Management of patients with heparin-induced thrombocytopenia: focus on recombinant hirudin

Thrombin inhibitors from different animals

Venous and arterial thromboembolic diseases are still the most frequent causes of death and disability in high-income countries. Clinical anticoagulants are inhibitors of enzymes involved in the coagulation pathway, such as thrombin and factor X(a). Thrombin is a key enzyme of blood coagulation system, activating the platelets, converting the fibrinogen to the fibrin net, and amplifying its self-generation by the activation of factors V, VIII, and XI. Thrombin has long been a target for the development of oral anticoagulants. Furthermore, selective inhibitors of thrombin represent a new class of antithrombotic agents. For these reasons, a number of specific thrombin inhibitors are under evaluation for possible use as antithrombotic drugs. This paper summarizes old and new interests of specific thrombin inhibitors described in different animals.

Evaluation and management of thrombocytopenia and suspected heparin-induced thrombocytopenia in hospitalized patients: The Complications After Thrombocytopenia Caused by Heparin (CATCH) registry

BACKGROUND

Thrombocytopenia and heparin-induced thrombocytopenia (HIT) are potentially devastating paradoxical side effects of heparin therapy. We explored the evaluation, management, and clinical consequences of thrombocytopenia occurring during heparin therapy in diverse clinical settings.

METHODS

CATCH was a prospective observational study that enrolled 3,536 patients in 48 US hospitals. Data were collected on 3 strata: patients receiving any form of heparin for > or =96 hours (n = 2,420); cardiac care unit (CCU) patients treated with heparin who developed thrombocytopenia (n = 1,090); patients who had an HIT assay performed (n = 449).

RESULTS

Thrombocytopenia occurred in 36.4% of patients in the prolonged heparin stratum and was associated with an increased risk of death or thromboembolic complication (OR 1.5, 95% CI 1.2-1.9). Among a subset of patients whose clinical presentation suggested they were at high risk for HIT, suspicion for HIT was uncommon (prolonged heparin stratum 19.8%, CCU stratum 37.6%) and often did not arise until > or =1 day after patients developed thrombocytopenia. Often patients were not evaluated for HIT until after they had had a thromboembolic complication (prolonged heparin stratum 43.8%, CCU stratum 61%). Even after HIT was suspected, patients often continued to receive heparin. Direct thrombin inhibitor use was infrequent (prolonged heparin stratum 29.4%, CCU stratum 35.6%). Among the few patients who underwent evaluation, HIT was confirmed in 46.7% of the prolonged heparin stratum and 31.4% of the CCU stratum.

CONCLUSIONS

Thrombocytopenia is common among patients receiving heparin, and it is associated with substantial risk for catastrophic complications. Despite the high risk for HIT in this population, recognition, evaluation, and appropriate treatment are infrequent and delayed.

Argatroban in extracorporeal membrane oxygenation

The objective of this study was to assess the required dose and anticoagulatory effect of argatroban (Mitsubishi, Pharma Deutschland GmbH, Düsseldorf, Germany), a direct thrombin inhibitor approved for anticoagulation in patients with heparin-induced thrombocytopenia (HIT) undergoing extracorporeal membrane oxygenation (ECMO). Nine consecutive patients undergoing ECMO for severe acute respiratory distress syndrome (ARDS) and presenting with suspected HIT were treated with a continuous argatroban infusion. Coagulation variables were measured and dose adjustments of argatroban were performed to target for an activated partial thromboplastin time (aPTT) of 50 to 60 s. The first patient received argatroban 2 microg/kg/min as recommended by the manufacturer. This resulted in excessive anticoagulation and severe bleeding. The consecutive eight patients received a 10-fold lower dose (0.2 microg/kg/min). This dose sufficiently increased aPTT time from 46 +/- 6 s to 65 +/- 14 s (P < 0.001) and thrombin time from 18 +/- 8 s to 45 +/- 11 s (P = 0.001). The maintenance dose averaged 0.15 microg/kg/min. Duration of argatroban infusion for ECMO averaged 4 +/- 1 days and no oxygenator or extracorporeal system clotting was observed. In three of nine patients (33%), HIT was confirmed. Argatroban is a feasible and effective anticoagulant for patients with suspected HIT undergoing ECMO. However, a dose 10-fold lower than that recommended by the manufacturer is sufficient to achieve appropriate anticoagulation in critically ill patients undergoing ECMO.

Spontaneous superior sagittal sinus thrombosis secondary to type II heparin-induced thrombocytopenia presenting as an acute subarachnoid hemorrhage

Cerebral sinus thrombosis is a rare cause of spontaneous subarachnoid hemorrhage. The development of cerebral sinus thrombosis as a complication of heparin-induced thrombocytopenia is even rarer. In this paper, we present a 59-year-old patient admitted to our service with cerebral sinus thrombosis secondary to type II heparin-induced thrombocytopenia. We also review the literature in regard to the incidence, pathophysiology and management of this rare clinicopathological entity.

Argatroban anticoagulation in critically ill patients

BACKGROUND

Despite long-term use of argatroban in clinical practice, no dosing recommendations exist for critically ill patients with multiple organ dysfunction (MODS) and suspected or proven heparin-induced thrombocytopenia (HIT).

OBJECTIVE

To determine the suitability of argatroban use in critically ill patients with MODS and HIT.

METHODS

We conducted prospective observation of 24 consecutive patients with suspected HIT who were being anticoagulated with argatroban (target activated partial thromboplastin time [aPTT] 1.5-2 times normal or 50-60 sec) using 2 microg/kg/min in the first 5 patients and 0.2 microg/kg/min in the subsequent 19 patients.

RESULTS

Infusion of argatroban 2 microg/kg/min over 4 hours caused bleeding complications in 3 patients as aPTT increased from 51 +/- 18 to 86 +/- 34 seconds (p = 0.02), prothrombin time (PT) decreased from 76 +/- 27% to 33 +/- 12% of normal reference values, and international normalized ratio (INR) increased from 1.4 +/- 0.4 to 2.5 +/- 0.9 (p = 0.007). Infusion of argatroban 0.2 microg/kg/min over 4 hours provided sufficient anticoagulation without bleeding complications. The aPTT in this population increased from 44 +/- 9 to 59 +/- 13 seconds (p < 0.001), and PT and INR remained unchanged (76 +/- 22% and 69 +/- 23% of normal reference values, 1.3 +/- 0.3 and after 1.3 +/- 0.3, respectively [p = 0.4]). Coagulation variables (aPTT, PT, INR) were significantly different between both dosing regimens after 4 hours of infusion (p = 0.042 and p = 0.003, respectively). The maintenance dose for target aPTT averaged 0.22 +/- 0.15 microg/kg/min in both groups.

CONCLUSIONS

In critically ill patients with MODS, argatroban 2 microg/kg/min, as recommended by the manufacturer, resulted in extensive anticoagulation. A tenfold lower starting dose is sufficient and safe for effective anticoagulation in this specific patient population.

Identification, Diagnosis and Treatment of Heparin-induced Thrombocytopenia and Thrombosis: A Registry of Prolonged Heparin Use and Thrombocytopenia among Hospitalized Patients with and without Cardiovascular Disease

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is estimated to occur in 1-5% of all patients receiving heparin, and 25-50% of such cases develop heparin-induced thrombocytopenia with thrombosis (HITT) A conservative estimate based only on cardiovascular patients suggests that in the United States approximately 100,000 patients develop thrombocytopenia, and 25-50,000 develop HITT annually. Both HIT and HITT are associated with high morbidity and mortality and represent substantial worldwide public health concerns.

REGISTRY DESIGN

The objective of the Complication After Thrombocytopenia Caused by Heparin (CATCH) Registry is to identify the incidence of HIT and/or HITT in patients treated with systemic heparin (unfractionated or low molecular weight heparin) in contemporary practice. Additional objectives include to: (1) provide a comprehensive database of patients with suspected HIT or HITT, (2) monitor and define clinical events, including thrombocytopenia, thrombosis, and mortality among patients treated with prolonged (> 96 hours) heparin, (3) describe the incidence and outcomes of HIT and HITT in patients who are treated with heparin and who develop thrombocytopenia in the Coronary Care Unit setting, and (4) document and characterize current diagnostic and therapeutic strategies of suspected HIT. The unblinded registry will record approximately 5,000 patients at 60-80 US hospitals with either prolonged systemic heparin administration or thrombocytopenia and those with suspected HIT or HITT. Enrollment began in the first quarter 2003 and was completed at the end of 2004.

IMPLICATIONS

The registry will provide valuable insights to the incidence and consequences of HIT and HITT that will enable improvements in diagnosis and treatment.

Argatroban dosing in intensive care patients with acute renal failure and liver dysfunction

STUDY OBJECTIVE

To demonstrate dosing adjustment difficulties of argatroban encountered in critically ill patients with acute liver dysfunction who are receiving continuous renal replacement therapy.

DESIGN

Case description.

SETTING

Medical and surgical intensive care unit in a tertiary care, university-affiliated hospital.

PATIENTS

Four consecutive patients with proven heparin-induced thrombocytopenia (HIT), acute renal failure requiring continuous renal replacement therapy, and various levels of transient hepatic impairment.

INTERVENTION

Argatroban, a direct synthetic thrombin inhibitor, was given continuously and stabilized at 0.125-0.85 microg/kg/minute to attain an activated partial thromboplastin time (aPTT) 1.5-2.5 times the normal value for periods of 6-36 days.

MEASUREMENTS AND RESULTS

Argatroban was started at the usual dosage of 2 microg/kg/minute, which resulted in significant overshooting of the aPTT and international normalized ratio (INR). No patient experienced bleeding or thrombotic complications. All patients were stabilized with reduced dosages such as those recommended for patients with chronic hepatic impairment.

CONCLUSION

We recommend argatroban therapy for intensive care patients with HIT, especially those with renal failure. However, in all patients with suspected liver dysfunction due to recent elevation of liver transaminase levels and combined renal failure, a decrease in the initial dosage and careful titration of the infusion are mandatory. Further studies are needed to fully elucidate argatroban elimination and dosage adjustments for intensive care patients.

Heparin-induced thrombocytopenia: a common complication in cardiac transplant recipients

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is an idiosyncratic complication of heparin therapy triggered by the development of immunoglobulin G (IgG) antibodies to platelet factor 4 heparin. It typically results in a 50% decrease in platelet count. Paradoxically, although bleeding is rare, there is a high risk of venous or arterial thrombotic events. Given that many patients awaiting transplantation are exposed to heparin for prolonged periods, we sought to determine the frequency of HIT and its consequences among patients before and after cardiac transplantation.

METHODS

We reviewed retrospectively the clinical, pathologic, and laboratory databases for all patients who underwent heart transplantation at our institution between January 1, 1998, and December 31, 2000. An enzyme-linked immunoabsorption assay (ELISA) that detected IgG, IgA, and IgM antibodies directed against platelet factor 4 heparin complex confirmed the diagnosis of HIT. We analyzed bleeding and thrombotic complications and determined the influence of HIT on post-transplant outcomes.

RESULTS

An assay for HIT antibody was performed before or after transplantation in 26 of 46 patients (46% of the entire cohort). In all cases, the clinical indication for testing was thrombocytopenia. Among patients screened, HIT antibody was detected in 11 patients (39%); HIT developed in 10 of 11 patients before transplantation. The mean platelet count at diagnosis was 88,000 +/- 22,000/mm(3). Heparin-induced thrombocytopenia with thrombosis syndrome developed in 5 of 11 patients (45%). Manifestations included splenic and renal infarctions, renal artery occlusion, coronary artery embolism with myocardial infarction, pulmonary embolism, and femoral and jugular venous occlusions. Alternative pre-operative anti-coagulation included lepirudin (n = 7), argatroban (n = 1), dalteparin (n = 1), and abciximab (n = 1). Two deaths occurred in the HIT-positive group; neither bleeding nor thrombosis caused either death. Actuarial 36-month survival did not differ between HIT-positive and HIT-negative cohorts (78% and 79%, respectively).

CONCLUSION

Heparin-induced thrombocytopenia is a frequent complication among patients hospitalized for heart failure who are awaiting heart transplantation. Timely HIT-antibody screening and the use of alternative forms of systemic anti-coagulation may permit successful transplantation with intermediate survival rates comparable to those of HIT-negative recipients.

Anaphylactoid reaction to enoxaparin in a patient with deep venous thrombosis

A 40-year-old Caucasian man diagnosed with right deep venous thrombosis secondary to trauma was treated with subcutaneous enoxaparin. Within minutes of administering the first dose (1 mg/kg), he experienced an apparent anaphylactoid reaction; symptoms were abdominal pruritus, severe cough, shortness of breath, anxiety, and global pruritus. Physical examination revealed an erythematous macular rash and stridor on auscultation secondary to cervical edema. No other drugs were given before the reaction occurred, and the patient's only drug therapy at home had consisted of a daily multivitamin, and acetaminophen and ibuprofen as needed. Administration of low-molecular-weight heparins such as enoxaparin is increasing, and clinicians must be aware of the potential for adverse drug events such as hypersensitivity reactions.

Heparin-induced thrombocytopenia with thrombotic sequelae: a review

Heparin-induced thrombocytopenia (HIT) occurs in 1-5% of patients treated with heparin. The pathogenesis involves the formation of antibodies to heparin-platelet factor 4 complexes, and the major clinical sequelae are thrombotic. Diagnosis is based on a combination of clinical and laboratory data. Treatment consists of stopping heparin, but, insofar as the risk of thrombosis remains high, treatment by alternative antithrombotic agents is indicated. Most clinical experience has been with danaparoid sodium and hirudin. The use of low-molecular-weight heparins (LMWH) in subsequent HIT episodes has been described, but is not recommended, especially with the introduction of new agents, such as oral thrombin inhibitors and pentasaccharides, which are hoped to reduce the use of heparins and the occurrence of HIT.

Treatment of heparin-induced thrombocytopenia

OBJECTIVE

To describe heparin-induced thrombocytopenia (HIT or HIT-2), an immune-mediated adverse reaction to heparin or low-molecular-weight heparin. Available treatment options and considerations in developing a therapy approach are discussed.

DATA SOURCES

A search of the National Library of Medicine (1992-June 2001) was done to identify pertinent literature. Additional references were reviewed from selected articles.

STUDY SELECTION

Articles related to laboratory recognition and treatment options of HIT, including the use of agents in selected clinical conditions, were reviewed and included.

CONCLUSIONS

HIT is a rare but potentially severe adverse reaction to heparin that was, until recently, poorly understood and had limited treatment options. Recent advances describing the recognition and clinical manifestations of immune-mediated HIT, including recently available antithrombotic treatment options, have dramatically changed outcomes for patients having this syndrome.