Argatroban for prevention and treatment of thromboembolism in heparin-induced thrombocytopenia

Magnetic nanoparticles immobilized thrombin ligand fishing to screen thrombin inhibitors in natural products

In this study, thrombin was immobilized with magnetic particles modified by glutaraldehyde. The changes in secondary structures of immobilized enzyme revealed an increment in conformational rigidity and stability, which can be reflected in temperature and pH stability as well as the tolerance of organic reagents. The optimal reutilization times of magnetic particle immobilized thrombin were 7 times, and the half-life of enzyme activity preserved at room temperature was 5 days, which was 2.5 times higher than that of free enzyme. Ligusticum chuanxiong and Anemarrhenae Rhizoma with high enzyme inhibitory activity were selected for primary screening, and six potential inhibitors of thrombin were identified by HPLC/MS. The results showed that three compounds in Anemarrhenae Rhizoma had better predictive thrombin inhibitory activity. Through the in vitro thrombin activity inhibition experiment, it was also verified that mangiferin and neo-mangiferin had an ideal thrombin activity inhibition effect, which was consistent with the results of molecular docking.

Anticoagulation Management during Extracorporeal Membrane Oxygenation-A Mini-Review

Extracorporeal membrane oxygenation (ECMO) has been established as a life-saving technique for patients with the most severe forms of respiratory or cardiac failure. It can, however, be associated with severe complications. Anticoagulation therapy is required to prevent ECMO circuit thrombosis. It is, however, associated with an increased risk of hemocoagulation disorders. Thus, safe anticoagulation is a cornerstone of ECMO therapy. The most frequently used anticoagulant is unfractionated heparin, which can, however, cause significant adverse effects. Novel drugs (e.g., argatroban and bivalirudin) may be superior to heparin in the better predictability of their effects, functioning independently of antithrombin, inhibiting thrombin bound to fibrin, and eliminating heparin-induced thrombocytopenia. It is also necessary to keep in mind that hemocoagulation tests are not specific, and their results, used for setting up the dosage, can be biased by many factors. The knowledge of the advantages and disadvantages of particular drugs, limitations of particular tests, and individualization are cornerstones of prevention against critical events, such as life-threatening bleeding or acute oxygenator failure followed by life-threatening hypoxemia and hemodynamic deterioration. This paper describes the effects of anticoagulant drugs used in ECMO and their monitoring, highlighting specific conditions and factors that might influence coagulation and anticoagulation measurements.

Cost-effectiveness analysis of alternative anticoagulation in suspected heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a life-threatening complication associated with high medical costs. Factor Xa inhibitors have gradually replace approved treatment with intravenous direct thrombin inhibitors despite their off-label indication, because of easier management and favorable economic profile.Whether they are cost-effective remains unclear. We evaluated the cost-effectiveness of approved and off-label anticoagulants in patients with suspected HIT, based on census data from the largest Swiss hospital between 2015 and 2018. We constructed a decision tree model that reflects important clinical events associated with HIT. Relevant cost data were obtained from the finance department or estimated based on the Swiss-wide cost tariff. We estimated averted adverse events (AE) and incremental cost-effectiveness ratio as primary outcome parameters. We performed deterministic and probabilistic sensitivity analyses with 2000 simulations to assess the robustness of our results. In the base-case analysis, the total cost of averting one AE was 49,565 CHF for argatroban; 30,380 CHF for fondaparinux, and 30,610 CHF for rivaroxaban; after adjusting for 4Ts score: 41,152 CHF (argatroban); 27,710 CHF (fondaparinux) and 37,699 CHF (rivaroxaban). Fondaparinux and rivaroxaban were more clinically-effective than argatroban with AE averted of 0.820; 0.834 and 0.917 for argatroban, fondaparinux and rivaroxaban, respectively. Treatment with fondaparinux resulted in less cost and more AE averted, hence dominating argatroban. Results were most sensitive to AE rates and prolongation of stay. Monte Carlo simulations affirmed our base-case analysis. This is the first cost-effectiveness analysis comparing argatroban with fondaparinux and rivaroxaban using primary data. Fondaparinux and rivaroxaban resulted in more averted AE but fondaparinux had greater cost savings. Fondaparinux could be a viable alternative to argatroban.

An online dual-enzyme co-immobilized microreactor based on capillary electrophoresis for enzyme kinetics assays and screening of dual-target inhibitors against thrombin and factor Xa

In this study, an online capillary electrophoresis (CE) based dual-enzyme (thrombin and factor Xa) co-immobilized microreactor (THR-FXa IMER) was constructed for studying enzyme kinetics and screening dual-target inhibitors against THR and FXa with the aid of the polydopamine/graphene oxide (PDA/GO) coating. Based on the developed THR-FXa IMER, the Michaelis-Menten constants (K_m) of THR and FXa were calculated to be 187.26 and 48.80 μM, respectively. The inhibition constants (K_i) for two known inhibitors, argatroban and rivaroxaban, on THR and FXa were determined to be 14.73 and 0.41 nM, respectively. In addition, after 30 consecutive runs, the enzymes' activity was remained 98% of the initial immobilized activity for both THR and FXa, which shows that the constructed IMER has good stability and repeatability. Finally, the developed method was successfully applied to screen dual-target inhibitors against THR and FXa from 30 small molecular compounds. Among them, 10 compounds such as salvianolic acid C and epigallocatechin gallate (EGCG) have dual-enzyme inhibitory activity, and 2 compounds named saikosaponin A and oleuropein have single THR inhibitory activity, 5 compounds such as rosemary acid and salvianolic acid B have single FXa inhibitory activity. Finally, the molecular interactions between enzyme and potential inhibitors were further verified via the molecular docking, and a new compound with a theoretically good coagulation inhibition effect was designed by the scaffold hopping study. In summary, the developed THR-FXa IMER is a reliable method for screening THR and/or FXa inhibitors.

Anticoagulation with direct thrombin inhibitors during extracorporeal membrane oxygenation

Use of extracorporeal membrane oxygenation to support patients with critical cardiorespiratory illness is increasing. Systemic anticoagulation is an essential element in the care of extracorporeal membrane oxygenation patients. While unfractionated heparin is the most commonly used agent, unfractionated heparin is associated with several unique complications that can be catastrophic in critically ill patients, including heparin-induced thrombocytopenia and acquired antithrombin deficiency. These complications can result in thrombotic events and subtherapeutic anticoagulation. Direct thrombin inhibitors (DTIs) are emerging as alternative anticoagulants in patients supported by extracorporeal membrane oxygenation. Increasing evidence supports DTIs use as safe and effective in extracorporeal membrane oxygenation patients with and without heparin-induced thrombocytopenia. This review outlines the pharmacology, dosing strategies and available protocols, monitoring parameters, and special use considerations for all available DTIs in extracorporeal membrane oxygenation patients. The advantages and disadvantages of DTIs in extracorporeal membrane oxygenation relative to unfractionated heparin will be described.

Thrombocytopenia in Critical Care Patients

Thrombocytopenia is a common laboratory finding in the intensive care unit (ICU) patient. Because the causes can range from laboratory artifact to life-threatening processes such as thrombotic thrombocytopenic purpura (TTP), identifying the cause of thrombocytopenia is important. In the evaluation of the thrombocytopenia patient, one should incorporate all clinical clues such as why the patient is in the hospital, medications the patient is on, and other abnormal laboratory findings. One should ensure that the patient does not suffer from heparin-induced thrombocytopenia (HIT) or one of the thrombotic microangiopathies (TMs). HIT can present in any patient on heparin and requires specific testing and antithrombotic therapy. TMs cover a spectrum of disease ranging from TTP to pregnancy complications and can have a variety of presentations. Management of disseminated intravascular coagulation depends on the patient’s condition and complication. Other causes of ICU thrombocytopenia include sepsis, medication side effects, post-transfusion purpura, catastrophic anti phospholipid antibody disease, and immune thrombocytopenia.

Thrombin inhibition with dabigatran protects against high-fat diet-induced fatty liver disease in mice

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of obesity and metabolic syndrome. Robust coagulation cascade activation is common in obese patients with NAFLD. We identified a critical temporal relationship between thrombin generation and the manifestation of hepatic steatosis, inflammation, and injury in C57BL/6J mice fed a high-fat diet (HFD) for 1, 2, and 3 months. Mice fed a HFD exhibited dramatic increases in hepatocellular injury and inflammation over time. Hepatic fibrin deposition preceded an increase in serum alanine aminotransferase, and the most dramatic changes in liver histopathology occurred in conjunction with a detectable increase in plasma thrombin-antithrombin levels at 3 months. To directly determine whether thrombin activity promotes NAFLD pathogenesis, mice were fed a HFD and simultaneously treated with the direct thrombin inhibitor dabigatran etexilate for 3 months. Notably, dabigatran treatment significantly reduced hepatic fibrin deposition, hepatic inflammation, hepatocellular injury, and steatosis in mice fed a HFD. Of interest, dabigatran treatment also significantly attenuated HFD-induced body weight gain. Gene expression analysis suggested that thrombin potentially drives NAFLD pathogenesis by altering the expression of genes associated with lipid metabolism and bile acid synthesis. Collectively, the results suggest that thrombin activity is central to HFD-induced body weight gain, liver injury, and inflammation and provide the proof-of-principle evidence that pharmacological thrombin inhibition could be effective in limiting NAFLD and associated pathologies.

Anticoagulant drugs: an update

Thromboembolic disorders continue to be a major cause of morbidity and mortality, resulting in an increased need for anticoagulant therapy. In recent years, new anticoagulant drugs have been developed at a rapid pace, prompted by the recognition of many undesirable properties of currently used agents, and by a greater knowledge of the active enzymatic sites of clotting factors. Furthermore, the structure of a thrombus is better understood, so that newer drugs can inhibit thrombin or Factor Xa not only on the surface of a thrombus, as in the case of heparin, but also the fibrin-bound thrombin or Factor Xa within the thrombus. These agents are usually small molecules synthesized on the basis of their inhibition of specific active sites in the respective coagulation factors. They possess many improved characteristics, such as greater efficacy and safety, oral administration, reliable pharmacokinetics, less need for laboratory monitoring and minimal interactions with other drugs and diet. Prominent among these are lepuridin (Refludan, Pfizer), fondaparinux (Arixtra, Sanofi-Synthelabo) and ximelagatran (Exanta, Astra Zeneca). However, these new drugs are still far from fulfilling the desired objectives. Most of them possess some but not all of the needed properties. Furthermore, many do not have specific antidotes for immediate reversal of their pharmacologic actions, and all are much more costly than conventional agents. Development of newer agents with properties closer to that of the ideal drug remains a challenge.

Looking at the proteases from a simple perspective

Proteases have received enormous interest from the research and medical communities because of their significant roles in several human diseases. Some examples include the involvement of thrombin in thrombosis, HIV-1 protease in Acquired Immune Deficiency Syndrome, cruzain in Trypanosoma cruzi infection, and membrane-type 1 matrix metalloproteinase in tumor invasion and metastasis. Many efforts has been undertaken to design effective inhibitors featuring potent inhibitory activity, specificity, and metabolic stability to those proteases involved in such pathologies. Protease inhibitors usually target the active site, but some of them act by other inhibitory mechanisms. The understanding of the structure-function relationships of proteases and inhibitors has an impact on new inhibitor drugs designing. In this paper, the structures of four proteases (thrombin, HIV-protease, cruzain, and a matrix metalloproteinase) are briefly reviewed, and used as examples of the importance of proteases for the development of new treatment strategies, leading to a longer and healthier life.

Lower extremity manifestations and treatment of heparin-induced thrombocytopenia syndromes: a cohort study

Heparin-induced thrombocytopenia (HIT) and heparin-induced thrombocytopenia with thrombosis (HITT) syndromes are the result of an adverse reaction to heparin that results in a spectrum of laboratory and end-organ manifestations secondary to thrombosis of both arterial and venous small and large vessels. HITT most often manifests in the extremities as acral ischemia and necrosis, with a spectrum of severity. The lower extremity surgical patient is at risk for deep venous thrombosis, and when exposed to heparin products, is also at risk for the development of a heparin-induced thrombocytopenic syndrome. This article reports on a cohort of patients from a tertiary referral lower extremity reconstruction practice with the HIT/HITT syndromes, with an analysis of the frequency, medical characteristics, clinical settings, lower extremity manifestations, management, and outcomes of patients with HIT/HITT.).

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.

Thrombocytopenia and other hot topics

A frequent issue in the management of cancer patients with thrombosis is thrombocytopenia, whether related to chemotherapy, heparin, or other drugs. The oncologist will have multiple new anticoagulants to choose from in the future, but for now, the effect of these experimental agents on cancer thrombosis is unknown. Despite the effectiveness of anticoagulation in cancer patients, survival benefit remains controversial. Given the ongoing clinical questions and new drugs, anticoagulant therapy in patients with cancer promises to have an exciting future.

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.

Efficacy of anti-coagulant treatment with argatroban on cardioembolic stroke

Argatroban, which is a thrombin inhibitor, has an indication as a treatment in the acute phase on atherosclerotic ischemic stroke in Japan. Howeve, in cardioembolic stroke, argatroban is considered to be contraindicated with the side effect of hemorrhage, though there is no clear clinical evidence to show that argatroban increases hemorrhagic compared with heparin. The efficacy of anticoagulant treatment with argatroban on cardioembolic stroke was evaluated retrospectively in this study. We identified 3,113 patients from the Japan Standard Stroke Registry Study who had had a cardioembolic ischemic stroke. We excluded patients with the anti-platelet treatment or the combination therapy of anticoagulation. Our analyses are therefore based on a cohort of 2,529 patients who were treated either with heparin, and argatroban, or with no anti-coagulation treatment. With multivariable regression, hemorrhagic it was shown that hemorrhage was significantly reduced in heparin and argatroban treatments in the patients with mild severity. There was no significant difference in the recurrence of ischemic stroke between the treatments. Both argatroban and heparin showed dramatic improvement compared with the no treatment standard, but only heparin achieved statistical significance for mortality and change in NIHSS score (admission to discharge) in the moderate stroke subgroup [NIHSS 11-22]. Both heparin and argatroban [more so than heparin alone] have a significantly reduced mortality risk. From the present study, it is suggested that argatroban may be useful on cardioembolic stroke, increasing the improvement of recovery of stroke severity without increasing the risk of hemorrhage. Further prospective studies are awaited for evaluating better the efficacy of argatroban on cardioembolic stroke.

[Heparin-induced thrombocytopenia]

Heparins are in widespread use as anticoagulants for the prophylaxis and therapy of thromboembolisms. A dangerous side-effect is heparin-induced thrombocytopenia type II (HIT type II) with the paradox of thromboembolic venous and arterial vascular occlusions. HIT type II is an immunological disease which results in activation of platelets and plasma coagulation. The main symptom is an acute onset of thrombocytopenia with a fall in thrombocytes to less than 50% of the initial value with or without newly arising thromboembolic complications between days 5 and 14 after the start of heparin therapy. Surgery patients are more often affected by subclinical antibody formation as well as by symptomatic HIT type II than clinical patients. In this review we will discuss the difficult diagnosis and the differential diagnosis with special emphasis on postoperative intensive care patients, as well as preventive measures and management on occurrence of HIT type II and associated thrombotic complications.

Critical care clotting catastrophies

Coagulation problems are very common in intensive care patients. It is important to recognize potential problems, perform a rapid assessment, and start therapy. The author reviews general clinical and laboratory approaches to diagnosis and treatment of the bleeding patient and to correction of coagulopathies. This review outlines a set of often catastrophic coagulation problems, which may present both thrombotic and bleeding challenges. These include heparin induced thrombocytopenia, thrombotic thrombocytopenic purpura, and disseminated intravascular coagulation.

Direct thrombin inhibitors: pharmacology and clinical relevance

Although heparin has been a cornerstone of treatment for the prevention of thrombosis, it is limited by its adverse effects and unpredictable bioavailability. Direct thrombin inhibitors are a novel class of drugs that have been developed as an effective alternative mode of anticoagulation in patients who suffer from heparin-induced thrombocytopaenia, and for the management of thromboembolic disorders and acute coronary syndromes. The main disadvantages of the direct thrombin inhibitors are the lack of an antidote or readily available clinical monitoring. The mechanism of action, the properties of direct thrombin inhibitors and their potential to replace currently available anticoagulants are reviewed.

Argatroban in Post-Cardiovascular Surgery Patient with Heparin-Induced Thrombocytopenia Requiring Hemodialysis and Continuous Hemofiltration

Objective:

To describe the use of argatroban in a postoperative cardiovascular surgery patient with heparin-induced thrombocytopenia (HIT) requiring hemodialysis and continuous veno-veno hemofiltration (CVVH).

Case Summary:

A 23-year-old white woman with HIT developed acute renal failure after cardiovascular surgery. Argatroban was used as a substitute for heparin during hemodialysis and CVVH. Both activated partial thromboplastin time (aPTT) and activated clotting time (ACT) were used to guide the dosage of argatroban. The patient was successfully dialyzed without clotting of the circuit. The dosage required in our patient was much lower than the manufacturer's recommendation.

Discussion:

Argatroban is a selective thrombin inhibitor that does not cross-react with heparin-induced antibodies. It is metabolized by the liver, and dosage adjustment is recommended in patients with severe hepatic impairment. The correct dosage for patients with unstable hemodynamics is not known. Our patient had apparently normal hepatic function at the initiation of therapy, but the dosage of argatroban recommended by the manufacturer resulted in prolonged elevation of the aPTT and ACT with associated gastrointestinal bleeding. This may be due to hepatic congestion secondary to poor cardiac function and/or severe generalized edema.

Conclusions:

When argatroban is considered for therapy in place of heparin for CVVH, it needs to be used with extreme caution since the correct initial dosage in patients with mild hepatic impairment and unstable hemodynamics is unclear.

The Direct Thrombin Inhibitors: Their Role and Use for Rational Anticoagulation

Major clinical advantages are achieved when direct thrombin inhibitors are used in venous thromboembolism. These agents provide more reliable anticoagulant response patterns because they are not significantly bound to plasma proteins and few, if any, drug-drug interactions are seen. The studies to date confirm that not all direct thrombin inhibitors are the same. The new reversible, short-acting catalytic site-specific drugs provide an excellent safety profile and high degree of efficacy for the prophylaxis and treatment of venous thromboembolism and pulmonary embolic states. The availability of the oral prodrug ximelagatran allows reproducible, effective, and safe direct thrombin inhibition without the requirement for coagulation laboratory monitoring; it appears destined to be the oral anticoagulant of the future.

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.

Direct thrombin inhibitors for anticoagulation

OBJECTIVE

To review the progress in developing direct thrombin inhibitors (DTIs) for anticoagulation within the context of existing anticoagulation therapies.

DATA SOURCES

Searches of MEDLINE (1993-June 2003) were conducted.

STUDY SELECTION AND DATA EXTRACTION

We examined English-language articles, human studies, and relevant animal studies, and obtained additional citations from the references of these articles.

DATA SYNTHESIS

Because of its pivotal role in hemostasis, thrombin is a key therapeutic target in the treatment and prevention of thromboembolic disorders. Conventional anticoagulant therapies, such as warfarin, unfractionated heparin, and low-molecular-weight heparin, exert their pharmacologic action by indirect thrombin inhibition. Although these agents are effective, each has limitations, prompting a search for more effective, specific, better-tolerated, and convenient anticoagulants. The efficacy and safety of factor Xa inhibitors are being investigated. Furthermore, the development of DTIs such as recombinant hirudin (lepirudin), bivalirudin, and argatroban continues. Challenges in the development of DTIs include establishing a binding affinity for thrombin that is not associated with excessive bleeding, attaining high thrombin specificity, achieving inhibition of both unbound and clot-bound thrombin, and producing an effective, fixed-dose oral anticoagulant to improve the practicality of anticoagulation therapy. Ximelagatran, an oral DTI designed to meet these standards, is currently in Phase III clinical trials.

CONCLUSIONS

Significant progress has been made in developing DTIs. The recent emergence of orally administered DTIs may simplify the prevention and treatment of thrombosis.

Prevention of Venous Thromboembolism Following Orthopaedic Surgery

Patients undergoing total hip or total knee replacement are at high risk of venous thromboembolism (VTE), and are therefore considered to be populations well suited for the evaluation and dose optimisation of new anticoagulants. Deep vein thrombosis may lead to life-threatening pulmonary embolism, disabling morbidity in the form of the post-thrombotic syndrome, and risk of recurrent thrombotic events. There is increasing evidence that anticoagulant treatment for the prevention of VTE should be extended from 1 to at least 4 weeks after surgery. Anticoagulation with vitamin K antagonists (such as warfarin), low molecular weight heparin or unfractionated heparin effectively lowers the risk of VTE, but these anticoagulants have limitations such as the need for coagulation monitoring and subsequent dose adjustment (vitamin K antagonists), difficulty of continuing prophylaxis out of hospital because of the requirement for parenteral administration, and risk of heparin-induced thrombocytopenia. The development of new anticoagulants has been pursued with the aim of finding more effective, safer and/or more convenient therapies. Thrombin is a central regulator in the coagulation and inflammation process and several direct thrombin inhibitors (DTIs) with distinct pharmacological profiles, as well as pharmacological differences from the conventional anticoagulants, are currently in clinical use for certain indications or are under development. Clinical experience with parenterally administered DTIs has accumulated since the mid 1990s, although only desirudin (a recombinant hirudin) is currently approved for use in patients undergoing orthopaedic surgery. Two oral DTIs, ximelagatran and dabigatran etexilate, are in clinical development. Dabigatran etexilate has recently been evaluated in phase II clinical trials in patients undergoing total hip replacement. Several large phase III trials have now demonstrated the efficacy and safety of ximelagatran in the prevention of VTE following total hip or knee replacement. Ximelagatran can be used with an oral fixed dose without the need for coagulation monitoring or dose adjustment. Hence, it offers significant potential to facilitate the management of anticoagulation in or out of hospital.

Decreased argatroban clearance unaffected by hemodialysis in anasarca

OBJECTIVE

To report the case of a patient with acute renal failure and anasarca undergoing hemodialysis who demonstrated a prolonged effect of argatroban despite having no hepatic dysfunction.

CASE SUMMARY

A 54-year-old white woman with a past medical history of St. Jude's prosthetic mitral valve placement was admitted for anasarca secondary to acute renal failure of unknown origin. In order to prevent valve thrombosis and stroke, argatroban was initiated. Despite having no hepatic dysfunction, the patient demonstrated an elevated activated partial thromboplastin time (aPTT) for a prolonged period of time, requiring a significant dose reduction. This suggested reduced clearance of argatroban. Furthermore, this prolonged effect persisted despite hemodialysis.

DISCUSSION

Patients with severe renal dysfunction eliminate argatroban at a rate similar to that in healthy volunteers, while those with hepatic disease have a marked decrease in argatroban elimination. Our patient apparently had a reduction in argatroban elimination similar to that in patients with hepatic dysfunction. The few published reports regarding the use of argatroban in patients undergoing hemodialysis generally lack any information regarding variations in plasma concentrations of argatroban, the aPTT, or the type of dialyzer used. The available data, as well as our report, suggest that dosing adjustment during hemodialysis may not be necessary in patients without associated hepatic dysfunction.

CONCLUSIONS

This report suggests that in patients who are fluid-overloaded, the anticoagulant effects of argatroban may be prolonged to a degree similar to that observed in patients with hepatic disease. Our report supports the previously published data that hemodialysis has little, if any, role in increasing argatroban elimination.

Current anticoagulant therapy--unmet clinical needs

Heparin and the vitamin K antagonist warfarin have been in clinical use for more than 50 years. However, both are associated with several well-documented drawbacks that limit their use. Warfarin can be administered orally, making it the agent of choice for long-term management of thromboembolic conditions, but frequent coagulation monitoring is necessary because of its unpredictable anticoagulant effect--the result, in part, of food and drug interactions-and its narrow therapeutic window. Heparin and low-molecular-weight heparin (LMWH) can be administered parenterally only. Coagulation monitoring is also required with heparin although not with LMWH, due to reduced levels of plasma protein binding. In the last 10 years, in the quest to develop new agents that are at least as effective as those currently available, with improved safety and greater ease of use, anticoagulants that target almost every step in the coagulation pathway have been developed. These include inhibitors of the factor VIIa (FVIIa)/tissue factor complex, FIXa inhibitors, direct and antithrombin-dependent FXa inhibitors, agents that enhance the protein C anticoagulant pathway, and direct thrombin inhibitors (DTIs) that inhibit the activity of thrombin. Of the new agents, three DTIs-hirudin, bivalirudin, and argatroban-and the synthetic pentasaccharide (Arixtra) are approved for clinical use. Three other new agents-activated protein C (APC), tissue factor pathway inhibitor (TFPI), and the oral DTI ximelagatran (Exanta, AstraZeneca)-have been evaluated in Phase III studies. The mechanism of action and properties of these new anticoagulants and their potential to replace those in current use will be reviewed here.

Argatroban dosing in patients with heparin-induced thrombocytopenia

OBJECTIVE

To retrospectively evaluate clinical experiences with argatroban dosing, particularly incremental dosage adjustments, during a clinical trial of argatroban anticoagulation in heparin-induced thrombocytopenia (HIT).

METHODS

Records of 304 patients with HIT administered argatroban during a prospective study were reviewed to determine each dose, incremental dosage adjustment, and duration of therapy. Dosing information (stratified by patient initial dose) and incremental adjustments (overall, and stratified by dose from which adjustment occurred) were summarized. The relationship between median incremental adjustments and adverse outcomes, including bleeding, was investigated.

RESULTS

Two hundred seventy-one (89%) patients received initial doses of 1.9-2.1 micro g/kg/min (group B). Twenty-six (9%) patients were started at a lower dose. Group B's median (5-95th percentile) final dose was 1.6 (0.25-4.0) micro g/kg/min. During a median of 6 days of argatroban therapy, patients underwent a median of 3.0 dosage adjustments using a median and mode incremental adjustment of 0.5 micro g/kg/min (5-95th percentile, 0.1-2.0 micro g/kg/min). Fifty-two (17%) patients required no dosage adjustment. Incremental adjustments decreased with decreasing current dose (e.g., median 0.25 micro g/kg/min from doses of 0.26-0.75 micro g/kg/min). Outcomes were similar between patients with no adjustment or with median incremental adjustments of </=0.4, 0.41-0.75, or >0.75 micro g/kg/min.

CONCLUSIONS

Based on this clinical experience, together with the established linear pharmacokinetics and pharmacodynamics of argatroban, appropriate dosage increments may be proposed for argatroban-treated patients with HIT. Incremental adjustments of 0.5 micro g/kg/min are reasonable for most patients. Smaller adjustments (e.g., 0.25 micro g/kg/min) should be used when modifying lower doses, such as those recommended for use in hepatically impaired patients.

Danaparoid: a review of its use in thromboembolic and coagulation disorders

Danaparoid (danaparoid sodium) is a low molecular weight heparinoid which has undergone clinical study for use as continued anticoagulant therapy in patients with heparin-induced thrombocytopenia (HIT), for the prophylaxis and treatment of deep vein thrombosis (DVT), and for the treatment of disseminated intravascular coagulation (DIC). A nonblind study in patients with HIT has reported that complete clinical resolution is significantly more likely in patients receiving danaparoid than in patients receiving dextran 70. In addition, retrospective analyses and noncomparative data support the use of danaparoid for continued anticoagulant therapy in patients with HIT. Studies in patients undergoing hip surgery have shown that danaparoid significantly reduces the incidence of postoperative DVT compared with aspirin, warfarin, dextran 70 and heparin-dihydroergotamine, while additional data suggest no difference between danaparoid, enoxaparin and dalteparin. In patients undergoing abdominal or thoracic surgery for removal of a malignancy, danaparoid reduced the incidence of postoperative DVT compared with placebo, but showed no significant difference when compared with unfractionated heparin (UFH). Two studies have compared danaparoid with UFH in the prophylaxis of DVT following acute ischaemic stroke; twice daily danaparoid was significantly superior to UFH whereas there was no significant difference between a once-daily dosage and UFH. Danaparoid did not differ from UFH in terms of efficacy in the treatment of existing DVT. In all comparative studies examining the efficacy of danaparoid in the prophylaxis or treatment of DVT (versus warfarin, dextran 70, enoxaparin, dalteparin, aspirin, heparin-dihydroergotamine, UFH and placebo), the incidence of haemorrhagic complications did not differ between treatment groups. In patients with DIC, 61.9% of those patients receiving danaparoid experienced either disappearance or reduction of symptoms of DIC whereas 62% of those receiving UFH showed either no change or aggravation of their symptoms. There was no significant difference between treatment groups in tolerability or overall improvement of DIC.

CONCLUSIONS

Danaparoid is an effective anticoagulant agent which has undergone clinical evaluation in a wide range of disease indications. Current guidelines support the use of danaparoid in prophylaxis of DVT following ischaemic stroke, and in patients who develop HIT. Danaparoid has shown efficacy in DIC, and for DVT prophylaxis in patients undergoing hip surgery although further data are required to establish the role of danaparoid in these indications. In particular, double-blind trials comparing danaparoid with such recommended therapies as the low molecular weight heparins will provide more definitive data on the place of danaparoid in the clinical management of these conditions and ultimately lead to improved patient outcomes.

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

Several counterintuitive treatment paradoxes complicate the management of immune heparin-induced thrombocytopenia (HIT). For example, simple discontinuation of heparin often fails to prevent subsequent HIT-associated thrombosis. Thus, current treatment guidelines recommend substituting heparin with a rapidly acting alternative anticoagulant (eg, danaparoid, lepirudin, or argatroban) even when HIT is suspected on the basis of thrombocytopenia alone ("isolated HIT"). Another paradox-coumarin (warfarin) anticoagulation-can lead to venous limb gangrene in a patient with HIT-associated deep-vein thrombosis. Thus, warfarin is not recommended during acute thrombocytopenia secondary to HIT. However, warfarin can be given as overlapping therapy with an alternative anticoagulant, provided that (1) initiation of warfarin is delayed until substantial platelet count recovery has occurred (to at least above 100 x 10(9)/L); (2) low initial doses of warfarin are used; (3) at least 5 days of overlapping therapy are given; and (4) the alternative agent is maintained until the platelet count has normalized. It has recently been recognized that HIT antibodies are transient and usually do not recur upon subsequent re-exposure to heparin. This leads to a further paradox-patients with previous HIT can be considered for a brief re-exposure to heparin under exceptional circumstances; for example, heart surgery requiring cardiopulmonary bypass, if HIT antibodies are no longer detectable using sensitive assays. For patients with acute or recent HIT who require urgent heart surgery, other approaches include use of alternative anticoagulants (eg, lepirudin or danaparoid) for cardiopulmonary bypass or antiplatelet agents (eg, tirofiban or epoprostenol) to permit intraoperative use of heparin.

Monitoring of argatroban in ARG310 study: potential recommendations for its use in interventional cardiology

Argatroban is a peptidomimimetic synthetic direct thrombin inhibitor with reversible and specific properties resulting in predictable anticoagulant effects. Usually, argatroban therapy is monitored by the activated dotting time (ACT) or activated partial thromboplastin time (aPTT). While other global dotting tests for the monitoring of anticoagulants are useful, their applicability to antithrombin agents (particularly of argatroban at higher dosages) is rather questionable. In this study, we sought to compare the argatroban anticoagulant levels in patients undergoing percutaneous transluminal angioplasty (PTCA) and stenting procedures, utilizing both functional and absolute quantitation methods. Argatroban produced a comparable increase of ACT and HMT, 5 to 10 minutes after administration. The level of anticoagulation achieved (400-450 seconds with ACT and HMT) following a slow bolus of argatroban (350 microg/kg) was maintained throughout the procedure using 25 microg/kg/min infusion. Following discontinuation of argatroban at the end of the procedure, the ACTs and HMTs showed a comparable progressive reduction in the anticoagulant response, which reflected the elimination of argatroban 2 to 3 hours after the procedure. No significant differences between the three methods (Hemotec, Hemochron, and HMT) were noted at any given sampling time. Argatroban dosage at 350 microg/kg intravenous slow bolus followed by 25 microg/kg/min infusion was adequate to perform PTCA and stenting procedures. There was no incidence of bleeding complications. Absolute quantitation of argatroban levels in patient plasmas by a newly developed HPLC method was found to be quite comparable with the ecarin dotting time (ECT) results. The ECT system was found to be less sensitive when compared to other tests, and therefore, could be used as a point-of-care test during the PTCA/stenting procedures to monitor argatroban.

Pharmacology and clinical use of bivalirudin

OBJECTIVE

To review the primary literature describing the pharmacology and clinical uses of bivalirudin.

DATA SOURCES

A MEDLINE search (January 1966-May 2001) was conducted that used bivalirudin, hirulog, and direct thrombin inhibitor as key words. References from retrieved articles and unpublished information acquired from the manufacturer and the Internet were also used.

STUDY SELECTION

All acquired articles that discussed the pharmacology, pharmacokinetics, and clinical efficacy of bivalirudin were reviewed.

DATA EXTRACTION

Articles were selected based on content regarding the pharmacology and clinical use of bivalirudin. Given the paucity of data pertaining to the clinical use of bivalirudin, most articles were used, including abstracts and communications with the manufacturer.

DATA SYNTHESIS

Bivalirudin is a direct thrombin inhibitor that inactivates both unbound and fibrin-bound thrombin. Bivalirudin rapidly induces anticoagulation and has a relatively short duration of action. Bivalirudin displays linear kinetics and is primarily eliminated renally. Bivalirudin was proven effective in preventing postprocedural ischemic complications in patients with unstable or postinfarction angina who received percutaneous transluminal coronary angioplasty (PTCA). Yet, further investigations that include less critically ill patients and use the current clinical practice of administering glycoprotein IIb/IIIa antagonists and/or inserting intracoronary stents are needed to fully evaluate its efficacy. Bivalirudin has also induced early patency in patients with myocardial infarction in combination with streptokinase, but its use with newer thrombolytics needs to be studied. Bivalirudin has been used in patients with immunologically mediated, heparin-induced thrombocytopenia (HIT) without complications. Bleeding is the major adverse effect and occurs more commonly in patients with renal dysfunction.

CONCLUSIONS

At present, bivalirudin is worthy of consideration in patients requiring PTCA who have HIT. Advocating the routine use of bivalirudin in patients experiencing an acute coronary syndrome or HIT is premature.

The role of thrombin inhibition during percutaneous coronary intervention

Acute coronary syndromes encompass a spectrum of conditions, including myocardial infarction and unstable angina. These syndromes are related to the formation and disruption of atherosclerotic plaque. Rupture of plaque leads to thrombin generation, fibrin deposition, and platelet aggregation, ultimately resulting in restriction of blood flow and ischemia of cardiac tissue. Percutaneous coronary intervention (PCI), including angioplasty and coronary stent placement, has been developed to open occluded arteries. The frequency with which these procedures are performed speaks to their largely successful outcomes. However, the mechanical manipulations of PCI result in additional plaque rupture and damage to the vessel wall, exposing subendothelial components to blood and resulting in the initiation of the clotting cascade and in platelet activation. Left unchecked, these intertwined processes lead to formation of arterial thrombi at the site of endothelial damage, and potentially to abrupt vessel closure or embolization of thrombi into the distal microcirculation. Thrombin plays a central role in thrombus formation and platelet activation, and its inhibition significantly reduces thrombus-related sequelae. Current antithrombotic strategies during PCI are based on the traditional indirect thrombin inhibitor heparin. Heparin has several limitations in efficacy and safety, due in part to its indirect mechanism of action. Bivalirudin, a direct thrombin inhibitor, offers significant improvement over heparin in the clinical outcomes and risks associated with PCI.

Argatroban

Antithrombotic and antiplatelet therapies are the cornerstones of management of cardiovascular disorders today. Due to the safety and efficacy limitations of the classic antithrombotic, unfractionated heparin, considerable effort has been directed at developing novel anticoagulants. Direct thrombin inhibitors as a class of drugs offer inhibition of clot-bound as well as fluid-phase thrombin and a more predictable anticoagulant response. Specifically, argatroban, a synthetic small molecule direct thrombin inhibitor, selectively inhibits the catalytic site of thrombin in a reversible manner. Overall, argatroban's short half-life, ease of monitoring with an activated partial thromboplastin time, and safety in renal failure patients make this drug the preferable mode therapy for prevention of thrombosis in heparin-induced thrombocytopenia. The role of adjunctive argatroban therapy in acute coronary syndromes and during percutaneous coronary intervention is currently being studied.