Subcutaneous Low-Molecular-Weight Heparin Fragmin Versus Intravenous Unfractionated Heparin in the Treatment of Acute Non Massive Pulmonary Embolism: An Open Randomized Pilot Study

Bleeding Risk in Elderly Patients with Venous Thromboembolism Who Would Have Been Excluded from Anticoagulation Trials

Older patients with venous thromboembolism (VTE) are underrepresented in clinical anticoagulation trials. We examined to which extent elderly patients with VTE would be excluded from such trials and compared the bleeding risk between hypothetically excluded and enrolled patients. We studied 991 patients aged ≥65 years with acute VTE in a prospective multicenter cohort. We identified 12 landmark VTE oral anticoagulation trials from the eighth and updated ninth American College of Chest Physician Guidelines. For each trial, we abstracted the exclusion criteria and calculated the proportion of our study patients who would have been excluded from trial participation. We examined the association between five common exclusion criteria (hemodynamic instability, high bleeding risk, comorbidity, co-medication, and invasive treatments) and major bleeding (MB) within 36 months using competing risk regression, adjusting for age, sex, and periods of anticoagulation. A median of 31% (range: 20-52%) of our patients would have been excluded from participation in the landmark trials. Hemodynamic instability (sub-hazard ratio [SHR]: 2.2, 95% CI: 1.1-4.7), comorbidity (SHR: 1.5, 95% CI: 1.1-2.2), and co-medication (SHR: 1.5, 95% CI: 1.0-2.3) were associated with MB. Compared to eligible patients, those with ≥2 exclusion criteria had a twofold (SHR: 2.16, 95% CI: 1.38-3.39) increased risk of MB. Overall, about one-third of older patients would not be eligible for participation in guideline-defining VTE anticoagulation trials. The bleeding risk increases significantly with the number of exclusion criteria present. Thus, results from such trials may not be generalizable to older, multimorbid, and co-medicated patients.

Once versus twice daily enoxaparin for the initial treatment of acute venous thromboembolism

Essentials In venous thromboembolism (VTE), it is uncertain if enoxaparin should be given twice or once daily. We compared the 15- and 30-day outcomes in VTE patients on enoxaparin twice vs. once daily. Patients on enoxaparin once daily had fewer major bleeds and deaths than those on twice daily. The rate of VTE recurrences was similar in both subgroups.

SUMMARY

Background In patients with acute venous thromboembolism (VTE), it is uncertain whether enoxaparin should be administered twice or once daily. Methods We used the RIETE Registry data to compare the 15- and 30-day rates of VTE recurrence, major bleeding and death between patients receiving enoxaparin twice daily and those receiving it once daily. We used propensity score matching to adjust for confounding variables. Results The study included 4730 patients: 3786 (80%) received enoxaparin twice daily and 944 once daily. During the first 15 days, patients on enoxaparin once daily had a trend towards more VTE recurrences (odds ratio [OR], 1.79; 95% confidence interval [CI], 0.55-5.88), fewer major bleeds (OR, 0.42; 95% CI, 0.17-1.08) and fewer deaths (OR, 0.32; 95% CI, 0.13-0.78) than those on enoxaparin twice daily. At day 30, patients on enoxaparin once daily had more VTE recurrences (OR, 2.5; 95% CI, 1.03-5.88), fewer major bleeds (OR, 0.40; 95% CI, 0.17-0.94) and fewer deaths (OR, 0.58; 95% CI, 0.33-1.00). On propensity analysis, patients on enoxaparin once daily had fewer major bleeds at 15 (hazard ratio [HR], 0.30; 95% CI, 0.10-0.88) and at 30 days (HR, 0.16; 95% CI, 0.04-0.68) and also fewer deaths at 15 (HR, 0.37; 95% CI, 0.14-0.99) and at 30 days (HR, 0.19; 95% CI, 0.07-0.54) than those on enoxaparin twice daily. Conclusions Our findings confirm that enoxaparin prescribed once daily results in fewer major bleeds than enoxaparin twice daily, as suggested in a meta-analysis of controlled clinical trials.

Fixed dose subcutaneous low molecular weight heparins versus adjusted dose unfractionated heparin for the initial treatment of venous thromboembolism

BACKGROUND

Low molecular weight heparins (LMWHs) have been shown to be effective and safe in preventing venous thromboembolism (VTE). They may also be effective for the initial treatment of VTE. This is the third update of the Cochrane Review first published in 1999.

OBJECTIVES

To evaluate the efficacy and safety of fixed dose subcutaneous low molecular weight heparin compared to adjusted dose unfractionated heparin (intravenous or subcutaneous) for the initial treatment of people with venous thromboembolism (acute deep venous thrombosis or pulmonary embolism).

SEARCH METHODS

For this update the Cochrane Vascular Information Specialist (CIS) searched the Cochrane Vascular Specialised Register (15 September 2016). In addition the CIS searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 8) in the Cochrane Library (searched 15 September 2016) and trials' registries.

SELECTION CRITERIA

Randomised controlled trials comparing fixed dose subcutaneous LMWH with adjusted dose intravenous or subcutaneous unfractionated heparin (UFH) in people with VTE.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, assessed for quality and extracted data.

MAIN RESULTS

Six studies were added to this update resulting in a total of 29 included studies (n = 10,390). The quality of the studies was downgraded as there was a risk of bias in some individual studies relating to risk of attrition and reporting bias; in addition several studies did not adequately report on the randomisation methods used nor on how the treatment allocation was concealed.During the initial treatment period, the incidence of recurrent venous thromboembolic events was lower in participants treated with LMWH than in participants treated with UFH (Peto odds ratio (OR) 0.69, 95% confidence intervals (CI) 0.49 to 0.98; 6238 participants; 18 studies; P = 0.04; moderate-quality evidence). After a follow-up of three months, the period in most of the studies for which oral anticoagulant therapy was given, the incidence of recurrent VTE was lower in participants treated with LMWH than in participants with UFH (Peto OR 0.71, 95% CI 0.56 to 0.90; 6661 participants; 16 studies; P = 0.005; moderate-quality evidence). Furthermore, at the end of follow-up, LMWH was associated with a lower rate of recurrent VTE than UFH (Peto OR 0.72, 95% CI 0.59 to 0.88; 9489 participants; 22 studies; P = 0.001; moderate-quality evidence). LMWH was also associated with a reduction in thrombus size compared to UFH (Peto OR 0.71, 95% CI 0.61 to 0.82; 2909 participants; 16 studies; P < 0.00001; low-quality evidence), but there was moderate heterogeneity (I² = 56%). Major haemorrhages occurred less frequently in participants treated with LMWH than in those treated with UFH (Peto OR 0.69, 95% CI 0.50 to 0.95; 8780 participants; 25 studies; P = 0.02; moderate-quality evidence). There was no difference in overall mortality between participants treated with LMWH and those treated with UFH (Peto OR 0.84, 95% CI 0.70 to 1.01; 9663 participants; 24 studies; P = 0.07; moderate-quality evidence).

AUTHORS' CONCLUSIONS

This review presents moderate-quality evidence that fixed dose LMWH reduced the incidence of recurrent thrombotic complications and occurrence of major haemorrhage during initial treatment; and low-quality evidence that fixed dose LMWH reduced thrombus size when compared to UFH for the initial treatment of VTE. There was no difference in overall mortality between participants treated with LMWH and those treated with UFH (moderate-quality evidence). The quality of the evidence was assessed using GRADE criteria and downgraded due to concerns over risk of bias in individual trials together with a lack of reporting on the randomisation and concealment of treatment allocation methods used. The quality of the evidence for reduction of thrombus size was further downgraded because of heterogeneity between studies.

Index clinical manifestation of venous thromboembolism predicts early recurrence type and frequency: a meta-analysis of randomized controlled trials

BACKGROUND

Observational studies suggest index clinical manifestation of venous thromboembolism (VTE) predicts recurrence type. Data regarding the association between index manifestation and recurrence rates are conflicting.

OBJECTIVES

To perform a meta-analysis of randomized controlled trials (RCTs) to determine the type and frequency of recurrent VTE (rVTE) in persons after an index deep vein thrombosis (DVT) or pulmonary embolism (PE).

PATIENTS/METHODS

We searched bibliographic databases for RCTs of acute (early) treatment of rVTE in persons with an index DVT or PE (±DVT), enrolling ≥ 50 subjects anticoagulated ≥ 3-months and reporting types of rVTE. We pooled (random-effects) the proportion of rVTEs that were DVTs, PEs, and fatal PEs, the proportion of recurrent PEs that were fatal, and absolute rVTE rates.

RESULTS

In nine RCTs (N = 13 640; 413 rVTEs) evaluating persons with an index PE; 66% (95% CI, 60-72%) of rVTEs were PE and 27% (95% CI, 22-33%) were fatal PE. Among 25 RCTs (N = 17 340; 692 rVTEs) evaluating persons with an index DVT, 36% (95% CI, 29-44%) experienced a recurrent PE and 10% (95% CI, 7-13%) a fatal PE. Recurrent PEs following an index PE had a higher fatality rate than after an index DVT (41%; 95% CI, 33-48% vs. 25%; 95% CI, 18-33%; P = 0.007). The rVTE rate was higher following an index DVT compared with a PE (2.6%; 95% CI, 1.6-3.8% vs. 4.9%; 95% CI, 4.0-6.0%; P = 0.002).

CONCLUSIONS

Our meta-analysis suggests most rVTEs will be the same type as the index event. While index DVTs are associated with a higher rVTE rate than index PEs; recurrent PEs are associated with high fatality.

Once versus twice daily low molecular weight heparin for the initial treatment of venous thromboembolism

BACKGROUND

In the initial treatment of venous thromboembolism (VTE) low molecular weight heparin (LMWH) is administered once or twice daily. A once daily treatment regimen is more convenient for the patient and may optimise home treatment. However, it is not clear whether a once daily treatment regimen is as safe and effective as a twice daily treatment regimen. This is the second update of a review first published in 2003.

OBJECTIVES

To compare the efficacy and safety of once daily versus twice daily administration of LMWH.

SEARCH METHODS

For this update the Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched the Specialised Register (last searched May 2013) and CENTRAL (2013, Issue 4).

SELECTION CRITERIA

Randomised clinical trials in which LMWH given once daily is compared with LMWH given twice daily for the initial treatment of VTE.

DATA COLLECTION AND ANALYSIS

Two review authors assessed trials for inclusion and extracted data independently.

MAIN RESULTS

Five studies were included with a total of 1508 participants. The pooled data showed no statistically significant difference in recurrent VTE between the two treatment regimens (OR 0.82, 0.49 to 1.39; P = 0.47). A comparison of major haemorrhagic events (OR 0.77, 0.40 to 1.45; P = 0.41), improvement of thrombus size (OR 1.41, 0.66 to 3.01; P = 0.38) and mortality (OR 1.14, 0.62 to 2.08; P = 0.68) also showed no statistically significant differences between the two treatment regimens. None of the five included studies reported data on post-thrombotic syndrome.

AUTHORS' CONCLUSIONS

Once daily treatment with LMWH is as effective and safe as twice daily treatment with LMWH.

Pulmonary emboli associated with isolated lower-extremity venous malformation: a case report

Pulmonary thromboembolism is a relatively rare entity in the pediatric population; however, it should always be part of the differential diagnosis in patients with the appropriate clinical presentation. We report the case of a 13-year-old girl with a history of a lower-extremity venous malformation status post sclerotherapy 2 years prior but otherwise healthy who presented with painless hemoptysis. She was found to have multiple bilateral pulmonary emboli on computed tomographic angiography of the chest. Magnetic resonance venography of the lower extremities showed stable venous changes from prior studies and no obvious source of emboli. She was started on anticoagulation and was discharged home.

Antithrombotic therapy for VTE disease: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

This article addresses the treatment of VTE disease.

METHODS

We generated strong (Grade 1) and weak (Grade 2) recommendations based on high-quality (Grade A), moderate-quality (Grade B), and low-quality (Grade C) evidence.

RESULTS

For acute DVT or pulmonary embolism (PE), we recommend initial parenteral anticoagulant therapy (Grade 1B) or anticoagulation with rivaroxaban. We suggest low-molecular-weight heparin (LMWH) or fondaparinux over IV unfractionated heparin (Grade 2C) or subcutaneous unfractionated heparin (Grade 2B). We suggest thrombolytic therapy for PE with hypotension (Grade 2C). For proximal DVT or PE, we recommend treatment of 3 months over shorter periods (Grade 1B). For a first proximal DVT or PE that is provoked by surgery or by a nonsurgical transient risk factor, we recommend 3 months of therapy (Grade 1B; Grade 2B if provoked by a nonsurgical risk factor and low or moderate bleeding risk); that is unprovoked, we suggest extended therapy if bleeding risk is low or moderate (Grade 2B) and recommend 3 months of therapy if bleeding risk is high (Grade 1B); and that is associated with active cancer, we recommend extended therapy (Grade 1B; Grade 2B if high bleeding risk) and suggest LMWH over vitamin K antagonists (Grade 2B). We suggest vitamin K antagonists or LMWH over dabigatran or rivaroxaban (Grade 2B). We suggest compression stockings to prevent the postthrombotic syndrome (Grade 2B). For extensive superficial vein thrombosis, we suggest prophylactic-dose fondaparinux or LMWH over no anticoagulation (Grade 2B), and suggest fondaparinux over LMWH (Grade 2C).

CONCLUSION

Strong recommendations apply to most patients, whereas weak recommendations are sensitive to differences among patients, including their preferences.

Guidelines on the diagnosis and management of acute pulmonary embolism: the Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC)

Non-thrombotic PE does not represent a distinct clinical syndrome. It may be due to a variety of embolic materials and result in a wide spectrum of clinical presentations, making the diagnosis difficult. With the exception of severe air and fat embolism, the haemodynamic consequences of non-thrombotic emboli are usually mild. Treatment is mostly supportive but may differ according to the type of embolic material and clinical severity.

Antithrombotic therapy for venous thromboembolic disease: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This chapter about treatment for venous thromboembolic disease is part of the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Grade 1 recommendations are strong and indicate that the benefits do or do not outweigh risks, burden, and costs. Grade 2 suggests that individual patient values may lead to different choices (for a full understanding of the grading, see "Grades of Recommendation" chapter). Among the key recommendations in this chapter are the following: for patients with objectively confirmed deep vein thrombosis (DVT) or pulmonary embolism (PE), we recommend anticoagulant therapy with subcutaneous (SC) low-molecular-weight heparin (LMWH), monitored IV, or SC unfractionated heparin (UFH), unmonitored weight-based SC UFH, or SC fondaparinux (all Grade 1A). For patients with a high clinical suspicion of DVT or PE, we recommend treatment with anticoagulants while awaiting the outcome of diagnostic tests (Grade 1C). For patients with confirmed PE, we recommend early evaluation of the risks to benefits of thrombolytic therapy (Grade 1C); for those with hemodynamic compromise, we recommend short-course thrombolytic therapy (Grade 1B); and for those with nonmassive PE, we recommend against the use of thrombolytic therapy (Grade 1B). In acute DVT or PE, we recommend initial treatment with LMWH, UFH or fondaparinux for at least 5 days rather than a shorter period (Grade 1C); and initiation of vitamin K antagonists (VKAs) together with LMWH, UFH, or fondaparinux on the first treatment day, and discontinuation of these heparin preparations when the international normalized ratio (INR) is > or = 2.0 for at least 24 h (Grade 1A). For patients with DVT or PE secondary to a transient (reversible) risk factor, we recommend treatment with a VKA for 3 months over treatment for shorter periods (Grade 1A). For patients with unprovoked DVT or PE, we recommend treatment with a VKA for at least 3 months (Grade 1A), and that all patients are then evaluated for the risks to benefits of indefinite therapy (Grade 1C). We recommend indefinite anticoagulant therapy for patients with a first unprovoked proximal DVT or PE and a low risk of bleeding when this is consistent with the patient's preference (Grade 1A), and for most patients with a second unprovoked DVT (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 at least 3 months of treatment with LMWH for patients with VTE and cancer (Grade 1A), followed by treatment with LMWH or VKA as long as the cancer is active (Grade 1C). For prevention of postthrombotic syndrome (PTS) after proximal DVT, we recommend use of an elastic compression stocking (Grade 1A). For DVT of the upper extremity, we recommend similar treatment as for DVT of the leg (Grade 1C). Selected patients with lower-extremity (Grade 2B) and upper-extremity (Grade 2C). DVT may be considered for thrombus removal, generally using catheter-based thrombolytic techniques. For extensive superficial vein thrombosis, we recommend treatment with prophylactic or intermediate doses of LMWH or intermediate doses of UFH for 4 weeks (Grade 1B).

Cost-effectiveness of low-molecular-weight heparin for treatment of pulmonary embolism

BACKGROUND

Low-molecular-weight heparin (LMWH) appears to be safe and effective for treating pulmonary embolism (PE), but its cost-effectiveness has not been assessed.

METHODS

We built a Markov state-transition model to evaluate the medical and economic outcomes of a 6-day course with fixed-dose LMWH or adjusted-dose unfractionated heparin (UFH) in a hypothetical cohort of 60-year-old patients with acute submassive PE. Probabilities for clinical outcomes were obtained from a meta-analysis of clinical trials. Cost estimates were derived from Medicare reimbursement data and other sources. The base-case analysis used an inpatient setting, whereas secondary analyses examined early discharge and outpatient treatment with LMWH. Using a societal perspective, strategies were compared based on lifetime costs, quality-adjusted life-years (QALYs), and the incremental cost-effectiveness ratio.

RESULTS

Inpatient treatment costs were higher for LMWH treatment than for UFH (dollar 13,001 vs dollar 12,780), but LMWH yielded a greater number of QALYs than did UFH (7.677 QALYs vs 7.493 QALYs). The incremental costs of dollar 221 and the corresponding incremental effectiveness of 0.184 QALYs resulted in an incremental cost-effectiveness ratio of dollar 1,209/QALY. Our results were highly robust in sensitivity analyses. LMWH became cost-saving if the daily pharmacy costs for LMWH were < dollar 51, if > or = 8% of patients were eligible for early discharge, or if > or = 5% of patients could be treated entirely as outpatients.

CONCLUSION

For inpatient treatment of PE, the use of LMWH is cost-effective compared to UFH. Early discharge or outpatient treatment in suitable patients with PE would lead to substantial cost savings.

Once versus twice daily LMWH for the initial treatment of venous thromboembolism

BACKGROUND

In the initial treatment of venous thromboembolism (VTE) low molecular weight heparin (LMWH) is administered once or twice daily. A once daily treatment regimen is more convenient for the patient and may optimise home treatment. However, it is not clear whether a once daily treatment regimen is as safe and effective as a twice daily treatment regimen.

OBJECTIVES

To compare the efficacy and safety of once daily versus twice daily administration of LMWH.

SEARCH STRATEGY

We identified trials through searching the Specialised Register of the Cochrane Peripheral Vascular Diseases Group (last searched April 2005), the Cochrane Central Controlled Trials Register (CENTRAL) (last searched Issue 2, 2005), handsearches of relevant journals, checking cross-references and through personal communication with experts.

SELECTION CRITERIA

Randomised clinical trials in which LMWH given once daily is compared to LMWH given twice daily for the initial treatment of venous thromboembolism.

DATA COLLECTION AND ANALYSIS

Two authors assessed trials for inclusion and extracted data independently.

MAIN RESULTS

Five studies were included with a total of 1508 participants. The pooled data showed a statistically non-significant difference in recurrent venous thromboembolism between the two treatment regimens (OR 0.82, 0.49 to 1.39). A comparison of major haemorrhagic events (OR 0.77, 0.40 to 1.45) and mortality (OR 1.14, 0.62 to 2.08) also showed a statistically non-significant difference between the two treatment regimens.

AUTHORS' CONCLUSIONS

Once daily treatment with LMWH is as effective and safe as twice daily treatment with LMWH. However, the 95% confidence interval implies that there is a possibility that the risk of recurrent VTE might be higher when people are treated once daily. Hence, the decision to treat a person with a once daily regimen will depend on the evaluated balance between increased convenience and the potential for a lower efficacy.

The therapeutic potential of novel anticoagulants

Conventional anticoagulant therapy has been based on indirect inhibition of coagulation factors with heparin and warfarin. These agents display liabilities prompting the development of new anticoagulants over the last two decades. The first to be developed was a series of low molecular weight heparins(LMWHs). Their favourable pharmacokinetic profiles and risk/benefit ratios led to widespread use in Europe and, more recently, approval for their use in the USA. Paralleling the development of LMWHs has been the pursuit of a different strategy focused on direct rather than indirect inhibition of enzymes in the coagulation cascade. In contrast to heparin, LMWHs, or other glycosaminoglycans, direct inhibitors exert their effects independent of either antithrombin III (ATIII) or heparin cofactor II (HCII) and more effectively inhibit clot-bound thrombin or FXa. Highly potent, selective (versus other serine proteases)direct thrombin and FXa inhibitors have been identified and isolated from natural sources, such as leeches, ticks and hookworms. The recombinant forms and analogues of the senatural proteins have been produced using molecular biology techniques, i.e., rHirudin, Hirulogs, recombinant tick anticoagulant peptide (rTAP), recombinant antistasin (rATS) and recombinant nematode anticoagulant peptide-5 (rNAP-5). The design of novel structures or the modification of existing chemicals has led to the synthesis of many non-peptide, low molecular weight inhibitors of thrombin and FXa. Some of them are orally active and may be suitable for long-term clinical use. In addition, considerable progress has been made in developing specific TF/VIIa complex inhibitors. The anticoagulation properties of the new agents are being characterised in experimental studies. Some of them have been advanced to large scale clinical trials and their effectiveness, and sometimes relative ineffectiveness,in arterial and venous thromboembolic disorders has been demonstrated. They are being tested for their potential as new antithrombotic agents that act via direct enzyme inhibition. Thus,the clinician should in future be able to target different thrombotic conditions with proven, specific anticoagulant interventions.

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.

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.

Treatment of venous thromboembolism with low-molecular-weight heparin: a synthesis of the evidence published in systematic literature reviews

OBJECTIVE

To evaluate the methodology and cumulative evidence presented in systematic reviews of clinical trials comparing low-molecular-weight heparin (LMWH) with unfractionated heparin (UFH) for the treatment of venous thromboembolism.

METHODS

We reviewed all systematic reviews of clinical trials published until March 2002. Fourteen systematic literature reviews were published between 1994 and 2000. Deficiencies in methodological quality were common, particularly in the description of search strategies, assessment of clinical trial quality, and methods used to combine results.

RESULTS

Results of reviews indicate that LMWH is superior to UFH for the treatment of venous thromboembolism, particularly in reducing mortality. Patients with isolated deep venous thrombosis or deep venous thrombosis with concomitant pulmonary embolism seemed to have similar benefit. However, the benefits of LMWH over UFH were smaller in magnitude in reviews that included more recent clinical trials.

[Multicenter, prospective study comparing enoxaparin with unfractionated heparin in the treatment of submassive pulmonary thromboembolism]

OBJECTIVE

To compare the safety and efficacy of enoxaparin and unfractionated heparin in the treatment of submassive pulmonary thromboembolism (PTE).

MATERIAL AND METHODS

Fifty-six patients with PTE who did not need fibrinolytic treatment were enrolled prospectively. The patients were randomly assigned to 2 treatment groups: Group A received enoxaparin (1 mg/kg every 12 hours) and Group B received adjusted doses of unfractionated heparin. The oral anticoagulant therapy was started on confirmation of the diagnosis and continued for 6 months. Incidences of recurrence of thromboembolism and of severe bleeding were assessed at the end of this period.

RESULTS

Six patients were withdrawn from the study. Twenty-nine of the 50 remaining patients were in Group A (enoxaparin) and 21 in Group B (unfractionated heparin). A recurrence of thromboembolism was diagnosed in 3 patients from Group A (10.7%) and 2 patients from Group B (9.5%). There were no significant differences. Two patients died, one death being attributed to bleeding secondary to the oral anticoagulant treatment (Group A) and the other to a process unrelated to PTE.

CONCLUSIONS

Enoxaparin seems to be as effective and safe as unfractionated heparin in the initial treatment of PTE.

Hospital guidelines for use of low-molecular-weight heparins

OBJECTIVE

To describe the development of guidelines for initial use of low-molecular-weight heparins (LMWHs) and other anticoagulants in acute-care hospitals that are part of a national group purchasing organization (GPO).

DATA SOURCES

A systematic literature search (1970-December 2001) was conducted to identify evidence on the efficacy of various anticoagulants for initial therapy in deep-vein thrombosis and pulmonary embolism, and in treatment of acute coronary syndrome. A group consensus method was then used to develop guidelines. Guidelines were reviewed and revised by an internal expert panel as well as an external expert panel. Final guidelines were disseminated to GPO members and assistance was provided with implementation at the local level.

RESULTS

The final set of guidelines is described. The guidelines are organized based on recommended therapeutic options for each indication. For each option, consensus opinion is provided on the level of evidence that exists in the literature, comparisons of cost and convenience, and additional dosing information. The guidelines were disseminated along with supporting material to interested GPO member hospitals, and teleconferences were held to facilitate implementation at the local level. The guidelines were initially implemented at 18 hospitals across the country.

CONCLUSIONS

The process by which these guidelines were developed, plus the final set of guidelines, may be useful to hospitals and healthcare systems contemplating or engaged in a similar effort with this class of drugs.

Outpatient management of the chronically anticoagulated patient for elective surgery

With the appropriate use of preadmission clinics, "hospital in the home" programs, and alternatives to intravenous heparin, the majority of chronically anticoagulated patients can be managed as outpatients prior to elective surgery. The preoperative management depends on the original indication for long-term anticoagulation, the interval since the last thromboembolic event, and the extent and type of surgery planned. Only patients who are undergoing major surgery, and who have a high risk of recurrent thrombosis or embolism, require preoperative admission to hospital and conversion to an intravenous heparin regimen. Patients undergoing minor surgery may require no change to their oral anticoagulation. The remainder require cessation of oral anticoagulation and alternative thromboprophylaxis preoperatively, which can be achieved on an outpatient basis using low molecular weight heparin. Outpatient anticoagulation management requires a clear protocol that is understood and agreed to by all parties involved in the care of surgical patients perioperatively.

Once versus twice daily LMWH for the initial treatment of venous thromboembolism

BACKGROUND

In the initial treatment of venous thromboembolism (VTE) low molecular weight heparin (LMWH) is administered once or twice daily. A once daily treatment regimen is more convenient for the patient and may optimise home treatment. However it is not clear whether a once daily treatment regimen is as safe and effective as a twice daily treatment regimen.

OBJECTIVES

The objective of this review was to compare the efficacy and safety of once daily administration to a twice daily administration of LMWH.

SEARCH STRATEGY

Trials were identified through the Specialised Register of the Cochrane Peripheral Vascular Diseases Group (last searched May 2001), the Cochrane Controlled Trials Register (CCTR/CENTRAL) (last searched Issue 1, 2002), by hand-searching other relevant journals, by checking cross-references and through personal communication with experts.

SELECTION CRITERIA

Randomised clinical trials in which a once daily treatment regimen with LMWH is compared to a twice daily regimen in the initial treatment of patients with venous thromboembolism.

DATA COLLECTION AND ANALYSIS

Two reviewers assessed trials on criteria for inclusion and extracted the data independently.

MAIN RESULTS

Five studies were included with a total of 1508 patients. The pooled data showed a statistically non-significant difference in recurrent venous thromboembolism between the two treatment regimens (OR 0.82; 0.49 - 1.39). A comparison of major haemorrhagic events (OR 0.77; 0.40 - 1.45) and mortality (OR 1.14; 0.62 - 2.08) also showed a statistically non-significant difference between the two treatment regimens.

REVIEWER'S CONCLUSIONS

Once daily treatment with LMWH is as effective and safe as twice daily treatment with LMWH. However, the 95% confidence interval implies that there is a possibility that the risk of recurrent VTE might be higher when patients are treated once daily. Hence the decision to treat the patient with a once daily regimen will depend on the evaluated balance between increased convenience and the potential for a lower efficacy.

Safety of low molecular weight heparins in the treatment of venous thromboembolism

Low molecular weight heparins (LMWHs) are commonly employed as a substitute for unfractionated heparin (UFH) in the treatment of venous thromboembolic events. Despite their higher cost, the preferential use of LMWHs seemed justified initially as, based on the results of earlier meta-analyses, these compounds were deemed to be more effective and safer than UFH. Although, in this respect, their purported superiority over UFH could not be confirmed by subsequent large, randomised trials and updated meta-analyses, other peculiar features of LMWHs were highlighted, favouring their preferential utilisation in patients with venous thromboembolism. Among these, the possibility of once-daily administration on an out-patient basis, the lower incidence of Type II heparin-induced thrombocytopenia and the lower likelihood of osteoporosis after prolonged treatment periods, appear to be especially prominent. This review attempts to evaluate the available evidence focusing on the safety of LMWHs for the treatment of venous thromboembolism and the current therapeutic options and potential advantages of LMWHs, either in general or in selected patient populations.

Acute subdural haematomas and enoxaparin

Townsville General Hospital (TGH) has 285 beds and serves a population of approximately 500,0000 in North Queensland. In the period November 1998 until December 1999 there were three acute subdural haematomas (ASDH) related to therapeutic doses of enoxaparin. These culminated in death or severe neurological disability. Unfractionated heparin (UFH) is probably used equivalently in TGH. There were no intracranial haemorrhages in this period with UFH. It is well known low molecular weight heparins (LMWH) have a proven place in the management of deep vein thrombosis (DVT) and ischaemic heart disease (IHD). There may however be some concerns regarding the haemorrhagic complications of therapeutic doses of enoxaparin in the central nervous system.

Structure and anticoagulant properties of sulfated glycosaminoglycans from primitive Chordates

Dermatan sulfates and heparin, similar to the mammalian glycosaminoglycans, but with differences in the degree and position of sulfation were previously isolated from the body of the ascidian Styela plicata and Ascidia nigra. These differences produce profound effects on their anticoagulant properties. S. plicata dermatan sulfate composed by 2-O-sulfated alpha-L-iduronic acid and 4-O-sulfated N-acetyl-beta-D-galactosamine residues is a potent anticoagulant due to a high heparin cofactor II activity. Surprisingly, it has a lower potency to prevent thrombus formation on an experimental model and a lower bleeding effect in rats than the mammalian dermatan sulfate. In contrast, A. nigra dermatan sulfate, also enriched in 2-O-sulfated alpha-L-iduronic acid, but in this case sulfated at O-6 of the N-acetyl-beta-D-galactosamine units, has no in vitro or in vivo anticoagulant activity, does not prevent thrombus formation but shows a bleeding effect similar to the mammalian glycosaminoglycan. Ascidian heparin, composed by 2-O-sulfated alpha-L-iduronic acid, N- and 6-O-sulfated glucosamine (75%) and alpha-L-iduronic acid, N- and 6-O-sulfated glucosamine (25%) disaccharide units has an anticoagulant activity 10 times lower than the mammalian heparin, is about 20 times less potent in the inhibition of thrombin by antithrombin, but has the same heparin cofactor II activity as mammalian heparin.

Outpatient treatment of patients with deep-vein thrombosis or pulmonary embolism

There have been a large number of randomized trials comparing standard unfractionated intravenous heparin with low-molecular-weight heparin for the treatment of deep-vein thrombosis, but only two of these have looked at outpatient therapy. There have been only two randomized trials including patients with symptomatic pulmonary embolism, and neither of these provided outpatient therapy. Postmortem and clinical studies have shown a strong association between pulmonary embolism and the presence of venous thrombosis in the lower limbs. Based on similar rates of venous thromboembolic recurrence and death, these studies suggest that initial treatment should be the same for deep-vein thrombosis and pulmonary embolism. The feasibility of providing outpatient care to many patients seeking treatment for deep-vein thrombosis or acute pulmonary embolism at certain tertiary care hospitals has become evident, but the data suggest that the proportion of eligible patients is institution dependent and may vary from 18% to 91%. In the author's institution, approximately 50% of patients with pulmonary embolism could be treated as outpatients, but there have been no other reports on outpatient therapy for patients with pulmonary embolism. If patients with pulmonary embolism meet criteria demonstrated to result in a higher risk of death, it is, of course, reasonable to not treat such patients on an outpatient basis. Low-molecular-weight heparin followed by oral anticoagulant therapy provides adequate therapy in most patients with deep-vein thrombosis or pulmonary embolism, and many patients can be treated as outpatients.

Low-molecular-weight heparins are essentially the same for treatment and prevention of venous thromboembolism

The pharmacodynamic properties of low-molecular-weight heparins differ. Data from randomized clinical trials show that despite these differences, the agents have similar efficacy and safety profiles in preventing and treating new and recurrent venous thromboembolism in patients who underwent general surgery or total hip or knee replacement. Dalteparin, enoxaparin, or tinzaparin, when administered at the dosages used in the reviewed clinical trials, are essentially indistinguishable.

Dosing and monitoring of low-molecular-weight heparins in special populations

As a result of numerous clinical trials and meta-analyses supporting the superior efficacy and relative safety of low-molecular-weight heparins (LMWHs) compared with unfractionated heparin (UFH), LMWHs are emerging as the antithrombotic agents of choice for the prevention and treatment of deep vein thrombosis and pulmonary embolism. In addition, data indicate that enoxaparin given with low-dosage aspirin is more effective than UFH in treating acute coronary syndromes. Anti-Xa activity can be used as a biologic marker of LMWH activity. Because of the more predictable anticoagulant response to subcutaneous administration of LMWHs compared with UFH, routine monitoring of anti-Xa activity in clinically stable adults with uncomplicated disease is not recommended. Because the optimal dosage of LMWHs has not been established for patients with renal insufficiency or extremes of body weight, during pregnancy, or for children, anti-Xa activity monitoring may be warranted in these subsets.

New-generation anticoagulants: the low molecular weight heparins

Heparin has been the mainstay of acute anticoagulation therapy for decades. Within the past 20 years, several different heparin fractions-collectively known as low molecular weight heparins (LMWHs)-have been evaluated in various medical and surgical settings in which anticoagulation is routinely warranted. The LMWHs are efficacious, safe, cost-effective, and easier to administer and monitor than standard, unfractionated heparin. As LMWH use becomes more widespread, emergency physicians will use these new agents instead of unfractionated heparin for unstable angina, non-Q-wave myocardial infarction, or thromboembolic disease. This review focuses on the pharmacologic properties of unfractionated heparin and LMWH, associated complications, and the use of these agents in acute ischemic coronary syndromes, thromboembolic disease, and other selected clinical situations.

Venous thromboembolism in the intensive care unit

Venous thromboembolic disease has emerged as a significant cause of morbidity and mortality in hospitalized patients. This article reviews the salient features of venous thromboembolism as they pertain to the critically ill. Emphasis is placed on identifying risk factors, diagnostic strategies, prophylaxis, and treatment of this disorder. Deep venous thrombosis and pulmonary embolism, both being manifestations of the same disease processes, are considered together in this discussion of venous thromboembolism.

Outpatient treatment of deep vein thrombosis: translating clinical trials into practice

To develop a rational approach to outpatient management, we review the pharmacologic properties of low-molecular-weight heparins and their efficacy in clinical trials of deep vein thrombosis treatment. Low-molecular-weight heparins have better bioavailability and more predictable anticoagulant activity than standard heparin and thus can be administered without routine laboratory monitoring. Randomized trials comparing subcutaneous low-molecular-weight heparin administered primarily at home with inpatient intravenous standard heparin have established the safety and efficacy of outpatient treatment of selected patients. However, many patients were excluded from these studies. The benefits demonstrated in carefully controlled clinical trials of outpatient treatment of deep vein thrombosis required a complex multidisciplinary organization of medical care that is not readily achievable in routine practice. A structured protocol is necessary to ensure that patient care is optimal. The essential components of an outpatient program include appropriate patient selection, adequate patient education, daily follow-up during therapy with low-molecular-weight heparin, and easy access to health-care professionals.

Low molecular weight heparins: current use and indications

Thromboembolic complications are associated with significant morbidity and mortality in postoperative patients. For many years, unfractionated heparin has been used successfully in primary and secondary prophylaxis of these complications. In recent times, however, the usefulness of LMWHs has caught the attention of clinicians because of improved bioavailability, predictable anticoagulation, ease of administration, and the lack of need for monitoring anticoagulation. In clinical situations, LMWHs have been tested and proved to be safe and equipotent or supe rior when compared with unfractionated heparin or warfarin (Table 5). It is clear from clinical trials that LMWHs are superior in primary prophylaxis of DVT in orthopaedic surgical procedures, treatment of unstable angina, and in patients with multiple traumas. LMWHs were also tested and found to be an acceptable alternative to unfractionated heparin in both the primary prophylaxis of DVT in high risk general surgical procedures and in the treatment of patients with DVT and pulmonary embolism. However, the role of LMWHs in ischemic heart diseases, valvular heart diseases, postcoronary angioplasty, and vascular surgery remains to be proved. The major impact of LMWHs would be in allowing clinicians to treat PE and DVT in an outpatient setting, which would directly impact medical economics. LMWHs are associated with similar complications as unfractionated heparin is, but the complications occur less frequently. Currently, the main limitation in using LMWHs in place of unfractionated heparin or warfarin is its cost. However, taking into account the cost incurred by hospitalization and longterm monitoring of anticoagulation in patients treated with unfractionated heparin, certain trials have proved the cost of LMWHs to be the same or less than the cost of unfractionated heparin overall. We envision that LMWHs will be widely used in the future and will bring welcomed change in the treatment of thromboembolic diseases.

Low-molecular-weight heparins

Low-molecular-weight heparins (LMWH) are a new group of parenteral anticoagulants. They represent a major clinical advance in anticoagulation since the identification of unfractionated heparin (UFH) in 1922 and the introduction of the synthetic coumarin derivative, warfarin, in 1948. Their predictable pharmacokinetics, increased bioavailability, and longer plasma half-life allow for once- or twice-daily dosing and eliminate the need for routine laboratory monitoring. This simplified administration stands to alter the clinical practice of anticoagulation. This review high-lights recent clinical trials and focuses on studies comparing LMWH with the other two major anticoagulants: UFH and coumadin.

Treatment of deep venous thrombosis and pulmonary embolism. Current recommendations

The therapy of deep venous thrombosis consists of several elements and depends on the localization, the age and the extent of the thrombus. This article discusses various types of initial therapy and long-term treatment of venous thromboembolism and also reviews future perspectives of pharmacological treatment. The initial treatment regimens comprise thrombolysis, thrombectomy, inferior vena cava filters and the anticoagulation with either unfractionated heparin or low molecular weight heparins. Various thrombin-inhibitors have been tested for initial treatment of thrombosis, however, further investigations of their efficacy, safety and cost-effectiveness will have to provide firm evidence on their superiority when compared to unfractionated or low molecular weight heparins.

Low-molecular-weight heparins in the treatment of pulmonary embolism

More than 621 patients diagnosed with a PE have been treated with LMWH. This review included five randomized clinical trials (> 433 patients treated with LMWH) comparing LMWH with UFH. The remainder of the clinical studies were dose-response trials, noncomparative trials, or trials that included a subset of patients diagnosed with a PE. Additionally, 138 patients diagnosed with a PE were included in the group of 510 patients with venous thromboembolism and were subsequently treated with an LMWH. The data available suggest that LMWHs may be safe and effective in the treatment of submassive PE. However, the current data on LMWHs are limited by small sample size, inadequate patient description, and inadequate follow-up. The majority of studies fail to provide concurrent disease state information (e.g., renal disease), thus limiting their usefulness. The results of these trials must be confirmed in comparative studies using different LMWHs (since they may not be interchangeable) in various patient populations before LMWHs are considered to be a safe and effective alternative to UFH in the management of submassive PE.

A comparison of low-molecular-weight heparin with unfractionated heparin for acute pulmonary embolism. The THESEE Study Group. Tinzaparine ou Heparine Standard: Evaluations dans l'Embolie Pulmonaire

BACKGROUND

Low-molecular-weight heparin appears to be at least as effective and safe as standard, unfractionated heparin for the treatment of deep-vein thrombosis, but only limited data are available on the use of low-molecular-weight heparin to treat acute symptomatic pulmonary embolism.

METHODS

We randomly assigned 612 patients with symptomatic pulmonary embolism who did not require thrombolytic therapy or embolectomy to either subcutaneous low-molecular-weight heparin (tinzaparin) given once daily in a fixed dose or adjusted-dose, intravenous unfractionated heparin. Oral anticoagulant therapy was begun between the first and the third day and was given for at least three months. We compared the treatments at day 8 and day 90 with respect to a combined end point of recurrent thromboembolism, major bleeding, and death.

RESULTS

In the first eight days of treatment, 9 of 308 patients assigned to receive unfractionated heparin (2.9 percent) reached at least one of the end points, as compared,with 9 of 304 patients assigned to low-molecular-weight heparin (3.0 percent; absolute difference, 0.1 percentage point; 95 percent confidence interval, -2.7 to 2.6). By day 90, 22 patients assigned to unfractionated heparin (7.1 percent) and 18 patients assigned to low-molecular-weight heparin (5.9 percent) had reached at least one end point (P=0.54; absolute difference, 1.2 percentage points; 95 percent confidence interval, -2.7 to 5.1). The risk of major bleeding was similar in the two treatment groups throughout the study.

CONCLUSIONS

Under the conditions of this study, initial subcutaneous therapy with the low-molecular-weight heparin tinzaparin appeared to be as effective and safe as intravenous unfractionated heparin in patients with acute pulmonary embolism.

Dalteparin: a low-molecular-weight heparin

OBJECTIVE

To discuss the chemistry, pharmacology, and pharmacokinetics of dalteparin, a low-molecular-weight heparin (LMWH), and to review the comparative clinical trial data evaluating the efficacy and safety of dalteparin and unfractionated heparin (UH) for the prophylaxis and treatment of venous thromboembolism.

DATA SOURCES

A MEDLINE search identified pertinent English-language publications on dalteparin and venous thromboembolism. Key search terms were dalteparin, Fragmin, LMWH, and venous thromboembolism. The search was supplemented by review articles, articles obtained from the bibliographies of the review articles, and the dalteparin approval database.

STUDY SELECTION

The most pertinent studies describing the pharmacology and pharmacokinetics of dalteparin in humans were selected; all abstracts and clinical evaluating the use of dalteparin for antithrombotic therapy were reviewed. Review articles by authors of international reputation were selected.

DATA EXTRACTION

Pertinent information from the review articles on the pharmacology of LMWHs and UH was summarized. Clinical trial data were extracted for study design, patient demographics, therapeutic regimens, methods of evaluation, and outcomes.

DATA SYNTHESIS

Dalteparin is an LMWH indicated for patients undergoing abdominal surgery who are considered to be at risk for deep-vein thrombosis (DVT), which may lead to pulmonary embolism (PE). In this population, numerous clinical trials have demonstrated comparable efficacy between dalteparin and fixed-dose UH for DVT prophylaxis. Dalteparin has a predictable dose response and can be administered as a standard single daily subcutaneous dose for all patients. In therapeutic doses, dalteparin does not alter coagulation tests and therefore does not require routine laboratory monitoring, in contrast with adjusted-dose UH. Bleeding risks with dalteparin are comparable with and possibly less than those associated with UH. Preliminary studies suggest that dalteparin may be effective for other indications, including DVT prophylaxis for hip replacement surgery and the treatment of DVT and PE. Comparative cost-effectiveness data are not yet available.

CONCLUSIONS

Dalteparin is the second LMWH to receive approval by the Food and Drug Administration. Dalteparin is indicated for prophylaxis against DVT in patients undergoing abdominal surgery. Clinical studies have shown that single daily doses of dalteparin provide a safe and effective alternative to fixed-dose UH therapy. Additional studies are needed to determine the cost-effectiveness of dalteparin compared with UH and other LMWHs.

Low-molecular-weight heparin: prophylaxis and treatment of venous thromboembolism

Intravenous heparin followed by warfarin has been the classical anticoagulant therapy of acute venous thromboembolism for the last 30 years. Furthermore, low-dose unfractionated heparin given two to three times daily has been the most popular form of prophylaxis for venous thrombosis. In recent years, a number of low-molecular-weight heparins have become available for clinical trials. These agents have many advantages over unfractionated heparin and are now being used widely internationally for the prevention and treatment of venous thromboembolism. Indeed, low-molecular-weight heparin will undoubtedly replace intravenous unfractionated heparin not only in the treatment of venous thromboembolism, but in other conditions where heparin therapy is indicated. Whether or not the low-molecular-weight heparins can decrease or eliminate some of the complications of unfractionated heparin will depend on the outcome of future clinical trials.