Current and future antithrombotic agents in children

EMPoWARed: Edmonton pediatric warfarin self-management study

BACKGROUND

Patient self-management (PSM) in adults is safer and more cost effective than conventional management. Warfarin is a narrow therapeutic index drug with individual patient response to changes and frequently a long-term therapy. Children and their families are proposed to be able to effectively manage their child's warfarin therapy. Increased health related quality of life is highly associated with effective therapy in patients with chronic conditions.

OBJECTIVES

The aim of this study is to evaluate the safety and efficacy of PSM over time including HRQOL and variables that may influence PFU success at PSM.

PATIENTS/METHODS

Children and their family units (PFUs) current performing patient self-testing/monitoring for ≥ 3 months were enrolled in this cohort study. PFUs participated in comprehensive education on warfarin testing and management followed by an apprenticeship. Socio-demographic, clinical, and laboratory data were collected to evaluate safety and efficacy and health related quality of life. Outcomes were compared between the first 6 months on PSM (phase 1) and the last 6 months data collected on PSM (phase 2).

RESULTS

Forty-two patients performed PSM for a median of 2.7 years (range: 1.1-6.2 years). Time in therapeutic range was 90% and 92.9% (p=0.30) in phases 1 and 2 respectively. All measures were strongly associated with improved heath related quality of life. PFUs socio-demographic status did not influence success at PSM. All PFUs maintained warfarin knowledge and INR testing competency. Warfarin dosing decision errors median 0 (range: 0-5, p=0.73) and a median 0 (range 0-4, p=0.55) per patient in phases 1 and 2 respectively. There were no adverse hemorrhagic or thrombotic events.

CONCLUSIONS

Empowering PFUs to self-manage warfarin results in increased knowledge and understanding of their health condition, improved commitment to their health care and adherence to medication regimens and is demonstrated to be sustainable over time.

UNBLOCK: an open-label, dose-finding, pharmacokinetic and safety study of bivalirudin in children with deep vein thrombosis

BACKGROUND

Direct thrombin inhibitors offer potential advantages over unfractionated heparin but have been poorly studied in children.

OBJECTIVES

To determine appropriate dosing of bivalirudin in children and adolescents and the relationship between activated partial thromboplastin time (APTT) and plasma bivalirudin concentration.

PATIENTS/METHODS

The UNBLOCK (UtilizatioN of BivaLirudin On Clots in Kids) study was an open-label, single-arm, dose-finding, pharmacokinetic, safety and efficacy study of bivalirudin for the acute treatment of deep vein thrombosis (DVT) in children aged 6 months to 18 years. Drug initiation consisted of a bolus dose (0.125 mg kg(-1) ) followed by continuous infusion (0.125 mg kg h(-1) ). Dose adjustments were based on the APTT, targeting a range of 1.5-2.5 times each patient's baseline APTT. Safety was assessed by specific bleeding endpoints and efficacy by repeat imaging at 48-72 h and 25-35 days.

RESULTS

Eighteen patients completed the study. Following the bolus dose and the initial infusion rate, most patients' APTT values were within the target range. The infusion rate bivalirudin correlated more closely with drug concentration than the APTT. At 48-72 h, nine (50%) patients had complete or partial thrombus resolution, increasing to 16 (89%) at 25-35 days. No major and one minor bleeding event occurred.

CONCLUSIONS

Bivalirudin demonstrated reassuring safety and noteworthy efficacy in terms of early clot resolution in children and adolescents with DVT. Although a widely available and familiar monitoring tool, the APTT correlates poorly with plasma bivalirudin concentration, possibly limiting its utility in managing pediatric patients receiving bivalirudin for DVT.

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

BACKGROUND

An increasing number of pediatric patients suffer from thrombotic events necessitating anticoagulation therapy including heparins. Some such patients develop heparin-induced thrombocytopenia (HIT) and thus require alternative anticoagulation. As such, studies evaluating the safety, efficacy, and dosing of alternative anticoagulants are required.

PROCEDURE

In this multicenter, single arm, open-label study, 18 patients ≤ 16 years old received argatroban for either a suspicion of or being at risk for HIT, or other conditions requiring nonheparin anticoagulation. Endpoints included thrombosis, thromboembolic complications, and bleeding.

RESULTS

Patients (ages, 1.6 weeks to 16 years) received argatroban usually for continuous anticoagulation (n = 13) or cardiac catheterization (n = 4). One catheterization patient received a 250 µg/kg bolus only; 17 patients received argatroban continuous infusion (median (range)) 1.1 (0.3-12) µg/kg/min (of whom four received a bolus) for 3.0 (0.1-13.8) days. In patients without bolus dosing, typically argatroban 1 µg/kg/min was initiated, with therapeutic activated partial thromboplastin times (aPTTs) (1.5-3× baseline) achieved within 7 hr. Within 30 days, thrombosis occurred in five patients (two during therapy). No one required amputation or died due to thrombosis during therapy. Two patients had major bleeding. Pharmacometric analyses demonstrated the optimal initial argatroban dose to be 0.75 µg/kg/min (if normal hepatic function), with dose reduction necessary in hepatic impairment.

CONCLUSIONS

In pediatric patients requiring nonheparin anticoagulation, argatroban rapidly provides adequate levels of anticoagulation and is generally well tolerated. For continuous anticoagulation, argatroban 0.75 µg/kg/min (0.2 µg/kg/min in hepatic impairment), adjusted to achieve therapeutic aPTTs, is recommended.

New Anticoagulants 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, low-molecular-weight heparins (LMWH), and warfarin. These agents, however, have significant limitations that are exaggerated in children. Novel anticoagulants such as direct thrombin inhibitors and the selective factor Xa inhibitor, fondaparinux, have been approved for use in adults and have properties that suggest they may be safer and more efficacious than the standard agents; however, until recently, publications using these agents in children were limited to case reports. Recently, clinical trials for two direct thrombin inhibitors, bivalirudin and argatroban, have been completed and a clinical trial of fondaparinux is under way. This review will compare the standard agents with the novel agents and briefly review the results of the clinical trials.

Treatment of thrombosis with fondaparinux (Arixtra) in a patient with end-stage renal disease receiving hemodialysis therapy

Treatment of thrombosis in children with end-stage renal disease (ESRD) is extremely challenging owing to the underlying risk of bleeding. Fondaparinux (Arixtra, Sanofi-Synthélabo), a synthetic pentasaccharide, is contraindicated in patients with compromised renal function as it is excreted via kidneys. We describe a unique case with ESRD and pulmonary embolism who was treated with fondaparinux owing to the toxicity and poor compliance with low-molecular-weight heparin. Despite regular hemodialysis, a gradual rise in drug levels was observed without significant bleeding complications. This report implies that although low dose fondaparinux can be an option in patients with ESRD under special circumstances, guidelines for laboratory monitoring and appropriate dose adjustments are urgently required to ensure the safety of the patient.

Pilot dose-finding and safety study of bivalirudin in infants <6 months of age with thrombosis

BACKGROUND

Thrombosis is not uncommon in children with serious medical conditions. Unfractionated heparin, the most commonly used anticoagulant in the acute management of thrombosis, has significant pharmacologic limitations, especially in infants. Newer anticoagulants have improved properties relative to heparin, and this may enhance the outcome in children.

OBJECTIVE

To determine dosing, and to assess the safety and efficacy of bivairudin for infants with thrombosis.

METHODS

Infants <6 months old were chosen for this pilot study as they may most benefit from a direct thrombin inhibitor because of their physiologically low antithrombin levels. This was an open label, dose-finding and safety study. Patients received one of three bolus doses and one of two initial infusion doses with subsequent dosing adjusted utilizing the activated partial thromboplastin time. Safety was assessed by specific bleeding endpoints. Efficacy was determined by reassessing the initial imaging study at 48-72 h and by measurement of molecular markers of thrombin generation.

RESULTS

Sixteen patients completed the study. All three bolus doses resulted in therapeutic anticoagulation, as did both initial infusion doses. A dose-response effect was noted for the continuous infusion but not the bolus dosing. Two patients met the study criteria for major bleeding, both with gross hematuria, which resolved with a reduction in the bivalirudin infusion rate. In terms of efficacy, 37.5% of patients had complete or partial resolution of their thrombosis by 48-72 h. There was a significant decrease in all three molecular markers of thrombin generation.

CONCLUSION

This study demonstrates the potential utility of bivalirudin in the pediatric population.

Neonatal thromboembolic emergencies

Thrombosis risk is multifactorial, with interaction of hereditary risk factors and acquired environmental and clinical conditions. Newborns are at particular risk for thrombotic emergencies secondary to the unique properties of their hemostatic system, influences of the maternal-fetal environment, and perinatal complications and interventions. Thrombotic complications range from arterial and venous catheter thrombosis to purpura fulminans. Prompt identification and appropriate management of thrombotic emergencies is critical in avoiding limb-, organ-, and life-threatening complications. Treatment strategies have been extrapolated from adult literature but clinical experience from small-scale neonatal studies has resulted in therapeutic guidelines, which should be individualized for each neonate, taking into consideration age and clinical status.

Diagnosis and treatment of thrombosis in children: general principles

Thrombosis is an increasingly recognized complication occurring primarily in children with serious underlying conditions and most often associated with intravenous catheters. There are few clinical trials available to guide the decision-making in the diagnosis and treatment of thrombosis. Although there are published guidelines which suggest how to manage such patients, they are based on data from adult studies and uncontrolled pediatric studies and it is unclear how widely these guidelines are utilized in clinical practice. What is clear is that many additional studies are needed to provide the data required to make evidence-based decisions. Nevertheless, patients today are being diagnosed with thrombosis and must be treated. Diagnosis is based largely on various diagnostic-imaging methods. While Doppler ultrasonography is non-invasive and relatively inexpensive, its sensitivity for the upper venous system is poor. Venography/angiography, the most sensitive method to diagnose venous/arterial thrombosis is underutilized due to the need for peripheral venous access for venography and arterial catheterization for angiography as well as interventional radiology. Newer methods such as computed tomography and magnetic resonance imaging are useful for large vessel disease but are not validated in pediatrics. Treatment is based on the methods that are best at restoring circulation rapidly balanced by the risk for bleeding. Both thrombolysis and anticoagulation can be utilized with the circumstances of each individual patient dictating the choice. The field of pediatric thrombosis continues to advance with numerous new studies currently underway or being planned. In the near future, the results of these studies will allow for better management of pediatric patients with thrombosis.

Argatroban anticoagulation in pediatric patients: a literature analysis

Argatroban, a direct thrombin inhibitor, is approved in the United States in adults as an anticoagulant for prophylaxis or treatment of thrombosis in heparin-induced thrombocytopenia (HIT) and in adults with or at risk for HIT undergoing percutaneous coronary intervention. The authors conducted a literature analysis to characterize the uses, dosing patterns, and safety of argatroban anticoagulation in pediatric patients. A comprehensive literature search identified nine articles describing 34 patients aged 1 week to 16 years who received argatroban anticoagulation for prophylaxis or treatment of thrombosis, cardiac catheterization, hemodialysis, extracorporeal membrane oxygenation or ventricular assist device support, or cardiopulmonary bypass. Most (85%) patients had HIT, a history of HIT, and/or HIT antibodies. For HIT thromboprophylaxis or treatment, argatroban dosing varied widely (0.1-12 mcg/kg/min), with no obvious relationship between patient age and dosage requirement. Overall, in these pediatric patients, therapeutic levels of anticoagulation were achieved despite the wide range of doses used. For pediatric patients undergoing cardiac catheterization, argatroban doses lower than those recommended in adults appeared to provide therapeutic anticoagulation. There was an unacceptably high bleeding risk with argatroban anticoagulation during pediatric cardiopulmonary bypass. Due to the limitations of case reports and/or case series, prospective studies with pharmacokinetic analyses are needed to evaluate the use of argatroban in pediatric patients.