Subcutaneous treatment of deep venous thrombosis with low molecular weight heparin. A dose finding study with LMWH-Novo

Tinzaparin—a review of its molecular profile, pharmacology, special properties, and clinical uses

Purpose

Low molecular weight heparins (LMWHs) are a group of heterogenous moieties, long used in the prevention and treatment of thrombosis. They derive from heparin and since they are prepared by different methods of depolymerization, they differ in pharmacokinetic properties and anticoagulant profiles, and thus are not clinically interchangeable.

Methods

In this review we provide an overview of tinzaparin's main characteristics and uses.

Results

Tinzaparin which is produced by the enzymatic depolymerization of unfractionated heparin (UFH) can be used for the treatment and prevention of deep venous thrombosis (DVT) and pulmonary embolism (PE); it has been also used in special populations such as elders, obese, pregnant women, and patients with renal impairment and/or cancer with favorable outcomes in both safety and efficacy, with a once daily dose regimen. Furthermore, LMWHs are extensively used in clinical practice for both thromboprophylaxis and thrombosis treatment of COVID-19 patients.

Conclusion

Tinzaparin features support the hypothesis for having a role in immunothrombosis treatment (i.e. in the context of cancer ,COVID-19), interfering not only with coagulation cascade but also exhibiting anti-inflammatory potency.

Once-daily vs. twice-daily dosing of enoxaparin for the management of venous thromboembolism: A systematic review and meta-analysis

The present study aimed to determine whether there is any difference in the efficacy and safety of once-daily vs. twice-daily enoxaparin when used for the initial treatment of venous thromboembolism (VTE). The PubMed, Embase, Cochrane Central Register of Controlled Trials, Science Direct and Google Scholar databases were searched for studies comparing once-daily and twice-daily enoxaparin for the initial treatment of VTE added from inception up to 1st October 2019. Studies utilizing any other low-molecular-weight heparin and using enoxaparin for VTE prophylaxis were excluded. A total of 6 studies were included in the systematic review and 5 in the meta-analysis. Only one study was a randomized controlled trial (RCT). Pooled analysis of 460 patients receiving once-daily enoxaparin and 464 patients receiving twice-daily enoxaparin indicated no significant difference between the two dosing regimens regarding VTE recurrence [odds ratio (OR)=1.48, 95%CI: 0.75-2.89, P=0.26; I²=0%]. No significant difference in major hemorrhagic complications was noted (OR=1.21, 95%CI: 0.52-2.81, P=0.66; I²=0%). Sub-group analysis based on study type and use of enoxaparin for bridging therapy did not change the overall results. In cancer patients, no statistically significant difference in the recurrence of VTE was obtained between once-daily and twice-daily enoxaparin, but the confidence intervals were wide with a tendency to favor twice-daily dosing (OR=2.28, 95%CI: 0.91-5.75, P=0.08; I²=0%). The overall quality of the studies was determined to be average. To conclude, while the present results suggested no significant difference in efficacy and safety of once-daily vs. twice-daily enoxaparin when used for the initial treatment of VTE, the quality of the evidence may not have been sufficiently high to support the conclusions with confidence. Further high-quality and adequately powered RCTs are required to corroborate the present results.

Advances in monitoring anticoagulant therapy

Anticoagulant drugs directly or indirectly influence coagulation factors preventing fibrin formation, thus preventing blood clotting. They are classified into two groups according to the mode of application, namely parenteral and oral drugs. Among the latter, vitamin K antagonists (most often warfarin) were most widely used for almost a century. In recent years new oral anticoagulant drugs have become available that directly target either factor IIa or Xa (direct oral anticoagulants, DOACs). The proportion of patients to whom DOACs are prescribed is increasing because clinical studies have proved they are at least as effective and safe as vitamin K antagonists. Some of the anticoagulant drugs require regular laboratory monitoring, while others only need assessment of blood drug levels in specific clinical situations. This chapter provides an overview of appropriate laboratory tests used for either regular laboratory monitoring of therapy or occasional assessment of the anticoagulant effect of both parenteral and oral anticoagulant drugs used in clinical practice.

Low-Molecular-Weight Heparin for the Treatment of Venous Thromboembolism in the Elderly

Venous thromboembolism (deep vein thrombosis and/or pulmonary embolism) is a common problem in the elderly population. Indeed, increasing age is a significant risk factor for venous thromboembolism. The treatment of venous thromboembolism in the elderly population presents certain unique problems related to aging, such as decreasing body weight, increasing renal insufficiency and numerous comorbid conditions, which complicate therapy. Treatment of venous thromboembolism in the elderly has been complicated by an increased incidence of bleeding, particularly with the use of warfarin. The risk of bleeding may be substantially reduced by carefully adjusting the warfarin dose to maintain a therapeutic INR and for this purpose anticoagulant management clinics have been shown to be useful. The low-molecular-weight heparins have been shown to be efficacious and safe for the treatment of venous thromboembolism in several clinical trials, including many patients in the older age brackets. Furthermore, these agents can safely be used in the out-of-hospital setting. Long-term use of low-molecular-weight heparin is an alternative to the use of oral anticoagulant therapy, particularly in patients with cancer or recurrent venous thromboembolism.

The Treatment of Proximal Vein Thrombosis with Subcutaneous Low-Mole Molecular-Weight Heparin Compared with Continuous Intravenous Heparin

Low-molecular-weight heparin, compared with unfractionated heparin, has a higher bioavailability and a more prolonged half-life. There are limited data comparing the use of low-molecular-weight heparin with unfractionated heparin for the treatment of deep vein thrombosis. We have compared fixed-dose, subcutaneous low-molecular-weight heparin given once daily with adjusted-dose intravenous heparin given by continuous infusion in a multicenter double-blind clinical trial for the initial treatment of patients with proximal vein thrombosis. Clinical outcomes were objectively documented. Six of 213 patients receiving low-molecular-weight heparin (2.8%) and 15 of 219 patients receiving intravenous heparin (6.9%) developed new episodes of venous thromboembolism (p = 0.07; 95% confidence interval for the difference, 0.02%-8.1%). During initial therapy, major bleeding occurred in one patient receiving low-molecular-weight heparin (0.5%) and in 11 patients receiving intravenous heparin (5.0%), a risk reduction of 91% (p = 0.006). This apparent protection against major bleeding was lost during long-term therapy. Minor bleeding complications were rare. During the period of the study, 10 patients receiving low-molecular-weight heparin (4.7%) died, as compared with 21 patients receiving intravenous heparin (9.6%), a risk reduction of 51%(p = 0.049). This study shows that low-molecular-weight heparin is at least as effective as classic intravenous heparin therapy and that there was a reduction in deaths and bleeding complications. Furthermore, low-molecular-weight heparin was more convenient to administer. The simplified therapy with low-molecular-weight heparin given by once-daily subcutaneous injection without monitoring may allow patients with uncomplicated proximal deep vein thrombosis to be cared for as outpatients. Key Words: Low-molecular-weight heparin—Unfractionated heparin—Deep vein thrombosis—Deaths—Bleeding complications.

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.

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.

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).

Suboptimal doses of low molecular weight heparin and acute venous thromboembolism. Data from the RIETE registry

The objective was to assess the use of suboptimal doses (60-149 UI kg(-1) day(-1)) of low molecular weight heparin (LMWH) in the treatment of acute venous thromboembolism (VTE) in actual clinical practice and to evaluate the outcomes compared to standard doses (> or = 150 UI kg(-1) day(-1)). Retrospective analysis of data from a multicenter registry of patients with VTE (RIETE; Registro Informatizado de Enfermedad TromboEmbólica). Patient characteristics, antithrombotic treatments, and 3-month outcomes were analyzed. We studied 12,302 patients with VTE; 10,524 patients were treated initially only with LMWH; 1,547 patients received suboptimal LMWH (mean = 122 UI kg(-1) day(-1)), and 8,977 patients received full-dose LMWH (mean = 191 UI kg(-1) day(-1)). The suboptimal group included significantly more patients with recent major bleeding, weight more than 100 kg, raised creatinine, or deep vein thrombosis. No significant differences in mortality rate (7.7 vs 7.8%), VTE recurrence (2.7 vs 2.3%), or fatal hemorrhage (0.6 vs 0.6%) occurred between the suboptimal and the standard group. Major bleeding episodes occurred more frequently in the patients with pulmonary embolism treated with suboptimal LMWH (4.5 vs 2.4%; p = 0.02). In the multivariate analysis, after adjusting for bleeding risk factors, major hemorrhage was not associated with the heparin dose. Suboptimal doses of LMWH are used in actual clinical practice in a reduced group of patients at an outcome rate not very different to that of standard doses. Bleeding episodes depend more on the patient's characteristics than on the LMWH dose. Randomized trials should be performed to corroborate these results.

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.

Tinzaparin in the treatment of venous thromboembolism

Low molecular weight heparin (LMWH) has been widely used for the initial treatment of patients presenting with venous thromboembolism. The LMWH, tinzaparin, has been shown in randomised clinical trials to be as effective and safe as unfractionated heparin for the initial treatment of venous thromboembolism and in clinical trials, it has been used in place of warfarin for the long-term treatment of deep vein thrombosis. Tinzaparin can safely be given to patients with significant renal impairment (creatinine clearance of > or = 20 ml/min) and the dose of tinzaparin does not need to be altered in patients with a body mass index of > 25.

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.

Tinzaparin: considerations for use in clinical practice

OBJECTIVE

To evaluate the safety and effectiveness of tinzaparin for the prevention and treatment of venous thromboembolism (VTE).

DATA SOURCES

A MEDLINE and PubMed database search (1980-December 2002) was conducted. Only articles written in English were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Articles reporting the safety, efficacy, and cost-effectiveness of tinzaparin in humans were evaluated. Emphasis was placed on randomized, controlled trials.

DATA SYNTHESIS

Tinzaparin sodium is a low-molecular-weight heparin (LMWH) that exerts its anticoagulant effect through inhibition of factors Xa and IIa and release of tissue factor pathway inhibitor from the vascular epithelium. Tinzaparin is indicated for treatment of acute symptomatic deep-vein thrombosis (DVT), with or without pulmonary embolism. Clinical studies suggest that tinzaparin is also effective for VTE prophylaxis, as well as other indications. Once-daily subcutaneous tinzaparin is equally or more effective than intravenous unfractionated heparin (UFH) for prevention and treatment of VTE, at least as safe as UFH for bleeding complications, and requires little or no monitoring. No dose "cap" is required for obese patients, and no initial dosing adjustments are necessary in elderly and/or renally impaired patients, although some monitoring is recommended. The few comparative data available suggest that tinzaparin efficacy may be comparable to that of other LMWHs; more comparative studies are needed. Pharmacoeconomic studies indicate a favorable cost-benefit ratio.

CONCLUSIONS

Tinzaparin is safe and effective for prevention and treatment of DVT. Consistent once-daily dosing may facilitate self-administration of tinzaparin in the outpatient setting.

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.

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.

Treatment of Venous Thromboembolism with Low-Molecular-Weight Heparin

There is now ample evidence to indicate that certain low-molecular-weight heparins given subcutaneously can replace continuous intravenous unfractionated heparin for the initial treatment of venous thromboembolism. The low-molecular-weight heparins have a predictably high absorption rate when given subcutaneously and a prolonged duration of action, permitting them to be given by a once or twice daily injection for the prevention or treatment of venous thrombosis. Furthermore, treatment does not require laboratory monitoring, thus eliminating the need for continuous IV infusion and permitting the early discharge of patients with venous thromboembolism. This should eventually lead to the outpatient treatment of venous thromboembolism. Studies to date indicate that low-molecular-weight heparin is more cost-effective than unfractionated heparin in the treatment of venous thromboembolism and the cost effectiveness will be increased by out-of-hospital treatment. At the present time, the findings associated with any individual low-molecular-weight heparin preparation cannot be extrapolated to different low-molecular-weight heparins, and therefore each must be evaluated in separate clinical trials. The information to date is that low-molecular-weight heparin is safer and more effective than continuous intravenous unfractionated heparin in the treatment of proximal venous thrombosis. The decreased mortality rate seen in two clinical trials, particularly in patients with metastatic cancer, was quite unexpected. This requires further confirmation in larger prospective randomized trials.

Low-molecular-weight heparins and unfractionated heparin in the treatment of patients with acute venous thromboembolism: results of a meta-analysis

PURPOSE

To obtain reliable estimates of the relative efficacy and safety of low-molecular-weight heparins (LMWHs) and unfractionated heparin (UFH) in the treatment of patients with venous thromboembolism.

METHODS

A literature search of randomized trials evaluating LMWH and UFH for the period from 1980 to 1994 was conducted to obtain data for a meta-analysis. Studies were classified as level 1 if they were double-blind or if there was blinded assessment of outcome measures, and level 2 if they did not provide assurance of blinded outcome assessment.

RESULTS

In level 1 studies, the relative risk (RR) of recurrent venous thromboembolism during the first 15 days and over the entire period of anticoagulant therapy was 0.24 (95% confidence intervals [CI] 0.06 to 0.80, P = 0.02) and 0.39 (95% CI 0.30 to 0.80, P = 0.006), respectively, in favor of LMWH treatment. The RR for major bleeding was 0.42 (95% CI 0.2 to 0.9, P = 0.01), in favor of LMWH. In level 2 studies, no significant differences in the rates of recurrent venous thromboembolism or major bleeding were observed. Pooling level 1 and level 2 studies, the RR for overall mortality and mortality in cancer patients was 0.51 (95% CI 0.2 to 0.9, P = 0.01), and 0.33 (95% CI 0.1 to 0.8, P = 0.01), respectively in favor of LMWH.

CONCLUSIONS

LMWH are likely to be more effective than UFH in preventing recurrent venous thromboembolism, to produce less major bleeding, and to be associated with a lower mortality rate, particularly in the subgroup of patients with cancer.

Low-molecular-weight heparins for the treatment of venous thromboembolism

Recent studies have indicated that certain low-molecular-weight heparins given subcutaneously may replace continuous intravenous unfractionated heparin for the treatment of venous thromboembolism. Low-molecular-weight heparins have a predictably high absorption rate when given subcutaneously and they do not require laboratory monitoring. These characteristics of low-molecular-weight heparin therapy raise the possibility of treating uncomplicated patients with deep venous thrombosis or pulmonary embolism in the outpatient setting. The advantages to the patient of avoiding in-hospital care and its associated hazards are obvious. Outpatient low-molecular-weight heparin will likely prove to be highly cost-effective. At the present time, the finding associated with an individual low-molecular-weight heparin preparation cannot be extrapolated to different low-molecular-weight heparins and each must be evaluated in separate clinical trials. Recent randomized clinical trials indicate that low-molecular-weight heparin may be safer and more effective than continuous intravenous unfractionated heparin in the treatment of proximal venous thrombosis. A decreased mortality rate, which was particularly striking in patients with metastatic carcinoma, was unexpected and requires confirmation in further prospective randomized trials.

Relationship between pharmacokinetics and pharmacodynamics of tinzaparin (logiparin), a low molecular weight heparin, in dogs

1. Pharmacodynamic models relating the plasma concentrations (C) of radioactive heparin material to anticoagulant effect (E) have been investigated after single i.v. and s.c. doses of 3H-tinzaparin (1 and 4 mg/kg), a radiolabelled low molecular weight heparin, to six dogs. 2. A counterclockwise hysteresis, characterizing the C versus E relationship, was observed in all animals after s.c., but not i.v., doses indicating a possible delay (lag-time) in the systemic availability of pharmacologically-active heparin material following extravascular administration. A constant (Ke) was introduced into the model to account for this hysteresis. 3. At high plasma concentrations of radioactivity (> 10 micrograms/ml), E was related to C by a sum of two sigmoid Emax models, whereas, at lower concentrations, this reduced to the well-known sigmoid Emax model. It was proposed that tinzaparin activates two 'receptors' having different affinities for the drug. The values of EC50 associated with the activation of a single 'receptor' and of a proposed additional 'receptor' were 3 and 13 micrograms/ml of heparin material, respectively. 4. Heparin material was predominantly eliminated by renal excretion and underwent widespread tissue distribution. After s.c. administration, input of heparin material into systemic plasma was complete within 12 h post-dose, and the absorption process was characterized by a bi-exponential function. 5. We conclude that sigmoid Emax models adequately describe the C versus E relationship after s.c. and i.v. doses of 3H-tinzaparin in dogs and that the interindividual variation of the pharmacodynamic parameters derived from this model was relatively small.

Subcutaneous low-molecular-weight heparin compared with continuous intravenous heparin in the treatment of proximal-vein thrombosis

BACKGROUND

Low-molecular-weight heparin has a high bioavailability and a prolonged half-life in comparison with conventional unfractionated heparin. Limited data are available for low-molecular-weight heparin as compared with unfractionated heparin for the treatment of deep-vein thrombosis.

METHODS

In a multicenter, double-blind clinical trial, we compared fixed-dose subcutaneous low-molecular-weight heparin given once daily with adjusted-dose intravenous heparin given by continuous infusion for the initial treatment of patients with proximal-vein thrombosis, using objective documentation of clinical outcomes.

RESULTS

Six of 213 patients who received low-molecular-weight heparin (2.8 percent) and 15 of 219 patients who received intravenous heparin (6.9 percent) had new episodes of venous thromboembolism (P = 0.07; 95 percent confidence interval for the difference, 0.02 percent to 8.1 percent). Major bleeding associated with initial therapy occurred in 1 patient receiving low-molecular-weight heparin (0.5 percent) and in 11 patients receiving intravenous heparin (5.0 percent), a reduction in risk of 91 percent (P = 0.006). This apparent protection against major bleeding was lost during long-term therapy. Minor hemorrhagic complications were infrequent. Ten patients receiving low-molecular-weight heparin (4.7 percent) died, as compared with 21 patients receiving intravenous heparin (9.6 percent), a risk reduction of 51 percent (P = 0.049).

CONCLUSIONS

Low-molecular-weight heparin is at least as effective and as safe as classic intravenous heparin therapy under the conditions of this study and more convenient to administer. The simplified therapy provided by low-molecular-weight heparin may allow patients with uncomplicated proximal deep-vein thrombosis to be cared for in an outpatient setting.