Long-term treatment of thrombosis with enoxaparin in pediatric and adolescent patients

The Trilogy of SARS-CoV-2 in Pediatrics (Part 3): Thrombosis, Anticoagulant, and Antiplatelet Considerations

The hypercoagulable state induced by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) affects all patients regardless of age. The incidence of venous thromboembolism in pediatric patients with SARS-CoV-2-related illnesses is not well established. Although deep vein thrombosis is rare in children in the absence of risk factors, coagulopathy and the development of thromboses have been described in pediatric patients with acute COVID-19 and multisystem inflammatory syndrome. This comprehensive review provides a detailed overview of SARS-CoV-2-associated coagulopathy as well as strategies for optimizing the evaluation, management, and prevention of thrombosis in pediatric patients.

[Enoxaparin and tinzaparin in pediatrics: Impact of recommendation on prescription quality and anti-Xa levels]

OBJECTIVES

A protocol has been written and distributed in May 2017 to all prescribers in a pediatric hospital to standardize and to secure the prescriptions of enoxaparin and tinzaparin considered as two high risk medications. The aim of this study is to evaluate the impact of the protocol on those prescriptions in a pediatric population.

METHODS

This is a monocentric retrospective study comparing prescriptions of this two low-molecular-weight heparins for patients under 18 years old in 2016 and 2018, thus before and after the protocol redaction.

RESULTS

In 2016, 2246 prescriptions of enoxaparin and tinzaparin were analyzed for 627 patients. Among them, 142 (22.6%) patients have had at least one anti-Xa level dosed. On the other hand, in 2018, 2061 prescriptions were written for 628 patients including 96 (15.3%) who have had at least one anti-Xa level dosed. The conformity rate of the first dose in IU/kg/administration of the first enoxaparin prescription goes from 36.3% before protocol to 52.1% after (P=0.03*). Concerning tinzaparin, the conformity rate goes from 69.2% to 83.3%. (P=0.19). The rate of first anti-Xa level in the range 0.4 to 1.2 IU/ml increase between 2016 and 2018 from 27.7% to 43.8% (P<0.001*).

CONCLUSION

This protocol enabled to improve the quality of prescriptions in terms of: dosage written in IU/kg/administration, frequency of administration, dilution conformity, and result of the first anti-Xa level. Some efforts must be made in writing the dose in IU not in mg or ml.

Management of Jugular Bulb Stenosis in Pediatric Vein of Galen Malformation: A Novel Management Paradigm

INTRODUCTION

Pediatric vein of Galen malformations (VOGMs) are fistulous intracranial malformations arising congenitally within the choroidal fissure that can present with an array of neurological and cardiac sequelae. Associated venous stenosis may result in intracranial venous hypertension and ischemia leading to severe, irreversible cerebral injury. Management of neonatal VOGMs typically involves staged embolization and angioplasty/stenting for relief of venous stenosis. Rarely, jugular foraminal narrowing has been identified as causing jugular bulb stenosis.

CASE PRESENTATION

We present the case of a 22-month-old female diagnosed with VOGM prenatally who displayed persistent intracranial venous hypertension despite multiple neuroembolization procedures during the neonatal period. Following initial reduction in arteriovenous shunting, she once again developed venous hypertension secondary to jugular bulb stenosis for which angioplasty was attempted. Failure of angioplasty to relieve the venous hypertension prompted skull base imaging, which revealed jugular foraminal ossification and stenosis. Microsurgical jugular foraminotomy followed by balloon angioplasty and stenting significantly reduced jugular pressure gradients. Restenosis requiring re-stenting developed postoperatively at 9 months, but the patient has remained stable with significant improvement in cortical venous congestion.

DISCUSSION/CONCLUSION

This case demonstrates the efficacy of microsurgical decompression of the jugular foramen and endovascular angioplasty/stenting as a novel treatment paradigm for the management of intracranial venous hypertension in the setting of VOGM.

Challenges and Opportunities in the Pharmacological Treatment of Acute Venous Thromboembolism in Children

Venous thromboembolism (VTE) is an important but historically under-recognized problem in pediatrics, with an incidence concentrated in hospitalized children. A number of specific VTE diseases with discrete triggers have been described, but the most common pediatric trigger is the presence of central venous access devices. VTE diseases, though heterogenous in etiology, are linked by the common therapeutic strategies shared by their management. Historically, the most commonly used drug therapies have been unfractionated heparin, low-molecular-weight heparins, and vitamin K antagonists, based on extrapolation from adult data rather than any specific pediatric trials. Although these widely used drugs appear safe and effective in expert hands, the historical lack of pediatric data is problematic in view of the recognized significant differences between children and adults with regards to hemostatic physiology, VTE etiology, and drug pharmacokinetics. The increasing adult usage of novel VTE pharmacotherapies such as direct oral anticoagulants (DOACs) has led to considerable interest in exploring the pediatric applications of these newer drugs. This review summarizes the advantages and disadvantages of existing VTE pharmacotherapies and outlines emerging novel pediatric VTE therapies, particularly DOACs, within the context of the current pediatric trial landscape.

The Edoxaban Hokusai VTE PEDIATRICS Study: An open-label, multicenter, randomized study of edoxaban for pediatric venous thromboembolic disease

BACKGROUND

Little evidence is available for treatment of pediatric venous thromboembolism (VTE). Large randomized controlled trials are challenging in children. Current antithrombotic agents have many limitations, including nonoral administration and frequent monitoring. Edoxaban is an oral direct inhibitor of factor Xa without need of monitoring. In adults with VTE, edoxaban has shown to be effective and safe.

OBJECTIVES

The Edoxaban Hokusai VTE PEDIATRICS Study is an open-label, randomized clinical trial to evaluate pharmacokinetics (PK) and pharmacodynamics (PD) of edoxaban and whether edoxaban is noninferior to standard of care in treatment of pediatric VTE.

METHODS

A goal of 274 patients will be recruited in 5 age categories. A multidose PK/PD assessment on day 5 in the first 12 patients of each age group is incorporated into this study. The primary composite efficacy outcome comprises symptomatic recurrent VTE, death due to VTE, and no change or extension of thrombotic burden. The principal safety end point is a combination of major and clinically relevant nonmajor bleeding. PK end points include apparent systemic clearance and volume of distribution of edoxaban. PD end points include prothrombin time, activated partial thromboplastin time, and anti-factor Xa level for the edoxaban treatment arm.

RESULTS

To increase feasibility, the multidose PK/PD study is integrated in the phase 3 trial. In addition, thrombotic burden, which is a prognostic factor for post thrombotic syndrome in children, is one of the components of the primary composite efficacy outcome.

CONCLUSION

This study will increase the level of evidence for treatment in pediatric VTE.

Neonatal thrombosis

Neonatal thromboembolism in pediatric patients is a rare but life-threatening condition mainly caused by combinations of at least 2 prothrombotic triggering risk factors such as the central venous lines, septic condition, and prematurity. Other risk factors include asphyxia, dehydration, liver dysfunction, inflammation, and maternal condition. Neonatal hemostatic system is different from one of the older children and adults. Coagulation proteins do not cross the placenta but are synthesized in the fetus from an early stage. In the term neonate, concentrations of several procoagulant proteins, particularly the vitamin K dependent and contact factors are reduced when compared with adults. Conversely, levels of antithrombin, heparin cofactor II and protein C and S are low at birth and fibrinolysis system is characterized by the decreased level of plasminogen and alpha-1-antiplasmin, increased tissue plasminogen activator. These features all tend to be gestational dependent and are more present in the preterm infant. Primarily in this context neonates appear to be at a higher risk of thrombosis than older children. Thrombotic complications reach their peak in the group of children born at 22-27 weeks. The role of inherited thrombophilic risk factors in neonatal VTE development is poorly defined. The presence of inherited and acquired thrombophilia in mother and newborn is also responsible for the development of thrombosis in neonates and should be considered. Thrombophilia in the mother can lead to increased coagulation potential and prethrombotic conditions during pregnancy, causing thrombotic vasculopathy at the placental level. The benefit of identifying thrombophilia in the sick preterm newborns who are in the group of risk for development of thrombotic complications may facilitate the thromboprophylaxis. Further research regarding assessment of risk factors, diagnostics and treatment strategy is required.

Retrospective comparison of two enoxaparin dosing and monitoring protocols at a pediatric hospital

PURPOSE

The study analyzes the effectiveness and safety of a higher than standard enoxaparin dosing protocol implemented for pediatric patients requiring initiation of therapeutic anticoagulation.

METHODS

A retrospective review of 2 enoxaparin dosing and monitoring protocols was performed. The standard protocol used 1.5 mg/kg/dose (in patients <3 months of age) and 1 mg/kg/dose (in patients ≥3 months of age) with anti-Xa monitoring following the first dose. The high-dose protocol was implemented at 1.7 mg/kg/dose (in patients <3 months of age), 1.5 mg/kg/dose (in patients 3 through 11 months of age), 1.2 mg/kg/dose (in patients 1 through 4 years of age), and 1.1 mg/kg/dose (in patients 5 through 17 years of age), with anti-Xa monitoring after the second dose. Primary outcomes were number of dosing changes prior to and time to first target anti-Xa level. Secondary outcomes included percentage of patients with anti-Xa levels above target level.

RESULTS

The median number of dose changes required to achieve a target anti-Xa level was 1 (interquartile range [IQR], 0-1.5) and 0 (IQR, 0-1) for the standard-dose (n = 87) and high-dose groups (n = 132) (p = 0.17), respectively. The median number of dose adjustments to achieve target anti-Xa levels in the 3 through 11 months of age subgroup declined from 2 (IQR, 1-3.25) to 0 (IQR, 0-1) in the standard- versus high-dose groups, respectively (p < 0.01). No difference was seen in other age subgroups. Patients with above-target levels did not differ statistically between groups.

CONCLUSION

Initiating enoxaparin at higher doses in pediatric patients may result in fewer dosing changes than standard dosing. Benefit was demonstrated for the 3-11 months of age high-dose subgroup. Across all groups, the high-dose strategy was safe and did not result in a statistically significant increase in above-target levels.

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.

Evaluation of the age-dependent dosing recommendations for the administration of daily tinzaparin in children with thrombosis

Essentials The once-daily dosing of tinzaparin provides an advantage over other low molecular weight heparins. The recommended age-dependent doses of tinzaparin in children have not previously been validated. Once-daily administration of tinzaparin is a safe and effective treatment of childhood thrombosis. Recommended doses are appropriate but monitoring may be required due to inter-individual variation.

SUMMARY

Background The recommended starting doses of tinzaparin for the treatment of thrombosis in children have not previously been validated. There are few data to support the efficacy and safety of once-daily tinzaparin dosing in children with thrombosis. Objectives To investigate the use of tinzaparin for the treatment of childhood thrombosis, and to evaluate the age-dependent dosing recommendations and define outcomes in terms of efficacy and safety. Methods This was a retrospective cohort study of children aged 0 to < 16 years treated for thrombosis at a large teaching hospital in the UK between 2008 and 2015. Medical records were reviewed to evaluate tinzaparin dosing, anti-activated factor X (FXa) levels, and patient outcomes. Results Seventy-nine children were identified as having received tinzaparin. Dosing information was available for 57. Younger children required higher doses to reach a therapeutic level. The therapeutic dose requirement varied within age groups, supporting the use of anti-FXa monitoring. Over a median follow-up of 35 months, there were 13 (16%) bleeding episodes (two major; seven clinically relevant but non-major; and four minor). There were two (3%) recurrent episodes of thrombosis. Children were treated for a median duration of 3 months, and the majority (86%) remained on tinzaparin for the duration of their anticoagulant therapy. Conclusion Once-daily tinzaparin is a safe and effective treatment for childhood thrombosis, with rates of recurrence and bleeding similar to those for other anticoagulants used in children. The recommended starting doses are appropriate, but anti-FXa monitoring may be required, owing to interindividual variability in the therapeutic dose requirement.

Reduced dosing of enoxaparin for venous thromboembolism in overweight and obese adolescents: a single institution retrospective review

BACKGROUND

The global obesity epidemic has created new challenges, including venous thromboembolisms (VTE) in obese adolescents. The data on whether to reduce the dose of low-molecular heparin in obese adults is conflicting, and information on adolescent patients is scarce.

OBJECTIVES

Our primary goal was to describe dosing, anti-Xa levels, and outcomes of overweight and obese adolescents who received reduced doses of enoxaparin at the initiation of therapy. The secondary goal was to compare their outcomes to overweight and obese adolescents who received standard 1 mg/kg dosing to determine if future trials for dose reduction are warranted.

PATIENTS/METHODS

We performed a retrospective cohort study of overweight and obese patients between the ages of 12 and 18 years old diagnosed with VTE who were treated with reduced dosing (RD) of enoxaparin, comparing their dosing, anti-Xa levels, and outcomes to overweight and obese adolescents who received standard dosing (SD).

RESULTS

RD patients (n=19) achieved therapeutic mean initial anti-Xa levels that were similar to SD patients (n=11). Of the RD patients, 53% did not require dose adjustments during treatment. Two RD patients had thrombus progression. A total of 25 patients ultimately completed therapy with RD.

CONCLUSIONS

Future trials are warranted to evaluate the efficacy and safety of reduced dosing of enoxaparin to treat overweight and obese adolescents with VTE.

Pharmacokinetics and pharmacodynamics of anticoagulants in paediatric patients

Given the rising incidence of thrombotic complications in paediatric patients, understanding of the pharmacologic behaviour of anticoagulant drugs in children has gained importance. Significant developmental differences between children and adults in the haemostatic system and pharmacologic parameters for individual drugs highlight potentially unique aspects of anticoagulant pharmacology in this special and vulnerable population. This review focuses on pharmacologic information relevant to the dosing of unfractionated heparin, low molecular weight heparin, warfarin, bivalirudin, argatroban and fondaparinux in paediatric patients. The bulk of clinical experience with paediatric anticoagulation rests with the first three of these agents, each of which requires higher bodyweight-based dosing for the youngest patients, compared with adults, in order to achieve comparable pharmacodynamic effects, likely related to an inverse correlation between age and bodyweight-normalized clearance of these drugs. Whether extrapolation of therapeutic ranges targeted for adult patients prescribed these agents is valid for children, however, is unknown and a high priority for future research. Novel oral anticoagulants, such as dabigatran, rivaroxaban and apixaban, hold promise for future use in paediatrics but require further pharmacologic study in infants, children and adolescents.

The development of evidence-based care recommendations to improve the safe use of anticoagulants in children

Evidence-based care recommendations and standardized protocols improve outcomes. In addition, anticoagulant management has been recognized by The Joint Commission (TJC) as an opportunity for improving patient safety. A National Patient Safety Goal requiring a standardized process for patients receiving anticoagulants was established by TJC. This requirement provided an opportunity to apply evidence-based care recommendations to the issue of safe anticoagulant use. To meet TJC requirement, the following searchable clinical question was drafted: "In children receiving anticoagulation therapy, what are the appropriate dosing, laboratory monitoring, timing, and dosing adjustments for warfarin, unfractionated heparin, and low-molecular-weight heparin to prevent coagulation-related complications?" The team used the Appraisal of Guidelines Research and Evaluation Collaboration (AGREE) instrument to evaluate the quality and relevance of identified guidelines in answering the clinical question. Best Evidence Statements (BESts) were developed for each of the medications (warfarin, low-molecular-weight heparin, and unfractionated heparin). BESts provide the format for the presentation of recommendations, discussion, and methods for point-of-care providers seeking synthesized evidence to guide care decisions. The primary goal of developing and implementing these statements was to standardize the use of anticoagulants and to prevent unsafe practices. A secondary goal was to ensure accessibility of the BESts throughout our organization, including the electronic medical record, various internal division home pages, and our organization's external website. The anticoagulant BESts developed at our organization show how an interprofessional approach to patient care results in the development of evidence-based care recommendations. The BESts were developed to standardize care associated with the use of anticoagulants and to provide dosing and monitoring parameters to ensure safe care to all patients receiving these medications. The development of evidence-based care recommendations can be accomplished with a focused interprofessional team dedicated to providing the safest possible care to patients.

Retrospective evaluation of enoxaparin dosing in patients 48 weeks' postmenstrual age or younger in a neonatal intensive care unit

BACKGROUND

Enoxaparin is the anticoagulant of choice in neonates because of the ease of administration, predictable pharmacokinetics, and reduced adverse effects when compared to heparin. The Chest guidelines recommend that therapy in patients younger than 2 months should be initiated with enoxaparin 1.5 mg/kg administered subcutaneously twice daily. This starting dosage may be inadequate, leading to a delay in achieving therapeutic anti-factor Xa plasma concentrations.

OBJECTIVE

To determine an enoxaparin dose for neonatal patients that achieves a therapeutic anti-factor Xa plasma concentration and compare that dose to the recommended enoxaparin dose per published guidelines for this patient population.

METHODS

The study was designed as a single-center chart review. Eligible patients were identified by pharmacy anticoagulation records or a search of the electronic medical record for enoxaparin orders. Patients must have received enoxaparin subcutaneously twice daily and have had a postmenstrual age of 48 weeks or younger. Patients diagnosed with renal failure and those receiving prophylactic doses of enoxaparin were excluded.

RESULTS

The mean (SD) initial dose of enoxaparin was 1.4 (0.3) mg/kg subcutaneously twice daily, resulting in 27 of 33 patients (81.8%) having a subtherapeutic anti-factor Xa concentration. A mean enoxaparin dose of 2.0 (0.5) mg/kg was required to achieve a therapeutic anti-factor Xa plasma concentration (p < 0.001). Patients born prematurely required a higher enoxaparin dose (2.2 [0.5] mg/kg) than did those born at full-term gestation (1.8 [0.4] mg/kg; p < 0.05).

CONCLUSIONS

For patients 48 weeks' postmenstrual age or younger who are treated in a neonatal intensive care unit, a higher initial dose of enoxaparin than that suggested by the Chest guidelines is required to attain a therapeutic antifactor Xa plasma concentration. Premature neonates require a larger starting dose of enoxaparin than do infants born at full-term gestation.

The impact of quality and duration of enoxaparin therapy on recurrent venous thrombosis in children

BACKGROUND

Venous thromboembolism (VTE) and recurrent venous thromboembolism (rVTE) are rare, but significant problems in pediatrics. Current recommendations for anticoagulant therapy arise from adult literature, and there is little data on clinical outcomes following therapeutic low-molecular-weight heparin in children.

METHOD

All patients <19 years of age that were diagnosed with a VTE or right atrial thrombus via standard imaging methods at St. Jude Children's Research Hospital were retrospectively identified from January 2004 through August 2008. Demographic characteristics, coexisting clinic conditions, description of anticoagulant therapy, and record of rVTE were chronicled following a comprehensive chart review. Descriptive statistics of clinical characteristics and anticoagulation are presented.

RESULTS

Venous thrombosis was identified in 149 children with 21% (31/149) developing a rVTE. Coexisting clinical conditions were identified in 93% of children at initial diagnosis with 48% (71/149) of patients having a coexisting malignancy. Seventy-seven percent (114/149) of children received anticoagulant therapy with UFH (10/114) or enoxaparin (104/114). Neither duration of enoxaparin therapy (>6, 3-6, <3 months) (P = 0.61), nor quality of therapy (≥75% of time on anticoagulation spent with an anti-FXa of 0.5-1.0 U/ml) (P = 1.0) were found to be protective against rVTE.

CONCLUSION

Anticoagulation with enoxaparin based on adult literature may be suboptimal in preventing rVTE in pediatric populations. Future prospective randomized controlled trials in pediatrics using clinical outcomes with anticoagulant therapy are urgently needed.

Antithrombotic therapy in neonates and children: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

Neonates and children differ from adults in physiology, pharmacologic responses to drugs, epidemiology, and long-term consequences of thrombosis. This guideline addresses optimal strategies for the management of thrombosis in neonates and children.

METHODS

The methods of this guideline follow those described in the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines.

RESULTS

We suggest that where possible, pediatric hematologists with experience in thromboembolism manage pediatric patients with thromboembolism (Grade 2C). When this is not possible, we suggest a combination of a neonatologist/pediatrician and adult hematologist supported by consultation with an experienced pediatric hematologist (Grade 2C). We suggest that therapeutic unfractionated heparin in children is titrated to achieve a target anti-Xa range of 0.35 to 0.7 units/mL or an activated partial thromboplastin time range that correlates to this anti-Xa range or to a protamine titration range of 0.2 to 0.4 units/mL (Grade 2C). For neonates and children receiving either daily or bid therapeutic low-molecular-weight heparin, we suggest that the drug be monitored to a target range of 0.5 to 1.0 units/mL in a sample taken 4 to 6 h after subcutaneous injection or, alternatively, 0.5 to 0.8 units/mL in a sample taken 2 to 6 h after subcutaneous injection (Grade 2C).

CONCLUSIONS

The evidence supporting most recommendations for antithrombotic therapy in neonates and children remains weak. Studies addressing appropriate drug target ranges and monitoring requirements are urgently required in addition to site- and clinical situation-specific thrombosis management strategies.

Fluctuations of anti-Xa concentrations during maintenance enoxaparin therapy for neonatal thrombosis

AIM

To evaluate fluctuations in anti-Xa concentrations in infants treated with enoxaparin for thrombosis and describe clinical outcomes.

METHODS

A retrospective chart review was performed on infants treated with enoxaparin in the Neonatal Intensive Care Unit, and data on enoxaparin doses, anti-Xa concentrations, clinical characteristics and outcomes were abstracted.

RESULTS

Our cohort (n = 26) had a median gestation of 36 (range, 23-41) weeks, birthweight of 2522 (510-3912) grams and 5-min Apgar score of 8(4-9). Fifteen (57.7%) infants were males. Thromboses was diagnosed at a median age of 22 (range, 1-97) days; enoxaparin was initiated at 27.5 (range, 4-98) days at a mean (SD) dose of 1.4 (0.3) mg/kg every 12 h. Therapeutic anti-Xa concentrations (0.5-1 U/mL) were achieved at a mean (SD) dose of 2.1 (0.6) mg/kg at 12.5 (12.2) days of treatment. Of the 143 anti-Xa concentrations, 39 (27%) were within the therapeutic range. During maintenance therapy following initial therapeutic anti-Xa concentration, 40% concentrations were therapeutic. Minor bleeding was noted in four infants and intracranial bleed in one infant; four infants died. During treatment, thrombocytopenia, renal and hepatic impairment during treatment were noted in 7, 2 and 4 infants, respectively. Clot resolution was observed in 21 (81%) infants.

CONCLUSIONS

Anti-Xa concentrations fluctuate during maintenance enoxaparin therapy, with therapeutic levels being achieved only sporadically in young infants. Despite this, enoxaparin appears efficacious in thrombosis resolution. Further studies on the impact of stringent control of concentrations on outcomes in this population are warranted.

Population pharmacokinetics of enoxaparin in infants, children and adolescents during secondary thromboembolic prophylaxis: a cohort study

BACKGROUND

Enoxaparin has been extensively studied in adults on its safety and efficacy during prevention of symptomatic thromboembolism when acute anticoagulation or secondary prevention is required as a result of venous thrombosis or stroke. In children, it is still used off-label and little is known about the pharmacokinetics in children.

OBJECTIVES

The aim of the present study was to evaluate whether a once- or twice-daily dosing regimen would be feasible in children to achieve appropriate plasma levels of enoxaparin.

PATIENTS/METHODS

A population pharmacokinetic model was developed using anti-factor (F)Xa activity data from 126 children (median age: 5.9 years) receiving enoxaparin either as a once- or twice-daily dosing regimen.

RESULTS

A two-compartment model was adequate for describing the enoxaparin kinetics. Body weight proved to be the most predictive covariate for clearance and central volume of distribution: clearance 15 mL h⁻¹ kg⁻¹, central volume of distribution 169 mL kg⁻¹, intercompartmental clearance 58 mL h⁻¹, peripheral volume of distribution 10 L and absorption rate 0.414 h⁻¹. Interindividual variability was found to be 54% for clearance and 42% for volume of distribution.

CONCLUSION

The model is capable of describing all age groups and dosing levels of our population and predicts 12 h and 24 h enoxaparin activities sufficiently. According to our results, a once-daily enoxaparin dosing regimen with frequent monitoring is feasible. In 53.2% of the patients the median 24 h trough level was above the desired range of 0.1 IU mL⁻¹ anti-FXa activity for prophylaxis therapy.

Nadroparin therapy in pediatric patients with venous thromboembolic disease

Low-molecular-weight heparins are increasingly used for treatment of pediatric venous thromboembolic disease (VTE). Pediatric data about therapeutic doses of nadroparin are not available. To evaluate pharmacodynamics and safety of therapeutic doses of nadroparin, consecutive patients (age 0 to 18 y) with objectively diagnosed VTE and treated with nadroparin were included in this single center study over a 12-year period. All patients started with 85.5 IU/kg of nadroparin twice daily. The target therapeutic range (TTR) was set at 0.5 to 1.0 anti-Xa IU/mL 4 hours postdose. Safety end points were major bleeding and therapy-related death. A total of 84 patients were enrolled, of whom 8 patients did not undergo measurement of anti-Xa levels. Fifty-four (71%) of 76 patients achieved TTR. The maintenance dose (mean+/-SE) was 448+/-42 IU/kg/d in neonates (<2 mo, n=6), 253+/-22 IU/kg/d in infants (2 mo to 1 y, n=10), 214+/-8 IU/kg/d in children (2 to 11 y, n=13), and 183+/-5 IU/kg/d in adolescents (12 to 18 y, n=25). Neonates required significantly more dose adjustments and time to achieve TTR than adolescents. No major bleeding or therapy-related death occurred. In summary, an age-dependent response to nadroparin exists in pediatric patients. Nadroparin therapy seems to be safe for treatment of pediatric VTE.

Pharmacokinetics, efficacy, and safety of LMWHs in venous thrombosis and stroke in neonates, infants and children

Since the early nineties it has been shown that low molecular weight heparin (LMWH) has significant advantages over unfractionated heparin and oral anticoagulants for both the treatment and the prevention of thrombosis, not only in adults, but also in children. The present review was based on an 'EMBASE', 'Medline' and 'PubMed' search including literature published in any language since 1980 on LMWH in neonates, infants and children. It included paediatric pharmacokinetic studies, the use of LMWH in children with venous thrombosis, LMWH administration in paediatric patients with ischaemic stroke, and its use in order to prevent symptomatic thromboembolism in children at risk. An increasing rate of off-label use of LMWH in children has been reported, showing that LMWHs offer important benefits to children with symptomatic thromboembolic events and poor venous access. Two well-conducted pharmacokinetic studies in this age group showed that neonates and younger infants require higher LMWH doses than older children to achieve the targeted anti-Xa levels, due to an increased extra vascular clearance. Recurrent symptomatic thromboses under LMWH occur in approximately 4% of children treated for venous thrombosis, and in 7% of children treated for stroke; major bleed was documented in 3% of children with therapeutic target LMWH anti-Xa levels, whereas minor bleeding was reported in approximately 23% of children receiving either therapeutic or prophylactic doses, respectively. Further randomized controlled trials are recommended to evaluate the optimum duration and application for different LMWH indications in children.