, volume of distribution) for size. Clearance is the key parameter used to calculate infusion rates or maintenance dosing at steady state. Dosing schedules recognize the curvilinear relationship, described using allometric theory, between clearance and size. Fat mass also has an indirect influence on clearance through both metabolic and renal function that is independent of its effects due to increased body mass. Fat-free mass, lean body mass and ideal body mass are not drug specific and fail to recognize the variable impact of fat mass contributing to body composition in children, both lean and obese. Normal fat mass, used in conjunction with allometry, may prove a useful size metric but computation by clinicians for the individual child is not facile. Dosing is further complicated by the need for multicompartment models to describe intravenous drug pharmacokinetics and the concentration effect relationship, both beneficial and adverse, is often poorly understood. Obesity is also associated with other morbidity that may also influence pharmacokinetics. Dose is best determined using pharmacokinetic-pharmacodynamic (PKPD) models that account for these varied factors. These models, along with covariates (age, weight, body composition), can be incorporated into programmable target-controlled infusion pumps. The use of target-controlled infusion pumps, assuming practitioners have a sound understanding of the PKPD within programs, provide the best available guide to intravenous dose in obese children.

Justification Of Empiric Methodology to Determine Dexmedetomidine Dose for the TREX Study

INTRODUCTION

Dexmedetomidine is the sedative agent administered in combination with remifentanil and low dose of sevoflurane in the interventional arm of the ongoing TREX trial (Trial Remifentanil DExmedetomidine). The TREX pilot study (published in Paediatr Anaesth 2019;29:59-67) established infusion rates higher than those initially proposed. This could be attributed to an inappropriate target concentration for sedation or incorrect initial pharmacokinetic parameter estimates.

METHODS

The TREX study is a Phase III, randomized, active controlled, parallel group, blinded evaluator, multicentre, superiority trial comparing neurological outcome after standard sevoflurane anaesthesia with dexmedetomidine/remifentanil and low dose sevoflurane anaesthesia in children aged less than 2 years undergoing anaesthesia of 2 hours or longer. In this report, dexmedetomidine pharmacokinetics were analysed in the interventional arm of the Italian population.

RESULTS

There were 162 blood samples from 32 infants (22 male and 10 female). The median (IQR) age was 12 (5.2-15.5) months, weight 9.9 (7.3-10.8) kg. Duration of anaesthesia ranged from 2-6 hours. None of the children were born premature (median postnatal age 39 weeks, IQR 38-40 weeks). A 3-compartment PK model that incorporated allometric scaling and a maturation function demonstrated plasma concentration observations from the current Italian arm of the TREX study were consistent with those predicted by a "universal" model using pooled data obtained from neonates to adults.

CONCLUSIONS

This current PK analysis from the Italian arm of the TREX study confirms that plasma concentration of dexmedetomidine is predictable using known covariates such as age and size. The initial target concentration (0.6 μg.L-1 ) used to sedate children cared for in the intensive care after cardiac surgery was inadequate for infants in the current TREX study. A target concentration 1 mcg.L-1 , corresponding to a loading dose of 1 mcg.kg-1 followed by an infusion of 1 mcg.kg-1 .hour-1 , provided adequate sedation.

Pharmacokinetic Pharmacodynamic Modelling Contributions to Improve Paediatric Anaesthesia Practice

The use of pharmacokinetic-pharmacodynamic models has improved anaesthesia practice in children through a better understanding of dose-concentration-response relationships, developmental pharmacokinetic changes, quantification of drug interactions and insights into how covariates (e.g., age, size, organ dysfunction, pharmacogenomics) impact drug prescription. Simulation using information from these models has enabled the prediction and learning of beneficial and adverse effects and decision-making around clinical scenarios. Covariate information, including the use of allometric size scaling, age and consideration of fat mass, has reduced population parameter variability. The target concentration approach has rationalised dose calculation. Paediatric pharmacokinetic-pharmacodynamic insights have led to better drug delivery systems for total intravenous anaesthesia and an expectation about drug offset when delivery is stopped. Understanding concentration-dependent adverse effects have tempered dose regimens. Quantification of drug interactions has improved the understanding of the effects of drug combinations. Repurposed drugs (e.g., antiviral drugs used for COVID-19) within the community can have important effects on drugs used in paediatric anaesthesia, and the use of simulation educates about these drug vagaries.

Population Pharmacokinetic Modelling of Acetaminophen and Ibuprofen: the Influence of Body Composition, Formulation and Feeding in Healthy Adult Volunteers

BACKGROUND AND OBJECTIVE

Combined acetaminophen and ibuprofen are common antipyretic and analgesic drugs. Formulation and feeding affect drug absorption. Drug clearance has a nonlinear relationship with total body weight. The covariate effect of fat mass on acetaminophen and ibuprofen pharmacokinetics remains unexplored. This study sought to quantify acetaminophen and ibuprofen pharmacokinetics with intravenous, tablet, sachet and oral suspension formulations in fed and fasted states.

METHODS

Pooled time-concentration data for acetaminophen and ibuprofen were available from fasting and fed healthy adults. Data from intravenous, tablet, sachet and suspension formulations were analysed using nonlinear mixed-effects models. Body composition was considered as a covariate on clearances and volumes of distribution (V_d). Size metrics investigated were total body weight, fat and fat-free mass. Theory-based allometry was used to scale pharmacokinetic parameters to a 70 kg individual. A factor on absorption half-life and lag time quantified delays due to feeding for oral formulations. Pharmacokinetic-pharmacodynamic simulations were used to explore the time courses of pain response for acetaminophen and ibuprofen for each formulation.

RESULTS

Pooled data included 116 individuals (18-49 years, 49-116 kg) with 6095 acetaminophen and 6046 ibuprofen concentrations available for analysis. A two-compartment pharmacokinetic model with first-order elimination described disposition for both drugs. Normal fat mass was the best covariate to describe acetaminophen clearance (CL), with a factor for fat contribution (FFATCL) of 0.816. Acetaminophen volume of distribution was described using total body weight. Normal fat mass was the best covariate to describe ibuprofen clearance (FFATCL = 0.863) and volume of distribution: (FFATV = 0.718). Clearance and central volume of distribution were 24.0 L/h/70 kg and 43.5 L/h/70 kg for acetaminophen. Ibuprofen clearance and central volume of distribution were 3.79 L/h/70 kg and 10.5 L/h/70 kg. Bioavailability and absorption half-life were 86% and 12 min for acetaminophen and 94% and 27 min for ibuprofen. Absorption lag times were 5.3 min and 6.7 min for acetaminophen and ibuprofen, respectively. Feeding increased both absorption half-life and absorption lag time when compared to the tablet formulation under fasting conditions. Feeding had the most pronounced effect on the lag time associated with tablet formulation for both drugs. Time to a pain score reduction of 2 points (visual analogue score, 0-10) differed by only 5-10 min across all formulations for acetaminophen and ibuprofen.

CONCLUSION

Fat mass was an important covariate to describe acetaminophen and ibuprofen pharmacokinetics. The absorption half-lives of acetaminophen and ibuprofen were increased in fed states. The delay in absorption, quantified by a lag time, was protracted for both drugs.

Characterizing Pharmacokinetics in Children With Obesity-Physiological, Drug, Patient, and Methodological Considerations

Childhood obesity is an alarming public health problem. The pediatric obesity rate has quadrupled in the past 30 years, and currently nearly 20% of United States children and 9% of children worldwide are classified as obese. Drug distribution and elimination processes, which determine drug exposure (and thus dosing), can vary significantly between patients with and without obesity. Obesity-related physiological changes, such as increased tissue volume and perfusion, altered blood protein concentrations, and tissue composition can greatly affect a drug's volume of distribution, which might necessitate adjustment in loading doses. Obesity-related changes in the drug eliminating organs, such as altered enzyme activity in the liver and glomerular filtration rate, can affect the rate of drug elimination, which may warrant an adjustment in the maintenance dosing rate. Although weight-based dosing (i.e., in mg/kg) is commonly practiced in pediatrics, choice of the right body size metric (e.g., total body weight, lean body weight, body surface area, etc.) for dosing children with obesity still remains a question. To address this gap, the interplay between obesity-related physiological changes (e.g., altered organ size, composition, and function), and drug-specific properties (e.g., lipophilicity and elimination pathway) needs to be characterized in a quantitative framework. Additionally, methodological considerations, such as adequate sample size and optimal sampling scheme, should also be considered to ensure accurate and precise top-down covariate selection, particularly when designing opportunistic studies in pediatric drug development. Further factors affecting dosing, including existing dosing recommendations, target therapeutic ranges, dose capping, and formulations constraints, are also important to consider when undergoing dose selection for children with obesity. Opportunities to bridge the dosing knowledge gap in children with obesity include modeling and simulating techniques (i.e., population pharmacokinetic and physiologically-based pharmacokinetic [PBPK] modeling), opportunistic clinical data, and real world data. In this review, key considerations related to physiology, drug parameters, patient factors, and methodology that need to be accounted for while studying the influence of obesity on pharmacokinetics in children are highlighted and discussed. Future studies will need to leverage these modeling opportunities to better describe drug exposure in children with obesity as the childhood obesity epidemic continues.

Opioids for acute pain management in children

Opioids are integral to multimodal analgesic regimens in children with moderate to severe acute pain. Throughout normal childhood there are marked changes in physiology, and social and psychological development that influence the perception and expression of pain, the pharmacology of opioids, and how they are used. A multidimensional pain assessment is key to guiding appropriate opioid prescribing. Most of the commonly used opioids in adults are used in children, with the increasing exception of codeine (as a result of regulatory change), and are generally well tolerated. Patient groups at increased risk of ventilatory impairment include neonates and those with obstructive sleep apnoea, severe neurodevelopmental conditions, trisomy 21, and severe epilepsy. Slow-release opioids are not recommended for general use, but may be used in select populations, for example, following scoliosis surgery, major trauma or burns. Prescribing and administration errors are a major issue in paediatrics generally; the potential consequences of opioid prescribing or administration errors are serious, particularly following hospital discharge. Opioids prescribed at discharge are frequently in excess of a child's analgesic requirements; three to five days supply appears sufficient for the majority of common paediatric operations. Discharge opioid prescriptions have been linked to long-term opioid use in adolescents with risk factors. Misuse of prescription opioids by adolescents is also concerning, with prevalence estimates ranging from 1.1% to 20%. Caregivers have a tendency to underdose opioids in their children; caregiver education may improve appropriate administration. Caregivers must also be provided with instructions on safe storage and disposal of unused opioids.

Interactions between Food and Drugs, and Nutritional Status in Renal Patients: A Narrative Review

Drugs and food interact mutually: drugs may affect the nutritional status of the body, acting on senses, appetite, resting energy expenditure, and food intake; conversely, food or one of its components may affect bioavailability and half-life, circulating plasma concentrations of drugs resulting in an increased risk of toxicity and its adverse effects, or therapeutic failure. Therefore, the knowledge of these possible interactions is fundamental for the implementation of a nutritional treatment in the presence of a pharmacological therapy. This is the case of chronic kidney disease (CKD), for which the medication burden could be a problem, and nutritional therapy plays an important role in the patient’s treatment. The aim of this paper was to review the interactions that take place between drugs and foods that can potentially be used in renal patients, and the changes in nutritional status induced by drugs. A proper definition of the amount of food/nutrient intake, an adequate definition of the timing of meal consumption, and a proper adjustment of the drug dosing schedule may avoid these interactions, safeguarding the quality of life of the patients and guaranteeing the effectiveness of drug therapy. Hence, a close collaboration between the nephrologist, the renal dietitian, and the patient is crucial. Dietitians should consider that food may interact with drugs and that drugs may affect nutritional status, in order to provide the patient with proper dietary suggestions, and to allow the maximum effectiveness and safety of drug therapy, while preserving/correcting the nutritional status.

Finerenone Dose-Exposure-Response for the Primary Kidney Outcome in FIDELIO-DKD Phase III: Population Pharmacokinetic and Time-to-Event Analysis

BACKGROUND

Finerenone is a nonsteroidal selective mineralocorticoid receptor antagonist that recently demonstrated efficacy in delaying chronic kidney disease progression and reducing cardiovascular events in patients with chronic kidney disease and type 2 diabetes in FIDELIO-DKD, where 5734 patients were randomized 1:1 to receive either titrated finerenone doses of 10 or 20 mg once daily or placebo, with a median follow-up of 2.6 years.

METHODS

Nonlinear mixed-effects population pharmacokinetic models were used to analyze the pharmacokinetics in FIDELIO-DKD, sparsely sampled in all subjects receiving finerenone. Post-hoc model parameter estimates together with dosing histories allowed the computation of individual exposures used in subsequent parametric time-to-event analyses of the primary kidney outcome.

RESULTS

The population pharmacokinetic model adequately captured the typical pharmacokinetics of finerenone and its variability. Either covariate effects or multivariate forward-simulations in subgroups of interest were contained within the equivalence range of 80-125% around typical exposure. The exposure-response relationship was characterized by a maximum effect model estimating a low half-maximal effect concentration at 0.166 µg/L and a maximal hazard decrease at 36.1%. Prognostic factors for the treatment-independent chronic kidney disease progression risk included a low estimated glomerular filtration rate and a high urine-to-creatinine ratio increasing the risk, while concomitant sodium-glucose transport protein 2 inhibitor use decreased the risk. Importantly, no sodium-glucose transport protein 2 inhibitor co-medication-related modification of the finerenone treatment effect per se could be identified.

CONCLUSIONS

None of the tested pharmacokinetic covariates had clinical relevance in FIDELIO-DKD. Finerenone effects on kidney outcomes approached saturation towards 20 mg once daily and sodium-glucose transport protein 2 inhibitor use provided additive benefits.

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.

Pharmacokinetic concepts for dexmedetomidine target-controlled infusion pumps in children

Pharmacokinetic parameter estimates are used in mathematical equations (pharmacokinetic models) to describe concentration changes with time in a population and are specific to that population. Simulation using these models and their parameter estimates can enrich understanding of drug behavior and serve as a basis for study design. Pharmacokinetic concepts are presented pertaining to future designs of dexmedetomidine target-controlled infusion pumps in children. This manuscript provides the pediatric anesthesiologist with an understanding of the nuances that should be considered when using target-controlled infusion pumps; how the central volume may differ between populations, how clearance changes with age, and the impact of adverse effects on dose. In addition, the ideal loading dose and rate of delivery to achieve target concentration without adverse cardiovascular effects are reviewed, and finally, dose considerations for obese children, based on contact-sensitive half-time, are introduced. An understanding of context-sensitive half-time changes with age enables anesthetic practitioners to better estimate duration of effect after cessation of dexmedetomidine infusion. Use of these known pharmacokinetic parameters and covariate information for the pediatric patient could readily be incorporated into commercial target-controlled infusion pumps to allow effective and safe open-loop administration of dexmedetomidine in children.

Precision dosing of intravenous busulfan in pediatric hematopoietic stem cell transplantation: Results from a multicenter population pharmacokinetic study

Busulfan (Bu) is a common component of conditioning regimens before hematopoietic stem cell transplantation (HSCT) and is known for high interpatient pharmacokinetic (PK) variability. This study aimed to develop and externally validate a multicentric, population PK (PopPK) model for intravenous Bu in pediatric patients before HSCT to first study the influence of glutathione‐s‐transferase A1 (GSTA1) polymorphisms on Bu's PK in a large multicentric pediatric population while accounting for fludarabine (Flu) coadministration and, second, to establish an individualized, model‐based, first‐dose recommendation for intravenous Bu that can be widely used in pediatric patients. The model was built using data from 302 patients from five transplantation centers who received a Bu‐based conditioning regimen. External model validation used data from 100 patients. The relationship between body weight and Bu clearance (CL) was best described by an age‐dependent allometric scaling of a body weight model. A stepwise covariate analysis identified Day 1 of Bu conditioning, GSTA1 metabolic groups based on GSTA1 polymorphisms, and Flu coadministration as significant covariates influencing Bu CL. The final model adequately predicted Bu first‐dose CL in the external cohort, with 81% of predicted area under the curves within the therapeutic window. The final model showed minimal bias (mean prediction error, −0.5%; 95% confidence interval [CI], −3.1% to 2.0%) and acceptable precision (mean absolute prediction error percentage, 18.7%; 95% CI, 17.0%–20.5%) in Bu CL prediction for dosing. This multicentric PopPK study confirmed the influence of GSTA1 polymorphisms and Flu coadministration on Bu CL. The developed model accurately predicted Bu CL and first doses in an external cohort of pediatric patients.

A Universal Pharmacokinetic Model for Dexmedetomidine in Children and Adults

A universal pharmacokinetic model was developed from pooled paediatric and adult data (40.6 postmenstrual weeks, 70.8 years, 3.1-152 kg). A three-compartment pharmacokinetic model with first-order elimination was superior to a two-compartment model to describe these pooled dexmedetomidine data. Population parameter estimates (population parameter variability%) were clearance (CL) 0.9 L/min/70 kg (36); intercompartmental clearances (Q2) 1.68 L/min/70 kg (63); Q3 0.62 L/min/70 kg (90); volume of distribution in the central compartment (V1) 25.2 L/70 kg (103.9); rapidly equilibrating peripheral compartment (V2) 34.4 L/70 kg (41.8); slow equilibrating peripheral compartment (V3) 65.4 L/70 kg (62). Obesity was best described by fat-free mass for clearances and normal fat mass for volumes with a factor for fat mass (FfatV) of 0.293. Models describing dexmedetomidine pharmacokinetics in adults can be applied to children by accounting for size (allometry) and age (maturation). This universal dexmedetomidine model is applicable to a broad range of ages and weights: neonates through to obese adults. Lean body weight is a better size descriptor for dexmedetomidine clearance than total body weight. This parameter set could be programmed into target-controlled infusion pumps for use in a broad population.

Hormonal Blood Pressure Regulationduring General Anesthesia Usinga Standardized Propofol Dosagein Children and Adolescents SeemsNot to Be Affected by Body Weight

Obesity in pediatric surgical patients is a challenge for the anesthesiologist. Despite potentially beneficial properties, propofol might also induce hypotension. This study examined whether a dose adjustment in overweight children could avoid hypotension and if there would be differences regarding hormonal regulation in children under anesthesia. Fifty-nine children undergoing surgery under general anesthesia were enrolled in this prospective observational trial. Participants were allocated into two groups according to their BMI. The induction of anesthesia was conducted using propofol (“overweight”: 2 mg/kgBW, “regular”: 3.2 mg/kgBW). The maintenance of anesthesia was conducted as total intravenous anesthesia. Hormone levels of renin, angiotensin II, aldosterone, copeptin, norepinephrine and epinephrine were assessed at different timepoints. Blood pressure dropped after the administration of propofol in both groups, with a nadir 2 min after administration—but without a significant difference in the strength of reduction between the two groups. As a reaction, an increase in the plasma levels of renin, angiotensin and aldosterone was observed, while levels of epinephrine, norepinephrine and copeptin dropped. By adjusting the propofol dosage in overweight children, the rate of preincision hypotension could be reduced to the level of normal-weight patients with a non-modified propofol dose. The hormonal counter regulation was comparable in both groups. The release of catecholamines and copeptin as an indicator of arginine vasopressin seemed to be inhibited by propofol.

Pharmacokinetic and pharmacodynamic considerations of general anesthesia in pediatric subjects

Introduction: The target concentration strategy uses PKPD information for dose determination. Models have also quantified exposure-response relationships, improved understanding of developmental pharmacokinetics, rationalized dose prescription, provided insight into the importance of covariate information, explained drug interactions and driven decision-making and learning during drug development.Areas covered: The prime PKPD consideration is parameter estimation and quantification of variability. The main sources of variability in children are age (maturation) and weight (size). Model use is mostly confined to pharmacokinetics, partly because anesthesia effect models in the young are imprecise. Exploration of PK and PD covariates and their variability hold potential to better individualize treatment.Expert opinion: The ability to model drugs using computer-based technology is hindered because covariate data required to individualize treatment using these programs remain lacking. Target concentration intervention strategies remain incomplete because covariate information that might better predict individualization of dose is absent. Pharmacogenomics appear a valuable area for investigation for pharmacodynamics and pharmacodynamics. Effect measures in the very young are imprecise. Assessment of the analgesic component of anesthesia is crude. While neuromuscular monitoring is satisfactory, depth of anaesthesia EEG interpretation is inadequate. Closed loop anesthesia is possible with better understanding of EEG changes.

Drug Dose Selection in Pediatric Obesity: Available Information for the Most Commonly Prescribed Drugs to Children

Obesity rates continue to rise in children, and little guidance exists regarding the need for adjustment away from total body weight-based doses for those prescribing drugs to this population of children. A majority of drugs prescribed to children with obesity result in either sub-therapeutic or supra-therapeutic concentrations, placing these children at risk for treatment failure and drug toxicities. In this review, we highlight available obesity-specific pharmacokinetic and dosing information for the most frequently prescribed drugs to children in the inpatient and outpatient clinical settings. We also comment on available dosing recommendations for drugs prescribed to treat common pediatric obesity-related comorbidities. This review highlights that there is no safe or proven 'rule of thumb,' for dosing drugs for children with obesity, and a striking lack of pharmacokinetic data to support the creation of dosing guidelines for children with obesity for the most commonly prescribed drugs. It is important that those prescribing for children with obesity are aware of these gaps in knowledge and of potential drug treatment failure or adverse events related to drug toxicity as a result of these knowledge gaps. Until more data are available, we recommend close monitoring of drug response and adverse events in children with obesity receiving commonly prescribed drugs.

A manual propofol infusion regimen for neonates and infants

AIMS

Manual propofol infusion regimens for neonates and infants have been determined from clinical observations in children under the age of 3 years undergoing anesthesia. We assessed the performance of these regimens using reported age-specific pharmacokinetic parameters for propofol. Where performance was poor, we propose alternative dosing regimens.

METHODS

Simulations using a reported general purpose pharmacokinetic propofol model were used to predict propofol blood plasma concentrations during manual infusion regimens recommended for children 0-3 years. Simulated steady state concentrations were 6-8 µg.mL^-1 in the first 30 minutes that were not sustained during 100 minutes infusions. Pooled clinical data (n = 161, 1902 plasma concentrations) were used to determine an alternative pharmacokinetic parameter set for propofol using nonlinear mixed effects models. A new manual infusion regimen for propofol that achieves a steady-state concentration of 3 µg.mL^-1 was determined using a heuristic approach.

RESULTS

A manual dosing regimen predicted to achieve steady-state plasma concentration of 3 µg.mL^-1 comprised a loading dose of 2 mg.kg^-1 followed by an infusion rate of 9 mg.kg^-1 .h^-1 for the first 15 minutes, 7 mg.kg^-1 .h^-1 from 15 to 30 minutes, 6 mg.kg^-1 .h^-1 from 30 to 60 minutes, 5 mg.kg^-1 .h^-1 from 1 to 2 hours in neonates (38-44 weeks postmenstrual age). Dose increased with age in those aged 1-2 years with a loading dose of 2.5 mg.kg^-1 followed by an infusion rate of 13 mg.kg^-1 .h^-1 for the first 15 minutes, 12 mg.kg^-1 .h^-1 from 15 to 30 minutes, 11 mg.kg^-1 .h^-1 from 30 to 60 minutes, and 10 mg.kg^-1 .h^-1 from 1 to 2 hours.

CONCLUSION

Propofol clearance increases throughout infancy to reach 92% that reported in adults (1.93 L.min.70 kg^-1 ) by 6 months postnatal age and infusion regimens should reflect clearance maturation and be cognizant of adverse effects from concentrations greater than the target plasma concentration. Predicted concentrations using a published general purpose pharmacokinetic propofol model were similar to those determined using a new parameter set using richer neonatal and infant data.

Practicalities of Total Intravenous Anesthesia and Target-controlled Infusion in Children

Propofol administered in conjunction with an opioid such as remifentanil is used to provide total intravenous anesthesia for children. Drugs can be given as infusion controlled manually by the physician or as automated target-controlled infusion that targets plasma or effect site. Smart pumps programmed with pharmacokinetic parameter estimates administer drugs to a preset plasma concentration. A linking rate constant parameter (keo) allows estimation of effect site concentration. There are two parameter sets, named after the first author describing them, that are commonly used in pediatric target-controlled infusion for propofol (Absalom and Kataria) and one for remifentanil (Minto). Propofol validation studies suggest that these parameter estimates are satisfactory for the majority of children. Recommended target concentrations for both propofol and remifentanil depend on the type of surgery, the degree of surgical stimulation, the use of local anesthetic blocks, and the ventilatory status of the patient. The use of processed electroencephalographic monitoring is helpful in pediatric total intravenous anesthesia and target-controlled infusion anesthesia, particularly in the presence of neuromuscular blockade.

Pharmacokinetics, toxicity and clinical efficacy of linezolid in Japanese pediatric patients

OBJECTIVES

The aims of the present study were (a) to evaluate the pharmacokinetics of linezolid, and (b) to assess the toxicity and clinical efficacy of linezolid in Japanese pediatric patients.

PATIENTS AND METHODS

Routine clinical data including serum linezolid total and unbound concentrations were collected from 15 pediatric patients (0-13 years old). Pharmacokinetics of linezolid was assumed to follow one-compartment with the first-order absorption model. The relationship between risk for thrombocytopenia and linezolid concentrations, and the variations in C-reactive protein (CRP) concentrations and body temperatures were evaluated as clinical efficacy assessment.

RESULTS

Body weight (WT) and maturation of body function were significant covariates for pharmacokinetics of linezolid in pediatric patients. The elimination half-life of linezolid in a pediatric patient with a WT of 9.9 kg and age of 24 months (median of this study) was 3.0 h. Thrombocytopenia was detected in three patients (21.4%), and the minimum concentrations (C_min) in these patients were significantly higher than those in patients without thrombocytopenia (P < 0.05). The CRP concentrations decreased more than 50% in all pediatric patients after the treatment with linezolid, however body temperatures at the end of treatment were higher than 37.5 °C in 6 patients (42.9%).

CONCLUSIONS

Although dose adjustment based on body size was performed for pediatric patients, thrombocytopenia was detected in 21.4% of pediatric patients, and higher C_min was associated with the risk of thrombocytopenia. These results encourage the implementation of individual dose adjustment based on linezolid serum concentrations for safe and appropriate treatment with linezolid.

Population Pharmacokinetics and Pharmacodynamics of Teicoplanin and C-Reactive Protein in Hospitalized Patients With Gram-Positive Infections

Teicoplanin is an antibiotic agent used for the treatment of Gram-positive infections. The clinical benefit of teicoplanin is associated with its blood concentrations, but the optimal dosing regimen is not yet known. To explore the optimal individual dosing regimen, we performed a population pharmacokinetic (PK) and pharmacodynamic (PD) analysis targeting a large-scale population, including patients with a wide range of ages, body weights, and renal functions. The PK of teicoplanin was described with a 2-compartment model, and the PD of C-reactive protein (CRP) concentrations was described with a turnover maximum inhibition model. The elimination half-life of teicoplanin calculated from the final estimated parameters was 169 hours, and renal function was a significant covariate of teicoplanin clearance. The teicoplanin concentration producing 50% of the maximum inhibition of CRP production was estimated to be 2.66 mg/L. The minimum concentration of teicoplanin in patients with higher loading doses (15 mg/kg) reached the target range (15-30 mg/L) with a probability of >50% in the dosing simulation. We described the influence of body size, body composition, and renal function on the PK of teicoplanin. The population PKPD model of teicoplanin and CRP in this study should provide useful information for development of a dosing strategy including the sequential clinical benefit of teicoplanin.

Acetaminophen pharmacokinetics in severely obese adolescents and young adults

BACKGROUND

Intravenous acetaminophen is commonly administered as an adjunctive to opioids during major surgical procedures, but neither the correct pharmacokinetic size descriptor nor the dose is certain in severely obese adolescents undergoing bariatric surgery.

METHODS

Adolescents, 14-20 years of age, with a body mass index (BMI) ≥95th percentile for age and sex or BMI ≥40 kg·m^-2 , presenting for laparoscopic or robotic assisted or vertical sleeve gastrectomy were administered intravenous acetaminophen (1000 mg) following completion of the surgical procedure. Venous blood was drawn for acetaminophen assay at eight time points, starting 15 minutes after completion of the infusion and up to 12 hours afterward. Time-concentration data profiles were analyzed using nonlinear mixed effects models. Parameter estimates were scaled to a 70-kg person using allometry. Normal fat mass was used to assess the impact of obesity on pharmacokinetic parameters.

RESULTS

The study cohort comprised 11 female patients, age 17 SD 2 years with a weight of 125 SD 19 kg and a mean BMI of 46 SD 5 kg·m^-2 . The plasma acetaminophen serum concentration was 17 (SD 4) μg·mL^-1 at 10-20 minutes after completion of the infusion and 5 (SD 6) μg·mL^-1 at 80-100 minutes. A two-compartment model, used to investigate pharmacokinetics, estimated clearance 10.6 (CV 72%) L·h·70 kg^-1 , intercompartment clearance 37.3 (CV 63%) L·h·70 kg^-1 , central volume of distribution 20.4 (CV 46%) L·70 kg^-1 , and peripheral volume of distribution 16.8 (CV 42%) L·70 kg^-1 . Clearance was best described using total body weight. Normal fat mass with a parameter that accounts for fat mass contribution (Ffat) of 0.88 best described volumes.

CONCLUSION

Current recommendations of acetaminophen to a maximum dose of 1000 mg resulted in serum concentrations below detection limits in all patients within 2 hours after administration. Dose is better predicted using total body mass with allometric scaling.

Advances in pharmacokinetic modeling: target controlled infusions in the obese

PURPOSE OF REVIEW

The use of conventional pharmacokinetic parameters sets 'models' derived from nonobese patients has proven inadequate to administer intravenous anesthetics in the obese population and is commonly associated with higher than anticipated plasma propofol concentrations when used with target (plasma or effect site) controlled infusion pumps. In this review we will describe recent modeling strategies to characterize the disposition of intravenous anesthetics in the obese patient and will show clinically relevant aspects of new model's performance in the obese population.

RECENT FINDINGS

Because clearance of a drug increases in a nonlinear manner with weight, nonlinear relationships better scale infusion rates between lean and obese individuals. Allometric concepts have been successfully used to describe size-related nonlinear changes in clearances. Other nonlinear scaling options include the use of descriptors such as body surface area, lean body weight, fat-free mass, and normal fat mass. Newer pharmacokinetic models, determined from obese patient data, have been developed for propofol and remifentanil using allometric concepts and comprehensive size descriptors.

SUMMARY

Pharmacokinetic models to perform target-controlled infusion in the obese population should incorporate descriptors that reflect with greater precision the influence of body composition in volumes and clearances of each drug. It is our hope that commercially available pumps will soon incorporate these new models to improve the performance of this technique in the obese population.