Pharmacokinetic model-guided enoxaparin dosing in the Neonatal ICU: Retrospective cohort study to plan for prospective feasibility trial

Traditional milligram per kilogram (mg/kg) dosing of enoxaparin in neonates frequently fails to achieve target anti-Xa levels promptly, necessitating repeated laboratory monitoring and dose adjustments. This study investigated whether a personalized dosing strategy based on predicted individual clearance and volume of distribution could improve outcomes, comparing standard-of-care (SOC) mg/kg dosing to pharmacokinetic (PK) model-informed precision dosing (MIPD). A retrospective analysis was conducted on hospitalized neonates treated with enoxaparin at less than 44 weeks postmenstrual age from 2019 to 2022. Data on demographics, drug dosing, PK model covariates, and clinical outcomes were extracted from electronic health records and analyzed using the Pumas-AI Lyv dosing tool. The primary focus was on comparing the initial SOC dose to the MIPD-recommended dose. The secondary outcome measured was the time required to achieve therapeutic anti-Xa levels. The study included 168 neonates with a median postnatal age of 15 days (range 1-149) and a median dosing weight of 3.1 kg (range: 0.82-5.2). MIPD-recommended initial doses were 20%-60% higher than SOC doses in 32% of the cases and over 60% higher in 11% of cases. Neonates who received SOC doses that were much lower than the MIPD recommendation showed the longest delays in reaching therapeutic anti-Xa levels. The results indicate that PK model-informed of enoxaparin dosing leads to higher initial dosages than SOC in neonates, potentially reducing the time to therapeutic anti-Xa levels. These findings are being utilized to define dosing limits for a prospective trial of MIPD in neonatal intensive care settings.

Enoxaparin treatment dosing for venous thromboembolism in pediatric patients with obesity

BACKGROUND

The optimal enoxaparin dosing for treatment of venous thromboembolism (VTE) in pediatric patients with obesity remains uncertain. We described the mean enoxaparin dose required to attain anti-factor Xa (anti-Xa) levels of 0.5-1 unit/mL in pediatric patients with obesity.

METHODS

Pediatric patients with obesity (body mass index [BMI] ≥95th percentile) who received treatment dose of enoxaparin from 2013 to 2022 and had at least one appropriately timed anti-Xa level were retrospectively evaluated. Daily enoxaparin dose required to achieve an anti-Xa level of 0.5-1 unit/mL was reviewed and compared by the severity of obesity. The correlation coefficients between enoxaparin dose requirement and BMI, BMI percentile, and weight were measured by Spearman's rank correlation coefficient.

RESULTS

Pediatric patients with obesity (n = 89) required a mean enoxaparin dose of 0.8 ± 0.18 mg/kg twice daily to attain a therapeutic anti-Xa level. Children with BMI 95th-99th percentile and weight ≤100 kg achieved the target level on a significantly higher weight-based enoxaparin dose compared to BMI greater than 99th percentile (0.95 ± 0.15 vs. 0.75 ± 0.15 mg/kg twice daily; p < .001) and weight greater than 100 kg (0.95 ± 0.14 vs. 0.7 ± 0.12 mg/kg twice daily; p < .001). BMI, BMI percentile, and weight showed a moderate to strong negative correlation with enoxaparin dose requirement.

CONCLUSIONS

Pediatric patients with obesity required a lower weight-based dose of enoxaparin to achieve a therapeutic anti-Xa than the recommended starting dose of 1 mg/kg twice daily for treatment of VTE. Among obesity indices, weight showed the strongest negative correlation with total daily enoxaparin requirement.

Characterizing Enoxaparin's Population Pharmacokinetics to Guide Dose Individualization in the Pediatric Population

BACKGROUND AND OBJECTIVE

Pediatric dosing of enoxaparin was derived based on extrapolation of the adult therapeutic range to children. However, a large fraction of children do not achieve therapeutic anticoagulation with initial dosing. We aim to use real-world anti-Xa data obtained from children receiving enoxaparin per standard of care to characterize the population pharmacokinetics (PopPK).Author names: Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Also, kindly confirm the details in the metadata are correct.The author names are accurately presented and the metadata are correct.  METHODS: A PopPK analysis was performed using NONMEM, and a stepwise covariate modeling approach was applied for the covariate selection. The final PopPK model, developed with data from 1293 patients ranging in age from 1 day to 18 years, was used to simulate enoxaparin subcutaneous dosing for prophylaxis and treatment based on total body weight (0-18 years, TBW) or fat-free mass (2-18 years, FFM). Simulated exposures in children with obesity (body mass index percentile ≥95th percentile) were compared with those without obesity.

RESULTS

A linear, one-compartment PopPK model that included allometric scaling using TBW (<2 years) or FFM (≥2 years) characterized the enoxaparin pharmacokinetic data. In addition, serum creatinine was identified as a significant covariate influencing clearance. Simulations indicated that in patients aged <2 years, the recommended 1.5 mg/kg TBW-based dosing achieves therapeutic simulated concentrations. In pediatric patients aged ≥2 years, the recommended 1.0 mg/kg dose resulted in exposures more comparable in children with and without obesity when FFM weight-based dosing was applied.

CONCLUSION

Using real-world data and PopPK modeling, enoxaparin's pharmacokinetics were characterized in pediatric patients. Using FFM and twice-daily dosing might reduce the risk of overdosing, especially in children with obesity.

An Evaluation of the Appropriateness of Initial Enoxaparin Dosing Among Pediatric Patients

Background Enoxaparin is a low molecular weight heparin that irreversibly inactivates factor Xa leading to the inhibition of clot formation. Despite the non-FDA approval in pediatrics, enoxaparin is recommended with an initial dose of 1.5mg/kg/q12hrs for patients aged ≤ 2 months and 1mg/kg/q12hrs for patients > 2 months, targeting therapeutic anti-Xa with a range of 0.5 to 1 units/mL. Due to more rapid clearance in pediatrics, our study aims to assess the need for initial higher doses than recommended by the guideline to reach the target anti-Xa level. Methods A retrospective chart review of all pediatric patients under all specialties who were treated with enoxaparin either in inpatient or outpatient settings between February 2021 and June 2022 at children's specialized hospital and meet the inclusion criteria, including age ≤ 15 years old and treated with enoxaparin with initial dose according to the American College of Chest Physicians (CHEST) guideline, while patients who received prophylaxis doses did not have anti-Xa levels or creatinine clearance < 30 mL/min/1.73m2 were excluded. Demographic data, laboratory data, and enoxaparin dosing were all collected to assess whether the initial enoxaparin dose will result in a therapeutic level as a primary endpoint and secondary endpoints including the average enoxaparin dose required to achieve the therapeutic level and to report any side effects. All data were entered and analyzed using the Statistical Package for the Social Sciences (IBM SPSS Statistics for Windows, IBM Corp., Version 25, Armonk, NY), and all categorical variables were reported as frequency and percentage while continuous variables expressed as mean ± SD and the study was approved by our research center institutional review board (IRB). Results Thirty patients were included in the study (17 males), 10 patients were aged ≤ 2 months, four were between 3 and 12 months and 16 were > 12 months, most of the patients received enoxaparin for deep vein thrombosis. In the majority of patients (76.7%), the initial dose failed to achieve the target anti-Xa while a mean dose of 2 mg/kg/q12hrs in patients ≤ 2 months, 1.7mg/kg/q12hrs in patients 3-12 months and 1.3 mg/kg/q12hrs in patients > 12 months was sufficient to reach the target level. After achieving a therapeutic anti-Xa level, only one patient experienced major bleeding while four patients experienced minor bleeding, no edema or thrombocytopenia were reported. Conclusion In conclusion, initiating enoxaparin according to the recommended dose by the guideline failed to achieve target anti-Xa in the majority of patients which necessitates starting enoxaparin with initial higher doses according to the patient's age to provide more prompt achievement of target anti-Xa.

Optimal dosing of enoxaparin in overweight and obese children

AIM

Current enoxaparin dosing guidelines in children are based on total body weight. This is potentially inappropriate in obese children as it may overestimate the drug clearance. Current evidence suggests that obese children may require lower initial doses of enoxaparin, therefore the aim of this work was to characterise the pharmacokinetics of enoxaparin in obese children and to propose a more appropriate dosing regimen.

METHODS

Data from 196 unique encounters of 160 children who received enoxaparin treatment doses were analysed. Enoxaparin concentration was quantified using the chromogenic anti factor Xa (anti-Xa) assay. Patients provided a total of 552 anti-Xa samples. Existing published pharmacokinetic (PK) models were fitted and evaluated against our dataset using prediction-corrected visual predictive check plots (pcVPCs). A PK model was fitted using a nonlinear mixed-effects modelling approach. The fitted model was used to evaluate the current standard dosing and identify an optimal dosing regimen for obese children.

RESULTS

Published models of enoxaparin pharmacokinetics in children did not capture the pharmacokinetics of enoxaparin in obese children as shown by pcVPCs. A one-compartment model with linear elimination best described the pharmacokinetics of enoxaparin. Allometrically scaled fat-free mass with an estimated exponent of 0.712 (CI 0.66-0.76) was the most influential covariate on clearance while linear fat-free mass was selected as the covariate on volume. Simulations from the model showed that fat-free mass-based dosing could achieve the target anti-Xa activity at steady state in 77.5% and 78.2% of obese and normal-weight children, respectively, compared to 65.2% and 75.5% for standard total body weight-based dosing.

CONCLUSIONS

A population PK model that describes the time course of anti-Xa activity of enoxaparin was developed in a paediatric population. Based on this model, a unified dosing regimen was proposed that will potentially improve the success rate of target attainment in overweight/obese patients without the need for patient body size categorisation. Therefore, prospective validation of the proposed approach is warranted.

Use of Real-World Data and Physiologically-Based Pharmacokinetic Modeling to Characterize Enoxaparin Disposition in Children With Obesity

Dosing guidance for children with obesity is often unknown despite the fact that nearly 20% of US children are classified as obese. Enoxaparin, a commonly prescribed low-molecular-weight heparin, is dosed based on body weight irrespective of obesity status to achieve maximum concentration within a narrow therapeutic or prophylactic target range. However, whether children with and without obesity experience equivalent enoxaparin exposure remains unclear. To address this clinical question, 2,825 anti-activated factor X (anti-Xa) surrogate concentrations were collected from the electronic health records of 596 children, including those with obesity. Using linear mixed-effects regression models, we observed that 4-hour anti-Xa concentrations were statistically significantly different in children with and without obesity, even for children with the same absolute dose (P = 0.004). To further mechanistically explore obesity-associated differences in anti-Xa concentration, a pediatric physiologically-based pharmacokinetic (PBPK) model was developed in adults, and then scaled to children with and without obesity. This PBPK model incorporated binding of enoxaparin to antithrombin to form anti-Xa and elimination via heparinase-mediated metabolism and glomerular filtration. Following scaling, the PBPK model predicted real-world pediatric concentrations well, with an average fold error (standard deviation of the fold error) of 0.82 (0.23) and 0.87 (0.26) in children with and without obesity, respectively. PBPK model simulations revealed that children with obesity have at most 20% higher 4-hour anti-Xa concentrations under recommended, total body weight-based dosing compared to children without obesity owing to reduced weight-normalized clearance. Enoxaparin exposure was better matched across age groups and obesity status using fat-free mass weight-based dosing.

Managing Antiphospholipid Syndrome in Children and Adolescents: Current and Future Prospects

Pediatric antiphospholipid syndrome (APS) is a rare acquired multisystem autoimmune thromboinflammatory condition characterized by thrombotic and non-thrombotic clinical manifestations. APS in children and adolescents typically presents with large-vessel thrombosis, thrombotic microangiopathy, and, rarely, obstetric morbidity. Non-thrombotic clinical manifestations are frequently seen in pediatric APS and may be present even before the vascular thrombotic events occur. We review insights into the pathogenesis of APS and discuss potential targets for therapy. The identification of multiple immunologic abnormalities in patients with APS reveals molecular targets for current or future treatment. Management strategies, especially for APS in adolescents, require screening for additional prothrombotic risk factors and consideration of counseling regarding contraceptive strategies, lifestyle recommendations, treatment adherence, and mental health issues associated with this autoimmune thrombophilia. The main goal of therapy in pediatric APS is the prevention of thrombosis. The management of acute thrombosis events in children and adolescents is the same as for primary APS, which involves isolated occurrences, and secondary APS, which is seen in association with another autoimmune disease, e.g., systemic lupus erythematosus. A pediatric hematologist should be consulted so other differential thrombophilic conditions can be eliminated. Therapy includes unfractionated heparin or low-molecular-weight heparin followed by vitamin K antagonists. Treatment of catastrophic APS involves triple therapy (anticoagulation, intravenous corticosteroid pulse therapy, and plasma exchange) and may include intravenous immunoglobulin for children and adolescents with this condition. New drugs such as eculizumab and sirolimus seem to be promising drugs for APS.

Low-molecular-weight heparin administered by subcutaneous catheter is a safe and effective anti-coagulation regimen in selected inpatient infants and children with complex congenital heart disease

BACKGROUND/HYPOTHESIS

Disadvantages of intravenous therapeutic unfractionated heparin, the first-line anti-coagulant agent in children with complex congenital heart disease, include unpredictable pharmacokinetics requiring frequent phlebotomies and the need for continuous intravenous access.

OBJECTIVE

To compare efficacy and safety of low-molecular-weight heparin administered by a subcutaneous indwelling catheter with intravenous unfractionated heparin.

MATERIALS AND METHODS

Clinical data from 31 inpatients prospectively enrolled to receive subcutaneous low-molecular-weight heparin were compared with those from a historical group of 44 inpatients receiving intravenous unfractionated heparin. Investigation of parents' satisfaction by telephone survey.

RESULTS

The percentage of anti-factor Xa levels outside therapeutic range was lower in the subcutaneous low-molecular-weight heparin group compared with the percentage of activated partial thromboplastin times outside therapeutic range in the intravenous unfractionated heparin group (40% versus 90%, p < 0.001). Neither group had a major complication. Transient local reactions occurred in 19% of patients of the subcutaneous low-molecular-weight heparin group. The number of needle punctures and that of placement of indwelling catheters were significantly lower in the subcutaneous low-molecular-weight heparin compared with the intravenous unfractionated heparin group (p < 0.001). In total, 84.2% of parents in the subcutaneous low-molecular-weight heparin group reported a positive experience when asked about comparison with prior intravenous unfractionated heparin treatment.

CONCLUSION

Subcutaneous low-molecular-weight heparin offers a safe anti-coagulation regimen for children with complex congenital heart disease providing more efficient therapeutic anti-coagulation and a reduction in needle punctures, thus causing less pain and anxiety in this children.

A Distinctive Approach to Venous Thromboembolism Treatment in a Pediatric, Hemodialysis Patient: A Case Report

Enoxaparin is a low molecular weight heparin (LMWH) that is the mainstay for treatment of pediatric patients with a venous thromboembolism, which provides better compliance compared with the use of unfractionated heparin (UFH) in long-term anticoagulation. Although data are limited in pediatric patients with renal insufficiency, enoxaparin can be used in this population. Data related to its use in hemodialysis (HD) pediatric patients is almost non-existent. A major concern for enoxaparin use in patients with renal insufficiency or for those on HD is bleeding. A few studies in adults showed an increased risk of bleeding, but the risk was similar to that of UFH when the two were compared. This case report describes the use of enoxaparin in an 8-year-old female who is on hemodialysis, without any bleeding or clotting complications. Although systematic trials are needed to support the safety and efficacy of LMWH in pediatric patients with renal dysfunction or on HD, this case will provide limited information for enoxaparin use in this population.

A Critical Evaluation of Enoxaparin Dose Adjustment Guidelines in Children

OBJECTIVES

The purposes of this study are to perform a large-scale evaluation of the standardized dosage adjustment nomogram recommended by the American College of Chest Physicians (CHEST) for the management of enoxaparin in hospitalized pediatric patients and to determine the necessity of routine and repeated anti-factor Xa (anti-Xa) levels.

METHODS

A retrospective cohort study was designed, and charts were reviewed in a single tertiary care institution for all patients who received enoxaparin between October 1, 2010, through September 30, 2016. Patients were included if they were receiving treatment doses of enoxaparin according to the pediatric CHEST guidelines, had a subtherapeutic or supratherapeutic anti-Xa level drawn at 3.5 to 6 hours after a dose, had a dose changed in an attempt to attain a therapeutic anti-Xa level, and had a second anti-Xa level drawn 3.5 to 6 hours after the dose change. Descriptive statistical methods were used to characterize the ability of dose adjustment via a nomogram to attain an anti-Xa of 0.5 to 1 unit/mL.

RESULTS

A total of 467 patients were identified who received the appropriate initial dose and dosage adjustment and whose levels were drawn according to the CHEST guidelines. In patients who had an initial anti-Xa level of <0.35 units/mL and received the nomogram recommended dose increase of 25% ± 5%, 28 out of 96 patients (29.2%) reached therapeutic levels. Of 197 patients who had an initial anti-Xa level between 0.35 and 0.49 units/mL and who received the nomogram recommended dose increase of 10% ± 5%, 116 (58.9%) reached therapeutic levels. Of 50 patients with an initial anti-Xa level between 1.1 and 1.5 units/mL and who received the nomogram dose decrease of 20% ± 5%, 31 (62%) reached therapeutic levels.

CONCLUSIONS

The current dosage adjustment nomogram recommended by the CHEST guidelines does not reliably lead to therapeutic anti-Xa levels when used to adjust enoxaparin doses in pediatric patients.