Shortened hospitalization by means of adjusted-dose subcutaneous heparin for deep venous thrombosis

Therapeutic monitoring of unfractionated heparin - trials and tribulations

INTRODUCTION

Heparin is one of the oldest biological medicines with an established role in prevention and treatment of arterial and venous thromboembolism. Published therapeutic ranges for unfractionated heparin (UFH) mostly precede the large increase in the number of activated partial thromboplastin time (APTT) reagent/instrument combinations that now show wide variability. Areas covered: This paper explores the use of UFH, the development of heparin therapeutic ranges (HTRs), and the strengths and limitations of the methods used to monitor heparin's anticoagulant effect. Expert commentary: Despite longstanding use of UFH for management of thromboembolic conditions, the optimal test for monitoring UFH remains undetermined. Although used extensively for monitoring UFH, routine APTT-derived HTRs are based on limited science that may have little relevance to current laboratory practice. Anti-FXa levels may provide better and more reliable HTRs; however, even these levels show considerable inter-laboratory variation, and there are insufficient clinical studies proving improved clinical efficacy. Alternative tests for monitoring UFH reported over time have not been proven effective nor feasible, secondary to technical or cost issues, or lack of general adoption. Thus, despite limited evidence of clinical utility, an uncomfortable marriage of convenience represented by heparin laboratory monitoring is unlikely to be terminated in the immediate future.

Periprocedural management of the chronically anticoagulated patient: critical pathways for bridging therapy

Periprocedural bridging of the patient on long-term anticoagulation is indicated in nonvalvular atrial fibrillation with additional risk factors, prosthetic heart valves, venous thromboembolism within 3 months of the procedure, and hypercoagulable conditions requiring oral anticoagulation. Until recently, intravenous unfractionated heparin was used for bridging. LMWH has now emerged as a safe and effective bridging alternative.

Subcutaneous unfractionated heparin compared with low-molecular-weight heparin for the initial treatment of venous thromboembolism

PURPOSE OF REVIEW

Low-molecular-weight heparin is the preferred choice for the initial treatment of acute, uncomplicated venous thromboembolism. In this context, unfractionated heparin is as safe and effective as low-molecular-weight heparin but requires strict laboratory monitoring. Twice-daily subcutaneous unfractionated heparin is more effective than, and as safe as, intravenous unfractionated heparin and may simplify patient treatment in or out of the hospital, being possibly cost saving, especially if it is used in weight-based, fixed, unadjusted doses. The present review focuses on the relative values of low-molecular-weight heparin and subcutaneous unfractionated heparin for the initial treatment of venous thromboembolism.

RECENT FINDINGS

The major advantages of low-molecular-weight heparin over unfractionated heparin seem to be ease of administration and cost savings associated with home therapy or early hospital discharge; however, many patients with venous thromboembolism are still admitted to the hospital for treatment, and unfractionated heparin is extensively used to this purpose, especially in the United States. Subcutaneous unfractionated heparin, adjusted according to activated partial thromboplastin time algorithms, is as safe and effective as low-molecular-weight heparin for the treatment of venous thromboembolism, allows for quick mobilization and early discharge of suitable patients, and represents a cost-effective strategy. Fixed-dose unfractionated heparin, like low-molecular-weight heparin, may be used for the home treatment of deep vein thrombosis.

SUMMARY

Subcutaneous unfractionated heparin, targeted on activated partial thromboplastin time results or in fixed doses, may be used in or out of the hospital for the treatment of venous thromboembolism, being possibly cost effective; however, these findings need confirmation through appropriate, large-sample, randomized clinical trials.

[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.

Heparin and low molecular weight heparin: background and pharmacology

The various LMWHs available for therapeutic use have multiple mechanisms of action, most of which are similar to the mechanisms of UH. The relative potencies of expression of the mechanisms differ between LMWH and UH and among specific LMWHs. The pharmacokinetics of LMWHs and UH are often measured according to the results of anti-Xa assays, although the correlation between anti-Xa levels and the antithrombotic activities of the drugs is questionable. Animal models of thrombosis give some information regarding the antithrombotic efficacy of different LMWHs when compared with UH and with other LMWHs, but the results are not directly applicable to human thrombosis. Unfortunately, no single measure of antithrombosis has been developed in humans whereby the potencies of LMWHs, UH, and other new anticoagulants can be directly compared. Large clinical outcome studies are expensive and difficult to carry out. Perhaps for this reason, different subcutaneous LMWHs have not been compared with each other in this format. Various LMWHs have demonstrated equivalent efficacy and safety when compared with intravenous UH and high-dose subcutaneous UH, and it is reasonable to assume that there would not be large differences in efficacy and safety among different agents. The superiority of one subcutaneous regimen over another can be confirmed (or refuted) only by the performance of well-planned clinical studies.

Venous thromboembolism guidebook

This venous thromboembolism guidebook incorporates evolving contemporary concepts in diagnosis and management of pulmonary embolism (PE) and deep venous thrombosis (DVT) into a user-friendly menu. The purpose of this document is to provide a literature-based review of the current clinical approach to venous thromboembolism and up-to-date references for further study in this important topic.

Optimal dosing of subcutaneous unfractionated heparin for the treatment of deep vein thrombosis

Twice-daily, inpatient, subcutaneous unfractionated heparin is at least as effective and safe as continuous intravenous unfractionated heparin for the treatment of acute deep vein thrombosis. Subcutaneous unfractionated heparin therefore may be suitable for outpatient treatment of deep vein thrombosis. The purpose of this study was to develop a dosing nomogram for a dose each 12 hours (2 doses per day) 12-hourly subcutaneous unfractionated heparin that is suitable for outpatient treatment of acute deep vein thrombosis. A cohort study was performed in patients with acute deep vein thrombosis in two phases. In both phases, the first subcutaneous loading dose of unfractionated heparin was 317 U/kg, and the second dose was 231 U/kg. The activated partial thromboplastin time was measured daily, 6 hours after the morning injection, and subsequent doses of unfractionated heparin were adjusted according to a nomogram, which was modified for phase II. Warfarin was started with unfractionated heparin. In phase I (14 outpatients), activated partial thromboplastin time results were frequently subtherapeutic (9:14) the day after starting unfractionated heparin (day 1), and were frequently supratherapeutic (27:40) after the first 2 days of unfractionated heparin therapy. In phase II (21 patients), to explain the frequently subtherapeutic activated partial thromboplastin time results that were obtained on day 1, the activated partial thromboplastin time results were measured after the initial loading dose. Mean activated partial thromboplastin time results of 86 and 61 seconds were obtained 6 and 12 hours after this dose, suggesting that 317 U/kg is a suitable subcutaneous loading dose. In contrast to phase I, in phase II, unfractionated heparin dose was not increased on day 1 in response to a low activated partial thromboplastin time result. This reduced the frequency of supratherapeutic activated partial thromboplastin time results during the early days of therapy without increasing the frequency of subtherapeutic results. Warfarin therapy had a substantal effect on the activated partial thromboplastin time that appeared to account for a high frequency of supratherapeutic results during the later days of unfractionated heparin therapy; the activated partial thromboplastin time increased by 20 seconds (95% CI, 14-27 seconds) with each increase in the International Normalized Ratio of 1.0. We had limited success at developing a dosing nomogram for subcutaneous unfractionated heparin that reliably achieved activated partial thromboplastin time results within the therapeutic range. However, as oral anticoagulants directly increased activated partial thromboplastin time results, we suggest that adjusting unfractionated heparin dose to achieve prespecified activated partial thromboplastin time results may not be appropriate in patients who are receiving concomitant warfarin therapy.

Deep venous thrombosis: early discharge strategies and outpatient management

Conventional management of acute deep venous thrombosis (DVT) consists of initiating continuous infusion intravenous unfractionated heparin (UFH) for 5 days in the hospital as well as warfarin. Low-molecular-weight heparins (LMWHs) appear to confer similar protection against recurrent DVT compared with UFH but exhibit prolonged bioavailability; increased ease of dosing, and fewer side effects. The advent of LMWH has resulted in increased numbers of patients undergoing initial management of acute DVT with only several days of hospitalization. While 3-month follow-up studies with LMWH demonstrate similar efficacy and safety to UFH, longer term experience with these new agents is necessary to determine their optimal use and safety. We suggest a system for triage in the initial management of DVT patients for: (1) complete outpatient management with LMWH, or (2) short-term hospitalization for initiation of LMWH, or (3) 5-day hospitalization for treatment with UFH. A review of DVT management with LMWH and algorithms for each of these pathways are provided.

Prevention and treatment of venous thromboembolism after major trauma

In prospective studies the incidence of deep venous thrombosis, documented by venography, is between 35% and 63% in patients with major trauma. Five independent risk factors for deep vein thrombosis have been identified in these patients: older age, fracture of the femur or tibia, surgery, spinal cord injury and blood transfusion. Mechanical antithrombotic methods and low-dose unfractionated heparin administered subcutaneously moderately decrease the risk of venous thromboembolism but are less effective than a fixed dose of subcutaneous unmonitored low molecular weight heparin. Prophylaxis with oral anticoagulants (International Normalized Ratio 2.0-3.0) is also effective but is much less used because of the bleeding risk. This is particularly the case in patients with intracranial neurosurgery and acute spinal cord injury. Only a few clinical studies have evaluated the treatment of venous thromboembolism in patients with major trauma. If the condition of a patient with major injury allows, the treatment of venous thromboembolism recommended after hip replacement is cautiously applied.

Cancer and venous thromboembolism

Neoplastic cells can activate the clotting system directly, thereby generating thrombin, or indirectly, by stimulating mononuclear cells to synthesize and express various procoagulants. Clinical manifestations of increased thrombin generation may be accentuated by down-regulation of endothelial cell counterregulatory mechanisms, such as decreased hepatic synthesis of antithrombin III and protein C. Cancer cells and chemotherapeutic agents can injure endothelial cells, thereby intensifying hypercoagulability. In addition, normal endothelial cell function. may be disrupted by various defects in platelet function. Currently, primary prevention of venous thrombosis should be considered for cancer patients (1) during and immediately after chemotherapy, (2) when long-term indwelling central venous catheters are placed; or (3) when hospitalization for cancer is characterized by prolonged immobilization, trauma, or surgery. Secondary prevention of recurrent venous thrombosis usually necessitates anticoagulation. In some patients with cancer, the condition is resistant to warfarin, and long-term adjusted high-dose heparin is required. For patients unable to tolerate heparin or warfarin because of major bleeding problems, placement of an inferior vena caval filter should be considered. The diagnosis of venous thrombosis may help to uncover previously occult carcinoma by prompting a complete physical examination, chest roentgenography, and mammography. However, extensive cancer screening with total-body computed tomography or magnetic resonance imaging has not been shown to be cost effective for patients with venous thrombosis.