Argatroban therapy in pediatric patients requiring nonheparin anticoagulation: an open-label, safety, efficacy, and pharmacokinetic study

How I treat pediatric venous thromboembolism in the DOAC era

ABSTRACT

The direct oral anticoagulants (DOACs) rivaroxaban and dabigatran are newly licensed for the treatment and prevention of venous thromboembolism (VTE) in children and mark a renaissance in pediatric anticoagulation management. They provide a convenient option over standard-of-care anticoagulants (heparins, fondaparinux, and vitamin K antagonists) because of their oral route of administration, child-friendly formulations, and significant reduction in monitoring. However, limitations related to therapeutic monitoring when needed and the lack of approved reversal agents for DOACs in children raise some safety concerns. There is accumulating experience of safety and efficacy of DOACs in adults for a broad scope of indications; however, the cumulative experience of using DOACs in pediatrics, specifically for those with coexisting chronic illnesses, is sparse. Consequently, clinicians must often rely on their experience for treating VTE and extrapolate from data in adults while using DOACs in children. In this article, the authors share their experience of managing 4 scenarios that hematologists are likely to encounter in their day-to-day practice. Topics addressed include (1) appropriateness of indication; (2) use for special populations of children; (3) considerations for laboratory monitoring; (4) transition between anticoagulants; (5) major drug interactions; (6) perioperative management; and (7) anticoagulation reversal.

Hemostasis in neonatal ECMO

Extracorporeal membrane oxygenation (ECMO) is a life-saving support for cardio-respiratory function. Over the last 50 years, the extracorporeal field has faced huge technological progress. However, despite the improvements in technique and materials, coagulation problems are still the main contributor to morbidity and mortality of ECMO patients. Indeed, the incidence and survival rates of the main hemorrhagic and thrombotic complications in neonatal respiratory ECMO are relevant. The main culprit is related to the intrinsic nature of ECMO: the contact phase activation. The exposure of the human blood to the non-endothelial surface triggers a systemic inflammatory response syndrome, which chronically activates the thrombin generation and ultimately leads to coagulative derangements. Pre-existing illness-related hemostatic dysfunction and the peculiarity of the neonatal clotting balance further complicate the picture. Systemic anticoagulation is the management's mainstay, aiming to prevent thrombosis within the circuit and bleeding complications in the patient. Although other agents (i.e., direct thrombin inhibitors) have been recently introduced, unfractionated heparin (UFH) is the standard of care worldwide. Currently, there are multiple tests exploring ECMO-induced coagulopathy. A combination of the parameters mentioned above and the evaluation of the patient's underlying clinical context should be used to provide a goal-directed antithrombotic strategy. However, the ideal algorithm for monitoring anticoagulation is currently unknown, resulting in a large inter-institutional diagnostic variability. In this review, we face the features of the available monitoring tests and approaches, mainly focusing on the role of point-of-care (POC) viscoelastic assays in neonatal ECMO. Current gaps in knowledge and areas that warrant further study will also be addressed.

Venous Thromboembolism in Premature Neonates

While the incidence of venous thromboembolism (VTE) is lower among children than adults, the newborn period is one of two bimodal peaks (along with adolescence) in VTE incidence in the pediatric population. Most VTE cases in neonates occur among critically ill neonates being managed in the neonatal intensive care unit, and most of these children are born premature. For this reason, the presentation, diagnosis, management, and outcomes of VTE among children born premature deserve special emphasis by pediatric hematologists, neonatologists, pharmacists, and other pediatric health care providers, as well as by the scientific community, and are described in this review.

Screening and diagnosis of heparin-induced thrombocytopenia in the pediatric population: A tertiary centre experience

INTRODUCTION

Heparin-induced thrombocytopenia (HIT) is a life-threatening side effect of heparin necessitating immediate heparin discontinuation. A missed diagnosis of HIT carries significant morbidity and mortality, while overdiagnosis may result in unnecessary and potentially harmful use of alternative anticoagulants in the pediatric population. We aimed to determine the proportion of HIT screening tests at our pediatric tertiary care centre ultimately leading to a diagnosis of HIT by functional assay (either lumi-aggregometry or serotonin-release assay). We hypothesized that the frequency of HIT at our centre would be lower than that reported in the literature.

MATERIALS AND METHODS

We conducted a retrospective review including children aged 0 to 18 years who had HIT testing performed at our centre between 2010 and 2018 (N = 189; 51% female). A screening enzyme immunoassay, if positive, is followed by a functional assay which must be positive to establish the diagnosis of HIT. Data were analyzed to establish trends in demographic and clinical features of patients with a positive HIT screening test. Our primary outcome was the rate of HIT confirmed by functional testing amongst children screened for HIT from 2010 to 2018.

RESULTS AND CONCLUSIONS

There were 233 screening tests performed on 189 distinct patients. Only one patient (0.4%) received a diagnosis of HIT based on functional assay. This patient was a 16-year-old female later found to have a JAK2 mutation. The false positive rate of the enzyme immunoassay was 9.4% (N = 22). There were no positive enzyme immunoassay tests in the neonatal age group (N = 49). These results reinforce that HIT is rare in children.

Comparative effectiveness and safety of anticoagulants for the treatment of heparin-induced thrombocytopenia

BACKGROUND

The effectiveness and safety of non-heparin anticoagulants for the treatment of heparin-induced thrombocytopenia (HIT) are not fully established, and the optimal treatment strategy is unknown. In a systematic review and meta-analysis, we aimed to determine precise rates of platelet recovery, new or progressive thromboembolism (TE), major bleeding, and death for all non-heparin anticoagulants and to study potential sources of variability.

METHODS

Following a detailed protocol (PROSPERO: CRD42020219027), EMBASE and Medline were searched for all studies reporting clinical outcomes of patients treated with non-heparin anticoagulants (argatroban, danaparoid, fondaparinux, direct oral anticoagulants [DOAC], bivalirudin, and other hirudins) for acute HIT. Proportions of patients with the outcomes of interest were pooled using a random-effects model for each drug. The influence of the patient population, the diagnostic test used, the study design, and the type of article was assessed.

RESULTS

Out of 3194 articles screened, 92 studies with 119 treatment groups describing 4698 patients were included. The pooled rates of platelet recovery ranged from 74% (bivalirudin) to 99% (fondaparinux), TE from 1% (fondaparinux) to 7% (danaparoid), major bleeding from 1% (DOAC) to 14% (bivalirudin), and death from 7% (fondaparinux) to 19% (bivalirudin). Confidence intervals were mostly overlapping, and results were not influenced by patient population, diagnostic test used, study design, or type of article.

DISCUSSION

Effectiveness and safety outcomes were similar among various anticoagulants, and significant factors affecting these outcomes were not identified. These findings support fondaparinux and DOACs as viable alternatives to conventional anticoagulants for treatment of acute HIT in clinical practice.

Clinical study of argatroban for preventing vascular thrombosis in the early period after pediatric living-related donor liver transplantation

OBJECTIVE

To evaluate the effect of heparin and argatroban on coagulation function and vascular thrombosis in the early period after pediatric LRDLT.

METHOD

Eighty-four congenital biliary atresia pediatric patients who had undergone LRDLT were studied. Patients were divided into two groups according to the method of anticoagulation (heparin or argatroban). AT-Ⅲ activity, APTT, and INR of the two groups were measured in the first 5 days after LRDLT. Vascular thrombosis was investigated by Doppler ultrasound daily.

RESULTS

There were no significant differences in gender, age, weight, graft-recipient weight ratio, and Kasai procedure between the two groups. The AT-Ⅲ activity of the two groups was low and increased gradually after surgery, with no significant difference between the two groups. There was no significant difference of APTT between the two groups immediately after and in the first day after surgery. After anticoagulation treatment, a significant difference in APTT between the two groups was observed. The incidences of vascular thrombosis were 4.76% (3/63) and 0% (0/21) in the heparin and argatroban groups, respectively, with no significant difference between the two groups. During the treatment, no serious complications such as active hemorrhage or drug allergy were observed in the two groups.

CONCLUSION

Argatroban is a direct anticoagulant, which is independent of AT-Ⅲ activity. Argatroban might be an alternative to heparin in uncomplicated LRDLT with recovered hepatic and coagulation function.

Heparin-induced thrombocytopenia complicating extracorporeal membrane oxygenation support: Review of the literature and alternative anticoagulants

Heparin-induced thrombocytopenia (HIT) is a life-threatening prothrombotic, immune-mediated complication of unfractionated heparin and low molecular weight heparin therapy. HIT is characterized by moderate thrombocytopenia 5-10 days after initial heparin exposure, detection of platelet-activating anti-platelet factor 4/heparin antibodies and an increased risk of venous and arterial thrombosis. Extracorporeal membrane oxygenation (ECMO) is a form of mechanical circulatory support used in critically ill patients with respiratory or cardiac failure. Systemic anticoagulation is used to alleviate the thrombotic complications that may occur when blood is exposed to artificial surfaces within the ECMO circuit. Therefore, when HIT complicates patients on ECMO support, it is associated with a high thrombotic morbidity and mortality. The risk for HIT correlates with the accumulative dosage of heparin exposure. In ECMO patients receiving continuous infusion of heparin for circuit patency, the risk for HIT is not neglected and must be thought of in the differential diagnosis of the appropriate clinical and laboratory circumstances. The following article reviews the current knowledge in HIT complicating ECMO patients and the alternative anticoagulation options in the presence of HIT.

Anticoagulation in Neonatal ECMO: An Enigma Despite a Lot of Effort!

Extracorporeal membrane oxygenation (ECMO) is a valuable modality used to support neonates, children, and adults with cardiorespiratory failure refractory to conventional therapy. It requires use of anticoagulation to prevent clotting in the extracorporeal circuit. Balancing bleeding from excessive anticoagulation with thrombotic risk remains a difficult aspect of ECMO care. Despite many advances in ECMO technology, better understanding of the coagulation cascade and new monitoring schemes to adjust anticoagulation, bleeding and thrombosis remain the most frequent complications in ECMO and are associated with morbidity and mortality. In neonates, ECMO is also complicated by the immature hemostatic system, laboratory testing norms which are not specific for neonates, lack of uniformity in management, and paucity of high-quality evidence to determine best practices. Traditional anticoagulation focuses on the use of unfractionated heparin. Direct thrombin inhibitors are also used but have not been well-studied in the neonatal ECMO population. Anticoagulation monitoring is complex and currently available assays do not take into account thrombin generation or platelet contribution to clot formation. Global assays may add valuable information to guide therapy. This review provides an overview of hemostatic alterations, anticoagulation, monitoring and management, novel anticoagulant use, and circuit modifications for neonatal ECMO. Future considerations are also presented.

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.

Adult and pediatric mechanical circulation: a guide for the hematologist

Mechanical circulatory support (MCS) is the overarching term that encompasses the temporary and durable devices used in patients with severe heart failure. MCS disturbs the hematologic and coagulation system, leading to platelet activation, activation of the contact pathway of coagulation, and acquired von Willebrand syndrome. Ischemic stroke and major hemorrhage occur in up to 30% of patients. Hematologists are an essential part of the MCS team because they understand the delicate balance between bleeding and clotting and alteration of hemostasis with antithrombotic therapy. However, prior to this important collaborative role, learning the terminology used in the field and types of MCS devices allows improved communication with the MCS team and best patient care. Understanding which antithromobotic therapies are used at baseline is also required to provide recommendations if hemorrhage or thrombosis occurs. Additional challenging consultations in MCS patients include the influence of thrombophilia on the risk for thrombosis and management of heparin-induced thrombocytopenia. This narrative review will provide a foundation to understand MCS devices how to prevent, diagnose, and manage MCS thrombosis for the practicing hematologist.

Heparin-induced thrombocytopenia complicating extracorporeal membrane oxygenation support in pediatric patients: review of the literature and alternative anticoagulants

Heparin-induced thrombocytopenia (HIT) is a prothrombotic, immune-mediated complication of unfractionated heparin (UFH) and low molecular weight heparin therapy. HIT is characterized by moderate thrombocytopenia 5-10 days after initial heparin exposure, detection of platelet-activating anti-platelet factor 4/heparin antibodies and an increased risk of venous and arterial thrombosis. Extracorporeal membrane oxygenation (ECMO) is a form of mechanical circulatory support used in critically ill patients with respiratory or cardiac failure. Systemic anticoagulation is used to alleviate the thrombotic complications that may occur when blood is exposed to artificial surfaces within the ECMO circuit. Therefore, when HIT complicates patients on ECMO support, it is associated with a high thrombotic morbidity and mortality. The following article reviews the current knowledge in pediatric HIT, especially in ECMO patients, and the alternative anticoagulation options in the presence of HIT.

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.

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.

Neonatal Venous Thromboembolism

Neonates are the pediatric population at highest risk for development of venous thromboembolism (VTE), and the incidence of VTE in the neonatal population is increasing. This is especially true in the critically ill population. Several large studies indicate that the incidence of neonatal VTE is up almost threefold in the last two decades. Central lines, fluid fluctuations, sepsis, liver dysfunction, and inflammation contribute to the risk profile for VTE development in ill neonates. In addition, the neonatal hemostatic system is different from that of older children and adults. Platelet function, pro- and anticoagulant proteins concentrations, and fibrinolytic pathway protein concentrations are developmentally regulated and generate a hemostatic homeostasis that is unique to the neonatal time period. The clinical picture of a critically ill neonate combined with the physiologically distinct neonatal hemostatic system easily fulfills the criteria for Virchow's triad with venous stasis, hypercoagulability, and endothelial injury and puts the neonatal patient at risk for VTE development. The presentation of a VTE in a neonate is similar to that of older children or adults and is dependent upon location of the VTE. Ultrasound is the most common diagnostic tool employed in identifying neonatal VTE, but relatively small vessels of the neonate as well as frequent low pulse pressure can make ultrasound less reliable. The diagnosis of a thrombophilic disorder in the neonatal population is unlikely to change management or outcome, and the role of thrombophilia testing in this population requires further study. Treatment of neonatal VTE is aimed at reducing VTE-associated morbidity and mortality. Recommendations for treating, though, cannot be extrapolated from guidelines for older children or adults. Neonates are at risk for bleeding complications, particularly younger neonates with more fragile intracranial vessels. Developmental alterations in the coagulation proteins as well as unique pharmacokinetics must also be taken into consideration when recommending VTE treatment. In this review, epidemiology of neonatal VTE, pathophysiology of neonatal VTE with particular attention to the developmental hemostatic system, diagnostic evaluations of neonatal VTE, and treatment guidelines for neonatal VTE will be reviewed.

[Haemostatic disorders in children]

Haemorrhagic and thrombotic events occur in both children and adults. The underlying causes are congenital or acquired disorders. In contrast to haemorrhagic disorders, inherited thrombotic disorders nearly exclusively in association with additional external risk factors lead to thrombotic events predominantly during the newborn period and adolescence. It is necessary to be aware of age-specific properties of coagulation in order to correctly interpret clinical and laboratory findings and to provide optimal care for children with haemorrhagic and thrombotic complications.

Challenging Argatroban Management of a Child on Extracorporeal Support and Subsequent Heart Transplant

A 6-year-old child developed heparin-induced thrombocytopenia while on extracorporeal life support. Hours after a difficult transition from heparin to argatroban for anticoagulation therapy, the child underwent heart transplantation. Intraoperative management was plagued with circuit thrombus formation while on cardiopulmonary bypass and subsequent massive hemorrhage after bypass. We review the child’s anticoagulation management, clinical challenges encountered, and review current literature related to the use of argatroban in pediatric cardiac surgery.

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.

Management of venous thrombosis in the pediatric patient

The incidence of venous thromboembolism in children has increased significantly over the past decade. The evaluation and management of the child with venous thromboembolism, while based on the adult experience, has its own particularities dictated by the differences in the hemostatic system of the newborn and child. The current review addresses the evaluation of pediatric patient with thrombosis as well as the established and emerging treatment interventions.

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.

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.

Survey results: characterization of direct thrombin inhibitor use in pediatric patients

OBJECTIVES

The objective of this multicenter survey is to characterize the use of direct thrombin inhibitors (DTIs) in the pediatric population. The results of this survey may be used to design a prospective multicenter study with the ultimate goal of developing a dosing/titration recommendation for the use of DTIs in the pediatric population.

METHODS

This is a multicenter, descriptive study to survey hospitals around the country regarding the use of DTIs (argatroban, bivalirudin, and lepirudin) in the pediatic population. Institutional review board approval was obtained. The survey consisted of 42 questions and was designed utilizing Survey Monkey. The survey was emailed to members of the Pediatric Pharmacy Advocacy Group. Listserv members who responded to the survey within 4 weeks of when the survey was emailed were included in the study. Descriptive statistics were performed utilizing Microsoft Excel 2007.

RESULTS

Responses were obtained from 56 institutions from 29 states in the United States. Multiple agents are available on formulary with argatroban being the most common (~80%). The large majority of institutions (41.1%) utilize DTIs 2 to 4 times a year with an additional 33.9% utilizing them less than twice a year. There is no consistent approach to dosing and titration amongst pediatric institutions.

CONCLUSIONS

There are a wide variety of methods used by pediatric institutions with regard to dosing and titration of DTIs. Recently published prospective studies and package insert updates should help guide practitioners toward a more consistent approach to dosing of these high-risk medications.

Systematic review on heparin-induced thrombocytopenia in children: a call to action

BACKGROUND

Heparin-induced thrombocytopenia (HIT) has increasingly been reported in children as an indication for use of new alternative anticoagulant drugs (NAADs).

OBJECTIVES

To systematically review the literature regarding: (i) the incidence and prevalence of seroconversion and HIT and (ii) the clinical/laboratory findings and management of HIT in children.

DESIGN/METHODS

MEDLINE and EMBASE databases were searched for studies that reported pediatric cases of HIT. Methodological reliability assessment of studies was performed with the Loney scale.

RESULTS

The incidence of seroconversion in neonates ranged between 0% and 1.7%. There were no cases of neonatal HIT in the included cohorts. The incidence range of seroconversion in the non-neonatal population was 1.3-52%. The incidence of HIT in non-neonates after cardiopulmonary bypass was 0.33% (95%CI, < 0.01-2.04). Whereas more than half of pediatric cases labeled as HIT (30/52) did not include pivotal features of this syndrome, 80% of them received NAADs.

CONCLUSION

The incidence of HIT is likely to have been overestimated in children, leading to potential misuse of NAADs in many cases. Clinical findings and laboratory assessment of pediatric cases are poorly described in the literature at present. Thorough laboratory investigation, proper reporting of cases and adequate design of studies are mandatory to elucidate the clinical/laboratory picture of pediatric HIT.

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.

Alternatives to standard unfractionated heparin for pediatric hemodialysis treatments

Despite advances in biomaterials and dialyzer design, thrombin generation occurs in the dialysis circuit because of platelet and leukocyte activation. As such, anticoagulation is required by the majority of children for successful dialysis to prevent clotting in the venous air detector and the capillary dialyzer, particularly for small children with slower blood flow rates. For many years unfractionated heparin has been the standard anticoagulant of choice, but is now being challenged by low-molecular-weight heparins (LMWHs) because they are simple to administer and reliable, particularly as the cost differential has been eroded. Alternative, nonheparin anticoagulants are more frequently available, but are often restricted to special circumstances: patients at high risk of hemorrhage; heparin allergy; or heparin-induced thrombocytopenia. These nonheparin alternatives are significantly more expensive than heparins, and may add a degree of complexity, such as citrate, which is a regional anticoagulant, although citrate-containing dialysate may permit short anticoagulant-free dialysis sessions. Systemic anticoagulants required for immune-mediated, heparin-induced thrombocytopenia are expensive and either have short half-lives, and therefore require continuous infusions, or prolonged half-lives, which, although allowing simple bolus administration, increases the risk of drug accumulation, over-dosage and hemorrhage.

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.

Results of a consensus meeting on the use of argatroban in patients with heparin-induced thrombocytopenia requiring antithrombotic therapy - a European Perspective

Argatroban has been introduced as an alternative parenteral anticoagulant for HIT-patients in several European countries in 2005. In 2009 a panel of experts discussed their clinical experience with argatroban balancing risks and benefits of argatroban treatment in managing the highly procoagulant status of HIT-patients. This article summarizes the main conclusions of this round table discussion. An ongoing issue is the appropriate dosing of argatroban in special patient groups. Therefore, dosing recommendations for different HIT-patient groups (ICU patients; non-ICU patients, paediatric patients, and for patients undergoing renal replacement therapies) are summarized in this consensus statement. Because of the strong correlation between argatroban dosing requirements and scores used to characterize the severity of illness (APACHE; SAPS, SOFA) suitable dosing nomograms are given. This consensus statement contributes to clinically relevant information on the appropriate use and monitoring of argatroban based on the current literature, and provides additional information from clinical experience. As the two other approved drugs for HIT, danaparoid and lepirudin are either currently not available due to manufacturing problems (danaparoid) or will be withdrawn from the market in 2012 (lepirudin), this report should guide physicians who have limited experience with argatroban how to use this drug safely in patients with HIT.

Heparin-Induced Thrombocytopenia Screening and Management in Pediatric Patients

The diagnosis and management of heparin-induced thrombocytopenia (HIT) in pediatric patients poses significant challenges. The cardinal findings in HIT, thrombocytopenia and thrombosis with heparin exposure, are seen commonly in critically ill children, but are most often secondary to etiologies other than HIT. However, without prompt diagnosis, discontinuation of heparin, and treatment with an alternative anticoagulant such as a direct thrombin inhibitor (DTI), HIT can result in life- and limb-threatening thrombotic complications. Conversely, DTIs are associated with higher bleeding risks than heparin in adults and their anticoagulant effects are not rapidly reversible; furthermore, the experience with their use in pediatrics is limited. Whereas immunoassays are widely available to aid in diagnosis, they carry a significant false positive rate. Age-dependent differences in the coagulation and immune system may potentially affect manifestations of HIT in children, but have not been extensively examined. In this chapter, diagnostic approaches and management strategies based on a synthesis of the available pediatric studies and adult literature on HIT are discussed.

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.

Direct thrombin and factor Xa inhibitors in children: a quest for new anticoagulants for children

Venous thrombosis and pulmonary embolism rarely occur in children but are associated with significant morbidity and mortality. Venous thromboembolism (VTE) mostly affects children with severe underlying conditions and multiple risk factors. Newborns and adolescents are at the highest risk. Standard and low molecular weight heparins and vitamin K antagonists are routinely used for the prevention and treatment of VTE. The new anticoagulants, both parenteral such as argatroban, bivalirudin and fondaparinux and oral such as dabigatran and rivaroxaban, have favourable pharmacological properties, all are approved for clinical use in adults and are currently being investigated in children. Argatroban is the only new anticoagulant licensed for use in children so far. The role of these new anticoagulants as alternative anticoagulants for children remains to be defined. This review focuses on the characteristics of VTE in children and reviews current knowledge on the use of the new thrombin and factor Xa inhibitors in this population.