Low-molecular-weight heparin in thrombotic disease in children and adolescents

[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.

Cartridge-Based Thromboelastography Can Be Used to Monitor and Quantify the Activity of Unfractionated and Low-Molecular-Weight Heparins

Thromboelastography is increasingly utilized in the management of bleeding and thrombotic complications where heparin management remains a cornerstone. This study assessed the feasibility of the cartridge-based TEG ^® 6s system (Haemonetics Corp., Braintree, Massachusetts, United States) to monitor and quantify the effect of unfractionated and low-molecular-weight heparin (UFH and LMWH). Blood samples from healthy donors were spiked with UFH ( n  = 23; 0–1.0 IU/mL) or LMWH (enoxaparin; n  = 22; 0–1.5 IU/mL). Functional fibrinogen maximum amplitude (CFF.MA), RapidTEG activated clotting time (CRT.ACT), and kaolin and kaolin with heparinase reaction time (CK.R and CKH.R) were evaluated for their correlation with heparin concentrations, as well as the combination parameters ΔCK.R − CKH.R, ratio CK.R/CKH.R, and ratio CKH.R/CK.R. Nonlinear mixed-effect modelling was used to study the relationship between concentrations and parameters, and Bayesian classification modelling for the prediction of therapeutic ranges. CK.R and CRT.ACT strongly correlated with the activity of LMWH and UFH ( p  < 0.001). Using combination parameters, heparin activity could be accurately quantified in the range of 0.05 to 0.8 IU/mL for UFH and 0.1 to 1.5 IU/mL for LMWH. CRT.ACT was able to quantify heparin activity at higher concentrations but was only different from the reference range ( p  < 0.05) at >0.5 IU/mL for UFH and >1.5 IU/mL for LMWH. Combination parameters classified blood samples into subtherapeutic, therapeutic, and supratherapeutic heparin ranges, with an accuracy of >90% for UFH, and >78% for LMWH. This study suggests that TEG 6s can effectively monitor and quantify heparin activity for LMWH and UFH. Additionally, combination parameters can be used to classify blood samples into therapeutic ranges based on heparin activity.

THROMBOTECT - a randomized study comparing low molecular weight heparin, antithrombin and unfractionated heparin for thromboprophylaxis during induction therapy of acute lymphoblastic leukemia in children and adolescents

Thromboembolism is a serious complication of induction therapy for childhood acute lymphoblastic leukemia. We prospectively compared the efficacy and safety of antithrombotic interventions in the consecutive leukemia trials ALL-BFM 2000 and AIEOP-BFM ALL 2009. Patients with newly diagnosed acute lymphoblastic leukemia (n=949, age 1 to 18 years) were randomized to receive low-dose unfractionated heparin, prophylactic low molecular weight heparin (enoxaparin) or activity-adapted antithrombin throughout induction therapy. The primary objective of the study was to determine whether enoxaparin or antithrombin reduces the incidence of thromboembolism as compared to unfractionated heparin. The principal safety outcome was hemorrhage; leukemia outcome was a secondary endpoint. Thromboembolism occurred in 42 patients (4.4%). Patients assigned to unfractionated heparin had a higher risk of thromboembolism (8.0%) compared with those randomized to enoxaparin (3.5%; P=0.011) or antithrombin (1.9%; P<0.001). The proportion of patients who refused antithrombotic treatment as allocated was 3% in the unfractionated heparin or antithrombin arms, and 33% in the enoxaparin arm. Major hemorrhage occurred in eight patients (no differences between the groups). The 5-year event-free survival was 80.9±2.2% among patients assigned to antithrombin compared to 85.9±2.0% in the unfractionated heparin group (P=0.06), and 86.2±2.0% in the enoxaparin group (P=0.10). In conclusion, prophylactic use of antithrombin or enoxaparin significantly reduced thromboembolism. Despite the considerable number of patients rejecting the assigned treatment with subcutaneous injections, the result remains unambiguous. Thromboprophylaxis - for the present time primarily with enoxaparin - can be recommended for children and adolescents with acute lymphoblastic leukemia during induction therapy. Whether and how antithrombin may affect leukemia outcome remains to be determined.

Risk of deep venous thrombosis in elective neurosurgical procedures: a prospective, Doppler ultrasound-based study in children 12 years of age or younger

OBJECTIVE The risk of venous thromboembolism (VTE) from deep venous thrombosis (DVT) is significant in neurosurgical patients. VTE is considered a leading cause of preventable hospital deaths and preventing DVT is a closely monitored quality metric, often tied to accreditation, hospital ratings, and reimbursement. Adult protocols include prophylaxis with anticoagulant medications. Children's hospitals may adopt adult protocols, although the incidence of DVT and the risk or efficacy of treatment is not well defined. The incidence of DVT in children is likely less than in adults, although there is very little prospectively collected information. Most consider the risk of DVT to be extremely low in children 12 years of age or younger. However, this consideration is based on tradition and retrospective reviews of trauma databases. In this study, the authors prospectively evaluated pediatric patients undergoing a variety of elective neurosurgical procedures and performed Doppler ultrasound studies before and after surgery. METHODS A total of 100 patients were prospectively enrolled in this study. All of the patients were between the ages of 1 month and 12 years and were undergoing elective neurosurgical procedures. The 91 patients who completed the protocol received a bilateral lower-extremity Doppler ultrasound examination within 48 hours prior to surgery. Patients did not receive either medical or mechanical DVT prophylaxis during or after surgery. The ultrasound examination was repeated within 72 hours after surgery. An independent, board-certified radiologist evaluated all sonograms. We prospectively collected data, including potential risk factors, details of surgery, and details of the clinical course. All patients were followed clinically for at least 1 year. RESULTS There was no clinical or ultrasound evidence of DVT or VTE in any of the 91 patients. There was no clinical evidence of VTE in the 9 patients who did not complete the protocol. CONCLUSIONS In this prospective study, no DVTs were found in 91 patients evaluated by ultrasound and 9 patients followed clinically. While the study is underpowered to give a definitive incidence, the data suggest that the risk of DVT and VTE is very low in children undergoing elective neurosurgical procedures. Prophylactic protocols designed for adults may not apply to pediatric patients. Clinical trial registration no.: NCT02037607 (clinicaltrials.gov).

The impact of femoral arterial thrombosis in paediatric cardiac catheterisation: a national study

BACKGROUND

Previous studies have identified risk factors for femoral arterial thrombosis after paediatric cardiac catheterisation, but none of them have evaluated the clinical and economic significance of this complication at the population level. Therefore, we examined the national prevalence and economic impact of femoral arterial thrombosis after cardiac catheterisation in children.

METHODS

Patients⩽18 years of age who underwent cardiac catheterisation were identified in the 2003-2009 Kids' Inpatient Database. Patients were stratified by age as follows: <1 year of age or 1-18 years of age. The primary outcome was arterial thrombosis of the lower extremity during the same hospitalisation as cardiac catheterisation. Propensity score matching was used to determine the impact of femoral arterial thrombosis on hospital length of stay, cost, and mortality.

RESULTS

Among the 11,497 paediatric cardiac catheterisations identified, 4558 catheterisations (39.6%) were performed in children <1 year of age. This age group experienced a higher prevalence of reported femoral arterial thrombosis, compared with children aged 1-18 years (1.3 versus 0.3%, p<0.001). After matching, femoral arterial thrombosis in children <1 year of age was associated with similar mortality (5.4 versus 1.8%, p=0.28), length of stay (8 versus 5 days, p=0.11), and total hospital cost ($27,135 versus $28,311, p=0.61), compared with absence of thrombosis.

CONCLUSIONS

Femoral arterial thrombosis is especially prevalent in children <1 year of age undergoing cardiac catheterisation. Clinicians should be vigilant in monitoring femoral arterial patency in neonates and infants after cardiac catheterisation.

Goal directed enoxaparin dosing provides superior chemoprophylaxis against deep vein thrombosis

INTRODUCTION

Optimal enoxaparin dosing for deep venous thrombosis (DVT) prophylaxis remains elusive. Prior research demonstrated that trauma patients at increased risk for DVT based upon Greenfield's risk assessment profile (RAP) have DVT rates of 10.8% despite prophylaxis. The aim of this study was to determine if goal directed prophylactic enoxaparin dosing to achieve anti-Xa levels of 0.3-0.5IU/ml would decrease DVT rates without increased complications.

MATERIALS AND METHODS

Retrospective review of trauma patients having received prophylactic enoxaparin and appropriately timed anti-Xa levels was performed. Dosage was adjusted to maintain an anti-Xa level of 0.3-0.5IU/ml. RAP was determined on each patient. A score of ≥5 was considered high risk for DVT. Sub-analysis was performed on patients who received duplex examinations subsequent to initiation of enoxaparin therapy to determine the incidence of DVT.

RESULTS

306 patients met inclusion criteria. Goal anti-Xa levels were met initially in only 46% of patients despite dosing of >40mg twice daily in 81% of patients; however, with titration, goal anti-Xa levels were achieved in an additional 109 patients (36%). An average enoxaparin dosage of 0.55mg/kg twice daily was required for adequacy. Bleeding complications were identified in five patients (1.6%) with three requiring intervention. There were no documented episodes of HIT. Subsequent duplex data was available in 197 patients with 90% having a RAP score >5. Overall, five DVTs (2.5%) were identified and all occurred in the high-risk group. All patients were asymptomatic at the time of diagnosis.

CONCLUSION

An increased anti-Xa range of 0.3-0.5IU/ml was attainable but frequently required titration of enoxaparin dosage. This produced a lower rate of DVT than previously published without increased complications.

The safety and efficacy of use of low-molecular-weight heparin in pediatric neurosurgical patients

OBJECT

Low-molecular-weight heparins (LMWHs), mainly enoxaparin, offer several advantages over standard anticoagulation therapies such as unfractionated heparin and warfarin, including predictable pharmacokinetics, minimal monitoring, and subcutaneous administration. The purpose of this study was to determine the safety and efficacy of LMWHs in pediatric neurosurgical patients.

METHODS

A retrospective study was performed with patients 18 years old or younger who were admitted to the Pediatric Neurosurgery Service at Texas Children's Hospital and treated with LMWH for either therapeutic or prophylactic purposes between March 1, 2011, and December 30, 2013. Demographic and clinical features and outcomes were recorded.

RESULTS

LMWH was administered for treatment of venous thromboembolic events (VTEs) in 17 children and for prophylaxis in 24 children. Clinical resolution of VTEs occurred in 100% (17 of 17) of patients receiving therapeutic doses of LMWH. No patient receiving prophylactic doses of LMWH developed a new VTE. Major or minor bleeding complications occurred in 18% (3 of 17 children) and 4% (1 of 24 children) of those receiving therapeutic and prophylactic doses, respectively. All 4 patients who experienced hemorrhagic complications had other bleeding risk factors-i.e., coagulopathies and antiplatelet medications.

CONCLUSIONS

LMWH seems to be safe and efficacious for both management and prophylaxis of VTEs in pediatric neurosurgery. However, pediatric practitioners should be aware of higher risk for bleeding complications with increasing doses of LMWH, especially in patients with preexisting bleeding disorders or concurrent use of antiplatelet agents.

Lack of anti-factor Xa assay standardization results in significant low molecular weight heparin (enoxaparin) dose variation in neonates and children

INTRODUCTION

Enoxaparin is a frequently used anticoagulant in children. Unlike in adults, consensus guidelines recommend therapeutic monitoring to a target anti-factor Xa level of 0.5-1 U mL(-1) . Therapeutic ranges are not well correlated with clinical outcomes (e.g. thrombosis or hemorrhage), and assays are not standardized. Owing to limited reagent supplies, our clinical laboratory conducted a validation process and switched anti-FXa assays. Although the assays correlated well with each other, anti-FXa values were, on average, 33% higher with the new assay. The target anti-FXa range was not altered. We evaluated how this change in anti-FXa assays influenced enoxaparin dosing (mg kg(-1) ).

METHODS

Enoxaparin dosing and anti-FXa values for all patients started on enoxaparin for the 6 months before and after assay change were retrospectively compiled and analyzed with a Student's t-test.

RESULTS

One hundred and nine children were started on enoxaparin before assay change, and 104 after assay change. The mean therapeutic enoxaparin dose (mg kg(-1) ) was significantly lower in subjects aged < 3 months (P = 0.01) and 3 months to 2 years (P < 0.0001), but not in subjects aged > 2 years (P = 0.18), after assay change. The median number of enoxaparin dose changes required to achieve the target range was significantly reduced after assay change, from 1 to 0 (P = 0.004).

CONCLUSIONS

The current pediatric practice of dose adjustment to achieve and maintain a target anti-FXa range is vulnerable to assay determination, which may provide false reassurance of efficacy and safety and represent misappropriation of time and resources. These data support a pediatric randomized controlled clinical trial comparing the safety and efficacy of enoxaparin weight-based dosing with or without dose titration based on anti-FXa.

Intracardiac thrombus in children: the fine equilibrium between the risk and the benefit

The medical records of 16 patients diagnosed as intracardiac thrombus were searched. The size, location and outcome of thrombus together with demographic data of patients were assessed. The median age of the patients was 2.2 years. Six patients were newborn and two patients were infant. The median size of thrombus was 9 mm. The localization was right atrium in seven, right ventricle in five, left ventricle in one, pulmonary artery in one, and superior vena cava in two patients. There was prematurity in five, ciyanotic congenital heart disease in one, blood culture positivity in three, malignancy in four, nephrotic syndrome in one, indwelling catheters in 10, and acquired or genetic thrombophilia in six patients as risk factors. In the treatment, the first choice was tissue plasminogen activator in two patients, heparin infusion in one patient and low molecular weight heparin in remaining 12 patients. In nine patients, therapy included parenteral antimicrobials together with anticoagulants. The result was complete resolution in 15 patients and in one patient thrombus was surgically removed. The median time was 16 (2-70) days for 50% resolution and 26 (3-93) days for complete resolution. There was a statistically significant (P = .027 and r = 0.5) correlation between the size and the complete resolution time. There was no anticoagulant therapy related major complication. In patients with intracardiac thrombus, selection of anticoagulant therapy may decrease the risk of complications. Surgery is rarely required and thrombolytics are not usually necessary for resolution of thrombus.

Anticoagulant therapy in pediatrics

Thromboembolic episodes are disorders encountered in both children and adults, but relatively more common in adults. However, the occurrence of venous thromboembolism and use of anticoagulants in pediatrics are increasing. Unfractionated Heparin (UH) is used as a treatment and prevention of thrombosis in adults and critically ill children. Heparin utilization in pediatric is limited by many factors and the most important ones are Heparin Induced Thrombocytopenia (HIT) and anaphylaxis. However, Low Molecular Weight Heparin (LMWH) appears to be an effective and safe alternative treatment. Hence, it is preferred over than UH due to favorable pharmacokinetic and side effect profile. Direct Thrombin Inhibitors (DTI) is a promising class over the other anticoagulants since it offers potential advantages. The aim of this review is to discuss the differences between adult and pediatric thromboembolism and to review the current anticoagulants in terms of pharmacological action, doses, drug reactions, pharmacokinetics, interactions, and parameters. This review also highlights the differences between old and new anticoagulant therapy in pediatrics.

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.

Current and future antithrombotic agents in children

Thromboembolic complications are increasing in children, and the use of anticoagulation has seen a dramatic increase despite the lack of randomized clinical trials. The most widely used agents in children are heparin and warfarin, however these agents have limitations that are exaggerated in children. This has led to the use of newer agents with improved pharmacologic properties such as low-molecular-weight heparin, however, the use of novel agents such as direct thrombin inhibitors has been limited to case reports. These agents, however, have potential advantages over heparin, low-molecular-weight heparin and warfarin. Current clinical trials are in progress to define the proper dose of two such agents--argatroban (Argatroban, GlaxoSmithKline) and bivalirudin (Angiomax, The Medicines Company). The selective Factor Xa inhibitor fondaparinux (Arixtra, Sanofi-Synthelabo) has not been used in children; however, there are situations in which this agent may be advantageous. This review will discuss the currently available agents, with an emphasis on those that are novel and their potential uses in children.

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.

Pulmonary embolism in children

Unlike in adults, pulmonary embolism (PE) is an infrequent event in children. It has a marked bimodal distribution during the paediatric years, occurring predominantly in neonates and adolescents. The most important predisposing factors to PE in children are the presence of a central venous line (CVL), infection, and congenital heart disease. Clinical signs of PE are non-specific in children or can be masked by underlying conditions. Diagnostic testing is necessary in children, especially with the lack of clinical prediction rules. Recommendations for tests are derived from adult studies with ventilation/perfusion (V/Q) scintigraphy being well established. There exists an increasing role for computerised tomography pulmonary angiography (CTPA) and magnetic resonance pulmonary angiography (MRPA). Thrombotic events in children are initially treated with unfractionated heparin (UFH) or low molecular weight heparin (LMWH). For the extended anticoagulant therapy LMWH or vitamin K antagonists can be used with duration of treatment recommendations extrapolated from adult data. Mortality rates for PE in children are reported to be around 10%, with death usually related to the underlying disease processes. Exact data about recurrence risk in children is unknown. Because of the difference in aetiology, presentation, diagnostic methods and treatment between adults and children further research is necessary to assess the validity of recommendations for children.

Current and future management of pediatric venous thromboembolism

Venous thromboembolism (VTE) is an increasingly common complication encountered in tertiary care pediatric settings. The purpose of this review is to summarize the epidemiology, current and emerging pharmacotherapeutic options, and management of this disease. Over 70% of VTE occur in children with chronic diseases. Although they are seen in children of all ages, adolescents are at greatest risk. Pediatric VTE is associated with an increased risk of in-hospital mortality; recurrent VTE and post-thrombotic syndrome are commonly seen in survivors. In recent years, anticoagulation with low molecular weight heparin has emerged as the mainstay of therapy, but compliance is limited by its onerous subcutaneous administration route. New anticoagulants either already approved for use in adults or in the pipeline offer the possibility of improved dose stability and oral routes of administration. Current recommended anticoagulation course durations are derived from very limited case series and cohort data, or extrapolations from adult literature. However, the pathophysiologic underpinnings of pediatric VTE are dissimilar from those seen in adults and are often variable within groups of pediatric patients. Clinical studies and trials in pediatric VTE are underway which will hopefully improve the quality of evidence from which therapeutic guidelines are derived.

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.

FondaKIDS: a prospective pharmacokinetic and safety study of fondaparinux in children between 1 and 18 years of age

BACKGROUND

The incidence of thromboembolic disease is increasing in children. New anticoagulants have been licensed in adults and need to be studied in children. This report describes the first prospective study of fondaparinux in children.

PROCEDURE

The purpose of the study was to determine the dosing, pharmacokinetics, and safety of fondaparinux in children with deep vein thrombosis (DVT) or heparin-induced thrombocytopenia (HIT). Hospitalized children between 1 and 18 years of age with DVT or HIT received fondaparinux 0.1 mg/kg once daily. Fondaparinux-based anti-factor Xa levels were assessed at 2, 4, 12, and 24 hr following the first dose, and peak levels were measured twice weekly thereafter. Detailed pharmacokinetic analyses were performed.

RESULTS

Twenty four subjects in 3 age cohorts were enrolled and completed the study. Pharmacokinetic modeling demonstrated that a once-daily dose of fondaparinux at 0.1 mg/kg resulted in similar concentrations known to be efficacious in adults. Safety was demonstrated with only two bleeding events: one which may have pre-dated study drug administration and one which led only to temporary discontinuation of study drug.

CONCLUSION

Dosing of fondaparinux at 0.1 mg/kg once daily in children resulted in PK profiles comparable to those in adults receiving standard dosing. Fondaparinux can be considered an attractive alternative to LMWH given its once-daily dosing, acceptable safety data, and other favorable properties.

Old and new antithrombotic drugs in neonates and infants

Thromboembolic complications are becoming more frequent in children and the use of anticoagulation has increased considerably. The most widely used agents in children, heparin, low molecular weight heparin, and warfarin all have limitations which are exaggerated in children. This has led to the study of newer agents with improved pharmacologic properties such as bivalirudin, argatroban, and fondaparinux. Clinical trials are under way to assess several new oral anticoagulants that are in late phase studies or already licensed in adults. Based on the completed studies in children, several recommendations for the use of currently available agents (bivalirudin, argatroban, and fondaparinux) are suggested for clinical use today. Additional studies need to be conducted for the these agents, so that their use may be expanded in selected indications. New regulatory requirements are leading to a number of studies in the newer anticoagulants that are yet to be licensed in adults for treatment of venous thromboembolism. Pediatric thrombosis is entering a fruitful era of research in anticoagulation management, which is sure to lead to significant changes in how children are treated in the next 10 years.

Treatment of Deep Vein Thrombosis with Continuous IV Infusion of LMWH: A Retrospective Study in 32 Children

Thirty-two consecutive children aged 0–18 years with VTE treated with LMWH administered as a continuous infusion (CI) were identified at the Children's University Hospital Brno. The treatment led to at least partial resolution of the thrombus within two weeks in 85% of patients. There were no adverse events or increased bleeding reported in any patients. No recurrences were observed during a followup period of 6 months. Although continuous infusion should not replace subcutaneous (SC) administration of LMWH, CI appeared to be safe and efficient and may provide an alternate method of administering LMWH in a subset of the paediatric population where SC administration may not be feasible. Further prospective studies are needed to support the promising findings of our pilot clinical observation.

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.

Aspects of anticoagulation in children

The number of children receiving anticoagulation is increasing. Thromboembolic events are associated with significant risk of morbidity and mortality although the optimal management of asymptomatic events remains unclear. Specific challenges in paediatrics include the diagnosis of thrombosis, delivery and monitoring of anticoagulation in a wide range of ages from neonates through to adolescents. The development of the haemostatic system as children age results in changing pathophysiology of thrombosis and response to anticoagulation agents. Although registry and observational studies have provided vital information, specific paediatric, prospective anticoagulation studies have been few and limited in design. The result is that much of current practice is extrapolated from adult studies. Traditional anticoagulants have significant limitations. Both heparin and warfarin are in widespread use but many fundamental questions regarding dose, therapeutic range, efficacy and optimum duration have not been fully answered. Alternative agents, such as direct thrombin inhibitors and the selective anti-factor Xa inhibitor fondaparinux, may have advantages for children. Clinical trials in adults and preliminary data in children are promising but caution should be applied until specific paediatric studies have demonstrated safety and efficacy.

Effects of Age and Weight-Based Dosing of Enoxaparin on Anti-Factor Xa Levels In Pediatric Patients

OBJECTIVE

The objective of this dose range study is to expand on the relationship between age and weight-based doses of enoxaparin and resulting levels of anti-factor Xa (anti-Xa) in pediatric patients. The primary outcome of this study is to determine the average dose of enoxaparin required to produce a therapeutic effect. Secondary outcomes include the number of enoxaparin dose changes required to achieve a therapeutic level of anti-Xa in each age group, the success rates of achieving and maintaining therapeutic anti-Xa levels, and the effect of serum antithrombin concentrations on anti-Xa levels. The study will also determine whether different dispensed concentrations of enoxaparin play a role in achieving therapeutic levels of anti-Xa.

METHODS

Single center, retrospective chart review. Patients were excluded from the study if they were older than 18 years of age, were receiving enoxaparin for prophylactic purposes, had a creatinine clearance &lt; 30 ml/min/1.73m2, and if no anti-factor Xa levels were drawn.

RESULTS

Average enoxaparin doses required for therapeutic levels of anti-factor Xa were 1.8 mg/kg for patients &lt;1 month, 1.64 mg/kg (1 month to 1 year), 1.45 mg/kg (1 to 6 years), and 1.05 mg/kg (&gt;6 years of age). An average of 3.24 dose changes was required for neonates to achieve therapeutic levels anti-factor Xa. The success rates for achieving and maintaining therapeutic levels were both 41%. Patients with low serum antithrombin levels were more likely to have low anti-Xa levels than those with normal or high values, 52% vs 40% vs 18%, respectively. Patients receiving diluted concentrations, 10 or 20 mg/mL, experienced lower anti-Xa levels than patients who received the standard manufactured concentration of 100 mg/mL, 61% vs 33%.

CONCLUSION

Based on this dose-range study, enoxaparin should be initiated at larger doses than recommended by the current guidelines to promptly achieve therapeutic anti-Xa levels. Doses should be divided into three age groups instead of two as currently suggested in the guidelines. To increase the likelihood of achieving therapeutic levels, the commercially available enoxaparin product should not be diluted if possible.

Low-Molecular-Weight Heparin Use in a Case of Noncardiogenic Multifocal Perinatal Thromboembolic Stroke

A full-term neonate suffered multifocal cerebral infarctions due to multiple large vessel thrombi. Thrombophilia and cardiovascular assessments were negative, but due to the severity of the lesions and the concern for expansion of the thrombi or future embolic events, treatment with low-molecular-weight heparin (LMWH) was initiated. No complications from treatment were experienced. We present this severe case in order to highlight difficult management decisions for newborns with multifocal perinatal thromboembolic stroke and to stress the need for further practice guidelines and research in this area.

Antithrombotic therapy in neonates and children: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This chapter about antithrombotic therapy in neonates and children is part of the Antithrombotic and Thrombolytic Therapy: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs, and Grade 2 suggests that individual patient values may lead to different choices (for a full understanding of the grading, see Guyatt et al in this supplement, pages 123S-131S). In this chapter, many recommendations are based on extrapolation of adult data, and the reader is referred to the appropriate chapters relating to guidelines for adult populations. Within this chapter, the majority of recommendations are separate for neonates and children, reflecting the significant differences in epidemiology of thrombosis and safety and efficacy of therapy in these two populations. Among the key recommendations in this chapter are the following: In children with first episode of venous thromboembolism (VTE), we recommend anticoagulant therapy with either unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) [Grade 1B]. Dosing of IV UFH should prolong the activated partial thromboplastin time (aPTT) to a range that corresponds to an anti-factor Xa assay (anti-FXa) level of 0.35 to 0.7 U/mL, whereas LMWH should achieve an anti-FXa level of 0.5 to 1.0 U/mL 4 h after an injection for twice-daily dosing. In neonates with first VTE, we suggest either anticoagulation or supportive care with radiologic monitoring and subsequent anticoagulation if extension of the thrombosis occurs during supportive care (Grade 2C). We recommend against the use of routine systemic thromboprophylaxis for children with central venous lines (Grade 1B). For children with cerebral sinovenous thrombosis (CSVT) without significant intracranial hemorrhage (ICH), we recommend anticoagulation initially with UFH, or LMWH and subsequently with LMWH or vitamin K antagonists (VKAs) for a minimum of 3 months (Grade 1B). For children with non-sickle-cell disease-related acute arterial ischemic stroke (AIS), we recommend UFH or LMWH or aspirin (1 to 5 mg/kg/d) as initial therapy until dissection and embolic causes have been excluded (Grade 1B). For neonates with a first AIS, in the absence of a documented ongoing cardioembolic source, we recommend against anticoagulation or aspirin therapy (Grade 1B).

Submucosal hematoma presenting as small bowel obturator obstruction in a patient on low-molecular-weight heparin

Recent studies have shown the efficacy of low-molecular-weight heparin (LMWH) in the treatment of venous thromboembolic disease in children. Compared to unfractionated heparin and coumadin, LMWH has more predictable pharmacokinetics and a reported lower incidence of osteoporosis and heparin-induced thrombocytopenia in children. The overall incidence of severe hemorrhage on LMWH in children is low. To date, there is a single report of a small bowel obstruction in a child secondary to a hematoma while on LMWH. We report the second case of a child, on enoxaparin (Lovenox) therapy, who underwent bowel resection secondary to a completely obstructing small bowel wall hematoma.

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.

Enoxaparin therapy for arterial thrombosis in infants with congenital heart disease

OBJECTIVE

To investigate efficacy and safety of enoxaparin for catheter-related arterial thrombosis in infants with congenital heart disease.

DESIGN

Prospective observational study.

SETTING

Pediatric Intensive Care and Cardiology Unit at the University Children's Hospital of Zurich.

PATIENTS

A cohort of 32[Symbol: see text]infants aged 0-12[Symbol: see text]months treated with enoxaparin for catheter-related arterial thrombosis from 2002 to 2005.

MEASUREMENTS

Dose requirements of enoxaparin, resolution of thrombosis by Doppler ultrasound, and bleeding complications.

RESULTS

Catheter-related arterial thrombosis was located in the iliac/femoral arteries in 31 (97%) infants and aorta in 1 infant, and was related to indwelling catheters and cardiac catheterization in 17 (53%) and 15 (47%) cases, respectively. Newborns required increased doses of enoxaparin to achieve therapeutic anti-FXa levels (mean 1.62[Symbol: see text]mg/kg per dose) compared with infants aged 2-12 months (mean 1.12 mg/kg per dose; p=0.0002). Complete resolution of arterial thrombosis occurred in 29 (91%) infants at a mean of 23 days after initiation of enoxaparin therapy. Partial or no resolution was observed in 1 (3%) and 2 (6%) infants, respectively, at a mean follow-up time of 4.3 months. Bleeding complications occurred in 1 (3%) infant.

CONCLUSION

Enoxaparin is efficient and safe for infants with congenital heart disease and catheter-related arterial thrombosis, possibly representing a valid alternative to the currently recommended unfractionated heparin.

Intracardiac thrombus causing systemic embolism in a child with idiopathic ventricular tachycardia and heterozygous activated protein C resistance

Systemic embolism in childhood is rare but often disastrous. Most often the concomitant occurrence of more than one prothrombotic factor is responsible for the acute event. We report on a child in whom an intracardiac thrombus embolized into the descending aorta resulting in subtotal occlusion. Causative for thrombus formation was an idiopathic ventricular tachycardia and a heterozygous activated protein C resistance, both previously unknown. Immediate surgical thrombectomy was successful without sequelae. Antithrombotic and antiarrhythmispioproptylactic treatment was started afterwards. We suggest that in cases of longstanding or repeated tachycardia and in children after thromboembolic events diagnostic work-up for thrombophilia should be undertaken.

Acute pulmonary embolism in childhood

Pulmonary embolism is an uncommon, but potentially fatal disease in children. Most children with pulmonary embolism have underlying clinical conditions, of which the presence of a central venous catheter is the most frequent. The clinical presentation is often subtle, or masked by the underlying clinical condition. Diagnostic as well as therapeutic strategies for pulmonary embolism in children are mostly extrapolated from studies in adults. Pulmonary angiography is still the gold standard in diagnosing pulmonary embolism, but several other radiographic tests can be used to diagnose pulmonary embolism, including ventilation-perfusion lung scanning, helical computed tomography, magnetic resonance imaging and echocardiography. The choice of treatment depends on the clinical presentation of the patient. Anticoagulation is the mainstay of therapy for children with pulmonary embolism. However, thrombolytic therapy can be considered for patients with hemodynamic instability. The outcome of pediatric pulmonary embolism is uncertain and needs to be studied.

A spontaneous intramural hematoma of the bowel presenting as obstruction in a child receiving low-molecular-weight heparin

Low-molecular-weight heparin (LMWH) is a safe and effective alternative to unfractionated heparin and coumadin in the treatment and prophylaxis of thrombosis in children. When compared with these more established anticoagulants, it is easier to achieve therapeutic levels and the incidence of hemorrhagic complications is equivalent or lower. In children there is less published experience than in adults, but the low frequency of significant bleeding appears to be similar. The authors describe a child on therapeutic doses of LMWH for a deep vein thrombosis who spontaneously developed an intramural hemorrhage in his small bowel, leading to infarction and a partial bowel resection.

Analysis of pediatric thrombotic patients in Turkey

This study analyzes the data of thrombotic children who were followed up in different pediatric referral centers of Turkey, to obtain more general data on the diagnosis, risk factors, management, and outcome of thrombosis in Turkish children. A simple two-page questionnaire was distributed among contact people from each center to standardize data collection. Thirteen pediatric referral centers responded to the invitation and the total number of cases was 271. All children were diagnosed with thromboembolic disease between January 1995 and October 2001. Median age at time of first thrombotic event was 7.0 years. Of the children 4% of the cases were neonates, 12% were infants less than 1 year old, and 17% were adolescents. Thromboembolic event was mostly located in the cerebral vascular system (32%), deep venous system of the limbs, femoral and iliac veins (24%), portal veins (10%), and intracardiac region (9%). Acquired risk factors were present in 86% of the children. Infection was the most common underlying risk factor. Inherited risk factors were present in 30% of the children. FVL was the most common inherited risk factor. Acquired and inherited risk factors were present simultaneously in 19% of the patients. Eleven children had a history of familial thrombosis. Due to the local treatment preferences, the treatment of the children varied greatly. Outcome of the 142 patients (52%) was reported: 88 (62%) patients had complete resolution, 47 (33%) had complications, 12 (9%) had recurrent thrombosis, and 34 (24%) died. Three children (2.1%) died as a direct consequence of their thromboembolic disease. The significant morbidity and mortality found in this study supports the need for multicentric prospective clinical trials to obtain more generalizable data on management and outcome of thrombosis in Turkish children.

An assessment of published pediatric dosage guidelines for enoxaparin: a retrospective review

OBJECTIVE

To evaluate the ability of published dosage guidelines for enoxaparin to achieve therapeutic anticoagulation and to determine whether the routine monitoring of anti-Xa levels is still necessary at a tertiary care pediatric institution.

METHODS

Consecutive charts and laboratory records were reviewed for all patients receiving treatment doses of enoxaparin for thrombosis in the authors institution over a 4-year period (1998-2002).

RESULTS

Sixty-six percent (25/38) of the anti-Xa levels were within the recommended therapeutic range (0.5-1.0 [+/- 10%] U/mL) after two doses. The success rates of achieving therapeutic levels were 1/6, 2/3, 6/9, 10/11, and 6/9, for patients 2 months or younger, more than 2 months to 1 year, more than 1 year to 6 years, more than 6 years to 12 years, and more than 12 years of age, respectively. Patients with cardiac or renal disease were more likely to achieve high anti-Xa levels. Thirty-seven percent of patients reported adverse effects. The most common effects were injection site-related bruising and minor bleeding. One patient experienced a major bleed that was not life-threatening.

CONCLUSIONS

Most patients achieved therapeutic anticoagulation when dosed according to the published guidelines. Children with cardiac conditions or renal insufficiency or those younger than 2 months were more likely to require dosage adjustments to achieve the therapeutic range. Routine monitoring of anti-Xa levels is still necessary in these patient populations, particularly when the early establishment of therapeutic anticoagulation may be critical. Enoxaparin appears to be well tolerated in the authors' patient population.

Pharmacodynamic and pharmacokinetic properties of enoxaparin : implications for clinical practice

Enoxaparin is a low-molecular-weight heparin (LMWH) that differs substantially from unfractionated heparin (UFH) in its pharmacodynamic and pharmacokinetic properties. Some of the pharmacodynamic features of enoxaparin that distinguish it from UFH are a higher ratio of anti-Xa to anti-IIa activity, more consistent release of tissue factor pathway inhibitor, weaker interactions with platelets and less inhibition of bone formation. Enoxaparin has a higher and more consistent bioavailability after subcutaneous administration than UFH, a longer plasma half-life and is less strongly bound to plasma proteins. These properties mean that enoxaparin provides a more reliable anticoagulant effect without the need for laboratory monitoring, and also offers the convenience of once-daily administration. Clinical studies have confirmed that these pharmacological advantages translate into improved outcomes. There are important pharmacokinetic and pharmacodynamic differences between enoxaparin, other LMWHs and UFH, and therefore these molecules cannot be regarded as interchangeable.

The use of enoxaparin in children with acute, nonhemorrhagic ischemic stroke

The use of low-molecular-weight heparin offers multiple advantages over unfractionated heparins in pediatric patients with acute ischemic stroke. The safety and efficacy of low-molecular-weight heparin have been demonstrated in adults, but less is known about their use in children. This study reviews retrospectively the use of low-molecular-weight heparin in children with acute, ischemic, nonhemorrhagic strokes. A database search was used to locate all children who experienced an ischemic stroke between July 1991 and January 2001 and who were subsequently treated with low-molecular-weight heparin. Eight children were identified (aged 37 months to 17 years; median age, 133 months) who were treated with the low-molecular-weight heparin enoxaparin. Enoxaparin was used in one case as the sole treatment, in six cases as a bridge to oral anticoagulant therapy with warfarin, and in one case as a replacement treatment after several days of warfarin therapy. The median duration of treatment with enoxaparin was 4 days. During this period, no major bleeding complications were observed, and no new thrombi or extensions of thrombi occurred. One patient did experience mild oozing at an intravenous site, and another experienced an episode of epistaxis. Enoxaparin was discontinued in one patient because of discomfort associated with the subcutaneous injections. Although the number of patients was limited, it appears that enoxaparin is a safe and efficacious alternative to the use of unfractionated heparin in children with acute, nonhemorrhagic ischemic stroke.

Use of low molecular mass heparin (enoxaparin) in newborn infants: a prospective cohort study of 62 patients

OBJECTIVE

To detail low molecular mass heparin (enoxaparin) use in the first few months of life.

DESIGN

Prospective, consecutive cohort of unselected newborn infants.

METHODS

Newborn infants were divided into groups by gestational age, underlying condition, hepatic and renal function, thrombocytopenia, and prothrombin time (PT/INR). Groups were analysed with respect to many aspects of enoxaparin treatment using multivariate methods.

RESULTS

Sixty two newborn infants received enoxaparin representing 5.39 treatment years. Thromboembolic events (TEs) occurred predominantly in the lower and upper venous system in the presence of indwelling catheters (69%). Preterm infants required longer than full term infants to achieve an anti-(factor Xa) level in the target range (six versus two days). Preterm infants required higher doses of enoxaparin than full term infants to maintain anti-(factor Xa) levels in the target range (2.1 v 1.7 mg/kg/12 h). Infants with congenital heart disease (CHD) required less enoxaparin than those without CHD to maintain an anti-(factor Xa) level in the target range (1.7 v 2.1 mg/kg/12 h). Impaired renal and liver function influenced the number of dose changes needed (three versus one a month). Complete or partial resolution of TE was accomplished in 59% of newborn infants. Four infants developed major bleeds (1.2% per patient year). Recurrent TE and clot extension occurred in three infants (0.9% per patient year).

CONCLUSIONS

Preterm infants are more difficult to treat with enoxaparin than full term infants. Enoxaparin appears to be an alternative to treatment with standard heparin or no treatment.

Thromboembolic diseases of childhood

Over the last decade, pediatric thrombophilia programs have emerged around the world as a new discipline in pediatric hematology. These programs specialize in the diagnosis, prevention and treatment of children with thromboembolic events (TEs) in both the venous and arterial systems. The need for separate pediatric programs has been discussed previously. (J Pediatr Hematol Oncol 1997; 19: 7-22.) The following article will update previous reviews (Hematol Oncol Clin North Am 1998; 12: 1283-1312; Thromb Haemost 1997; 78: 715-725) and will concentrate on three aspects: (1) The risk factors for acquiring TEs; (2) The confirmatory diagnostic tests used in children with TEs; and (3) The different antithrombotic agents used for prevention and treatment. The current knowledge in respect to the above points is only the "tip of the iceberg". Well-designed prospective trials are required to establish the contribution of congenital prothrombotic disorders, appropriate diagnostic strategies, and optimal therapy for children with TEs.

Safety of low molecular weight heparins in the treatment of venous thromboembolism

Low molecular weight heparins (LMWHs) are commonly employed as a substitute for unfractionated heparin (UFH) in the treatment of venous thromboembolic events. Despite their higher cost, the preferential use of LMWHs seemed justified initially as, based on the results of earlier meta-analyses, these compounds were deemed to be more effective and safer than UFH. Although, in this respect, their purported superiority over UFH could not be confirmed by subsequent large, randomised trials and updated meta-analyses, other peculiar features of LMWHs were highlighted, favouring their preferential utilisation in patients with venous thromboembolism. Among these, the possibility of once-daily administration on an out-patient basis, the lower incidence of Type II heparin-induced thrombocytopenia and the lower likelihood of osteoporosis after prolonged treatment periods, appear to be especially prominent. This review attempts to evaluate the available evidence focusing on the safety of LMWHs for the treatment of venous thromboembolism and the current therapeutic options and potential advantages of LMWHs, either in general or in selected patient populations.