Comparison of low-intensity warfarin therapy with conventional-intensity warfarin therapy for long-term prevention of recurrent venous thromboembolism

Ximelagatran: An orally active direct thrombin inhibitor

PURPOSE

The chemistry, pharmacology, pharmacokinetics, clinical efficacy, dosage and administration, contraindications, and adverse effects of ximelagatran are reviewed.

SUMMARY

Ximelagatran is the first orally active direct thrombin inhibitor to be tested in Phase III clinical trials. After oral administration, ximelagatran is rapidly converted to its active metabolite, melagatran. Melagatran (after oral ximelagatran administration) predictably inhibits thrombin function without need for routine anticoagulation monitoring. Melagatran effectively inhibits both free and clot-bound thrombin-a potential pharmacodynamic advantage over heparin products. Melagatran has a half-life of 2.4-4.6 hours, necessitating twice-daily administration. Melagatran is primarily eliminated by the kidneys and has not been studied clinically in patients with severe renal failure. Ximelagatran has undergone 10 Phase III trials (6 for prophylaxis of venous thromboembolism [VTE] due to orthopedic surgery, 1 for initial treatment of VTE, 1 for long-term prevention of VTE recurrence, and 2 for stroke prophylaxis due to atrial fibrillation). Results were generally positive. AstraZeneca applied in December 2003 for marketing approval of ximelagatran for prevention of VTE after total knee replacement surgery, long-term prevention of VTE recurrence after standard therapy, and stroke prevention due to atrial fibrillation. FDA denied approval of ximelagatran for all indications, mainly because of increased rates of coronary artery disease events in ximelagatran recipients in some studies and the possibility of hepatic failure when the medication is used for long-term therapy.

CONCLUSION

Ximelagatran has shown promise as a possible alternative to warfarin and other anticoagulants but will require further study to ensure its safety.

Eight-year follow-up of patients with permanent vena cava filters in the prevention of pulmonary embolism: the PREPIC (Prevention du Risque d'Embolie Pulmonaire par Interruption Cave) randomized study

BACKGROUND

In a randomized trial in patients with proximal deep-vein thrombosis, permanent vena cava filters reduced the incidence of pulmonary embolism but increased that of deep-vein thrombosis at 2 years. An 8-year follow-up was performed to assess their very long-term effect.

METHODS AND RESULTS

Four hundred patients with proximal deep-vein thrombosis with or without pulmonary embolism were randomized either to receive or not receive a filter in addition to standard anticoagulant treatment for at least 3 months. Data on vital status, venous thromboembolism, and postthrombotic syndrome were obtained once a year for up to 8 years. All documented events were reviewed blindly by an independent committee. Outcome data were available in 396 patients (99%). Symptomatic pulmonary embolism occurred in 9 patients in the filter group (cumulative rate 6.2%) and 24 patients (15.1%) in the no-filter group (P=0.008). Deep-vein thrombosis occurred in 57 patients (35.7%) in the filter group and 41 (27.5%) in the no-filter group (P=0.042). Postthrombotic syndrome was observed in 109 (70.3%) and 107 (69.7%) patients in the filter and no-filter groups, respectively. At 8 years, 201 (50.3%) patients had died (103 and 98 patients in the filter and no-filter groups, respectively).

CONCLUSIONS

At 8 years, vena cava filters reduced the risk of pulmonary embolism but increased that of deep-vein thrombosis and had no effect on survival. Although their use may be beneficial in patients at high risk of pulmonary embolism, systematic use in the general population with venous thromboembolism is not recommended.

A review of the oral direct thrombin inhibitor ximelagatran: not yet the end of the warfarin era

Ximelagatran is a direct thrombin inhibitor that offers numerous potential advantages compared with traditional anticoagulants. It is given orally, has a rapid onset of action, does not require laboratory monitoring, and is not associated with immune-mediated thrombocytopenia. Numerous phase III trials with ximelagatran focusing on deep vein thrombosis prophylaxis and treatment, stroke prevention in patients with atrial fibrillation, and secondary prevention after acute myocardial infarction have been conducted. Results of these trials indicate that ximelagatran has similar efficacy and risk of bleeding compared with currently used anticoagulants. Accordingly, the potential of this agent to replace warfarin therapy for a variety of indications has been widely touted. Ximelagatran has already been approved in Europe for prophylaxis of venous thromboembolism in patients undergoing hip or knee surgery. However, an adverse effect of ximelagatran is liver enzyme elevation, which has been observed in 5% to 10% of patients with chronic administration of the drug. Although initially felt to be transient in nature, subsequent data presented to the Federal Drug Administration suggest a small but real risk of significant hepatotoxicity. These data led the advisory committee to the Federal Drug Administration to recommend against immediate approval of ximelagatran pending further information. The consistent results of completed trials with ximelagatran suggest that it has the potential to be used in many conditions that currently require treatment with warfarin and heparin products. The potential benefit that may be achieved by the replacement of these historically problematic narrow therapeutic index agents must be weighed against as yet undetermined long-term risks of hepatotoxicity.

Venous thromboembolism: diagnosis and management of pulmonary embolism

Pulmonary embolism (PE) affects 0.5-1 per 1000 people in the general population each year, and is one of the most common preventable causes of death among hospitalised patients. The clinical diagnosis of PE is unreliable and must be confirmed objectively with ventilation perfusion scanning or computed tomography pulmonary angiography. The diagnosis of PE can be reliably excluded, without the need for diagnostic imaging, if the clinical pretest probability for PE is low and the D-dimer assay result is negative. The initial treatment of PE is low-molecular-weight heparin or unfractionated heparin for at least 5 days, followed by warfarin (target international normalised ratio [INR], 2.0-3.0) for at least 3-6 months. Patients with a high clinical pretest probability of PE should commence treatment immediately while awaiting the results of the diagnostic work-up. Thrombolysis is indicated for patients with objectively confirmed PE who are haemodynamically unstable. Percutaneous transcatheter or surgical embolectomy may be life-saving in patients ineligible for, or unresponsive to, thrombolytic therapy. Unresolved issues in the management of venous thromboembolism include the roles of thrombophilia testing, thrombolysis for the treatment of stable PE patients who present with right ventricular dysfunction, and new anticoagulants; and the duration of anticoagulation for first unprovoked venous thromboembolism.

Oral anticoagulation strategies after a first idiopathic venous thromboembolic event

PURPOSE

The optimal duration and intensity of warfarin therapy after a first idiopathic venous thromboembolic event are uncertain. We used decision analysis to evaluate clinical and economic outcomes of different anticoagulation strategies with warfarin.

METHODS

We built a Markov model to assess 6 strategies to treat 40- to 80-year-old men and women after their first idiopathic venous thromboembolic event: 3-month, 6-month, 12-month, 24-month, and unlimited-duration conventional-intensity anticoagulation (International Normalized Ratio, 2-3) and unlimited-duration low-intensity anticoagulation (International Normalized Ratio, 1.5-2). The model incorporated age- and sex-specific clinical parameters, utilities, and costs. Using a societal perspective, we compared strategies based on quality-adjusted life-years (QALYs), lifetime costs, and incremental cost-effectiveness ratios.

RESULTS

In our baseline analysis, incremental cost-effectiveness ratios were lower in younger patients and in men, reflecting the higher bleeding risk at older ages, and the lower risk of recurrence among women. Based on a willingness-to-pay of <$50000/QALY, the 24-month strategy was most cost-effective in 40-year-old men ($48805/QALY), while the 6-month strategy was preferred in 40-year-old women ($35977/QALY) and 60-year-old men ($29878/QALY). In patients aged >/=80 years, 3-month anticoagulation was less costly and more effective than other strategies. Cost-effectiveness results were influenced by the risks associated with recurrent venous thromboembolism, the major bleeding risk of conventional-intensity anticoagulation and the disutility of taking warfarin.

CONCLUSION

Longer initial conventional-intensity anticoagulation is cost-effective in younger patients while 3 months of anticoagulation is preferred in elderly patients. Patient age, sex, clinical factors, and patient preferences should be incorporated into medical decision making when selecting an appropriate anticoagulation strategy.

Anticoagulant therapy for the thrombotic complications of the antiphospholipid antibody syndrome

Patients with antiphospholipid antibodies (APLA) are at risk of arterial thromboembolism (ATE) or venous thromboembolism (VTE). The true strength of the association between APLA and first TE is unknown as there are no prospective studies of a large, well-characterized inception cohort of matched patients with and without APLA. Thus, evidence-based treatment recommendations for primary prophylaxis of TE in such patients cannot be made. Optimal therapy of patients with recent TE and APLA remains controversial; although there is no doubt that some such patients have a malignant hypercoagulable state characterized by resistance to "usual intensity" anticoagulation; recent evidence suggests that most such patients are adequately treated with "usual therapy". After warfarin discontinuation, such patients appear to be at increased risk of recurrent TE, as demonstrated in a series of studies of discontinuation of secondary TE prophylaxis in patients with APLA and venous TE (VTE). Because of this increased risk of recurrent TE, after anticoagulants are discontinued, most "experts" recommend extended duration therapeutic dose warfarin for such patients. This paper will briefly review this evidence.

Predictors of the post-thrombotic syndrome during long-term treatment of proximal deep vein thrombosis

BACKGROUND

The post-thrombotic syndrome is a chronic, poorly understood complication of deep venous thrombosis (DVT).

OBJECTIVES

To evaluate predictors of the post-thrombotic syndrome, including intensity of long-term anticoagulation, and to assess the impact of the post-thrombotic syndrome on quality of life.

PATIENTS AND METHODS

The setting was 13 Canadian hospitals and one US hospital. One hundred and forty-five patients with an unprovoked episode of proximal DVT who were initially treated with 3 months of conventional-intensity warfarin [target International Normalized Ratio (INR) of 2.5] then participated in a trial comparing two intensities of long-term warfarin therapy (target INR 2.5 vs. INR 1.7). Post-thrombotic syndrome was assessed at the end of the trial using a validated clinical scale. Generic and venous disease-specific quality of life was compared in patients with and without the post-thrombotic syndrome. Multivariable regression analyses were performed to identify predictors of the post-thrombotic syndrome and of its severity.

RESULTS

After an average follow-up of 2.2 years, the prevalence of post-thrombotic syndrome was 37% and of severe post-thrombotic syndrome was 4%. Quality of life was worse in patients with the post-thrombotic syndrome compared with patients who did not have it. The presence of factor (F)V Leiden or the prothrombin gene mutation was an independent predictor of both a lower risk (P = 0.006) and reduced severity (P = 0.045) of the post-thrombotic syndrome. Intensity of anticoagulation did not influence the risk of developing the post-thrombotic syndrome.

CONCLUSIONS

The post-thrombotic syndrome is a frequent and burdensome complication of proximal DVT, even among patients maintained on long-term oral anticoagulation. While the presence of FV Leiden or prothrombin gene mutation appears to be associated with a reduced risk of post-thrombotic syndrome, this finding requires further evaluation in prospective studies.

Deep vein thrombosis

Deep vein thrombosis and its sequelae pulmonary embolism and post-thrombotic syndrome are some of the most common disorders. A thrombus either arises spontaneously or is caused by clinical conditions including surgery, trauma, or prolonged bed rest. In these instances, prophylaxis with low-dose anticoagulation is effective. Diagnosis of deep vein thrombosis relies on imaging techniques such as ultrasonography or venography. Only about 25% of symptomatic patients have a thrombus. Thus, clinical risk assessment and D-dimer measurement are used to rule out deep vein thrombosis. Thrombus progression and embolisation can be prevented by low-molecular-weight heparin followed by vitamin K antagonists. Use of these antagonists for 3-6 months is sufficient for many patients. Those with antithrombin deficiency, the lupus anticoagulant, homozygous or combined defects, or with previous deep vein thrombosis can benefit from indefinite anticoagulation. In cancer patients, low-molecular-weight heparin is more effective than and is at least as safe as vitamin K antagonists. Women seem to have a lower thrombosis risk than men, but pregnancy or use of oral contraceptives or hormone replacement therapy represent important risk factors.

Thrombotic complications and thromboprophylaxis in breast and gynaecological malignancies

PURPOSE OF REVIEW

Thrombotic complications are a common cause of morbidity and mortality in patients with gynaecological or advanced breast malignancies. There are several manifestations of thromboembolism in these patients, but deep venous thrombosis of the legs is the usual presentation. This review highlights various manifestations of thrombotic complications in these malignancies, and also describes the current evidence base for various forms of thromboprophylaxis.

RECENT FINDINGS

Several trials have suggested that low molecular weight heparin therapy is at least as effective as oral anticoagulation for secondary prophylaxis. It has also been suggested that low molecular weight heparin therapy may prolong survival in cancer patients, but this was not shown in the results of one recently published placebo-controlled randomized trial.

SUMMARY

Primary thromboprophylaxis in cancer should be individualized and considered according to the risk category of each patient. Low molecular weight heparin therapy can be used for secondary thromboprophylaxis in patients with breast or gynaecological malignancy. However, more studies are needed to substantiate their acceptance in cancer patients.

Individual time within target range in patients treated with vitamin K antagonists: main determinant of quality of anticoagulation and predictor of clinical outcome. a retrospective study of 2300 consecutive patients with venous thromboembolism

The efficacy and safety of vitamin K antagonists (VKA) are related to the actual level of anticoagulation (given as the international normalized ratio, INR). It is often difficult to maintain an optimal INR over time. We assessed the clinical impact of the individual time spent within INR target range (ITTR) in 2304 consecutive patients with venous thromboembolism. Annual incidences of recurrent thromboembolism and major bleeding were 6.2% and 2.8% respectively. The relative risk (RR) of thromboembolism was 4.5 [95% confidence interval (CI) 3.1-6.6, P < 0.001] at INR < 2.0, for major bleeding it was 6.4 (2.5-16.1, P < 0.001) at INR > 5.0, compared with INR 2.0-3.0. Patients with ITTR < 45% were at higher risk than those with ITTR > 65% (RR 2.8, 1.9-4.3, P < 0.001), while no difference was demonstrated comparing ITTR 45-65% and ITTR > 65% (RR 1.2, 0.7-1.8, P = 0.54). Annual incidences of recurrent thromboembolism were 16.0%, 4.9% and 4.6% at ITTR < 45%, 45-60% and >65% respectively. For major bleeding these were 8.7%, 2.1% and 1.9% respectively. ITTR < 37% during the first 30 treatment days was highly predictive for the total treatment time ITTR < 45% (RR 24.2, 13.5-43.1, P < 0.001). In conclusion, ITTR can be used to identify patients on VKA at risk of recurrent thromboembolism or major bleeding. Since the 30-d ITTR is highly predictive for total treatment ITTR, these patients can be identified soon after start of treatment.

Importance of device evaluation for point-of-care prothrombin time international normalized ratio testing programs

OBJECTIVE

To determine the accuracy of 2 commercially available point-of-care devices relative to plasma international normalized ratio (INR) values.

PATIENTS AND METHODS

Point-of-care INR testing was performed with the CoaguChek and ProTime 3 devices in consecutive patients attending an anticoagulation clinic between June 18, 2003, and August 6, 2003. Results were compared with plasma INRs using a sensitive thromboplastin (International Sensitivity Index, 1.0).

RESULTS

Ninety-four patients agreed to participate in the study. Relative to the plasma INR, values were in agreement +/-0.4 INR unit 82% and 39% of the time for the CoaguChek and ProTime 3 devices, respectively. The mean +/- SD CoaguChek INRs were 0.2+/-0.31 unit lower, whereas ProTime 3 INRs were 0.8+/-0.68 unit higher than plasma INR values. Treatment decisions based on these data would have resulted in inappropriate dose adjustments 10% and 22% of the time for these 2 respective devices. Correlation with plasma was greater for the CoaguChek (r2=0.90) compared with the ProTime 3 device (r2=0.73).

CONCLUSIONS

Optimal warfarin treatment requires accurate measurement of the INR. The choice of a point-of-care device for INR management depends on the reliability of INR data generated by the device.

Extended anticoagulation therapy for the primary and secondary prevention of venous thromboembolism

Extending the period of anticoagulation is an active area of investigation in both primary and secondary prevention of venous thromboembolic disease. In orthopaedic surgery, particularly in patients undergoing hip surgery, there is a growing interest in using extended anticoagulation beyond that traditionally given in the postoperative period using low-molecular weight heparin, oral anticoagulants, or newer agents such as fondaparinux sodium. Most studies show a benefit to extending anticoagulation without a considerable increase in major bleeding. There have been several large clinical trials addressing the question of extending oral anticoagulation in secondary prevention of venous thromboembolism (VTE). Just how long anticoagulation should be given in the treatment of venous thromboembolic disease remains an open question, depending on the nature of the initial VTE, associated patient risk factors and the risks of major bleeding. Future directions include the use of newer agents for anticoagulation as well as methods of better defining who will benefit most from extended anticoagulation based on an identification of risk factors with the aid of markers such as D-dimer or residual vein thrombosis.

Vitamin K antagonists and direct thrombin inhibitors: present and future

Warfarin and related compounds are efficacious and safe in a variety of clinical thrombotic disorders; however, these drugs have a narrow therapeutic window, whereby inadequate therapy is associated with an increased thrombotic risk and overanticoagulation is associated with bleeding. Therefore, attempts have been made to develop alternatives to warfarin. Ximelagatran, an oral direct thrombin inhibitor, has been shown to be as efficacious and safe as warfarin for the prevention and treatment of different thrombotic disorders. This article reviews the pharmacology of the coumarins, the most commonly used vitamin K antagonists, and the practical aspects regarding their use in the management of thrombotic disorders. The future role of the oral direct thrombin inhibitor ximelagatran also is reviewed.

The Role of Ximelagatran in the Treatment of Venous Thromboembolism

Clinical-based evidence demonstrates that long-term oral anticoagulant therapy with the vitamin K antagonists is highly effective for the secondary prevention of venous thromboembolism (VTE). However, owing to fear of bleeding complications and the inconvenience of coagulation monitoring, many patients do not receive the required duration of treatment. This can lead to a high incidence of recurrent VTE events and has prompted the evaluation of alternative treatment strategies and the development of new anticoagulants for VTE management. For patient groups in which it is particularly difficult to maintain the target intensity of anticoagulation, low-molecular-weight heparin (LMWH) has been found to significantly reduce the risk of recurrent VTE without increasing bleeding risk. The parenteral administration of LMWH, however, is a drawback for long-term use in the outpatient setting. Long-term warfarin use at a lower intensity (international normalized ratio [INR] 1.5-2.0) has also been assessed as a possible strategy to reduce bleeding complications and the need for monitoring, but results were disappointing when compared with conventional-intensity warfarin (INR 2.0-3.0). New therapies in development that may potentially offer a more favourable benefit-risk profile and greater consistency and predictability of response include the synthetic pentasaccharides, fondaparinux and idraparinux. These par enterally administered indirect factor Xa inhibitors have a predictable pharmacokinetic profile, allowing use without coagulation monitoring. Fondaparinux to date has only been evaluated in the initial treatment (5-7 days) of symptomatic deep vein thrombosis. In contrast, idraparinux, with its longer half-life (80 h) allowing once-weekly parenteral dosing, has the potential for long-term treatment and is currently being assessed in phase III trials for the secondary prevention of VTE. Currently, the most promising new therapeutic option is the first of the oral direct thrombin inhibitors, ximelagatran. The THRombin Inhibitor in VEnous thromboembolism (THRIVE) clinical trial programme has demonstrated that this agent is as effective as standard therapy for the acute treatment (THRIVE Treatment) and secondary prevention (THRIVE lll) of VTE events and is well tolerated when used for 6 months or over extended periods up to 1.5 years. Furthermore, with oral administration, fixed dosing and no requirement for anticoagulation monitoring, ximelagatran has the potential to facilitate optimal use and duration of VTE treatment by overcoming the limitations of current agents.

Inherited risk factors for venous thrombosis

Venous thrombosis occurs as a consequence of genetic and environmental risk factors. Since the discovery of factor V Leiden, the most common genetic risk factor, there has been intense interest in clarifying the roles of genes and the environment with thrombosis risk. The translation of this risk information to clinical practice is a challenging one in the setting of a rapidly expanding knowledge base that includes application of genetic medicine. There are benefits, but also potential harms, of testing for inherited disorders associated with thrombosis. This paper reviews inherited risk factors for thrombosis and discuss clinical applications of testing.

Prevention and Treatment of Deep Vein Thrombosis and Pulmonary Embolism in Critically Ill Patients

Deep vein thrombosis and pulmonary embolism remain common problems in the intensive care unit, with limb- and life-threatening complications that are potentially preventable. The intensive care unit clinician is called on to be vigilant with diagnosis and facile with prevention and treatment of thromboembolic disease (venous thromboembolism). This article reviews background, current options, and recommendations regarding the occurrence of deep vein thrombosis and pulmonary embolism in the intensive care unit population.

Prevention of thrombosis with warfarin, aspirin, and mechanical methods

Venous thromboembolism (VTE) is a serious disorder and a major cause of morbidity and mortality among acutely ill medical patients. However, despite the growing number of patients with acute medical illnesses who have an associated risk of VTE, the widespread use of VTE prophylaxis does not yet occur for both surgical and nonsurgical patients. Although individuals at greatest risk for VTE include patients undergoing major orthopedic surgery and those with medical conditions that require prolonged immobilization, all patients who have acute medical illnesses should be considered for VTE prophylaxis. Several strategies, including various mechanical and pharmacologic approaches, are currently used for VTE prophylaxis. Increased awareness about the full range of options for VTE prophylaxis can help health care providers select the appropriate course of action to help reduce the incidence of VTE among patients with acute medical illnesses.

Clinical potential of oral direct thrombin inhibitors in the prevention and treatment of venous thromboembolism

Current antithrombotic therapies are associated with various practical limitations and risks that restrict their utility in the management of venous thromboembolism. The coagulation factor, thrombin, has been the focus of extensive investigation as a pharmacological target in efforts to improve the management of venous thromboembolism. Hirudin, desirudin, bivalirudin and argatroban are direct thrombin inhibitors that have been launched for limited indications as anticoagulants. Their usefulness for long-term prophylaxis is limited by a requirement for parenteral administration, restricted licensing and bleeding/tolerability profile. Ximelagatran--which, after oral administration, is rapidly converted to its active form, melagatran--is the first oral direct thrombin inhibitor and the first new oral anticoagulant to become available in 60 years. Clinical studies have shown that melagatran/ximelagatran, without coagulation monitoring, is effective and well tolerated for the prevention of venous thromboembolism after hip replacement and knee replacement surgery. Ximelagatran is also effective in the acute treatment of venous thromboembolism and long-term secondary prevention of recurrent venous thromboembolism, the prevention of stroke in patients with atrial fibrillation and in the prevention of cardiovascular events after myocardial infarction. Oral direct thrombin inhibitors have a promising role in the management of venous thromboembolism and other associated medical conditions.

[Occlusion of the innominate artery in association with a primary antiphospholipid syndrome: treatment by angioplasty stenting]

INTRODUCTION

Antiphospholipid syndrome may be associated with stroke.

CASE REPORT

We report a case of a symptomatic occlusion of the innominate artery in a 37-year-old patient, who developed primary anti-phospholipid syndrome. This association, to our knowledge, has not been reported in the literature. Occlusion of the innominate artery was treated by angioplasty-stenting. Effective oral anticoagulation was given to prevent a new thrombotic event.

CONCLUSION

Systematic search for antiphospholipid antibodies is needed as part of the etiology work-up in young stroke victims.

Treatment of venous thromboembolism and long-term prevention of recurrence: present treatment options and ximelagatran

Despite the effectiveness of anticoagulant therapy for the treatment of acute venous thromboembolism and the prevention of recurrent venous thromboembolism, existing antithrombotic therapies are suboptimal. Unfractionated heparin, low-molecular-weight heparin (LMWH) and warfarin have practical limitations and carry the risk of treatment-related adverse events that restrict their clinical benefits and reduce cost-effectiveness. Efforts to achieve optimal venous thromboembolism prophylaxis by modifying the intensity of oral warfarin treatment have produced equivocal results, and there is a need for new, efficacious antithrombotic drugs providing predictable, well-tolerated oral dosing without the need for coagulation monitoring. Such agents would ideally have no significant food or drug interactions, and be suitable for both short- and long-term treatment. Ximelagatran, the first oral direct thrombin inhibitor, has the potential to fulfill many of the unmet needs in the management of venous thromboembolism.

Prevention of Recurrent Idiopathic Venous Thromboembolism

Idiopathic venous thromboembolism (VTE), unassociated with surgery or trauma, is a chronic illness that warrants the implementation of strategies to prevent recurrence over a lifetime. Clinical trials show that the benefit associated with extended anticoagulation therapy < or =1 year in patients with idiopathic VTE is not maintained over the long term once treatment is discontinued. Controlled trials have established the efficacy of indefinite-duration anticoagulation, even if the therapy used is a novel agent that is not a coumarin derivative. The PREVENT, ELATE, and THRIVE III trials demonstrate that a strategy of long-term anticoagulation in patients with idiopathic VTE, including those with isolated calf deep vein thrombosis, is safe and effective. This successful strategy appears beneficial across all subgroups, regardless of the presence of an identified thrombophilic state. These include both young and old patients of both sexes, those with factor V Leiden or the prothrombin gene mutation, and those with first-time or recurrent VTE. Thus, the default strategy for idiopathic VTE should be universal anticoagulation unless contraindicated. Implementing this proven approach on a population basis would enable prevention of VTE recurrence with minimal individualization of treatment. Because lifelong therapy can exact a psychological and medical cost on the patient as well as the health care provider, future research should be directed to risk stratification of those most susceptible to recurrence. Avenues of investigation currently being evaluated include measurement of d-dimer levels, examination of residual venous thrombosis on ultrasound, and application of risk nomograms.

The management of thromboembolic disease in patients with central nervous system malignancies

Venous thromboembolic disease (VTE) is a common complication of malignancies affecting the central nervous system (CNS), both in the perioperative period and throughout the disease course. Until recently, the perceived risk of intracranial hemorrhage in patients with CNS malignancies was felt to be a relative contraindication to systemic anticoagulation, and most patients were managed with nonpharmacologic methods in both the prophylactic and treatment setting. However, several studies of the safety and efficacy of anticoagulation in both neurosurgical and cancer patients have challenged the previous dogma, and routine use of unfractionated heparin or low molecular weight heparin (LMWH) for VTE prophylaxis in patients undergoing craniotomy for CNS malignancy is recommended. Likewise, treatment of established VTE in this population with heparins is recommended, at least initially, followed by long-term treatment either with heparin or oral warfarin. Complications of inferior vena cava (IVC) filters, used as an alternative to systemic anticoagulation, appear to be more common in brain tumor patients with VTE, lending further support to treatment with systemic anticoagulation when possible. We advocate a multimodality approach utilizing compression stockings, intermittent compression devices, and heparin in the perioperative setting as the best proven method to reduce the risk of VTE. In the absence of a strict contraindication to systemic anticoagulation, such as previous intracranial hemorrhage or profound thrombocytopenia, LMWH is recommended in brain tumor patients with newly diagnosed VTE, followed by long-term warfarin or LMWH.

[Treatment of deep vein thrombosis. When to use which substance?]

Current antithrombotic therapy of deep vein thrombosis (DVT) consists of an initial course of heparin, followed by the secondary prevention with oral anticoagulation (OAC). Low molecular weight heparin has several advantages over unfractionated heparin, however, renal insufficiency has to be observed to avoid accumulation. The synthetic pentasaccharide Fondaparinux is a factor Xa inhibitor, that will shortly be available for the initial treatment of DVT. Oral anticoagulation with vitamin K antagonists (VKA) is highly effective, the standard target INR is 2.0-3.0. For a first episode of DVT the duration of OAC usually is six months, but has to be adjusted according to the estimated risk for recurrence. Because of the narrow therapeutic window of VKA, low molecular weight heparins are increasingly being used for secondary prevention in patients with an increased risk for bleeding, mostly in 1/2-therapeutic dose. At present, several new antithrombotic agents are being studied and may become available shortly for DVT treatment.

Early Evaluation of Hematuria in a Patient Receiving Anticoagulant Therapy and Detection of Malignancy

A 63-year-old Caucasian man had a painless episode of dark-colored urine while taking warfarin 62.5 mg/week for lone atrial fibrillation in the presence of documented stable anticoagulation. Urinalysis revealed microscopic hematuria. Three weeks later, he had an episode of gross, painless hematuria. Thorough evaluation of the upper and lower urinary tract with renal ultrasound, intravenous pyelography, and cystoscopy revealed poorly differentiated, early-stage, transitional cell carcinoma of the bladder. The patient was not aware of any exposure to carcinogens known to predispose to bladder cancer, nor was he a tobacco user. Early identification of the malignancy allowed for aggressive surgical intervention. Although this patient was considered low risk for the development of bladder cancer and was taking anticoagulants, the presence of hematuria was indicative of underlying pathology. Timely and thorough evaluation of hematuria in patients taking anticoagulants is necessary to identify and treat clinically important pathology.

Warfarin reversal: consensus guidelines, on behalf of the Australasian Society of Thrombosis and Haemostasis

For most warfarin indications, the target maintenance international normalised ratio (INR) is 2-3. Risk factors for bleeding complications with warfarin use include age, history of past bleeding and specific comorbid conditions. To reverse the effects of warfarin, vitamin K(1) can be given. Immediate reversal is achieved with a prothrombin complex concentrate (PCC) and fresh frozen plasma (FFP). Vitamin K(1) is essential for sustaining the reversal achieved by PCC and FFP. When oral vitamin K(1) is used for warfarin reversal, the injectable formulation of vitamin K(1) is preferable to tablets because of its flexible dosing; this formulation can be given orally or injected. To temporarily reverse the effect of warfarin when there is a need to continue warfarin therapy, vitamin K(1) should be given in a dose that will quickly lower the INR to a safe, but not subtherapeutic, range and will not cause resistance once warfarin is reinstated. Prothrombinex-HT is the only PCC approved in Australia and New Zealand for warfarin reversal. It contains factors II, IX and X, and low levels of factor VII. FFP should be added to Prothrombinex-HT as a source of factor VII when used for warfarin reversal. Simple dental or dermatological procedures may not require interruption to warfarin therapy. If necessary, warfarin therapy can be withheld 5 days before elective surgery, when the INR usually falls to below 1.5 and surgery can be conducted safely. Bridging anticoagulation therapy for patients at high risk for thromboembolism should be undertaken in consultation with the relevant experts.

The pharmacology and management of the vitamin K antagonists: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy

This article concerning the pharmacokinetics and pharmacodynamics of vitamin K antagonists (VKAs) is part of the Seventh American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. The article describes the antithrombotic effect of VKAs, the monitoring of anticoagulation intensity, the clinical applications of VKA therapy, and the optimal therapeutic range of VKAs, and provides specific management recommendations. Grade 1 recommendations are strong, and indicate that the benefits do, or do not, outweigh the risks, burdens, and costs. Grade 2 suggests that individual patient's values may lead to different choices (for a full understanding of the grading see Guyatt et al, CHEST 2004; 126:179S-187S). Among the key recommendations in this article are the following: for dosing of VKAs, we suggest the initiation of oral anticoagulation therapy with doses between 5 and 10 mg for the first 1 or 2 days for most individuals, with subsequent dosing based on the international normalized ratio (INR) response (Grade 2B). In the elderly and in other patient subgroups with an elevated bleeding risk, we suggest a starting dose at < or = 5 mg (Grade 2C). We recommend basing subsequent doses after the initial two or three doses on the results of INR monitoring (Grade 1C). The article also includes several specific recommendations for the management of patients with INRs above the therapeutic range and for patients requiring invasive procedures. For example, in patients with mild to moderately elevated INRs without major bleeding, we suggest that when vitamin K is to be given it be administered orally rather than subcutaneously (Grade 1A). For the management of patients with a low risk of thromboembolism, we suggest stopping warfarin therapy approximately 4 days before they undergo surgery (Grade 2C). For patients with a high risk of thromboembolism, we suggest stopping warfarin therapy approximately 4 days before surgery, to allow the INR to return to normal, and beginning therapy with full-dose unfractionated heparin or full-dose low-molecular-weight heparin as the INR falls (Grade 2C). In patients undergoing dental procedures, we suggest the use of tranexamic acid mouthwash (Grade 2B) or epsilon amino caproic acid mouthwash without interrupting anticoagulant therapy (Grade 2B) if there is a concern for local bleeding. For most patients who have a lupus inhibitor, we suggest a therapeutic target INR of 2.5 (range, 2.0 to 3.0) [Grade 2B]. In patients with recurrent thromboembolic events with a therapeutic INR or other additional risk factors, we suggest a target INR of 3.0 (range, 2.5 to 3.5) [Grade 2C]. As models of anticoagulation monitoring and management, we recommend that clinicians incorporate patient education, systematic INR testing, tracking, and follow-up, and good communication with patients concerning results and dosing decisions (Grade 1C+).

Antithrombotic therapy for venous thromboembolic disease: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy

This chapter about antithrombotic therapy for venous thromboembolic disease is part of the seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy: Evidence Based Guidelines. Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs. Grade 2 suggests that individual patients' values may lead to different choices (for a full understanding of the grading see Guyatt et al, CHEST 2004; 126:179S-187S). Among the key recommendations in this chapter are the following: for patients with objectively confirmed deep vein thrombosis (DVT), we recommend short-term treatment with subcutaneous (SC) low molecular weight heparin (LMWH) or, alternatively, IV unfractionated heparin (UFH) [both Grade 1A]. For patients with a high clinical suspicion of DVT, we recommend treatment with anticoagulants while awaiting the outcome of diagnostic tests (Grade 1C+). In acute DVT, we recommend initial treatment with LMWH or UFH for at least 5 days (Grade 1C), initiation of vitamin K antagonist (VKA) together with LMWH or UFH on the first treatment day, and discontinuation of heparin when the international normalized ratio (INR) is stable and > 2.0 (Grade 1A). For the duration and intensity of treatment for acute DVT of the leg, the recommendations include the following: for patients with a first episode of DVT secondary to a transient (reversible) risk factor, we recommend long-term treatment with a VKA for 3 months over treatment for shorter periods (Grade 1A). For patients with a first episode of idiopathic DVT, we recommend treatment with a VKA for at least 6 to 12 months (Grade 1A). We recommend that the dose of VKA be adjusted to maintain a target INR of 2.5 (INR range, 2.0 to 3.0) for all treatment durations (Grade 1A). We recommend against high-intensity VKA therapy (INR range, 3.1 to 4.0) [Grade 1A] and against low-intensity therapy (INR range, 1.5 to 1.9) compared to INR range of 2.0 to 3.0 (Grade 1A). For the prevention of the postthrombotic syndrome, we recommend the use of an elastic compression stocking (Grade 1A). For patients with objectively confirmed nonmassive PE, we recommend acute treatment with SC LMWH or, alternatively, IV UFH (both Grade 1A). For most patients with pulmonary embolism (PE), we recommend clinicians not use systemic thrombolytic therapy (Grade 1A). For the duration and intensity of treatment for PE, the recommendations are similar to those for DVT.

Invasive approaches to treatment of venous thromboembolism

Deep vein thrombosis (DVT) occurs in one-quarter of a million individuals annually in the United States and results in significant disability from pulmonary embolism and chronic venous insufficiency, especially when the proximal iliofemoral is involved. Treatment has centered on early institution of adequate anticoagulation to prevent thrombus propagation and embolism, but anticoagulation alone does not always restore venous patency and many patients are left with venous outflow obstruction and valvular incompetence-the anatomic underpinnings of the postthrombotic syndrome. Various strategies have been used to restore patency of thrombosed veins, including open surgical thrombectomy, pharmacological thrombolysis, and percutaneous mechanical thrombectomy. Each modality has benefits and shortcomings. Surgical thrombectomy had previously been abandoned secondary to poor long-term results. More recently, with improved techniques and better patient selection, surgical thrombectomy has regained a therapeutic role in treating acute DVT in young patients with short segment occlusions. The advent of percutaneous techniques has allowed thrombolysis, percutaneous mechanical thrombectomy, and stenting to be used in conjunction with each other-allowing for better resolution of venous clot burden than when an individual modality is used alone. Practitioners who treat patients with DVT should be familiar with all the options available to restore venous patency, preserve valvular function, and thereby minimize the risk of late postthrombotic complications.

New anticoagulants for treatment of venous thromboembolism

Treatment of venous thromboembolism (VTE) usually starts with concomitant administration of heparin or low-molecular-weight heparin (LMWH) and a vitamin K antagonist. The parenteral anticoagulant, which is given for at least 5 days, is stopped once the vitamin K antagonist produces a therapeutic level of anticoagulation. Although the introduction of LMWH has simplified the initial treatment of VTE, problems remain. LMWH must be given by daily subcutaneous (SC) injection and vitamin K antagonists require routine coagulation monitoring, which is inconvenient for patients and physicians. Recently, 3 new anticoagulants have been introduced in an attempt to overcome these limitations. These include fondaparinux and idraparinux, synthetic analogs of the pentasaccharide sequence that mediates the interaction of heparin and LMWH with antithrombin, and ximelagatran, an orally active inhibitor of thrombin. These agents produce a predictable anticoagulant response; thus, routine coagulation monitoring is unnecessary. Because they do not bind to platelets or platelet factor 4, fondaparinux and idraparinux do not cause heparin-induced thrombocytopenia (HIT). Unlike vitamin K antagonists, ximelagatran has a rapid onset of action, thereby obviating the need for concomitant administration of a parenteral anticoagulant when starting treatment. The lack of an antidote for these new agents is a drawback, particularly for idraparinux, which has a long half-life.

The Role of Oral Direct Thrombin Inhibitors in the Treatment of Venous Thromboembolism

Unfractionated heparin and warfarin have been the mainstay of treatment of venous thromboembolism (VTE) for approximately half a century. However, both agents are difficult to dose accurately, require frequent blood testing and dosage adjustment, and can cause serious adverse effects. Oral direct thrombin inhibitors may provide more predictable anticoagulation with oral dosing, without the need for frequent blood test monitoring and without the adverse effects seen with conventional agents. The oral direct thrombin inhibitor closest to being marketed is ximelagatran, which has been through phase III trials. Available data thus far suggest that the efficacy and safety of this agent may allow it to replace both heparin (and low-molecular-weight heparin) and warfarin for VTE treatment and long-term prophylaxis. Concerns about ximelagatran that require further study are a 5-9% rate of transient elevation in liver enzyme levels, drug interactions, how patient adherence can be ensured in the absence of blood tests, and whether alterations in renal or hepatic function will require dosage adjustments. Although there is more to learn about ximelagatran, available data suggest that it is likely to be the most significant therapeutic advance in this area in over 50 years.

Pulmonary Embolism

Pulmonary embolism is a commonly suspected but underdiagnosed condition of clinical significance. Preventable deaths continue to occur. We begin this article with an overview of prognosis, clinical evidence, signs and symptoms, and risk factors, followed by an in-depth evaluation of diagnostic techniques and treatment modalities. The greatest improvement in mortality from pulmonary embolism is likely to come from improved and aggressive prevention and prophylaxis by the critical care team.

Anticoagulation in Hypercoagulable Conditions: Special Considerations in the Treatment and Prevention of Venous Thromboembolism

Patients with hypercoagulable conditions, including malignancy, are at increased risk of recurrent venous thromboembolic events (VTE). The general approach to treatment and prevention of VTE in patients with thrombophilia is similar to that of patients who present with VTE associated with transient risk factors, including immobility, trauma, and surgery. However, several important issues must be considered in the initial management of acute VTE, in the long-term prevention of VTE following an initial event, and in VTE prophylaxis in patients with hypercoagulable conditions. Patients with antithrombin deficiency are prone to heparin resistance and may require concurrent antithrombin concentrates or anticoagulation with direct thrombin inhibitors for adequate treatment of acute VTE. In patients with malignancy, low-molecular-weight heparins have been found to be more effective than unfractionated heparin for the initial treatment of VTE. Long-term prevention is preferred for most patients with hypercoagulable conditions, and the latest trials show that low-intensity warfarin is not as effective as typical moderate-intensity therapy for chronic therapy. Primary prophylaxis of asymptomatic carriers is not warranted unless they are exposed to additional risk factors, including surgery, trauma, immobilization, and pregnancy. Prolonged prophylaxis may be appropriate in patients with malignancy who undergo surgical procedures.

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.

Ximelagatran: an oral direct thrombin inhibitor

OBJECTIVE

To present the chemistry, pharmacology, and pharmacokinetics of ximelagatran, an oral direct thrombin inhibitor (DTI), and to review available comparative clinical trial data evaluating its efficacy and safety relative to other antithrombotic agents in the prevention and treatment of thromboembolism.

DATA SOURCES

A search of the PubMed and Cochrane databases (1995-August 2004), supplemented by a manual search of article bibliographies, conference abstracts, and data on file from the manufacturer, was conducted. Key search terms were ximelagatran, melagatran, H376/95, and direct thrombin inhibitors.

STUDY SELECTION AND DATA EXTRACTION

Pertinent information from available clinical trials, including study design, patient demographics, dosing regimens, anticoagulant comparators, methods for evaluating effectiveness, treatment outcomes, adverse events, and pharmacokinetic and pharmacodynamic evaluations, was extracted.

DATA SYNTHESIS

Ximelagatran is an orally administered DTI under development for use in the treatment of venous thromboembolism (VTE), long-term prevention of a second VTE event, stroke secondary to atrial fibrillation, prevention of VTE after orthopedic procedures, and recurrent ischemic events after acute myocardial infarction.

CONCLUSIONS

Ximelagatran, in twice-daily doses of 24 or 36 mg, is an alternative to low-molecular-weight heparins or warfarin in thromboprophylaxis following orthopedic knee replacement, atrial fibrillation, or initial treatment of VTE. Improved outcomes versus placebo were seen in the long-term prevention of VTE in patients who completed an initial 6 months of treatment. Liver-related effects need further clarification.

Low intensity warfarin: is it clinically useful in venous thromboembolism management?

Therapy for a first episode of venous thromboembolism (VTE) typically includes a vitamin K antagonist, such as warfarin, for 3-6 months at an international normalized ratio (INR) of 2-3. After the cessation of warfarin therapy, unprovoked VTE is associated with a recurrence rate of 5-15% per year. Prolonging initial therapy does not reduce the recurrence risk once warfarin is discontinued and is not routinely recommended for such patients. The Prevention of Recurrent Venous Thromboembolism (PREVENT) and Extended Low-Intensity Anticoagulation for Thromboembolism (ELATE) trials were undertaken to evaluate the efficacy and safety of low-intensity warfarin (INR 5-2) in this population. While both trials demonstrated that low-intensity warfarin offers substantial protection against recurrent VTE, only the ELATE trial included a standard intensity arm; this arm showed a significantly lower recurrence rate and a major bleed rate that, surprisingly, was similar to the low-intensity arm. There still remains no consensus that long-term warfarin at an INR of 2-3 should be recommended for all patients who sustain a first unprovoked venous thromboembolic event, which largely stems from our current inability to reliably identify those patients most likely to develop recurrences. Given that an individualized approach is required in deciding the duration of anticoagulation, it is the author's belief that low-intensity warfarin, which the PREVENT trial demonstrated could be monitored every other month, is a useful option for some patients with a first episode of VTE.

Bleeding profiles of anticoagulants, including the novel oral direct thrombin inhibitor ximelagatran: definitions, incidence and management

Ximelagatran is a novel oral direct thrombin inhibitor (oral DTI) that is currently in advanced clinical development for the prevention and treatment of thromboembolic events in a wide range of patient populations and indications. The clinical development of novel anticoagulant therapies requires that treatments be assessed according to both their clinical benefit (reduction of risk of thromboembolic events) and safety profile (primarily bleeding). Definition and assessment of bleeding severity is thus an important factor in clinical trial design. Lack of consistency in bleeding definitions used in different clinical trial programmes makes comparison of bleeding event data difficult. Standard bleeding definitions would be required to make fair comparisons between clinical trials possible. The definitions of bleeding events used in clinical trials of ximelagatran are broadly consistent with those used in many other major trials. Results of phase II and III trials comparing ximelagatran with currently available anticoagulant therapies demonstrate that ximelagatran can be used with fixed dosing with no coagulation monitoring, dose titration, or dose adjustment, without compromising efficacy or safety. The incidences of major bleeding events in clinical trials of ximelagatran have been low and similar to those with other anticoagulant drugs. Adequate treatment in case of emergency situations such as serious bleeding should include cessation of treatment and maintenance of adequate diuresis.

Hemorrhagic Complications of Anticoagulant Treatment

This chapter about hemorrhagic complications of anticoagulant treatment is part of the seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy: Evidence Based Guidelines. Bleeding is the major complication of anticoagulant therapy. The criteria for defining the severity of bleeding varies considerably between studies, accounting in part for the variation in the rates of bleeding reported. The major determinants of vitamin K antagonist-induced bleeding are the intensity of the anticoagulant effect, underlying patient characteristics, and the length of therapy. There is good evidence that vitamin K antagonist therapy, targeted international normalized ratio (INR) of 2.5 (range, 2.0 to 3.0), is associated with a lower risk of bleeding than therapy targeted at an INR > 3.0. The risk of bleeding associated with IV unfractionated heparin (UFH) in patients with acute venous thromboembolism (VTE) is < 3% in recent trials. This bleeding risk may increase with increasing heparin dosages and age (> 70 years). Low molecular weight heparin (LMWH) is associated with less major bleeding compared with UFH in acute VTE. UFH and LMWH are not associated with an increase in major bleeding in ischemic coronary syndromes, but are associated with an increase in major bleeding in ischemic stroke. Information on bleeding associated with the newer generation of antithrombotic agents has begun to emerge. In terms of treatment decision making for anticoagulant therapy, bleeding risk cannot be considered alone, ie, the potential decrease in thromboembolism must be balanced against the potential increased bleeding risk.