Heparin induced thrombocytopenia and re-thrombosis associated with warfarin and fondaparinux in a child

Intravenous Direct Thrombin Inhibitors for Acute Venous Thromboembolism or Heparin-Induced Thrombocytopenia with Thrombosis in Children: A Systematic Review of the Literature

Intravenous direct thrombin inhibitors (DTIs) are used for thromboembolic disorders. This systematic review aims to characterize intravenous DTI agents, dosing, monitoring strategies (or use), bleeding, and mortality, in pediatric patients with acute venous thromboembolism (VTE) or heparin-induced thrombocytopenia with thrombosis (HITT). MEDLINE, Embase, and Cochrane's CENTRAL were searched from inception through July 2023. Case series, retrospective studies, and prospective studies providing per-patient or summary data for patients < 18 years of age with VTE or HITT treated with an intravenous DTI were included. Selection and data extraction were conducted independently by two reviewers. Sixteen studies (7 case reports, 1 case series, 5 retrospective studies, 3 prospective studies) with 85 patients were included. Target conditions included acute VTE in 54 (64%) and HITT in 31 (36%) patients. Bivalirudin, argatroban, and lepirudin were used in 52 (61%), 27 (32%), and 6 (7%) patients, respectively. Fifty-two (61%) patients received a bolus dose, and weighted mean infusion rates for bivalirudin, argatroban, and lepirudin were 0.2 mg/kg/hr, 1.2 mcg/kg/min, and 0.15 mg/kg/hr, respectively. The activated partial thromboplastin time was utilized for monitoring in 82 (96%) patients. Complete or partial thrombus resolution was reported in 53 (62%) patients, mortality in 6 (7%) patients, and bleeding complications in 14 (16%) patients. In this systematic review involving 85 pediatric patients treated with an intravenous DTI for acute VTE or HITT, bivalirudin was the most commonly utilized agent, with a rate of resolution over 60% despite a high acuity in the population studied. Prospective collaborative studies are warranted to establish optimal dosing and further characterize VTE and bleeding outcomes.

Effects of argatroban, danaparoid, and fondaparinux on trombin generation in heparin-induced thrombocytopenia

There is no in vitro data on the comparison of the effects of danaparoid, argatroban and fondaparinux on thrombin generation in patients with heparin-induced thrombocytopenia. It was the study objective to compare the in vitro anticoagulant potential of argatroban, danaparoid and fondaparinux using a thrombin generation assay TGA on a mixture of control platelet-rich plasma (PRP) and HIT patient platelet-poor plasma (PPP). The plasma of seven patients with a clear HIT diagnosed at our institution was selected. Mixtures of donor PRP and patient PPP were incubated with unfractionated heparin 0.2 U.mL-1, argatroban at 600 ng.mL-1, argatroban at 400 ng.mL-1, danaparoid at 0.65 IU.mL-1 and fondaparinux at 1 [uni03BC]g.mL-1. Thrombin generation was assessed by calibrated thrombinography. The percentage of inhibition of the endogenous thrombin potential observed with argatroban at 600 ng.mL-1 was statistically significantly higher compared with those observed with fondaparinux (median: 53.6% vs. 3.9%; p = 0.031) but not compared with argatroban at 400 ng.mL-1 and danaparoid. The percentage of inhibition of the thrombin peak observed with argatroban at 600 ng.mL-1 was statistically significantly higher compared with those observed with danaparoid (median: 71.2 vs. 56.8; p = 0.031) and fondaparinux (mean: 71.2 vs. 30; p = 0.031) but not with argatroban at 400 ng.mL-1. In conclusion, the in vitro effect of argatroban and danaparoid on thrombin generation seems to corroborate the results of clinical studies of these drugs in the treatment of HIT in term of efficiency. Fondaparinux showed a very small effect on thrombin generation evaluated by calibrated thrombinography.

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

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

Successful use of fondaparinux in a child with heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a well described side effect of heparin therapy. A 12-year-old boy developed deep-vein thrombosis. Risk factors for initial thrombosis are antiphospholipid syndrome and heterozygous mutation for prothrombin G20210A. Anticoagulant therapy with warfarin for 12 months was effective, but discontinuation of warfarin after 12 months resulted in recurrence of thrombosis. Unfractionated heparin (UFH) was initiated during the acute period, but heparin-induced thrombocytopenia developed. Transition from UFH to fondaparinux resulted in successful anticoagulation for a period of platelet recovery. We report a case of HIT developing with a background of prothrombotic genetic risk factors and antiphospholipid syndrome. This case study highlights several difficulties in pediatric HIT cases.

Antithrombotic therapy in neonates and children: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

Neonates and children differ from adults in physiology, pharmacologic responses to drugs, epidemiology, and long-term consequences of thrombosis. This guideline addresses optimal strategies for the management of thrombosis in neonates and children.

METHODS

The methods of this guideline follow those described in the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines.

RESULTS

We suggest that where possible, pediatric hematologists with experience in thromboembolism manage pediatric patients with thromboembolism (Grade 2C). When this is not possible, we suggest a combination of a neonatologist/pediatrician and adult hematologist supported by consultation with an experienced pediatric hematologist (Grade 2C). We suggest that therapeutic unfractionated heparin in children is titrated to achieve a target anti-Xa range of 0.35 to 0.7 units/mL or an activated partial thromboplastin time range that correlates to this anti-Xa range or to a protamine titration range of 0.2 to 0.4 units/mL (Grade 2C). For neonates and children receiving either daily or bid therapeutic low-molecular-weight heparin, we suggest that the drug be monitored to a target range of 0.5 to 1.0 units/mL in a sample taken 4 to 6 h after subcutaneous injection or, alternatively, 0.5 to 0.8 units/mL in a sample taken 2 to 6 h after subcutaneous injection (Grade 2C).

CONCLUSIONS

The evidence supporting most recommendations for antithrombotic therapy in neonates and children remains weak. Studies addressing appropriate drug target ranges and monitoring requirements are urgently required in addition to site- and clinical situation-specific thrombosis management strategies.

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.

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

BACKGROUND

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

PROCEDURE

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

RESULTS

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

CONCLUSION

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

Fondaparinux: does it cause HIT? Can it treat HIT?

Heparin-induced thrombocytopenia (HIT) is an antibody-mediated prothrombotic disorder triggered by PF4-binding polyanions, usually heparin. The pentasaccharide anticoagulant, fondaparinux, despite its negative charge and structural similarity to heparin, does not usually promote antibody binding to PF4 (owing to absent/weak 'cross-reactivity'). Thus, despite its ability to trigger anti-PF4/heparin antibodies ('immunogenicity'), fondaparinux has low - but not zero - risk of inducing HIT de novo, or of exacerbating HIT when antibodies are already present. Indeed, despite rare reports of fondaparinux-induced HIT, this 'dissociation' between immunogenicity and cross-reactivity suggests that fondaparinux should be effective in treating HIT, as supported by several observational studies. An emerging issue: will clinicians accept this favorable experience of fondaparinux for treating HIT when a lack of randomized trials will hinder regulatory approval for this indication?

Successful use of fondaparinux in a patient with a mechanical heart valve replacement and a history of heparin-induced thrombocytopenia

The development of heparin-induced thrombocytopenia (HIT) is an antibody-mediated clinicopathologic syndrome. The resultant thrombocytopenia and thrombosis can be severe and life-threatening. Fondaparinux is a parenteral factor Xa inhibitor used for venous thromboembolism prevention and treatment. Fondaparinux has minimal affinity for platelet factor 4, making it an alternative agent to unfractionated heparin (UFH) and low-molecular weight heparin (LMWH) and a plausible consideration for patients with a history of HIT. The use of fondaparinux in patients with mechanical heart valve replacement and a history of HIT has never been discussed in the literature. We report on the case of a patient with a mechanical aortic heart valve replacement and a history of HIT who was successfully bridged postoperatively with fondaparinux. While there is currently no literature to support the use of fondaparinux in patients with mechanical heart valves, this drug may offer an option for management of such patients who cannot use heparin products. However, further clinical investigations are warranted to confirm both the safety and efficacy of this agent in the mechanical heart valve population.

Pneumothorax, pneumomediastinum, and pulmonary embolism

This article discusses pneumothorax, pneumomediastinum, and pulmonary embolism in pediatric practice. Although children appear to have better outcomes than adults, the risk factors are substantial. Topics covered include the pathophysiology incidence, presentation, diagnosis, and management of these diseases.