Reducing harm associated with anticoagulation: practical considerations of argatroban therapy in heparin-induced thrombocytopenia

Off-pump coronary artery bypass with heparin in a patient with a history of heparin-induced thrombocytopenia: a case report

Background

Cardiovascular surgery for patients with a history of heparin-induced thrombocytopenia (HIT) with thrombosis requires careful perioperative anticoagulation therapy. When cardiovascular surgery is required for patients having ‘remote’ HIT, such as those who had a history of HIT and platelet factor-4/heparin antibodies turned out to be negative, it is recommended that re-exposure to heparin should be limited only to the intraoperative phase. However, few case reports have described detailed strategies for perioperative anticoagulation regimens.

Case presentation

We present the case of a 76-year-old woman, presenting with unstable angina pectoris and requiring coronary artery bypass grafting. She had a history of cardiac resuscitation and percutaneous coronary intervention for unstable angina pectoris with ventricular tachycardia 7 years prior, which caused HIT with thrombosis resulting in amputation of four fingers. On admission, platelet factor-4/heparin antibodies, biomarkers for HIT were not detected; the platelet count was 18.0 × 10⁴/µl. Off-pump coronary artery bypass grafting was performed using heparin; argatroban infusion was continued until 9 h prior to the operation and restarted 3 h postoperatively, bridged with regular warfarin from 4 days to 3 months postoperatively. Platelet factor-4 /heparin antibodies were detected on postoperative day 8 without any clinical symptoms and became negative by day 91.

Conclusion

We consider this anticoagulation strategy is effective especially in countries, where bivalirudin is not available. Re-exposure to heparin in cardiovascular surgery for patients with a history of ‘remote HIT’ is reasonable, and appropriate anticoagulation is important for an uneventful postoperative course.

Early Identification of Argatroban Resistance and the Consideration of Factor VIII

BACKGROUND

Argatroban, a synthetic, parenteral, nonheparin anticoagulant, is a direct thrombin inhibitor indicated for the prophylaxis or treatment of venous thromboembolism (VTE) in patients with heparin-induced thrombocytopenia with thrombosis (HITT) and for use during percutaneous coronary intervention (PCI) in patients who have or are at risk for developing HITT. Although heparin resistance occurs in approximately 0.5% to 5% of heparin-treated patients and is well documented in the literature, argatroban resistance is limited to a single case report. The objective of this case is to describe a case in which argatroban resistance was suspected in a patient with critical limb ischemia.

METHODS

This is a case report of a single patient.

RESULTS

A 68-year-old female admitted for critical limb ischemia requiring vascular intervention was treated for presumed HITT with argatroban. A therapeutic activated partial thromboplastin time (aPTT) was not attained (31 seconds) despite multiple uptitrations of the dose to 2.8 μg/kg/min (adjusted based on the institutional protocol and with consideration of organ dysfunction). A coagulopathy workup revealed a high level of factor VIII (265%).

CONCLUSION

This case supports early assessment of factor VIII levels and the consideration of argatroban resistance and in patients who have a subtherapeutic aPTT, despite multiple increases in dose with an elevated factor VIII level. Early identification should prompt the use of an alternative anticoagulant to ensure efficacy.

Efficacy and Safety of Argatroban and Bivalirudin in Patients with Suspected Heparin-Induced Thrombocytopenia

Background: Argatroban is the only commercially available Food and Drug Administration (FDA)–approved anticoagulant for managing heparin-induced thrombocytopenia (HIT). However, bivalirudin may be an attractive alternative. Objective: To assess the efficacy and safety of argatroban and bivalirudin in patients with suspected HIT. Methods: This single-center, retrospective analysis included patients who received argatroban or bivalirudin for at least 24 hours between January 1, 2000, and June 30, 2012. The primary end point assessed anticoagulation goals, specifically time to therapeutic activated partial thromboplastin time (aPTT) goal and percentage of aPTT values within therapeutic range. Secondary end points included new thromboembolic events, bleeding, and mortality. Results: Of the 68 patients who met the inclusion criteria, 48 received argatroban and 20 received bivalirudin. Baseline characteristics were similar between the 2 groups except for age, percentage of patients with liver dysfunction, aPTT immediately prior to drug initiation, and the serotonin release assay results. The mean ± SD times to reach therapeutic aPTT goal for argatroban and bivalirudin were 14 ± 15 and 7 ± 8 hours, respectively ( P = 0.024). The mean ± SD percentage of aPTT values within therapeutic aPTT goal was 69% ± 23% for argatroban and 84% ± 18% for bivalirudin ( P = 0.005). Rates of thromboembolic events were similar between the 2 groups, as were the rates of bleeding and all-cause mortality. Conclusions: Bivalirudin appears to reach therapeutic aPTT goal faster with more aPTT values within therapeutic aPTT goal while achieving similar clinical outcomes. Although not approved by the FDA for managing HIT, bivalirudin may be an attractive alternative anticoagulant.

Intravenous warfarin and heparin-induced thrombocytopenia: making the diagnosis, management, modern monitoring, and multidisciplinary care

OBJECTIVE

To describe the diagnosis, management, and monitoring of a patient with heparin-induced thrombocytopenia (HIT) with thrombosis and simultaneous bleeding risk treated with argatroban and transitioned to intravenous (IV) warfarin secondary to the inability to administer enteral medications.

CASE SUMMARY

A 71-year-old man was admitted to the surgical intensive care unit (SICU) following aortic valve repair, coronary artery bypass, and ascending aortic aneurysm repair. On postoperative day 9, he was found to have a pulmonary embolism, and therapeutic heparin was started. The following day, his platelet count was found to have dropped precipitously. HIT was diagnosed, heparin was discontinued, and argatroban was initiated. On postoperative day 22, anticoagulation was discontinued because of massive gastrointestinal bleeding. On postoperative day 35, multiple venous thromboses were found, and argatroban was restarted. The patient developed a high-output enterocutaneous fistula, eliminating the option of enteral route of medication administration. The multidisciplinary SICU team transitioned the patient from argatroban to IV warfarin for long-term anticoagulation. The international normalized ratio was monitored and remained therapeutic throughout his admission without further thrombotic complications.

DISCUSSION

HIT occurs when antibodies develop to heparin-platelet factor 4 complexes, causing simultaneous hypercoagulability and thrombocytopenia. It is diagnosed based on both clinical factors and laboratory testing. Treatment includes discontinuation of all forms of heparin; initiation of a nonheparin anticoagulant, such as argatroban; and transition to warfarin.

CONCLUSIONS

IV warfarin is a therapeutic option for patients with malabsorption issues. A multidisciplinary team in an intensive care setting optimizes cost-effective, patient-centered, and safe care.

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.

Diagnosis and management of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a prothrombotic disorder caused by antibodies to platelet factor 4/heparin (PF4/H) complexes. It presents with declining platelet counts 5 to 14 days after heparin administration and results in a predisposition to arterial and venous thrombosis. Establishing the diagnosis of HIT can be extremely challenging. It is essential to conduct a thorough clinical evaluation in addition to laboratory testing to confirm the presence of PF4/H antibodies. Multiple clinical algorithms have been developed to aid the clinician in predicting the likelihood of HIT. Once HIT is recognized, an alternative anticoagulant should be initiated to prevent further complications.

Coagulation management in patients undergoing mechanical circulatory support

The incidence of bleeding and thrombo-embolic complications in patients undergoing mechanical circulatory support therapy remains high and is associated with bad outcomes and increased costs. The need for anticoagulation and anti-platelet therapy varies widely between different pulsatile and non-pulsatile ventricular-assist devices (VADs) and extracorporeal membrane oxygenation (ECMO) systems. Therefore, a unique anticoagulation protocol cannot be recommended. Notably, most thrombo-embolic complications occur despite values of conventional coagulation tests being within the targeted range. This is due to the fact that conventional coagulation tests such as international normalised ratio (INR), activated partial thromboplastin time (aPTT) and platelet count cannot detect hyper- or hypofibrinolysis, hypercoagulability due to tissue factor expression on circulating cells or increased clot firmness, and platelet aggregation as well as response to anti-platelet drugs. By contrast, point-of-care (POC) whole blood viscoelastic tests (thromboelastometry/-graphy) and platelet function tests (impedance or turbidimetric aggregometry) reflect in detail the haemostatic status of patients undergoing mechanical circulatory support therapy and the efficacy of their anticoagulation and antiaggregation therapy. Therefore, monitoring of haemostasis using POC thromboelastometry/-graphy and platelet function analysis is recommended during mechanical circulatory support therapy to reduce the risk of bleeding and thrombo-embolic complications. Notably, these haemostatic tests should be performed repeatedly during mechanical circulatory support therapy since thrombin generation, clot firmness and platelet response may change significantly over time with a high inter- and intra-individual variability. Furthermore, coagulation management can be hampered in non-pulsatile VADs by acquired von Willebrand syndrome, and in general by acquired factor XIII deficiency as well as by heparin-induced thrombocytopenia. In addition, POC testing can be used in bleeding patients to guide calculated goal-directed therapy with allogeneic blood products, haemostatic drugs and coagulation factor concentrates to optimise the haemostasis and to minimise transfusion requirements, transfusion-associated adverse events and to avoid thrombo-embolic complications, as well. However, coagulation management in patients undergoing mechanical circulatory support therapy is somehow like navigating between Scylla and Charybdis, and development of protocols based on POC testing seems to be beneficial.

Challenges encountered with argatroban anticoagulation during cardiopulmonary bypass

Use of argatroban as an alternative to heparin during cardiopulmonary bypass (CPB) in patients with heparin-induced thrombocytopenia has gained some attention in the past two decades. Dosing of argatroban during CPB is complex due to lack of complete understanding of its pharmacokinetic profile and the various elements during CPB that may alter its plasma levels. We report a case where the challenges in dosing argatroban led to failure to provide adequate anticoagulation during CPB, as evidenced by clot formation in the oxygenator, and extensive bleeding in the postoperative period.

Treatment and prevention of heparin-induced thrombocytopenia: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is an antibody-mediated adverse drug reaction that can lead to devastating thromboembolic complications, including pulmonary embolism, ischemic limb necrosis necessitating limb amputation, acute myocardial infarction, and stroke.

METHODS

The methods of this guideline follow 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 in this supplement.

RESULTS

Among the key recommendations for this article are the following: For patients receiving heparin in whom clinicians consider the risk of HIT to be > 1%, we suggest that platelet count monitoring be performed every 2 or 3 days from day 4 to day 14 (or until heparin is stopped, whichever occurs first) (Grade 2C). For patients receiving heparin in whom clinicians consider the risk of HIT to be < 1%, we suggest that platelet counts not be monitored (Grade 2C). In patients with HIT with thrombosis (HITT) or isolated HIT who have normal renal function, we suggest the use of argatroban or lepirudin or danaparoid over other nonheparin anticoagulants (Grade 2C). In patients with HITT and renal insufficiency, we suggest the use of argatroban over other nonheparin anticoagulants (Grade 2C). In patients with acute HIT or subacute HIT who require urgent cardiac surgery, we suggest the use of bivalirudin over other nonheparin anticoagulants or heparin plus antiplatelet agents (Grade 2C).

CONCLUSIONS

Further studies evaluating the role of fondaparinux and the new oral anticoagulants in the treatment of HIT are needed.

Adverse effects of heparin

All the adverse effects of heparins are related to their wide variety of biological activities, with bleeding being the most important safety issue, resulting directly from the potency of heparin as an anticoagulant. However, it is hard to define the bleeding risk, since it depends on numerous parameters including the indication, dosage, method, and duration of heparin application, the clinical study design and definition of bleeding as well as patient characteristics and determinants of bleeding such as type of surgery and co-medication. Nonbleeding complications of heparins are caused by binding of heparin molecules to proteins other than antithrombin and to cells, which is generally more pronounced with unfractionated heparin than with low-molecular-weight heparins. Accordingly, heparin-induced thrombocytopenia, the most severe nonbleeding adverse reaction, occurs about 10 times less with low-molecular-weight heparins than with unfractionated heparin. Frequent and therefore important adverse reactions of heparins are skin lesions resulting from delayed-type hypersensitivity reactions. All the other undesirable effects are discussed as well, but they are mostly clinically irrelevant.

HIT heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a significant complication of heparin therapy. The NP is in a pivotal position to identify patients at greater risk for HIT and promptly diagnose and intervene to prevent serious thrombotic complications.

Pharmacology of argatroban

Argatroban is a synthetic, small-molecule direct thrombin inhibitor that is approved in the USA, the EU and Japan for prophylaxis or treatment of thrombosis in patients with heparin-induced thrombocytopenia (HIT), and for anticoagulation of HIT patients undergoing PCI. Argatroban binds reversibly to, and inhibits both soluble and clot-bound thrombin. Argatroban does not generate antibodies, is not susceptible to degradation by proteases and is cleared hepatically. It has a predictable anticoagulant effect and there is a good correlation between dose, plasma concentration and pharmacodynamic effect. Initial clinical studies suggest that further investigations to establish the use of argatroban in ischemic stroke, acute coronary syndrome, hemodialysis, blood oxygenation, off-pump cardiac surgery and other clinical indications are warranted.

Monitoring of the anticoagulants argatroban and lepirudin: a comparison of laboratory methods

Monitoring of direct inhibitors of thrombin (DTI) is critical for their safe and effective use as anticoagulants. We examined samples containing several concentrations of argatroban or lepirudin in reconstituted standard human plasma and plasma from medical outpatients and intensive care patients. Prothrombin time (PT), activated partial thromboplastin time (aPTT), and thrombin time (TT) were determined using automated analyzers. Ecarin clotting time (ECT) was measured using a 10 IU/mL dilution of ecarin in 0.05 mol/L CaCl(2). Calibration curves were approximately linear for TT and ECT in samples containing argatroban and lepirudin, respectively. Activated partial thromboplastin curves reached a plateau at DTI concentrations ≥2 µg/mL, suggesting that the aPTT may not reliably detect overdosing. Prothrombin time increased exponentially. A broad range of clotting times was seen in patient samples with all tests suggesting that individual morbidity and therapies may strongly influence test results and may lead to underestimation of DTI doses.

Adverse drug events associated with disorders of coagulation

Disorders of coagulation are common adverse drug events encountered in critically ill patients and present a serious concern for intensive care unit (ICU) clinicians. Dosing strategies for medications used in the ICU are typically developed for use in noncritically ill patients and, therefore, do not account for the altered pharmacokinetic and pharmacodynamic properties encountered in the critically ill as well as the increased potential for drug-drug interactions, given the far greater number of medications ordered. This substantially increases the risk for coagulation-related adverse reactions, such as a bleeding or prothrombotic events. Although many medications used in the ICU have the potential to cause coagulation disorders, the exact incidence will vary based on the specific medication, dose, concomitant drug therapy, ICU setting, and patient-specific comorbidities. Clinicians must strongly consider these factors when evaluating the risk/benefit ratio for a particular therapy. This review surveys recent literature documenting the risk for adverse drug reactions specific to bleeding and/or clotting with commonly used medications in the ICU.

Argatroban: a review of its use in the management of heparin-induced thrombocytopenia

Argatroban, a highly selective direct thrombin inhibitor, is indicated for use as an anticoagulant for the treatment and prophylaxis of thrombosis in patients with heparin-induced thrombocytopenia (HIT), and in patients undergoing percutaneous coronary intervention (PCI) who have, or are at risk for, HIT. Intravenous argatroban improved clinical outcomes and was generally well tolerated in adults with HIT or HIT with thrombosis syndrome (HITTS). In two pivotal, open-label, historically controlled studies in adults with HIT, the incidence of the primary composite endpoint (all-cause death, all-cause amputation, or new thrombosis) was significantly lower in argatroban recipients than in historical controls, and more argatroban recipients than historical controls stayed event-free during the study according to a Kaplan-Meier analysis. In adults with HITTS in these trials, although the incidence of the primary composite endpoint did not differ significantly between argatroban recipients and historical controls, a Kaplan-Meier analysis showed that more patients receiving argatroban than historical controls remained event-free during the study. Major and minor bleeding rates in argatroban recipients were generally similar to those in historical controls in these studies. Argatroban was also an effective anticoagulant in patients with HIT undergoing PCI in three small, uncontrolled trials, pooled data from which showed that most (>or=95%) patients achieved a satisfactory outcome of the PCI procedure and adequate anticoagulation (coprimary endpoints). It was generally well tolerated in these patients, with the incidence of major bleeding being <or=1.1%. The efficacy and safety of argatroban in pediatric patients has not been established. However, a small uncontrolled, preliminary study suggests that it may be useful in seriously ill pediatric patients requiring nonheparin anticoagulation.