Diagnosis and treatment of heparin-induced thrombocytopenia in neonates and children

Heparin Induced Thrombocytopenia - Pathophysiology, Diagnosis and Treatment: A Narrative Review

Heparin-induced thrombocytopenia (HIT) is a life-threatening, immune-mediated complication following heparin exposure and is considered to be the most severe adverse reaction to heparin treatment that is not associated with bleeding. Development of autoantibodies against platelet factor 4 (PF4) - heparin complex constitutes the basis of the pathophysiological changes in patients suffering from HIT, which then binds to the surface of platelets and monocytes, thus provoking their activation and subsequent aggregation, ultimately leading to the formation of thrombosis. Formation of arterial and venous thrombosis is aggravated by the simultaneous activation of platelets and monocytes with a substantial mortality rate. The incidence of HIT is reported to be significantly lower in pediatric patients compared with adults. Diagnosis of HIT in pediatric population remains a clinical entity supplemented by laboratory evaluation. The positive predictive value of laboratory evaluation is further elevated by the use of scoring systems and predictive models used for hastening the diagnosis of HIT. Use of alternative anticoagulants like direct thrombin inhibitors and factor Xa inhibitors form the mainstay of treatment in cases of HIT, however, more prospective studies would be required in the pediatric population to delineate definitive guidelines for proper management of patients in this age-group. This article delivers diagnostic and treatment approach in case of patients with HIT, wherein the pathophysiology, clinical manifestations, diagnostic approach and the management of patients with HIT has been described.

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.

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.

Venous Thromboembolism in Children: From Diagnosis to Management

Venous thromboembolism (VTE) in children is a rare occurrence, although in recent decades we have seen an increase due to several factors, such as the rise in survival of subjects with chronic conditions, the use of catheters, and the increased sensitivity of diagnostic tools. Besides inherited thrombophilia, acquired conditions such as cardiovascular diseases, infections, chronic disorders, obesity and malignancy are also common risk factors for paediatric VTE. The treatment of paediatric VTE consists of the use of heparins and/or vitamin K antagonists to prevent dissemination, embolization, and secondary VTE. Randomized clinical trials of direct oral anticoagulants in paediatric VTE are ongoing, with the aim to improve the compliance and the care of patients. We reviewed the physiological and pathological mechanisms underlying paediatric thrombosis and updated the current diagnosis and treatment options.

Heparin-induced thrombocytopenia in solid organ transplant recipients: The current scientific knowledge

Exposure to heparin is associated with a high incidence of immunization against platelet factor 4 (PF4)/heparin complexes. A subgroup of immunized patients is at risk of developing heparin-induced thrombocytopenia (HIT), an immune mediated prothrombotic adverse drug effect. Transplant recipients are frequently exposed to heparin either due to the underlying end-stage disease, which leads to listing and transplantation or during the transplant procedure and the perioperative period. To review the current scientific knowledge on anti-heparin/PF4 antibodies and HIT in transplant recipients a systematic PubMed literature search on articles in English language was performed. The definition of HIT is inconsistent amongst the publications. Overall, six studies and 15 case reports have been published on HIT before or after heart, liver, kidney, and lung transplantation, respectively. The frequency of seroconversion for anti-PF4/heparin antibodies ranged between 1.9% and 57.9%. However, different methods to detect anti-PF4/heparin antibodies were applied. In none of the studies HIT-associated thromboembolic events or fatalities were observed. More importantly, in patients with a history of HIT, reexposure to heparin during transplantation was not associated with thrombotic complications. Taken together, the overall incidence of HIT after solid organ transplantation seems to be very low. However, according to the current knowledge, cardiac transplant recipients may have the highest risk to develop HIT. Different alternative suggestions for heparin-free anticoagulation have been reported for recipients with suspected HIT albeit no official recommendations on management have been published for this special collective so far.

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.

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.

Meningococcemia and heparin-induced thrombocytopenia: a dangerous combination

We present a dramatic case of a patient presenting with disseminated intravascular coagulation related to meningococcal sepsis who developed heparin-induced thrombocytopenia following heparin administration during continuous renal replacement therapy. Association of these two prothrombotic conditions led to severe limbs ischemia and finally to bilateral legs amputation. We stress the importance of suspect heparin-induced thrombocytopenia in intensive care unit patients, especially when an improvement of other coagulation parameters is observed, and heparin therapy was started.

Therapeutic sesamol attenuates monocrotaline-induced sinusoidal obstruction syndrome in rats by inhibiting matrix metalloproteinase-9

We investigated the therapeutic effect of sesamol against monocrotaline-induced sinusoidal obstruction syndrome (SOS) in rats. Male Sprague-Dawley rats were gavaged with a single dose of monocrotaline (90 mg/kg) to induce SOS. Sesamol (5, 10, 20, and 40 mg/kg) was subcutaneously injected 24 h after monocrotaline treatment. Control rats were given saline only. Aspartate transaminase, alanine transaminase, mast cells, CD 68(+) Kupffer cells, neutrophils, myeloperoxidase, matrix metalloproteinase-9 (MMP-9), tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), laminin, and collagen were assessed 48 h after monocrotaline treatment. All tested parameters, except for TIMP-1, laminin, and collagen, were significantly higher in monocrotaline-treated rats than in control rats, and, except for TIMP-1, laminin, and collagen, significantly lower in sesamol-treated rats than in monocrotaline-treated rats. In addition, liver pathology revealed that sesamol offered significant protection against SOS. We conclude that a single dose of sesamol therapeutically attenuated SOS by decreasing the recruitment of inflammatory cells, downregulating MMP-9, and upregulating TIMP-1 expression.

Heparin-induced thrombocytopenia in the pediatric population: a review of current literature

Heparin-induced thrombocytopenia is a rare and serious reaction to unfractionated heparin and low-molecular-weight heparins in children. Quick recognition, discontinuation of heparin, and subsequent treatment with an alternative anticoagulant are essential steps to prevent serious complications such as thrombus and limb amputation. The purpose of this review is to describe the clinical features of heparin-induced thrombocytopenia in children and to summarize the data available for its management. This paper summarizes data and relates the use of direct thrombin inhibitors with clinical outcomes. A literature search was conducted with Ovid, using the key terms argatroban, bivalirudin, hirulog, danaparoid, lepirudin, direct thrombin inhibitor, heparin-induced thrombocytopenia, thrombosis, warfarin, and fondaparinux. Articles were excluded if they were classified as editorials, review articles, or conference abstracts or if they involved patients 18 years of age or older or described disease states not related to thrombosis. Nineteen articles containing 33 case reports were identified and evaluated for this review. Of the 33 cases, 14, 10, 4, and 2 cases described the use of lepirudin, danaparoid, argatroban, and bivalirudin, respectively. Two cases did not report the type of anticoagulant used, and 1 case used aspirin. The most commonly reported complication was bleeding.

Venous thrombosis in children: an emerging issue

More and more cases of venous thrombosis are diagnosed in children thanks to newer imaging modalities. Central venous catheters have become commonplace in the care of critically ill children and have contributed to the increased rate of thrombotic events. Lastly, children who develop life-threatening or chronic medical conditions are surviving longer because of advanced medical therapies; these intensive therapies can be complicated by events such as thrombosis. Over the last 10 years, specific guidelines for treating thrombosis in children have become available. Nevertheless, in many situations anticoagulant treatment is specially tailored to each individual patient's needs. Some new antithrombotic drugs which have undergone clinical testing in adults might be beneficial to paediatric patients with thromboembolic disorders; unfortunately, clinical data and reports on the use of these drugs in children, when available, are extremely limited. The aim of this review is to provide physicians with enough background information to be able to manage thrombosis in children. First, by helping them detect a thrombotic event in a child. Upon confirmation of the diagnosis, the physician will request the appropriate tests and will choose the best treatment on the basis of the guidelines and recommendations. Moreover, the paediatrician will have the information he or she needs to identify which children are at highest risk of acute thrombotic events and relevant long-term sequelae and, therefore, to decide on the appropriate prophylactic or pharmacologic strategy. Lastly, we would like to provide the paediatrician with information on future drugs with regard to the treatment and prophylaxis of thrombosis.

Craniocervical arterial dissection in children: diagnosis and treatment

OPINION STATEMENT

Diagnosis of craniocervical arterial dissection (CCAD) in children begins with a careful history and physical in a child with a transient ischemic attack (TIA) or arterial ischemic stroke (AIS). The extent of radiologic evaluation for suspected CCAD is based upon careful consideration of the risks associated with the best imaging techniques, weighed against the benefits of enhanced vascular imaging with better diagnostic sensitivity. Although conventional angiography (CA) and CT angiography (CTA) have a higher sensitivity than magnetic resonance angiography (MRA), they are accompanied by risks: for CA, femoral hematoma, femoral arterial pseudoaneurysm, recurrent AIS, and radiation exposure; for CTA, radiation. For children (non-neonates) with suspected CCAD, MRI with MRA is recommended as the first-line imaging study. MRI usually includes diffusion-weighted, FLAIR, and T1 images of the brain, and T1 or T2 fat-saturation axial imaging through the neck. MRA should include 3D time-of-flight MRA of the head and neck (from the aortic arch through the circle of Willis). Contrast-enhanced MRA should be highly considered in neck imaging. If MRI/MRA is equivocal, CCAD is strongly suspected but not detected on MRI/MRA (especially in the posterior circulation), or the child has recurrent events, additional imaging of the craniocervical vasculature is likely warranted. Individual clinical circumstances warrant careful, case-by-case consideration. Treatment of CCAD in children is challenging and differs for intracranial and extracranial dissections. In extracranial CCAD, we most commonly use anticoagulation for 6 weeks to 6 months in patients with TIA or AIS. Typically, unfractionated heparin is used in the acutely ill patient at heightened risk for bleeding (because of its short half-life), whereas low-molecular-weight heparin (LMWH) or warfarin are reserved for the stable patient. If the history is suspicious for dissection (head and neck trauma, recent cervical chiropractic manipulation, recent car accident, or neck pain), we consider treatment for dissection even with normal MRI/MRA. For patients with CCAD with a stroke size greater than one third to one half of the middle cerebral artery territory (or other bleeding risk factors) and extracranial CCAD, in whom there is concern about heightened risk for hemorrhagic conversion, we commonly use aspirin therapy during the acute phase. Regardless of their treatment in the initial weeks to months, we subsequently treat all patients with aspirin for 1 year after their event, and sometimes longer if they have other risk factors. Interventional techniques, such as extracranial cerebral arterial stent placement or selective occlusion, are understudied in children. Interventional techniques are typically reserved for patients who fail aggressive medical management and have recurrent TIA or AIS. The diagnosis and treatment of intracranial dissection is extraordinarily challenging in children, in whom inflammatory intracranial arteriopathies are common. When intracranial arteriopathy is clearly associated with dissection, the clinician should look for the presence of subarachnoid hemorrhage and/or dissecting aneurysm. Treatment decisions should be made by a multidisciplinary pediatric stroke team, given the lack of data in this area. Intracranial cerebral artery stent placement carries high risk and is not recommended for intracranial CCAD in children. Most importantly, we educate all children with CCAD and their parents about the paucity of evidence in the treatment of this disease, the risks of enhanced imaging techniques such as CTA or CA, and the challenges involved in weighing the risks of aggressive therapies and interventions against the costs of unclear diagnosis and potentially ineffective treatments. We also educate our patients with CCAD about the signs and symptoms of recurrence and the importance of emergent evaluation.

Novel techniques in the use of bivalirudin for cardiopulmonary bypass anticoagulation in a child with heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) occurs in both the pediatric and adult populations after exposure to heparin. Bivalirudin has been used as an alternative to heparin for adults undergoing cardiac surgery and cardiopulmonary bypass, but has only been used minimally in children for this purpose. We report the successful use of bivalirudin for anticoagulation during cardiopulmonary bypass in a small child with HIT, using novel techniques not previously described.

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.

Aspects of anticoagulation in children

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

Direct thrombin inhibitors: pharmacology and application in intensive care medicine

PURPOSE

Anticoagulation is part of the daily routine of intensive care physicians. As the possibilities of pharmacological anticoagulation are becoming more numerous and diverse, intensive care physicians have to be familiar with indications, contraindications, dosing, and reversal of many different substances. This paper presents an overview of the substance group of direct thrombin inhibitors (DTI) indicated for alternative anticoagulation in intensive care medicine.

METHODS

The review is a synopsis of scientific evidence, expert opinion, open forum commentary, and clinical feasibility data.

RESULTS AND CONCLUSIONS

Due to their antithrombotic potential without direct activation of platelets, DTI could offer potential advantages over heparins and vitamin K antagonists in critically ill patients, especially regarding heparin-induced thrombocytopenia. Because of multiple organ dysfunction, organ failure, and comedications, simple extrapolation of results of medical to critically ill patients is not permissible. The fine line between thrombosis and bleeding in intensive care patients requires cautious dosing and close drug monitoring. Studies dealing with DTI in the intensive care setting are of utmost clinical interest.

Association between drug and vaccine use and acute immune thrombocytopenia in childhood: a case-control study in Italy

Immune thrombocytopenic purpura (ITP) is an immunomediated disease characterized by a decrease in platelet count and, in its more severe forms, by bleeding symptoms. Many drugs have been implicated in the pathogenesis of drug-induced thrombocytopenia in adults; only limited data on drug-related ITP in children have been published. Our study was set up to evaluate the consistency of the association between drug and vaccine use and ITP in children. This study is part of an Italian multicentre study on adverse drug reactions in children, coordinated by the Italian National Institute of Health, which was started in November 1999 and is ongoing. The study was conducted by enrolling all children aged more than 1 month who were hospitalized through the paediatric emergency department for the following conditions: thrombocytopenia (platelet count <100 x 103/L); acute neurological disorders; non-infectious mucocutaneous diseases and vasculitis; and endoscopically confirmed gastroduodenal lesions and/or clinically defined haematemesis and melaena. Children with chronic pathologies or concomitant diagnoses of cancer or immunodeficiency were not included in our study. During hospital admission, a physician interviewed parents using a structured questionnaire. The main aim of the interview was to collect information on drug exposure in a time period of 3 weeks and vaccine exposure in a period of 6 weeks preceding hospitalization. Using a case-control study design, exposure of children with thrombocytopenia (cases) to drugs and vaccines was compared with similar exposure of children with gastroduodenal lesions and neurological disorders (controls); this allowed us to estimate the odds ratios (ORs) of the occurrence of thrombocytopenia associated with the use of drugs or vaccines. Up to December 2007, the study population included 387 cases of thrombocytopenia and 1924 controls. Despite the low platelet count, ITP was generally a mild disease, without serious bleeding in the majority of cases and associated with a short length of hospital stay. After adjusting for concurrent use of other drugs, use of the antibacterials was associated with a more than 2-fold increase in the risk of developing ITP (OR 2.4; 95% CI 1.8, 3.1). Mucolytics and NSAIDs were associated with an OR of 1.9; 95% CI 1.2, 2.9 and 1.5; 95% CI 1.0, 2.1 respectively, while paracetamol (acetaminophen) was associated with an OR of 1.5; 95% CI 1.2, 2.0. MMR vaccination was associated with an increased risk of developing ITP (OR 2.4; 95% CI 1.2, 4.7). The results of this study provide evidence for an association between ITP and exposure to selected antibacterials, NSAIDs, paracetamol, mucolytics and MMR vaccination.

Thrombocytopenia and anemia in infants and children

Thrombocytopenia and anemia are the two most common hematologic conditions seen in the pediatric emergency department. Providers of emergency pediatric care must have an understanding of the causes and therapies for the various conditions that result from thrombocytopenia and anemia. This article reviews the common causes of isolated thrombocytopenia and anemia in infancy and childhood.

Cerebral venous thrombosis and heparin-induced thrombocytopenia in an 18-year old male with severe ulcerative colitis

The risk of thromboembolism is increased in inflammatory bowel disease and its symptoms may be overlooked. Furthermore, its treatment can be complex and is not without complications. We describe a case of an adolescent boy who developed a cerebral sinus venous thrombosis during a relapse of his ulcerative colitis and who, while on treatment with heparin, developed heparin-induced thrombocytopenia (HIT). The treatment was then switched to fondaparinux, a synthetic and selective inhibitor of activated factor X.

Successful use of bivalirudin for superior vena cava recanalization and stent placement in a child with heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a potentially life-threatening, adverse effect of heparin therapy. Patients with this complication require an alternative approach to anticoagulation. Bivalirudin is a direct thrombin inhibitor with an efficacy comparable to that of heparin, a short half-life, and reduced bleeding complications in adults. We present the case of a 2-year-old boy with HIT Type II who underwent recanalization of an occluded superior vena cava and stent placement, utilizing bivalirudin as anticoagulant.

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.

Heparin-Induced Thrombocytopenia: Treatment Options and Special Considerations

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse effect that typically manifests several days after the start of heparin therapy, although both rapid- and delayed-onset HIT have been described. Its most serious complication is thrombosis. Although not all patients develop thrombosis, it can be life threatening. The risk of developing HIT is related to many factors, including the type of heparin product administered, route of administration, duration of therapy, patient population, and previous exposure to heparin. The diagnosis of HIT is typically based on clinical presentation, exposure to heparin, and presence of thrombocytopenia with or without thrombosis. Antigen and activation laboratory assays are available to support the diagnosis of HIT. However, because of the limited sensitivity and specificity of these assays, bedside probability scales for HIT were developed. When HIT is suspected, prompt cessation of all heparin therapy is necessary, along with initiation of alternative anticoagulant therapy. Two direct thrombin inhibitors--argatroban and lepirudin--are approved for the management of HIT in the United States, and bivalirudin is approved for use in patients with HIT who are undergoing percutaneous coronary intervention. Other agents, although not approved to manage HIT, have also been used; however, their role in therapy requires further evaluation. A comprehensive HIT management strategy involves the evaluation of numerous factors. Many patients, including those undergoing coronary artery bypass surgery, those with acute coronary syndromes, those with hepatic or renal insufficiency, and children, require special attention. Clinicians must become familiar with the available information on this serious adverse effect and its treatment so that optimum patient management strategies may be formulated.

Successful use of bivalirudin for cardiac transplantation in a child with heparin-induced thrombocytopenia

Bivalirudin, a direct thrombin inhibitor, has recently emerged as a promising option for anti-coagulation during cardiopulmonary bypass in patients who cannot receive heparin. There is limited experience with the use of bivalirudin in children. We present the case of a child with heparin-induced thrombocytopenia with thrombosis (HIT Type II) who underwent successful orthotopic cardiac transplantation using bivalirudin as the primary anti-coagulant for cardiopulmonary bypass.