The Influence of Infusions of 1-Desamino-8-D-Arginine vasopressin (DDAVP) In Vivo on the Anticoaguhht Effect of Recombinant Hirudin (CGP39393) In Vitro

Pathology consultation on monitoring direct thrombin inhibitors and overcoming their effects in bleeding patients

OBJECTIVES

Direct thrombin inhibitors (DTIs), a relatively new class of anticoagulants, present several challenges regarding monitoring of their anticoagulant effects and overcoming bleeding associated with their use. The aim of this article is to (1) briefly present the pharmacologic properties of currently available DTIs, (2) discuss approaches to laboratory assessment of these drugs, and (3) review management of bleeding associated with their use.

METHODS

Published literature on DTIs, including clinical trials, case reports, and experimental animal models, was reviewed. The primary authors also reviewed their first-hand experiences with DTI anticoagulation.

RESULTS

Based on the literature review and the practical experiences of the authors, suggestions for the monitoring of DTIs and algorithmic approaches for the management of DTI-associated bleeding were developed.

CONCLUSIONS

Routine coagulation assays (eg, the prothrombin time) show a relatively poor correlation with the degree of anticoagulation and DTI drug concentrations. Newer assays, such as the ecarin clotting time and dilute thrombin time, may be more useful in assessing DTI anticoagulation, but these assays are not yet widely available. Low-grade DTI-associated bleeds are best managed with cessation of the drug and supportive care, while higher-grade and/or life-threatening bleeds may best be reversed by active drug removal (eg, via the administration of activated charcoal or hemodialysis). At present there is little evidence to suggest that transfusion products such as factor concentrates or thawed plasma are of any particular benefit in DTI reversal; however, these products may play a supportive role in the management of bleeding.

Newer anticoagulants in critically ill patients

Critically ill patients are at increased risk for development of thrombosis. In addition, thrombosis is often unrecognized in this population. Furthermore, these patients are particularly susceptible to bleeding complications from anticoagulants. Herein the authors review the pharmacology, data from clinical trials, management of bleeding complications, and perioperative use of these agents in the intensive care unit population. Well-designed clinical trials are needed to improve our understanding of the safety and efficacy of these newer agents in critically ill patients.

Management of bleeding complications in the anticoagulated patient

As new anticoagulants become available, and the number of anticoagulated patients continues to rise, it is necessary to know how to deal with associated bleeding complications. In this review, reversal strategies for traditional anticoagulants (warfarin and heparin) as well as newer anticoagulants are described. Prothrombin complex concentrates (PPCs) can be used to reverse vitamin K antagonists (VKA), and plasma may be used where they are not available. Recombinant activated factor VII (rFVIIa) may be useful to reverse pentasaccharide anticoagulants. 1-Desamino-8-D-arginine vasopressin (DDAVP), cryoprecipitate, PCCs, and dialysis may help to reverse direct thrombin inhibitors, while rFVIIa seems to be ineffective. The effect of direct factor Xa inhibitors may be reversed by PCCs, FVIIa, or factor Xa concentrates.

Hospital-based clinical implications of the novel oral anticoagulant, dabigatran etexilate, in daily practice

Dabigatran etexilate is an oral direct thrombin inhibitor that has been approved by the US Food and Drug Administration for the prevention of stroke and systemic embolization in patients with nonvalvular atrial fibrillation. It has also been studied for the prevention of venous thromboembolism in patients after hip and knee arthroplasty and for treatment of venous thromboembolism. Although routine laboratory monitoring is not needed, there are clinical scenarios in which physicians will need to have a clear understanding of drug pharmacology, laboratory assessment, and reversibility of this drug to make appropriate clinical decisions. We review the pharmacology of dabigatran etexilate, pertinent clinical trials, and the effects of dabigatran etexilate on prothrombin time, activated partial thromboplastin time, thrombin time, and ecarin clotting time. We also provide an approach to patients on dabigatran etexilate who are bleeding, have a suspected therapeutic failure, or require periprocedural management.

Questions and answers on the use of dabigatran and perspectives on the use of other new oral anticoagulants in patients with atrial fibrillation. A consensus document of the Italian Federation of Thrombosis Centers (FCSA)

Dabigatran and other new oral anticoagulants (OAC) represent a step forward in stroke prevention in patients with atrial fibrillation (AF). They indeed have been shown to be an alternative to vitamin K antagonists (VKAs) without the burden of laboratory control. However, these new drugs compete with an effective and well-established therapy, thus bringing about a series of questions and doubts. In this report members of the board of the Italian Federation of Thrombosis Centers (FCSA) answer some questions every clinician might be confronted with.

Direct thrombin inhibitors: pharmacology and application in intensive care medicine

PURPOSE

Anticoagulation is part of the daily routine of intensive care physicians. As the possibilities of pharmacological anticoagulation are becoming more numerous and diverse, intensive care physicians have to be familiar with indications, contraindications, dosing, and reversal of many different substances. This paper presents an overview of the substance group of direct thrombin inhibitors (DTI) indicated for alternative anticoagulation in intensive care medicine.

METHODS

The review is a synopsis of scientific evidence, expert opinion, open forum commentary, and clinical feasibility data.

RESULTS AND CONCLUSIONS

Due to their antithrombotic potential without direct activation of platelets, DTI could offer potential advantages over heparins and vitamin K antagonists in critically ill patients, especially regarding heparin-induced thrombocytopenia. Because of multiple organ dysfunction, organ failure, and comedications, simple extrapolation of results of medical to critically ill patients is not permissible. The fine line between thrombosis and bleeding in intensive care patients requires cautious dosing and close drug monitoring. Studies dealing with DTI in the intensive care setting are of utmost clinical interest.

Emergency reversal of anticoagulation and antiplatelet therapies in neurosurgical patients

Intracranial hemorrhage (ICH) is a common problem encountered by neurosurgeons. Patient outcomes are influenced by hematoma size, growth, location, and the timing of evacuation, when indicated. Patients may have abnormal coagulation due to pharmacological anticoagulation or coagulopathy due to underlying systemic disease or blood transfusions. Strategies to reestablish the integrity of the clotting cascade and platelet function assume a familiarity with these processes. As patients are increasingly treated with anticoagulants and antiplatelet agents, it is essential that the physicians who care for patients with ICH understand these pathways and recognize how they can be manipulated to restore hemostasis.

Hämostyptika

Desmopressin (DDAVP) wurde 1966 als Abkömmling des antidiuretischen Hypophysenhormons Arginin-Vasopressin synthetisch hergestellt. Zu den antidiuretischen Indikationen zählen Diabetes insipidus und Enuresis nocturna, zudem wird es in Tests zur Bestimmung der Nierenkonzentrationsfähigkeit verwendet

[Direct thrombin inhibitors: pharmacology and application in cardiovascular anesthesia]

The options for drug-controlled anticoagulation are becoming noticeably more manifold. In the area of anaesthesiology and intensive care, there are furthermore special disease patterns, such as heparin-induced thrombocytopenia (HIT) to be known, diagnosed and treated. This article gives a review of the substance groups of the direct thrombin inhibitors (DTI) as alternative anticoagulants for HIT in combination with cardiovascular diseases. For the administration of DTIs, experience and the correct dose are the keys to success and are the deciding factors for the two sides of haemostasis: thrombosis and haemorrhage.

Bleeding risk and the management of bleeding complications in patients undergoing anticoagulant therapy: focus on new anticoagulant agents

For more than 60 years, heparin and coumarin have been mainstays of anticoagulation therapy. They are widely available, inexpensive, effective, and have specific antidotes but are regarded as problematic because of their need for careful monitoring. In addition, coumarin has a delayed onset of action, interacts with many medications, has a narrow therapeutic window, and is paradoxically prothrombotic in certain settings (ie, can precipitate “coumarin necrosis”). Heparin may require monitoring of its therapeutic effect and can also cause thrombosis (heparin-induced thrombocytopenia/thrombosis syndrome). These limitations have led to the development of new anticoagulants with the potential to replace current agents. These newer agents fall into 2 classes, based on whether they are antithrombin dependent (low-molecular-weight heparin, fondaparinux) or antithrombin independent (direct inhibitors of factor Xa and thrombin [factor IIa]). This paper addresses newer anticoagulants, reviewing their efficacy and limitations, and focuses on the risk of major bleeding that may complicate their use. In contrast to heparin and coumarin, none of these newer agents has a specific antidote that completely reverses its anticoagulant effect. Available data on the efficacy and safety of current and experimental agents for anticoagulant reversal are reviewed, and a plan for management of anticoagulant-induced bleeding is presented.

Anticoagulants and Their Reversal

In an exciting era with many alternatives to the old anticoagulants heparin and warfarin emerging on the scene, awareness of the possibility to reverse their effect is mandatory. In this review, the traditional antidotes for warfarin (vitamin K, plasma, and prothrombin complex concentrate) and for heparin (protamine) are described together with the newer alternatives (recombinant activated factor VII, concatameric peptides, and recombinant platelet factor 4). For some of the newer anticoagulants, possible antidotes have been identified, whereas other alternatives have been discarded. There is a very limited experience of deamino-d-arginine vasopressin or a von Willebrand factor VIII concentrate to counteract hirudin. The small direct thrombin inhibitors may be reversed with activated prothrombin complex concentrate but not with recombinant activated factor VII, whereas the latter agent appears to be effective against the pentasaccharides and the recombinant nematode anticoagulant protein C2. Additional options that may become available in the future are also discussed briefly.

Managing Complications of Anticoagulant Therapy

Understanding the frequency, risk factors, and management of anticoagulant-induced adverse events will assist clinicians in optimizing patient outcomes. The most frequent adverse event of all anticoagulants is major bleeding. Risk factors for major bleeding have been identified with the heparin compounds, the direct thrombin inhibitors (DTIs), fondaparinux, and warfarin therapy. Understanding these risk factors can help prevent bleeding events. For cases of clinically significant bleeding, reversal agents exist primarily for heparin and warfarin. Although less common, nonbleeding adverse events of anticoagulant therapy can also be life threatening. The heparin compounds are associated with the development of heparin-induced thrombocytopenia (HIT) and osteoporosis. HIT can result in life-threatening thrombosis and is usually managed with a DTI. Nonbleeding adverse events with warfarin therapy include skin reactions and the development of venous limb gangrene. Appropriate initiation of warfarin therapy may decrease the risk of venous limb gangrene.

Drugs for the prevention and treatment of thrombosis in patients with heparin-induced thrombocytopenia

Most patients with heparin-induced thrombocytopenia (HIT), a serious adverse effect of heparin mediated by platelet-activating heparin-dependent antibodies, require alternative anticoagulation. This is because HIT is highly prothrombotic and is characterized by markedly increased thrombin generation. Unfractionated heparins seem to induce HIT more often than low molecular weight heparins. There are three anticoagulants for which there is an emerging consensus for their efficacy in management of HIT, and which are currently approved for treatment of HIT in several countries: the recombinant hirudin, lepirudin, a direct thrombin inhibitor; the synthetic direct thrombin inhibitor, argatroban; and the heparinoid, danaparoid sodium, mainly exhibiting antifactor-Xa activity. Recommendations for optimal use of these drugs in HIT are given in this review stressing the need for immediate treatment of patients with HIT without awaiting laboratory diagnosis. Hirudin, the drug for which most data from prospective trials exists, can be safely and effectively used in patients with HIT, its dramatically increased elimination half-life in patients with renal failure being the most important drawback. Argatroban, which is mainly eliminated by the liver, could be used preferentially in such patients with renal impairment. Interference with the international normalized ratio makes oral anticoagulation, which is necessary in many patients with HIT, problematic. Activated partial thromboplastin time is sufficient to monitor lepirudin and argatroban treatment in most cases. Danaparoid sodium, with an antifactor-X activity half-life of about 24 hours seems to be best suited for thrombosis prophylaxis in patients with HIT. In some patients monitoring by determining antifactor-Xa activity is necessary. No antidote is available for any of the drugs discussed, and bleeding complications are the most important adverse effects. In situations such as hemodialysis or cardiopulmonary bypass, not only the characteristics of the drug in use itself, but also availability of monitoring methods play an important role. Adjunctive treatments have not been systematically evaluated and should be used cautiously. Recent data suggest that re-exposure of patients with a history of HIT with heparin, for example during cardiopulmonary bypass, can be well tolerated provided no circulating HIT antibodies are detectable at the time of re-exposure, and heparin is strictly avoided pre- and postoperatively.

Direct thrombin inhibitors

This review deals with a newly-developed category of antithrombotic drugs - the direct thrombin inhibitors. These agents interact with thrombin and block its catalytic activity on fibrinogen, platelets and other substrates. Heparin and its derivatives (low molecular weight heparins and the active pentasaccharide) inhibit thrombin and/or other coagulation serine proteases indirectly via antithrombin, and the warfarin-type drugs interfere with the synthesis of the precursors of the coagulation serine proteases. The direct thrombin inhibitors approved for clinical use at present (lepirudin, desirudin, bivalirudin, argatroban) and another in the advanced clinical testing stage (melagatran/ximelagatran), are the subject of this review. The chemical structure; kinetics of thrombin inhibition; pharmacokinetics and clinical use of each of these is discussed.

Alternative methods of anticoagulation for dialysis-dependent patients with heparin-induced thrombocytopenia

Dialysis patients who are continually exposed to heparin are at risk for heparin-induced thrombocytopenia (HIT). Heparin-induced antibodies have been reported to occur in 0-12% of hemodialysis (HD) patients. The diagnosis or suspicion of HIT in this patient population requires careful confirmation of the diagnosis and substitution of heparin with an alternate anticoagulant for dialysis. Alternate agents such as the direct thrombin inhibitors (hirudin and argatroban) are available, but careful dosing and monitoring of the anticoagulant effect are required. Despite careful dosing, hemorrhagic complications have occurred with these agents. Unfortunately there are limited options for treatment of hemorrhagic complications and no specific antidotes are available for the direct thrombin inhibitors. In this report the currently available alternatives to heparin for dialysis, including dosing and monitoring recommendations, are reviewed.

Direct thrombin inhibitors

Direct thrombin inhibitors interact with thrombin and block its catalytic activity on a wide range of substrates. Their action is in contrast to heparin and its derivatives, which inhibit thrombin and other coagulation serine proteases via antithrombin, and to the warfarin-type drugs that interfere with synthesis of the precursors of the coagulation serine proteases. There are three direct thrombin inhibitors approved for clinical use at present (lepirudin, bivalirudin, argatroban) and another in advanced clinical testing (melagatran/ximelagatran). The chemical structure, kinetics of thrombin inhibition, pharmacokinetics, and clinical use of each of these agents are discussed.

Recombinant hirudin in clinical practice: focus on lepirudin

Clinical applications for recombinant hirudins have been investigated for the past 10 years. The first indication for which a hirudin-lepirudin-has been approved is treatment of heparin-induced thrombocytopenia (HIT). Also, the recently completed trials for use of lepirudin in unstable angina indicate a potentially new indication. This review describes pharmacology and clinical applications of lepirudin with an emphasis on HIT and unstable angina. An overview of usage of lepirudin in acute coronary syndromes is given, as well as a summary of rare indications for lepirudin, such as extracorporeal circulation, for which comprehensive data are lacking.

Effects of agents, used to treat bleeding disorders, on bleeding time prolonged by a very high dose of a direct thrombin inhibitor in anesthesized rats and rabbits

Melagatran is the active form of the oral, direct thrombin inhibitor, H 376/95, that is under evaluation in clinical trials for the prevention and treatment of thromboembolism. In this study, a single dose, calculated on body weight basis, of antifibrinolytic treatment, factor VIIa, factor VIII with and without von Willebrand factor (vWF), factor IX, activated (APCC) or nonactivated (PCC) prothrombin complex concentrates was given intravenously to rats and rabbits, in an attempt to reverse the prolonged bleeding time during intensive anticoagulation with melagatran (2 micromol/kg/h). The doses used were at or above human therapeutic doses. The cutaneous tail bleeding time in the rat, as well as the ear incision bleeding time and cuticle bleeding time, and the blood loss in the rabbit were used for evaluation of the hemostatic effects of these agents. In vivo Feiba (APCC) and Prothromplex-T (PCC) shortened the prolonged cutaneous bleeding times in rats (P<.05); Feiba and Autoplex (APCC) shortened the cutaneous bleeding times in rabbits (P<.05). In contrast, Prothromplex-T prolonged bleeding times and blood loss in the rabbits (P<.05). Ex vivo Feiba, Autoplex and NovoSeven (rF VIIa) significantly (P<.05) shortened the prolonged whole blood clotting time (WBCT). Prothromplex-T significantly prolonged WBCT, activated clotting time (ACT) and activated partial thromboplastin time (APTT). Feiba, Autoplex, and Prothromplex-T increased thrombin generation measured as increased thrombin-antithrombin complex (TAT) formation. In conclusion, APCCs were found to be the most effective agents for reversing bleeding time induced by a very high plasma concentration of melagatran. APCC and recombinant activated factor FVII (rF VIIa) effectively shortened the prolonged WBCT. Thus, stimulating thrombin generation with the use of APCC may counteract the anticoagulant effect observed with a very high dose of a thrombin inhibitor.

Prothrombin conversion intermediate effectively neutralizes toxic levels of hirudin

Meizothrombin, the stable intermediate product of ecarin-induced prothrombin conversion, was investigated for its ability to bind hirudin in blood. After in vitro pre-incubation of rat plasma with ecarin, the prolongation of the thrombin time caused by hirudin was reduced. The extent of hirudin neutralization was found to be dependent on the duration of incubation with ecarin. In vivo, after bilateral nephrectomy in Wistar rats and following administration of hirudin at a dose of 1 or 5 mg/kg, the blood level of hirudin remained constant after 2 h. After infusion of ecarin following hirudin administration, the hirudin blood level dropped sharply, reaching significantly reduced values, and bleeding stopped. Platelet count and fibrinogen level in plasma remained unchanged in the experiments using ecarin-induced prothrombin conversion intermediate generation. It is concluded that meizothrombin, a naturally occurring prothrombin conversion intermediate, provides an effective agent to neutralize toxic blood levels of hirudin.

The effect of short-term exercise on plasma procoagulant activity in patients with type II (non-insulin-dependent) diabetes and healthy volunteers

The effect of exercise on plasma coagulant activity was studied in 16 subjects with newly-diagnosed type II diabetes without vascular complications and 9 healthy volunteers. Generation of thrombin was determined by a computer-assisted chromogenic method and results expressed as time to generate 50% maximal thrombin activity (T50/s). In addition, APTT, factor VIII and thrombin-antithrombin III (TAT) complex levels were measured. Pre-exercise FVIII:C [mean (+/- SD)] was increased in diabetic compared to control subjects [1.5 (0.4); 0.9 (0.2) IU ml-1; (p < 0.001) respectively]. No significant differences in APTT, TAT or T50 were detected between the groups. Exercise induced a rise in FVIII complex, reduction of APTT [33 (2) s to 31 (2) s; (p = 0.004)] and T50 [58 (6) s to 53 (6) s; (p = 0.01)] in controls and an increase in FVIII complex but no significant changes in APTT or T50 in diabetic patients, with no change in TAT in either group. A greater increase in FVIII:C than vWF levels occurred in controls [0.2 (0.1); 0.1 (0.1) IU ml-1; (p = 0.005)] and patients [0.3 (0.4); 0.2 (0.1) IU ml-1; (p = 0.032)]. In patients, FVIII:C correlated inversely with APTT (r = -0.522, p = 0.038) and T50 (r = -0.592, p = 0.016). The results show that FVIII:C levels are increased at diagnosis in patients with type II diabetes without vascular disease but there is no enhancement of plasma procoagulant activity. In healthy individuals, exercise induced activation of coagulation which was not seen in patients, suggesting that it does not precipitate a state of accelerated thrombogenesis in subjects with uncomplicated type II diabetes.

Generation of thrombin activity in relation to factor VIII:C concentrations and vascular complications in type 1 (insulin-dependent) diabetes mellitus

A possible association between plasma coagulant activity and the presence of vascular complications in patients with diabetes mellitus was studied by measuring the generation of thrombin in plasma of 20 control subjects and 50 diabetic patients classified according to the presence or absence of microvascular complications. Thrombin production was determined in defibrinated plasma using a semi-automated technique with measurement of thrombin activity using chromogenic peptide S2238. Values determined were the lag time to appearance of thrombin activity and time taken to generate 50% maximal thrombin activity. Thrombin activity was related to concentrations of coagulant factor VIII activity and fibrinopeptide A and these were correlated with HbA1C levels. The median time to generate 50% maximal thrombin activity was not significantly reduced in diabetic patients compared with control subjects (53 vs 54 s, p = 0.076) and there were no significant differences between patients with and without microvascular complications. There were no differences in median fibrinopeptide A concentrations between the diabetic and control subjects (1.5 vs 2.2 nmol/l, p = 0.169). Time to 50% maximal thrombin activity correlated inversely with factor VIII:C concentrations in diabetic patients (r = -0.344, p = 0.015, n = 50) and both this and lag time correlated with factor VIII:C in diabetic patients and control subjects combined (r = -0.395, p less than 0.01; r = -0.327, p = 0.006, n = 70). Factor VIII:C concentrations increased with age of the subject and with HbA1C concentrations. The results failed to show enhancement of coagulation in contact-activated diabetic plasma compared with control plasma and suggest that a relationship between high levels of factor VIII:C in diabetes and the development of mcirovascular complications is unlikely to be mediated through procoagulant activity in plasma.

Hirudin, a new therapeutic tool?

Hirudin is the most potent natural inhibitor of thrombin known to date. It is gaining popularity as an anticoagulant now that recombinant and synthesized forms are available. It is a monospecific and co-factor-independent thrombin inhibitor with otherwise inert pharmacological properties. Being a surprisingly weak immunogen, its administration has exhibited no side effects, particularly on platelets. Bleeding complications are not to be expected at therapeutic doses. Effective anticoagulatory doses can be easily predicted and laboratory control is no problem. Application of hirudin or derivatives thereof may be indicated for: prophylaxis and treatment of postoperative venous thrombosis and diffuse microthrombosis; prevention of arterial thrombosis, especially in cardiac surgery; enhancement of fibrinolytic therapy and/or angioplasty to prevent reocclusion; extracorporeal circulation; and plastic surgery. Hirudin may be a particularly useful alternative anticoagulatory agent in patients sensitized to heparin or in patients with hereditary or acquired antithrombin III deficiency. However, whether hirudin is really an effective therapeutic tool and whether it can replace heparin in certain clinical indications can be judged only after extended clinical experience has been accumulated.