Use of an algorithm for administering subcutaneous heparin in the treatment of deep venous thrombosis

How I treat venous thromboembolism in patients with cancer

Venous thromboembolism (VTE) is a frequent complication in cancer patients and represents an important cause of morbidity and mortality. Especially in patients who have a poor life expectancy, preventing death from pulmonary embolism is the mainstay of treatment. Critically ill patients should promptly be administered thrombolytic drugs. Except for selected patients requiring aggressive therapy, the initial VTE treatment should be conducted with either adjusted-dose unfractionated heparin or fixed-dose low-molecular-weight heparin (LMWH). LMWHs have the potential to greatly simplify the initial treatment of VTE, making the treatment of suitable patients feasible in an outpatient setting. During anticoagulant therapy, cancer patients have a 2- to 4-fold higher risk of recurrent VTE and major bleeding complications when compared with noncancer patients. The long-term administration of LMWH should be considered as an alternative to anti-vitamin K drugs in patients with advanced disease and in those with conditions limiting the use of oral anticoagulants. Prolongation of anticoagulation should be considered for as long as the malignant disorder is active. The evidence of lowered cancer mortality in patients on LMWH has stimulated renewed interest in these agents as antineoplastic drugs and raises the distinct possibility that cancer and thrombosis share common mechanisms.

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.

Pharmacokinetics of UH and LMWH are similar with respect to antithrombin activity

BACKGROUND

The ability to administer low molecular weight heparins (LMWH) subcutaneously without laboratory monitoring contributes to their popularity for the treatment of thrombotic disorders. Subcutaneous unfractionated heparin, although less expensive, is deemed to require routine laboratory monitoring on the basis of more variability in drug effect compared to LMWH. However, the more predictable pharmacokinetic profiles of low molecular weight heparins are largely based on anti-Xa activity, while antithrombin activity may be at least as important to their mechanisms of action.

METHODS

We performed a clinical pharmacokinetic trial to compare the variability in peak antithrombin effect between subcutaneous unfractionated heparin and various LMWHs, all given in recommended weight-adjusted treatment doses. Sixty-one patients enrolled in a warfarin clinic were randomized to receive one of four different weight-adjusted subcutaneous heparin doses: unfractionated heparin, 250 units/kg (n=15); tinzaparin, 175 units/kg (n=15); dalteparin, 200 units/kg (n=15); or enoxaparin, 1 mg/kg (n=16). The areas under the curves of antithrombin levels during the first 3 h after administration were determined for each patient, and the coefficients of variation (CV) and 95% confidence intervals of the AUCs were compared among the treatment groups.

RESULTS

There was no statistically significant difference in the coefficients of variation of antithrombin effect between unfractionated heparin (52.8, 95% CI: 32.6-72.9) and enoxaparin (56.5, 95% CI: 35.7-77.4) or dalteparin (43.5, 95% CI 25.4-61.6). Tinzaparin had statistically significant decrease in coefficients of variation (21.6, 95% CI: 12.2-30.9) relative to unfractionated heparin, dalteparin and enoxaparin.

CONCLUSIONS

LMWHs, as a class of drugs, are no more predictable in antithrombin effect after subcutaneous injection than unfractionated heparin. There were considerable differences among LMWHs in the observed variability of antithrombin effects, with tinzaparin being somewhat more predictable than the other drugs tested.

Perioperative anticoagulation management in patients who are receiving oral anticoagulant therapy: a practical guide for clinicians

The management of patients who require temporary interruption of oral anticoagulant therapy because of surgery or other invasive procedures is a clinically important topic because of the increasing prevalence of patients who are receiving oral anticoagulants and the availability of low-molecular-weight heparins (LMWHs), which allow out-of-hospital perioperative anticoagulation. The optimal management of such patients has been hampered by the lack of well-designed prospective studies investigating the efficacy and safety of different perioperative management strategies. The two main issues that need to be considered in perioperative anticoagulant management is the patient's risk of thromboembolic event when anticoagulant therapy is interrupted and the risk of bleeding that is associated with the surgery or procedure. An assessment of these factors will determine the perioperative management approach. The objectives of this review are to focus on practical issues relating to perioperative anticoagulation and the implementation of a perioperative anticoagulation management approach that can be used in everyday clinical practice.

Pulmonary embolism

Pulmonary embolism (PE) is a common problem for which prompt diagnosis and treatment is essential to minimize mortality. The clinical presentation is more variable than sudden dyspnea and chest pain, especially in the critical care patient. Recognition of venous thromboembolic (VTE) risk factors can help develop a good clinical suspicion for PE. A wide range of diagnostic tests are available to the clinician. The ventilation/perfusion scan, pulmonary arteriogram, and lower extremity investigations are still important for diagnosis. Other noninvasive tests such as spiral CT with venography, echocardiography, and D-dimers are becoming more accepted. Heparin is the mainstay of PE therapy, but thrombolytic treatment may be lifesaving in the unstable patient. VTE prophylaxis should be considered in all post-operative or critical care patients.

The diagnosis of lower extremity deep venous thrombosis

The diagnosis of lower extremity deep venous thrombosis (DVT) is critical to emergency physicians because of the risk of pulmonary embolism. This article reviews the diagnostic modalities available for patients with suspected lower extremity DVT. The use of compression ultrasonography and the recent advances in the D-dimer assays are emphasized. A clinical algorithm that utilizes a non invasive approach to this potentially life threatening disease is presented.

Direct and indirect antithrombins. Heparins, low molecular weight heparins, heparinoids, and hirudin

With the eclipse of UH by newer anticoagulants, the field has opened up to search for new and better drugs. Hirulog or bivalirudin is another direct antithrombin that has been used in initial trials. It is smaller than hirudin, at 20 amino acids. Currently under investigation, it seems to have a short half-life, a narrow therapeutic window, and a reverse dose effect, with lower levels achieving better cardiac post-thrombolysis patency than higher doses. Other antithrombins being examined are the hirudisins, where four amino acids of hirudin have been replaced by the RGDS integrin-binding sequence and thrombin receptor antagonist peptides. In addition, many other inhibitors of activated clotting factors are being studied for future therapeutic value. Tick anticoagulant protein studies are underway, as are studies on a group of benzamidine isoxazoline derivates, which are direct Xa inhibitors. We are truly at an age of discovery with the newer anticoagulants and it may take many years until we can distinguish the advantages and disadvantages of all the newer therapies. It looks like an ever more real possibility that medicine may find an antithrombotic regimen that is highly effective, highly reversible, and nontoxic.

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-vein thrombosis of the lower limbs: diagnosis and management

Acute deep venous thrombosis (DVT) of the lower extremities is a serious and potentially fatal disorder which often complicates the course of severely ill, hospitalized patients but may also affect ambulatory and otherwise healthy people. It is uncommon in young individuals and becomes more frequent with advancing age. The clinically important problems associated with DVT are death from pulmonary embolism (PE), morbidity resulting from the acute event, the post-thrombotic syndrome, and the inconvenience and side-effects of investigations and treatment. Furthermore, an often underemphasized problem is the anxiety that may occur in those patients who have suffered a thrombotic episode.