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

Anticoagulation in Pediatric Patients

The use of antithrombotic agents is increasing in infants, children and adolescents. The more recent routine inclusion of children in FDA-monitored clinical trials has propelled the rapid accumulation of safety and efficacy data on these agents in pediatric patients. Antithrombotic agents in current use include indirect or antithrombin-dependent anticoagulants, intravenous direct thrombin inhibitors, direct oral anticoagulants (DOACs) targeting thrombin or factor Xa, antiplatelet agents and thrombolytic therapies. Each class of antithrombotic agent has distinct mechanisms of action, clearance routes, half-lives, safety and dosing. Anticoagulant efficacy is dependent upon the specific clinical indication and stability of the pediatric patient. Duration of anticoagulant course is also dependent upon the clinical indication as well as rate of thrombus resolution. This manuscript reviews the mechanism of action, route of administration, route of clearance and plasma half-life for the antithrombotic agents in current use in children. Use of anticoagulation in the context of thrombolytic therapy is discussed.

Unlocking the potential of fondaparinux: guideline for optimal usage and clinical suggestions (2023)

Background: Thromboembolic disease is associated with a high rate of disability or death and gravely jeopardizes people's health and places considerable financial pressure on society. The primary treatment for thromboembolic illness is anticoagulant medication. Fondaparinux, a parenteral anticoagulant medicine, is still used but is confusing due to its disparate domestic and international indications and lack of knowledge about its usage. Its off-label drug usage in therapeutic settings and irrational drug use are also common. Objective: The aim of this guideline is to enhance the judicious clinical application of fondaparinux by consolidating the findings of evidence-based research on the drug and offering superior clinical suggestions. Methods: Seventeen clinical questions were developed by 37 clinical pharmacy experts, and recommendations were formulated under the supervision of three methodologists. Through methodical literature searches and the use of recommendation, assessment, development and evaluation grading techniques, we gathered evidence. Results: This guideline culminated in 17 recommendations, including the use of fondaparinux for venous thromboembolism (VTE) prevention and treatment, perioperative surgical prophylaxis, specific diseases, special populations, bleeding and overdose management. For different types of VTE, we recommend first assessing thrombotic risk in hospitalized patients and then administering the drug according to the patient's body mass. In surgical patients in the perioperative period, fondaparinux may be used for VTE prophylaxis, but postoperative use usually requires confirmation that adequate hemostasis has been achieved. Fondaparinux may be used for anticoagulation prophylaxis in patients hospitalized for oncological purposes, in patients with atrial fibrillation (AF) after resuscitation, in patients with cirrhosis combined with portal vein thrombosis (PVT), in patients with antiphospholipid syndrome (APS), and in patients with inflammatory bowel disease (IBD). Fondaparinux should be used with caution in special populations, such as pregnant female patients with a history of heparin-induced thrombocytopenia (HIT) or platelet counts less than 50 × 109/L, pregnant patients with a prethrombotic state (PTS) combined with recurrent spontaneous abortion (RSA), and children. For bleeding caused by fondaparinux, dialysis may partially remove the drug. Conclusion: The purpose of this guideline is to provide all healthcare providers with high-quality recommendations for the clinical use of fondaparinux and to improve the rational use of the drug in clinical practice. Currently, there is a lack of a dedicated antidote for the management of fondaparinux. The clinical investigation of activated prothrombin complex concentrate (APCC) or recombinant activated factor VII (rFⅦa) as potential reversal agents is still pending. This critical gap necessitates heightened scrutiny and research emphasis, potentially constituting a novel avenue for future inquiries into fondaparinux sodium. A meticulous examination of adverse events and safety profiles associated with the utilization of fondaparinux sodium will contribute significantly to a more comprehensive understanding of its inherent risks and benefits within the clinical milieu.

Application of a clinical decision rule and laboratory assays in pediatrics: Adult heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is rare among pediatric patients. The diagnosis of HIT depends upon clinical decision tools to assess its pretest probability, supported by laboratory evidence of anti-platelet factor 4 (anti-PF4)/heparin antibodies.

AIMS

To compare the use of the 4Ts score clinical decision tool, clinical characteristics, and laboratory findings between pediatric and adult patients with suspected HIT.

METHODS

We compiled all pediatric patients in our center for whom HIT testing was performed during the years 2015-2021. These were compared with a cohort of consecutive adult patients. Laboratory diagnosis of HIT was performed with particle gel immunoassay (PaGIA) as screening test and confirmed by an automated latex-enhanced immunoturbidimetric assay (LIA) and/or by functional flow cytometry assay (FCA).

RESULTS

The cohort included 34 children (under 18 years) and 105 adults. Adults mostly received heparins for thromboembolism prophylaxis and treatment (72.4%, n = 76), and were more frequently treated with low-molecular-weight heparin (LMWH). Children were mostly exposed during cardiopulmonary bypass and extracorporeal membrane oxygenation (ECMO, 61.8%, n = 21), and were more frequently treated with unfractionated heparin (UFH). Compared with adults, children had significantly higher 4Ts scores. Nevertheless, adults had a slightly higher rate of a positive diagnosis of HIT. Six out of 16 adults with confirmed HIT presented with thrombosis (37.5%), whereas all three pediatric patients with HIT presented with thrombosis (p = .087).

CONCLUSIONS

4Ts scores are higher in children compared with adult patients for whom laboratory tests for HIT were obtained. A potentially higher incidence of thrombosis in children with HIT may be attributable to the severity of underlying illness.

Thrombosis Prevention and Anticoagulation Management in the Pediatric Patient with Congenital Heart Disease

Thrombosis is one of the most frequent complications affecting children with congenital heart disease (CHD). Palliative and reparative cardiac surgeries are some of the main players contributing to the thrombosis risk in this patient population. Additional risk factors related to the CHD itself (e.g., cardiac dysfunction, arrhythmias, and polycythemia in cyanotic cardiac disorders) can contribute to thrombogenicity alone or combined with other factors. Thrombotic complications have been recognized as a significant cause of morbidity and mortality in this patient population. Here, we provide an overview of the pathophysiology and risk factors for thrombosis as well as the indications for and use of different anticoagulation, antiplatelet, and thrombolytic agents. In addition, we describe some of most common thrombotic complications and their management in the pediatric CHD population.

Revised recommendations of the Italian Society of Pediatrics about the general management of Kawasaki disease

Aim of these revised recommendations for the general management of Kawasaki disease is to encourage its prompter recognition and warrant the most appropriate therapy, based on ascertained scientific data, raising awareness of the complications related to misdiagnosis or delayed treatment. A set of 20 synthetic operative statements is herein provided, including the definition of Kawasaki disease, its protean presentations, clinical course and seminal treatment modalities of all disease phases. The application of these recommendations should improve prognosis of Kawasaki disease and prevent the progression to permanent vascular abnormalities, thereby diminishing morbidity and mortality.

FondaKIDS III: A long-term retrospective cohort study of fondaparinux for treatment of venous thromboembolism in children

BACKGROUND

The incidence of venous thromboembolism (VTE) and use of anticoagulation are rising in children, but treatment options remain limited. As a newer anticoagulant, fondaparinux may be a safe and effective alternative with the benefit of once-daily dosing, but there is relatively little data supporting its use.

PROCEDURE

This retrospective cohort study describes the long-term dosing, efficacy, and safety of fondaparinux for treatment of VTE in children at a single institution. The study included children <18 years old treated with fondaparinux for VTE between 2008 and 2018. Descriptive statistics were used to present the findings.

RESULTS

A total of 277 patients were identified and analyzed in this study. Seventy-six percent of patients reached therapeutic levels with 0 or 1 dose adjustments over a median treatment duration of 93 days. Of the patients included in the efficacy analysis, 91% of patients had improvement in their clot status, including 69% (160/233) with complete resolution and 22% (53/233) with partial resolution. Twenty-six patients (11%) had VTE recurrence, but only seven (3%) of the new thrombi developed while on fondaparinux. Major bleeding occurred in seven patients (2.5%), primarily in patients with underlying medical conditions with increased bleeding risk. Minor bleeding occurred in 53 patients (19%).

CONCLUSIONS

This study demonstrates the stable long-term pediatric dosing of fondaparinux with similar efficacy and safety when compared to other anticoagulants. Given its advantages, fondaparinux can be considered a reasonable alternative for treatment of VTE in children.

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.

Treatment of venous thromboembolism in pediatric patients

Venous thromboembolism (VTE) is rare in healthy children, but is an increasing problem in children with underlying medical conditions. Pediatric VTE encompasses a highly heterogenous population, with variation in age, thrombosis location, and underlying medical comorbidities. Evidence from pediatric clinical trials to guide treatment of VTE is lacking so treatment is often extrapolated from adult trials and expert consensus opinion. Aspects unique to children include developmental hemostasis and the major role of central venous access devices. There is an absence of information regarding the optimal target levels of anticoagulation for neonates and infants and lack of suitable drug formulations. Anticoagulants, primarily low-molecular-weight heparin and warfarin, are used to treat children with symptomatic VTE. These drugs have significant limitations, including the need for subcutaneous injections and frequent monitoring. Randomized clinical trials of direct oral anticoagulants in pediatric VTE are ongoing, with results anticipated soon. These trials will provide new evidence and options for therapy that have the potential to improve care. International collaborative registries offer the ability to study outcomes of rare subgroups of pediatric VTE (eg, renal vein thrombosis), and will be important to ultimately guide therapy in a more disease-specific manner.

Pulmonary Embolism in Children

Pulmonary embolism is an uncommon but potentially life-threatening event in children. There has been increasing awareness of pulmonary embolism in children with improved survival in children with systemic disease and advancements in diagnostic modalities. However, literature regarding pulmonary embolism in children is sparse, and thus current guidelines for management of pulmonary embolism in children are extrapolated from adult literature and remain controversial. This article reviews the background and pathophysiology of venous thromboembolism, as well as current diagnostic approach and recommended management of pulmonary embolism in children.

Exploratory evaluation of pharmacodynamics, pharmacokinetics and safety of rivaroxaban in children and adolescents: an EINSTEIN-Jr phase I study

BACKGROUND

The EINSTEIN-Jr program will evaluate rivaroxaban for the treatment of venous thromboembolism (VTE) in children, targeting exposures similar to the 20 mg once-daily dose for adults.

METHODS

This was a multinational, single-dose, open-label, phase I study to describe the pharmacodynamics (PD), pharmacokinetics (PK) and safety of a single bodyweight-adjusted rivaroxaban dose in children aged 0.5-18 years. Children who had completed treatment for a venous thromboembolic event were enrolled into four age groups (0.5-2 years, 2-6 years, 6-12 years and 12-18 years) receiving rivaroxaban doses equivalent to 10 mg or 20 mg (either as a tablet or oral suspension). Blood samples for PK and PD analyses were collected within specified time windows.

RESULTS

Fifty-nine children were evaluated. In all age groups, PD parameters (prothrombin time, activated partial thromboplastin time and anti-Factor Xa activity) showed a linear relationship versus rivaroxaban plasma concentrations and were in line with previously acquired adult data, as well as in vitro spiking experiments. The rivaroxaban pediatric physiologically based pharmacokinetic model, used to predict the doses for the individual body weight groups, was confirmed. No episodes of bleeding were reported, and treatment-emergent adverse events occurred in four children and all resolved during the study.

CONCLUSIONS

Bodyweight-adjusted, single-dose rivaroxaban had predictable PK/PD profiles in children across all age groups from 0.5 to 18 years. The PD assessments based on prothrombin time and activated partial thromboplastin time demonstrated that the anticoagulant effect of rivaroxaban was not affected by developmental hemostasis in children.

TRIAL REGISTRATION

ClinicalTrials.gov number, NCT01145859.

Deep vein thrombosis in pediatric patients

Due to advances in caring for critically ill children and those with chronic diseases, rates of deep vein thrombosis (DVT) are increasing in children. Risk factors consist of central venous catheters, chronic medical conditions, thrombophilia, and various medications. Compression Doppler ultrasonography is the method most commonly used to diagnose DVT, and patients will usually present with pain and swelling of the affected limb. Anticoagulation via subcutaneous injection is the most common treatment regime for children with DVT, and the new, direct oral anticoagulants are currently under investigation. Prevention techniques are not established, but clinical studies are addressing this need.

Pentasaccharides for the treatment of deep vein thrombosis

BACKGROUND

Standard treatment of deep vein thrombosis (DVT) is based on antithrombotic therapy, initially with parenteral administration of unfractionated heparin or low molecular weight heparins (LMWH) for five to seven days, then subsequent long-term therapy with oral vitamin K antagonists (e.g. warfarin). Pentasaccharides are novel anticoagulants that may be favourable over standard therapy due to their predictable effect, no need for frequent monitoring or re-dosing, and few known drug interactions. Heparin-induced thrombocytopenia, a harmful effect of heparins, appears to be rare during treatment with pentasaccharides.

OBJECTIVES

To assess the efficacy and harms of pentasaccharides for the treatment of deep vein thrombosis.

SEARCH METHODS

The Cochrane Vascular Information Specialist (CIS) searched the Specialised Register (22 March 2017) and the Cochrane Central Register of Controlled Trials (CENTRAL) (2017, Issue 2) (searched 22 March 2017). We searched clinical trials databases for details of ongoing or unpublished studies and the reference lists of relevant articles for additional citations.

SELECTION CRITERIA

We included randomised controlled trials in which people 18 years of age or older with a DVT confirmed by standard imaging techniques were allocated to receive a pentasaccharide (fondaparinux, idraparinux, or idrabiotaparinux) for the treatment of DVT in comparison with standard therapy or other treatments.

DATA COLLECTION AND ANALYSIS

We extracted data characterising the included trials according to the methods, participants, interventions, and outcomes. We assessed risk of bias using Cochrane's 'Risk of bias' tool and employed the GRADE methodology to evaluate the quality of the evidence.The main primary outcome for efficacy was recurrent venous thromboembolism (VTE), and the main primary outcome for harm was major and clinically relevant bleeding. Since our outcomes were dichotomous, we calculated the risk ratio (RR) with a 95% confidence interval (CI). We combined the effects of different comparisons through a meta-analysis using a fixed-effect model.

MAIN RESULTS

We included five randomised controlled trials of 6981 participants comparing pentasaccharides with standard therapy or other pentasaccharides. The quality of the evidence varied depending on the outcome and was judged as of moderate to very low quality. We downgraded the quality of the evidence due to risk of bias or imprecision, or both.Two studies evaluated fondaparinux, at doses of 5.0 mg, 7.5 mg, and 10.0 mg, plus vitamin K antagonist in comparison with standard therapy. A meta-analysis of these two studies showed no clear difference in the risk of recurrent VTE (RR 0.80, 95% CI 0.43 to 1.47; 2658 participants); moderate-quality evidence. The frequencies of major bleeding were similar between interventions in the initial period of treatment (approximately five days) (RR 1.15, 95% CI 0.39 to 3.44; 2645 participants) and at three months' follow-up (RR 1.05, 95% CI 0.64 to 1.71; 2645 participants). We judged the quality of the evidence as moderate.One study (757 participants) compared idrabiotaparinux (3.0 mg) with idraparinux (2.5 mg) and demonstrated no clear difference in the risk of recurrent VTE at six months' follow-up (RR 0.72, 95% CI 0.31 to 1.69); low-quality evidence. Major bleeding during the initial treatment period was not reported. Major bleeding at six-month follow-up was less frequent in participants receiving idrabiotaparinux versus participants treated with idraparinux (RR 0.21, 95% CI 0.06 to 0.71); low-quality evidence.The effect of an initial treatment with LMWH followed by three months of idraparinux (10 mg) showed no clear difference from standard therapy for risk of recurrent VTE (RR 1.51, 95% CI 0.26 to 8.90; 263 participants); very low-quality evidence; one study. Major bleeding during the initial treatment period was not reported. The frequency of major and other clinically relevant bleeding at three months' follow-up ranged from 2% to 15% in participants receiving LMWH and increasing doses of idraparinux of 2.5 mg, 5 mg, 7.5 mg, or 10 mg. When dosage groups were combined, there was no clear difference in major plus other clinically relevant bleeding or in major bleeding alone between the idraparinux treatment group and the standard therapy group (RR 1.30, 95% CI 0.70 to 2.40; 659 participants; RR 3.76, 95% CI 0.50 to 28.19; 659 participants, respectively); very low-quality evidence.One study (2904 participants) compared idraparinux (2.5 mg) to standard therapy. There was no clear difference in the risk of recurrent VTE at three months' follow-up (RR 0.98, 95% CI 0.64 to 1.48); low-quality evidence. Major bleeding during the initial treatment period was not reported. Major bleeding at three months of follow-up appeared to be similar in the idraparinux group and the standard therapy group (RR 0.71, 95% CI 0.34 to 1.47); very low-quality evidence.

AUTHORS' CONCLUSIONS

We found moderate-quality evidence that the effects of fondaparinux at doses of 5.0 mg, 7.5 mg, and 10.0 mg plus vitamin K antagonist are similar in terms of recurrent VTE and risk of major bleeding compared with standard treatment for DVT.Low-quality evidence suggests equal efficacy of idraparinux at 2.5 mg and the equimolar dose of 3.0 mg of idrabiotaparinux with regard to recurrent VTE, but a higher frequency of major bleeding was observed in participants treated with idraparinux.We judged evidence on the effectiveness of idraparinux compared with standard therapy, with or without initial treatment with LMWH, and on associated bleeding risk to be low to very low quality, therefore we have very limited confidence in the estimated effects.The observed similar effectiveness in terms of recurrent DVT and harmful effects in terms of bleeding risk with fondaparinux plus vitamin K antagonist compared to standard treatment for DVT suggest that it may be an alternative to conventional anticoagulants for the treatment of DVT in certain circumstances.

Anticoagulation Therapies in Children

Venous thromboembolism is occurring with increasing frequency in children resulting in the more widespread use of anticoagulation in pediatrics. Antithrombotic drugs in children can be divided into the standard and alternative agents. This review discusses standard and alternative anticoagulants. Because standard anticoagulants have significant limitations, including variable pharmacokinetics, issues with therapeutic drug monitoring, frequency of administration, efficacy, and adverse effects, it is expected that the use of alternative anticoagulants will increase over time. With their improved properties and recent prospective clinical trial data, the current and future use of these agents will likely slowly replace of the standard anticoagulants.

How I treat pediatric venous thromboembolism

The incidence of pediatric venous thromboembolism (VTE) has been increasing significantly over the past decade in part as a result of increased recognition of this serious disorder but more so because of the increased use of central venous catheters and other technological advancements involved in the care of ill children. Management of pediatric VTE is a complex undertaking, considering that the vast majority of children who develop this complication have serious underlying medical disorders. Although the incidence is rising, in comparison with adults, this remains a relatively rare disorder, and as such, large-scale clinical trials have not been completed, rendering management decisions to be based on extrapolation from adult data and the experience of the treating physician. Clearly, both are fraught with problems. Thus, day-to-day management remains more art than science until such time that the results from clinical trials (many of which are under way) become available. This edition of "How I Treat" describes the author's experience in managing 3 common scenarios that one may encounter in pediatric thrombosis and suggests a logical approach to such situations. Furthermore, the author provides 3 algorithms to help guide management decisions.

Anticoagulation in children: Making the most of little patients and little evidence

Thrombotic complications are increasing at a steady and significant rate in children resulting in the more widespread use of anticoagulation in this population. Anticoagulant drugs in children can be divided into the standard agents (heparin, low molecular weight heparin, and vitamin K antagonists) and alternative agents (argatroban, bivalirudin, and fondaparinux). This review will compare and contrast the standard and alternative anticoagulants and suggest situations in which it may be appropriate to use argatroban, bivalirudin, and fondaparinux. Clearly, the standard anticoagulants all have significant shortcomings including variable pharmacokinetics, issues with therapeutic drug monitoring, frequency of administration, efficacy, and adverse effects. The alternative anticoagulants have properties which overcome these shortcomings and prospective clinical trial data are presented supporting the current and future use of these agents in place of the standard anticoagulants.

How We Manage Pediatric Deep Venous Thrombosis

Over the past two decades, the incidence and recognition of venous thromboembolism (VTE) in children has significantly increased, likely as a result of improvements in the medical care of critically ill patients and increased awareness of thrombotic complications among medical providers. Current recommendations for the management of VTE in children are largely based on data from pediatric registries and observational studies, or extrapolated from adult data. The scarcity of high-quality evidence-based recommendations has resulted in marked variations in the management of pediatric VTE among providers. The purpose of this article is to summarize our institutional approach for the management of VTE in children based on available evidence, guidelines, and clinical practice considerations. Therapeutic strategies reviewed in this article include the use of conventional anticoagulants, parenteral targeted anticoagulants, new direct oral anticoagulants, thrombolysis, and mechanical approaches for the management of pediatric VTE.

Pediatric Cardiac Intensive Care Society 2014 Consensus Statement: Pharmacotherapies in Cardiac Critical Care Anticoagulation and Thrombolysis

OBJECTIVE

Thrombotic complications are increasingly being recognized as a significant cause of morbidity and mortality in pediatric and congenital heart disease. The objective of this article is to review the medications currently available to prevent and treat such complications.

DATA SOURCES

Online searches were conducted using PubMed.

STUDY SELECTION

Studies were selected for inclusion based on their scientific merit and applicability to the pediatric cardiac population.

DATA EXTRACTION

Pertinent information from each selected study or scientific review was extracted for inclusion.

DATA SYNTHESIS

Four classes of medications were identified as potentially beneficial in this patient group: anticoagulants, antiplatelet agents, thrombolytic agents, and novel oral anticoagulants. Data on each class of medication were synthesized into the follow sections: mechanism of action, pharmacokinetics, dosing, monitoring, reversal, considerations for use, and evidence to support.

CONCLUSIONS

Anticoagulants, antiplatelet agents, and thrombolytic agents are routinely used successfully in the pediatric patient with heart disease for the prevention and treatment of a wide range of thrombotic complications. Although the novel oral anticoagulants have been approved for a limited number of indications in adults, studies on the safety and efficacy of these agents in children are pending.

Current Clinical Trials on the Use of Direct Oral Anticoagulants in the Pediatric Population

Common treatment options for deep vein thrombosis and venous thromboembolism in the pediatric population include unfractionated heparin, low molecular weight heparin, and warfarin. Other alternatives are bivalirudin, argatroban, and fondaparinux. Warfarin is the only approved oral option, but an oral agent without frequent monitoring would be optimal for pediatric patients. Thus, there is an increasing need for new anticoagulation options in this population. None of the current direct oral anticoagulants have FDA-approved indications and dosing in children. The two classes of DOACs and the drugs they are comprised of are factor Xa inhibitors (rivaroxaban, apixaban, edoxaban) and direct thrombin inhibitor (dabigatran). Off-label usage of these agents is largely based on adult doses. By far, rivaroxaban and dabigatran have the most published data and ongoing trials in pediatric patients compared to edoxaban and apixaban. After evaluating the current literature available on these agents, it is, however, still too early to make any definitive recommendations on their usage in this special population.

Improving evidence on anticoagulant therapies for venous thromboembolism in children: key challenges and opportunities

Venous thromboembolism (VTE) is increasingly diagnosed in pediatric patients, and anticoagulant use in this population has become common, despite the absence of US Food and Drug Administration (FDA) approval for this indication. Guidelines for the use of anticoagulants in pediatrics are largely extrapolated from large randomized controlled trials (RCTs) in adults, smaller dose-finding and observational studies in children, and expert opinion. The recently FDA-approved direct oral anticoagulants (DOACs), such as dabigatran, rivaroxaban, apixaban, and edoxaban, provide potential advantages over oral vitamin K antagonists and subcutaneous low-molecular-weight heparins (LMWHs). However, key questions arise regarding their potential off-label clinical application in pediatric thromboembolic disease. In this Perspective, we provide background on the use of LMWHs such as enoxaparin as the mainstay of treatment of pediatric provoked VTE; identify key questions and challenges with regard to DOAC trials and future DOAC therapy in pediatric VTE; and discuss applicable lessons learned from the recent pilot/feasibility phase of a large multicenter RCT of anticoagulant duration in pediatric VTE. The challenges and lessons learned present opportunities to improve evidence for anticoagulant therapies in pediatric VTE through future clinical trials.

Anticoagulants in children and adolescents

Thrombotic complications are increasing at a steady and significant rate in children, resulting in the more widespread use of anticoagulation in this population. Anticoagulant drugs in children can be divided into the older multitargeted agents (heparin, low-molecular-weight heparin, and warfarin) and the newer targeted agents (argatroban, bivalirudin, and fondaparinux). This review will compare and contrast the multitargeted and targeted anticoagulants and suggest situations in which it may be appropriate to use argatroban, bivalirudin, and fondaparinux. The various agents differ in their pharmacokinetics, requirements for therapeutic drug monitoring, frequency of administration, efficacy, and adverse effects. The targeted anticoagulants have properties that may make them more attractive for use in specific clinical situations. Prospective clinical trial data are presented supporting the current and future use of these agents in children.

Anticoagulants in children and adolescents

Thrombotic complications are increasing at a steady and significant rate in children, resulting in the more widespread use of anticoagulation in this population. Anticoagulant drugs in children can be divided into the older multitargeted agents (heparin, low-molecular-weight heparin, and warfarin) and the newer targeted agents (argatroban, bivalirudin, and fondaparinux). This review will compare and contrast the multitargeted and targeted anticoagulants and suggest situations in which it may be appropriate to use argatroban, bivalirudin, and fondaparinux. The various agents differ in their pharmacokinetics, requirements for therapeutic drug monitoring, frequency of administration, efficacy, and adverse effects. The targeted anticoagulants have properties that may make them more attractive for use in specific clinical situations. Prospective clinical trial data are presented supporting the current and future use of these agents in children.

Multicenter randomized controlled trial on Duration of Therapy for Thrombosis in Children and Young Adults (the Kids-DOTT trial): pilot/feasibility phase findings

BACKGROUND

Randomized controlled trials (RCTs) on pediatric venous thromboembolism (VTE) treatment have been challenged by unsubstantiated design assumptions and/or poor accrual. Pilot/feasibility (P/F) studies are critical to future RCT success.

METHODS

The Kids-DOTT trial is a multicenter RCT investigating non-inferiority of a 6-week (shortened) versus 3-month (conventional) duration of anticoagulation in patients aged < 21 years with provoked venous thrombosis. Primary efficacy and safety endpoints are symptomatic recurrent VTE at 1 year and anticoagulant-related, clinically relevant bleeding. In the P/F phase, 100 participants were enrolled in an open, blinded-endpoint, parallel-cohort RCT design.

RESULTS

No eligibility violations or randomization errors occurred. Of the enrolled patients, 69% were randomized, 3% missed the randomization window, and 28% were followed in prespecified observational cohorts for completely occlusive thrombosis or persistent antiphospholipid antibodies. Retention at 1 year was 82%. Interobserver agreement between local and blinded central determination of venous occlusion by imaging at 6 weeks after diagnosis was strong (k-statistic = 0.75; 95% confidence interval [CI] 0.48-1.0). The primary efficacy and safety event rates were 3.3% (95% CI 0.3-11.5%) and 1.4% (95% CI 0.03-7.4%).

CONCLUSIONS

The P/F phase of the Kids-DOTT trial has demonstrated the validity of vascular imaging findings of occlusion as a randomization criterion, and defined randomization, retention and endpoint rates to inform the fully powered RCT.

A guide to the use of anticoagulant drugs in children

Increasing thrombotic complications in children with complex medication conditions have led to more widespread use of anticoagulants [Raffini et al. in Pediatrics 124(4):1001-8, 2009]. While current guidelines for the management of antithrombotic therapy in neonates and children exist, they are based on low- and very low-quality evidence [Monagle et al. in Chest 141(2 Suppl):e737-801S, 2012]. Despite numerous differences, current anticoagulation practice is largely extrapolated from adult studies. This is sub-optimal, particularly in neonates who have a rapidly evolving hemostatic system. The majority of pediatric patients have underlying medical conditions that may significantly influence drug choice and bleeding risk. This article reviews the use of anticoagulants in children with thrombosis, focusing on practical aspects such as dosing, monitoring, and complications. Low molecular weight heparin has become the preferred anticoagulant in children, although unfractionated heparin and warfarin remain frequently used. Other anticoagulants, including fondaparinux, direct thrombin inhibitors, and the newer target-specific oral anticoagulants are also discussed. Given the many unique challenges surrounding the use of anticoagulants in children, pediatric hospitals should have written practice guidelines as well as experienced providers to care for children with thrombosis. This is an evolving field, and further studies of the use of anticoagulants in neonates and children are greatly needed to help optimize care.

New developments in pediatric venous thromboembolism and anticoagulation, including the target-specific oral anticoagulants

PURPOSE OF REVIEW

Pediatric venous thromboembolism (VTE) can affect children of all ages, requiring considerable pharmacologic intervention and is often associated with significant morbidity. Current research efforts are directed toward the development of risk-stratified VTE prevention strategies employing pharmacologic thromboprophylaxis, the optimization of conventional anticoagulation, and the investigation of the safety and efficacy of target-specific oral anticoagulants (TSOACs) in children.

RECENT FINDINGS

Recent research has considerably improved the understanding of risk factors of hospital-acquired VTE and how these factors may be employed in risk-stratified paradigms for VTE prevention in children. Additional insight has been gained in the optimization of conventional anticoagulants in special populations such as neonates and children with inflammatory conditions, and in improving the overall safety and compliance with periprocedural anticoagulation and the use of home International Normalized Ratio monitoring. Furthermore, the use of TSOACs has been described in children and is the focus of numerous ongoing clinical trials that are evaluating the safety and efficacy of these agents in children with VTE.

SUMMARY

Identification of hospital-acquired VTE risk factors may inform pediatric VTE prevention strategies. Although initial use of TSOACs may be promising, investigation of safety and efficacy in children is still underway.

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.

Venous thromboembolism in critically ill children

PURPOSE OF REVIEW

To review the current literature on venous thromboembolism (VTE) in critically ill children.

RECENT FINDINGS

There is an increasing concern for VTE and its complications in critically ill children. Critically ill children are at increased risk of thromboembolism because of the treatment that they are receiving and their underlying condition. A complex relationship exists between thrombosis and infection. A thrombus is a nidus for infection, while infection increases the risk of thrombosis. Pediatric-specific guidelines for the prevention and treatment of thromboembolism are lacking. Current guidelines are based on the data from adults. Novel anticoagulants are now available for use in adults. Studies are ongoing to determine their safety in children. Risk assessment tools have recently been developed to determine the risk of thromboembolism in critically ill children. Certain molecules are associated with thromboembolism in adults.

SUMMARY

Pediatric critical care practitioners should be cognizant of the importance of VTE in critically ill children to allow early identification and treatment. Adequately powered clinical trials are critically needed to generate evidence that will guide the treatment and prevention of thromboembolism in critically ill children. Risk assessment tools that incorporate biomarkers may improve our ability to predict the occurrence of thromboembolism in critically ill children.

Practical considerations for dose selection in pediatric patients to ensure target exposure requirements

Pediatric dosing recommendations are often not based on allometry, despite recognition that metabolic processes in mammals scale to the ¾ power. This report reviews the allometric size model for clearance and its implications for defining doses for children while considering practical limitations. Fondaparinux exposures in children were predicted using allometric and mg/kg dosing. Additional simulations further refined the dose based on the predicted Cmax, target exposure range, complexity of the dosing regimen, and previous exposure/response data. The percent reduction of the adult dose of an oral lozenge fixed-dose formulation which would predict similar exposures in children and adults was recommended based on simulations. Allometric dosing predicted a consistent fondaparinux exposure across the weight range. Size-optimized mg/kg dosing, which partially approximates the allometric relationship, allows for consistent fondaparinux exposures (i.e., 0.12 mg/kg ≤35 kg or 0.1 mg/kg >35 kg). Simulations of the oral lozenge formulation demonstrated rapidly changing clearance in children less than 6 years prohibiting practical dosing recommendations for satisfying all conventional exposure metrics (Cmax and AUC) in this age group. In children between 13 and 18 or 6 and 13 years, a 8.6% and 54% reduction in dose would maintain target exposures but dose reductions of 12.5% or 62.5% were ultimately recommended as deemed manufacturable. Dose selection in children should consider the known and/or predicted covariate relationships which affect exposure. Presented examples applied the allometric model in dose selection with the goal of PK bridging and considered practical limitations in dose selection.

Fondaparinux in an obese child with heparin-induced thrombocytopenia and a history of renal failure

A 9-year-old obese child with a history of ulcerative colitis was admitted to the intensive care unit for significant blood loss, hemorrhagic shock, and acute renal failure. Following complications from total colectomy secondary to multiple perforations, the patient developed heparin-induced thrombocytopenia (HIT) and subsequent portal vein thrombosis. Subcutaneous (SQ) fondaparinux therapy was initiated because the patient was unable to transition to oral anticoagulation. An anti-factor Xa assay was developed and used to adjust his fondaparinux therapy. Based on hemorrhagic complications and fondaparinux-based anti-factor Xa assay results, the fondaparinux was adjusted to a final dosage of 4.5 mg (0.066 mg/kg) SQ daily. In children unable to transition to oral anticoagulation, fondaparinux may be an alternative for the treatment of thrombosis associated with HIT. We noted that our patient required a lower dose per kilogram of fondaparinux than described in previous published reports. Despite this lower dosage per kilogram, our patient developed bleeding despite dosage reductions; subsequently, a few doses were held. It is unclear if this was related to his obesity, history of renal failure, or a combination of factors. Future studies should determine the optimal dose for special populations of children (e.g., those with obesity and renal failure). Until then, clinicians should routinely monitor and titrate fondaparinux therapy, ideally using a fondaparinux-specific anti-factor Xa assay.

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.

Dosing and monitoring of enoxaparin therapy in children: experience in a tertiary care hospital

Pediatric deep vein thrombosis (DVT) is an emerging problem in tertiary care hospitals, recent reviews shows a rate of 40.2/10,000 admissions. Experts affirm that enoxaparin has become in the drug of choice for DVT therapy. Despite this, there is a little information regarding the optimal dose schedule for enoxaparin therapy in children and the therapeutic guidelines for enoxaparin use in children are extrapolated from adult guidelines. Monitoring by antifactor Xa (anti-Xa) measurement and target concentrations between 0.5-1 U/ml at 4-6 h postdose are recommended. This study was designed to analyse our experience in paediatric-specific dosage requirements for enoxaparin therapy. A retrospective study was performed with patients less than 16 years old, who were treated with enoxaparin for DVT and monitored by anti-Xa concentration, between January 2005 and March 2012. Demographic and clinical characteristics and outcomes were obtained. Fourteen patients were analyzed: boy/girl ratio, 8/4; median age, 3.5 months. Cerebral venous sinus thrombosis was the most common indication for therapy. All patients presented thrombosis risks factors. Dose increases were necessary only in patients less than 6 years old. Target anti-Xa concentrations were achieved in 12 (85%) patients. Children younger than 1 year required a higher dose of enoxaparin/kg (1.5-2.7 mg/kg per 12 h). Complete resolutions of DVT were registered in all cases. The mean number of dose increases was three and a median of 11 days to achieve target anti-Xa concentration. This study indicates that an initial higher enoxaparin dose may be necessary in neonates and infants, but other factors must be considered to improve management.

Antithrombotic therapies: anticoagulation and thrombolysis

Pediatric deep vein thrombosis is an increasingly recognized phenomenon, especially with advances in treatment and supportive care of critically ill children and with better diagnostic capabilities. High-quality evidence and uniform management guidelines for antithrombotic treatment, particularly thrombolytic therapy, remain limited. Optimal dosing, intensity and duration strategies for anticoagulation as well as thrombolytic regimens that maximize efficacy and safety need to be determined through well-designed clinical trials using use of a risk-stratified approach.

Updates in thrombosis in pediatrics: where are we after 20 years?

The incidence of venous thromboembolism (VTE) in the pediatric population is increasing. Technological advances in medicine and imaging techniques, improved awareness of the disease, and longer survival of life-threatening or chronic medical conditions all contribute to the increase in VTE rates. There is a paucity of data on management of VTE based on properly designed clinical trials, but there is significant advancement in the last 2 decades. This review summarizes the progress made in pediatric thrombosis, including epidemiological changes, advances in anticoagulant agents, and outcomes of VTE.

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.

Fondaparinux - data on efficacy and safety in special situations

New anticoagulants promise to have better efficacy, more safety and/or a better manageability than traditional anticoagulants. However, knowledge is limited regarding special situations such as renal insufficiency, obesity, pregnancy, long-term therapy, heparin-induced thrombocytopenia, treatment in patients with mechanical heart valves, use for children, and in patients with a high risk of thromboembolic complications. These situations have rarely or even never been the objective of randomised controlled trials. The purpose of the present article is to summarize and discuss available data on efficacy and safety in these special situations for one of the first new anticoagulants, the indirect factor-Xa inhibitor fondaparinux. Furthermore, we discuss safety in licensed indications and management of bleeding complications and comment on measuring of drug concentration in plasma.