Current agents for the treatment of patients with heparin-induced thrombocytopenia

Updates in Anticoagulation Therapy Monitoring

In the past six decades, heparin and warfarin were the primary anticoagulants prescribed for treatment and prophylaxis of venous thromboembolism worldwide. This has been accompanied by extensive clinical knowledge regarding dosing, monitoring, and reversal of these anticoagulants, and the resources required to do so have largely been readily available at small and large centers alike. However, with the advent of newer oral and parenteral anticoagulants such as low molecular weight heparins, factor Xa inhibitors, and direct thrombin inhibitors in recent years, new corresponding practice guidelines have also emerged. A notable shift in the need for monitoring and reversal agents has evolved as well. While this has perhaps streamlined the process for physicians and is often desirable for patients, it has also left a knowledge and resource gap in clinical scenarios for which urgent reversal and monitoring is necessary. An overview of the currently available anticoagulants with a focus on the guidelines and available tests for anticoagulant monitoring will be discussed in this article.

Anticoagulants: A Review of the Pharmacology, Dosing, and Complications

Anticoagulants remain the primary strategy for the prevention and treatment of thrombosis. Unfractionated heparin, low molecular weight heparin, fondaparinux, and warfarin have been studied and employed extensively with direct thrombin inhibitors typically reserved for patients with complications or those requiring intervention. Novel oral anticoagulants have emerged from clinical development and are expected to replace older agents with their ease of use and more favorable pharmacodynamic profiles. Hemorrhage is the main concerning adverse event with all anticoagulants. With their ubiquitous use, it becomes important for clinicians to have a sound understanding of anticoagulant pharmacology, dosing, and toxicity.

Heparin-dependent and -independent anti-platelet factor 4 autoantibodies in patients with systemic lupus erythematosus

OBJECTIVE

Antibodies that recognize complexes formed by platelet factor 4 (PF4) and heparin are involved in the pathogenesis of heparin-induced thrombocytopenia (HIT). This study was undertaken to investigate the prevalence and clinical correlations of anti-PF4 autoantibodies in patients with SLE.

METHODS

We studied 118 patients with SLE, 78 with primary immune thrombocytopenia (ITP), 27 with primary APS, 2 with HIT (as positive controls) and 47 healthy controls. Heparin-dependent and -independent anti-PF4 antibodies were measured with an ELISA. Antibody binding was confirmed to be heparin-dependent when inhibited by the presence of a high concentration of heparin. Pathogenic anti-PF4 antibody was assessed by serotonin-release assay.

RESULTS

Heparin-dependent anti-PF4 antibodies were detected in 11 SLE (9%) and 2 primary ITP (3%) patients, but at much lower levels than in HIT patients. In serotonin-release assays, only the HIT sera induced platelet activation in vitro. Heparin-independent anti-PF4 antibodies were detected in 17 SLE patients (14%). There was no correlation between the levels of heparin-dependent and -independent anti-PF4 antibodies. Cross-reactivity between these two antibodies was not detectable by ELISA competitive assay. Heparin-dependent anti-PF4 antibodies were associated with thrombocytopenia and IgM aCLs (P = 0.007 for both comparisons), while heparin-independent anti-PF4 antibody levels were correlated with SLE disease activity index (P = 0.0005). None of the SLE patients with anti-PF4 antibodies had previous heparin exposure.

CONCLUSION

PF4 is an autoimmune target in SLE patients. Heparin-dependent and -independent anti-PF4 autoantibodies may be involved in different aspects of pathophysiology of SLE.

The AVAIL ME study: a multinational survey of VTE risk and prophylaxis

Venous thromboembolism (VTE) is a major public health issue that is frequently underestimated. The primary objective of this multinational survey was to identify patients at risk for VTE, and to define the rate of patients receiving appropriate prophylaxis in the Middle Eastern region. Standardized case report forms were filled by trained individuals on one predefined day in selected hospitals. Data were then entered and analyzed by independent biostatisticians. Risk was categorized according to American College of Chest Physicians (ACCP) guidelines, 2004. Logistic regressions were carried out to assess factors that determined VTE prophylaxis. 845 (37%) medical and 1421 (63%) surgical patients were eligible for the study. Patients were at low (4.2%), moderate (51.7%), high (9%) and very high risk (35.2%) for VTE. Any VTE prevention was given in 17.9, 41.7, 60.6 and 66.9% of respective risk categories, while ACCP guidelines were applied in 86.3, 41.1, 48.3 and 24.5% of these categories. Surgical patient type, immobility on admission, and contraceptive use were the most important drivers of VTE prophylaxis in those who were eligible to it (OR ≥ 2). Surgical patient type, immobility during hospitalization, existence of a VTE protocol and chronic heart failure were the most important drivers for VTE prophylaxis application in patients who were not eligible for it (OR ≥ 3). A concordance κ value of 0.16 was found between eligibility for VTE prophylaxis on one hand and its application in practice (P < 0.001). Risk factors for VTE and eligibility for VTE prophylaxis are common, but VTE prophylaxis and guidelines application are low.

The prevention and treatment of venous thromboembolism with LMWHs and new anticoagulants

As the risk factors for thrombosis are becoming better understood, so is the need for anticoagulation. The inherent difficulties with warfarin are such that a low-molecular-weight heparin (LMWH) is often the key therapeutic. However, there are several different species of LMWH available to the practitioner, which leads to the need for an objective guide. New agents are coming onto the marketplace, and these may supersede both warfarin and the heparins. The current report will review the biochemistry and pharmacology of different LWMHs and identify which are more suitable for the different presentations of venous thromboembolism. It will conclude with a brief synopsis of new agents which may supersede warfarin and heparin.

Review: Recent Advances in Argatroban-Warfarin Transition in Patients With Heparin-induced Thrombocytopenia

Heparin-induced thrombocytopenia is a devastating, life-threatening, immune-mediated complication of therapy with unfractionated heparin, and less frequently, with low molecular weight heparin. Direct thrombin inhibitors are now standard therapy for the prevention of thrombosis in heparin-induced thrombocytopenia. Argatroban, a small synthetic molecule that inhibits thrombin at its active site, is increasingly used as the direct thrombin inhibitors of choice. Transition to longer term oral anticoagulation needs to be instituted after the platelet count has risen, because of the persistent risk of thrombosis. Although guidelines available in the literature outline the management of heparin-induced thrombocytopenia, they are not presented in a concise and comprehensive manner easily followed by physicians. This article reviews current recommendations, relevant studies, and clinical management trials carried out on patients with heparin-induced thrombocytopenia and provides updated, detailed guidelines for treatment of heparin-induced thrombocytopenia with emphasis on a key part of the management, the argatroban—warfarin transition.

Heparin-induced thrombocytopenia in intensive care patients

OBJECTIVE

To summarize new information on frequency of heparin-induced thrombocytopenia (HIT) in patients treated in intensive care units (ICU), developments in the interpretation of assays for detecting anti-PF4/heparin antibodies, and treatment of HIT patients.

STUDY SELECTION

All data on the frequency of laboratory-confirmed HIT in ICU patients were included; for laboratory testing of HIT and treatment of patients, this review focuses on recent data that became available in 2005 and 2006.

DATA EXTRACTION AND SYNTHESIS

HIT is a potentially life-threatening adverse effect of heparin treatment caused by platelet-activating antibodies of immunoglobulin G class usually recognizing complexes of platelet factor 4 and heparin. HIT is more often caused by unfractionated heparin than low-molecular-weight heparin and is more common in postsurgical than in medical patients. In the ICU setting, HIT is uncommon (0.3-0.5%), whereas thrombocytopenia from other causes is very common (30-50%). For laboratory diagnosis of HIT antibodies, both antigen assays and functional (platelet activation) assays are available. Both tests are very sensitive (high negative predictive value) but specificity is problematic, especially for the antigen assays, which also detect nonpathogenic immunoglobulin M and immunoglobulin A class antibodies. Detection of immunoglobulin M or immunoglobulin A antibodies could potentially lead to adverse events such as bleeding if a false diagnosis of HIT prompts replacement of heparin by an alternative anticoagulant. For treatment of HIT, three alternative anticoagulants are approved: the direct thrombin inhibitors, lepirudin and argatroban, and the heparinoid, danaparoid (not approved in the United States). Recent data indicate that the approved dosing regimens of the direct thrombin inhibitors are too high, especially in ICU patients.

CONCLUSIONS

HIT affects <1% of ICU patients even though 30-50% develop thrombocytopenia. The choice of the optimal alternative anticoagulant depends on patient characteristics. Many ICU patients require lower doses of alternative anticoagulant than those recommended by the manufacturer.

Treatment of coumarin-associated coagulopathy: a systematic review and proposed treatment algorithms

BACKGROUND

An excessive anticoagulant effect because of coumarins is frequently encountered.

OBJECTIVE

To review available literature on the management of warfarin-associated coagulopathy and to propose evidence-based treatment algorithms.

METHODS

Data sources were Medline and Embase. Papers published between 1966 and December 2005 describing randomized trials or prospective cohort studies evaluating treatments for coumarin-associated coagulopathy were abstracted.

RESULTS

Low dose oral vitamin K rapidly and reliably returns the international normalized ratio (INR) to the usual therapeutic range in non-bleeding patients. Simple withholding of acenocumarol results in rapid correction of its anticoagulant effect. The impact of oral vitamin K on phenprocumon-associated coagulopathy cannot be determined from available literature. Intravenous vitamin K and coagulation factors should be given to patients with major or life-threatening hemorrhage. The optimal dose and type of coagulation factor is not known.

CONCLUSIONS

Vitamin K therapy is an effective treatment for INR prolongation in patients with coumarin-associated coagulopathy; coagulation factor replacement is required, in addition, in patients with major bleeding or with indication for immediate correction of their INR. Clinical trials powered to detect differences in rates of bleeding and thrombosis are now required to determine if vitamin K reduces the risk of bleeding without causing thrombosis in non-bleeding patients with prolonged INR.

Use of bivalirudin, a direct thrombin inhibitor, and its reversal with modified ultrafiltration during heart transplantation in a patient with heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an increasingly common clinical finding in patients presenting for cardiac transplantation. Bivalrudin, a reversible direct thrombin inhibitor, is a molecular anti-coagulant with short half-life and the potential for removal by intraoperative hemofiltration. Herein we describe the dosing and intraoperative management of bivalrudin anti-coagulation in a patient undergoing urgent cardiac transplantation in the context of recently diagnosed HIT.

Recognition, treatment, and prevention of heparin-induced thrombocytopenia: Review and update

Heparin-induced thrombocytopenia (HIT) is one of the most important life- and limb-threatening adverse drug events encountered by physicians. Serious sequelae associated with HIT can be avoided with early recognition and appropriate treatment. This review examines the recommendations published in 2004 by the American College of Chest Physicians on the recognition, treatment, and prevention of HIT together with more recent data, especially regarding treatment with direct thrombin inhibitors.

Heparin-induced thrombocytopenia in neonates

Heparin-induced thrombocytopenia (HIT), an immune-mediated response to heparin administration, has been recognized in adults for some time, but only recently recognized in neonates and children. HIT Type I is a mild, self-limiting condition. HIT type II is a severe immune reaction to heparin that leads to thrombocytopenia and often thromboembolic complications. The incidence of HIT Type II is 2-5 percent in adults on heparin products and may be as high in neonates and children. The mortality rate from HIT in adults is 7-30 percent and is unknown but potentially high in newborns as well. The cardinal sign of HIT is a drop in platelet count by 50 percent or platelet counts below 70,000-100,000/mm3. This drop usually occurs five to ten days after the first exposure to heparin. Treatment is immediate cessation of all heparin therapy and initiation of alternative anticoagulants, especially the direct thrombin inhibitors lepirudin and argatroban. This article reviews the literature on HIT and presents a case of neonatal HIT following heart surgery.

Heparin-induced thrombocytopenia with acute aortic and renal thrombosis in a patient treated with low-molecular-weight heparin

Heparin-induced thrombocytopenia is a rare but serious complication of heparin therapy. Most of cases are related to unfractionated heparin, but a few are due to low molecular weight heparin sometimes associated with unfractionated heparin. A patient with pulmonary contusions after chest injury developed a catheter related subclavian vein thrombosis on day 16. He was treated by increasing doses of low molecular weight heparin. Aortic and renal thromboses occurred on day 21. Surgical thrombectomy, performed after starting alternative anticoagulation treatment led to complete arterial recovery. In case of suspicion of heparin-induced thrombocytopenia, with unfractionated or low-molecular-weight heparin, heparin treatment must be discontinued before the results of biological tests become available. Arterial and/or venous thrombosis is a serious complication of heparin-induced thrombocytopenia. The treatment has two aims: first, to restore arterial patency by clot removal by thrombectomy, bypass or thrombolysis, and second, to avoid new thrombosis formation by substitutive anticoagulation treatment: danaparoid may have cross-reaction with heparin, or lepirudin has anaphylactic risks and needs biological follow-up. Heparin-induced thrombocytopenia and thrombosis can be complicated by death or disabilities such as amputations, stroke, renal or bowel infarction. Once HIT has been diagnosed heparin should never be given again, but if cardiopulmonary bypass is required, it might be reintroduced during operation only if serum antibodies have disappeared.

Heparin-induced thrombocytopenia (HIT) in pediatric cardiac surgery: an emerging cause of morbidity and mortality

Unfractionated heparin (UFH) is immunogenic, and heparin-dependent antibodies can be demonstrated 5 to 10 days postoperatively in 25% to 50% of adult postcardiac surgery patients. In a minority of these cases (1% to 3% if UFH is continued longer than 1 week) these antibodies strongly activate platelets, causing thrombocytopenia and massive thrombin generation (HIT syndrome). HIT is an intensely procoagulant disorder, and in adult cardiac surgery patients carries both significant thrombotic morbidity (38% to 81%) and mortality (28%). Despite the ubiquitous use of UFH in pediatric intensive care units, and the repeated and sustained exposures to UFH in neonates and young children with congenital heart disease, HIT has been infrequently recognized and reported in this patient population. However, emerging experience at our institution and elsewhere suggests that HIT is significantly under-recognized in pediatric congenital heart disease patients, and may in fact have an incidence and associated thrombotic morbidity and mortality in this patient group comparable to that seen in adult cardiac surgery patients. This article will review HIT in pediatric patients with congenital heart disease and emphasize the special challenges posed in clinical recognition, laboratory diagnosis, and treatment of HIT in this patient group. We will also outline our experience with the off-label use of the direct thrombin inhibitor, argatroban, in pediatric patients with HIT.