An International Standard for Low Molecular Weight Heparin

Heparin resistance in severe thermal injury: A prospective cohort study

BACKGROUND

Low molecular-weight heparin (LMWH) is routinely administered to burn patients for thromboprophylaxis. Some studies have reported heparin resistance, yet the mechanism(s) and prevalence have not been systematically studied. We hypothesized that nucleosomes, composed of histone structures with associated DNA released from injured tissue and activated immune cells in the form of neutrophil extracellular traps (NETs or NETosis), neutralize LMWH resulting in suboptimal anticoagulation, assessed by reduction in anti-factor Xa activity.

METHODS

Blood was sampled from >15% total body surface area (TBSA) burn patients receiving LMWH on days 5, 10 and 14. Peak anti-factor Xa (AFXa) activity, anti-thrombin (ATIII) activity, cell-free DNA (cfDNA) levels and nucleosome levels were measured. Mixed effects regression was adjusted for multiple confounders, including injury severity and ATIII activity, and was used to test the association between nucleosomes and AFXa.

RESULTS

A total of 30 patients with severe burns were included. Mean TBSA 43% (SD 17). Twenty-three (77%) patients were affected by heparin resistance (defined by AFXa activity <0.2 IU/mL). Mean peak AFXa activity across samples was 0.18 IU/mL (SD 0.11). Mean ATIII was 81.9% activity (SD 20.4). Samples taken at higher LWMH doses were found to have significantly increased AFXa activity, though the effect was not observed at all doses, at 8000 IU no samples were heparin resistant. Nucleosome levels were negatively correlated with AFXa (r = -0.29, p = 0.050) consistent with the hypothesis. The final model, with peak AFXa as the response variable, was adjusted for nucleosome levels (p = 0.0453), ATIII activity (p = 0.0053), LMWH dose pre-sample (p = 0.0049), drug given (enoxaparin or tinzaparin) (p = 0.03), and other confounders including severity of injury, age, gender, time point of sample.

CONCLUSIONS

Heparin resistance is a prevalent issue in severe burns. Nucleosome levels were increased post-burn, and showed an inverse association with AFXa consistent with the hypothesis that they may interfere with the anticoagulant effect of heparin in vivo and contribute to heparin resistance. Accurate monitoring of AFXa activity with appropriate therapy escalation plans are recommended with dose adjustment following severe burn injury.

Comparative Studies on the Anticoagulant Profile of Branded Enoxaparin and a New Biosimilar Version

Low molecular weight heparins (LMWH) represent depolymerized heparin prepared by various methods that exhibit differential, biochemical and pharmacological profiles. Enoxaparin is prepared by benzylation followed by alkaline depolymerization of porcine heparin. Upon the expiration of its patent, several biosimilar versions of enoxaparin have become available. Heparinox (Sodic enoxaparine; Cristália Produtos Químicos Farmacêuticos LTDA, Sao Paulo, Brazil) is a new biosimilar form of enoxaparin. We assessed the molecular weight and the biochemical profile of Heparinox and compared its properties to the original branded enoxaparin (Lovenox; Sanofi, Paris, France). Clotting profiles compared included activated clotting time, activated partial thromboplastin time (aPTT), and thrombin time (TT). Anti-protease assays included anti-factor Xa and anti-factor IIa activities. Thrombin generation was measured using a calibrated automated thrombogram and thrombokinetic profile included peak thrombin, lag time and area under the curve. USP potency was determined using commercially available assay kits. Molecular weight profiling was determined using high performance liquid chromatography. We determined that Heparinox and Lovenox were comparable in their molecular weight profile. Th anticoagulant profile of the branded and biosimilar version were also similar in the clot based aPTT and TT. Similarly, the anti-Xa and anti-IIa activities were comparable in the products. No differences were noted in the thrombin generation inhibitory profile of the branded and biosimilar versions of enoxaparin. Our studies suggest that Heparinox is bioequivalent to the original branded enoxaparin based upon in vitro tests however will require further in vivo studies in animal models and humans to determine their clinical bioequivalence.

History of heparin

The history of heparin is described from its initial discovery in 1916 to recent developments in knowledge of its mechanism of action and clinical use. Commercial production started soon after its discovery, in the 1920s, and improved purification methods led to animal studies and the first clinical trials in the 1930s. Research into heparin's chemical structure proved difficult, with uncertainty about the uronic acid moiety and the N-acetyl content, but the structure of the basic disaccharide unit was established by the 1960s, though knowledge of the heterogeneity and fine structure of heparin chains continued to accumulate over the next 20 years. In 1976, it was found that only one third of heparin chains bound with high affinity to antithrombin, and subsequent studies identified a unique pentasaccharide sequence, which was essential for antithrombin binding and anticoagulant activity - this pentasaccharide was synthesised in 1983. Clinical usage of heparin continued to increase and two major developments were the use of low- dose heparin for prevention of deep vein thrombosis and pulmonary embolism, and the development of low-molecular-weight heparin as a separate drug.

Standardisation of unfractionated and low-molecular-weight heparin

Unfractionated and low-molecular-weight heparins are complex biologicals. Standardisation and global harmonisation of units and methods of measurement are essential for safety and efficacy of this important class of anticoagulants. This chapter describes the traceability of the international unit and current status of the relationship between the international and pharmacopoeial standards, together with a review on current pharmacopoeial assay methods.

[Orthopedic patients with or without thrombophilia. Diagnostic, therapy and peri-operative strategies]

Venous thrombosis and pulmonary embolisms are currently associated with high mortality rates in Europe as well as in the United States (mortality rate >300,000-500,000/year). The highest risk is attributed to orthopedic surgery. Besides the use of antithrombotic agents, surgical and anesthesiological procedures as well as a multitude of trigger mechanisms, many thrombophilic risk conditions have to be considered. The incidence of thrombotic complications could be continuously reduced by the improvement of different antithrombotic strategies and use of drugs. According to national and international guidelines low molecular weight heparins and fondaparinux (besides aPTT adjusted strategies by using unfractionated heparin) are mainly indicated in high risk patients undergoing hip and knee surgery.The use of newly developed anti-IIa and anti-Xa inhibitors (e.g. dabigatran etexilate, rivaroxaban) is not yet established in guidelines. The discovery of pentasaccharide has further improved the antithrombotic efficiency, but it is still unknown how to manage patients with thrombophilia. Otherwise the knowledge of thrombophilia is not mandatory to know how to manage high risk patients. In contrast information on a history of thrombotic complications as well as indications gained from the family history are of great importance. Whether and to what extent, which patients with or without thrombophilic disposition, under which conditions from which medication within an anti-coagulation prophylaxis profit most over which time period, will be of future interest. Fundamentally, the age of the patient as well as liver and kidney function values and possible interactions between medications must be taken into consideration for selection of individual anti-thrombotic drugs. Even prolongation of medical immobilization prophylaxis can lead to accumulative risks, such as heparin-induced thrombocytopenia, the risk of which grows with increased exposition to the triggering agent.

Anticoagulation with low-molecular-weight heparin (dalteparin) in plasmapheresis therapy: initial experience

BACKGROUND

In contrast to other extracorporeal treatments no established regime exists for anticoagulation with low-molecular-weight heparin (LMWH) in plasmapheresis therapy. A study was conducted to investigate whether LMWH (dalteparin-Na) is suitable as an effective anticoagulant in plasmapheresis therapy.

STUDY DESIGN AND METHODS

Eleven patients with autoimmune neurological diseases and the necessity for a plasmapheresis therapy were enrolled. A capillary membrane filter was used. A total of 2000 mL of human plasma was isovolumetrically exchanged per plasmapheresis cycle. The anticoagulation was accomplished with a single bolus of LMWH (dalteparin) of 80 to 90 IU per kg of body weight. The system was visually monitored. Anti-factor (F)Xa activity, thrombin-antithrombin III complex (TAT), and prothrombin fragment 1+2 (F 1+2) were determined at regular intervals. Samples were taken from the collected plasma pool to determine the loss of LMWH during the plasmapheresis procedure.

RESULTS

All plasmapheresis cycles with LMWH were successful without complications. Approximately 40 percent of the initially administered LMWH bolus was lost by the large porous filter during the plasmapheresis. The anti-FXa values were determined to be 0.5 IU per mL during the entire plasmapheresis. TAT values were elevated (TAT median, 14.3 microg/L). F 1+2 values measured before the filter cartridge remained within the normal range for the entire plasmapheresis cycle (<1.2 nmol/L) and were increasingly elevated after the filter.

CONCLUSION

Our initial experiences with LMWH for anticoagulation in plasmapheresis indicate that a body weight adjusted dose of LMWH (dalteparin) is suitable for anticoagulation in plasmapheresis therapy. No complications were observed. The data are encouraging. Further investigations will show if and how the present anticoagulation regime could be further optimized.

Development of Generic Low Molecular Weight Heparins: A Perspective

It is clear that the introduction of generic versions of low molecular weight heparins (LMWHs) is inevitable; however, it is important that the generic products are manufactured in strict compliance with the manufacturing specification of the branded product. Furthermore, regulatory agencies should require additional data on the chemical biologic, pharmacologic/toxicologic, and dose-response relationship in specific settings. Although there is strong opposition to stop the introduction of these drugs, their development will reduce cost and permit availability to all patients who need them. Some objective guidelines for the proper development of these drugs are needed. Only expert groups and advisory panels to the regulatory bodies can develop these guidelines.

Dalteparin sodium

Dalteparin sodium (Fragmin, Pharmacia Corporation) is a low molecular weight heparin (LMWH) with a mean molecular weight of approximately 5000 Da. As with the other LMWHs, dalteparin sodium has certain advantages over unfractionated heparin (UFH), most important of which are improved bio-availability by sc. injection, a prolonged antithrombotic activity which is highly correlated with body weight permitting the o.d. administration of the drug. Dalteparin sodium has been subjected to a large number of well-designed randomised clinical trials for the prevention and treatment of thrombotic disorders. Based on data from the randomised clinical trials, dalteparin sodium has been approved internationally for a wide spectrum of clinical indications (e.g., prevention of thromboembolic events after surgery). Dalteparin sodium has also been studied in randomised controlled trials in the maintenance of graft patentcy following peripheral vascular surgery, in place of warfarin for the long-term treatment of patients presenting with deep vein thrombosis (DVT), in the prevention of upper extremity thrombosis in patients with indwelling portacath devices and in pregnant patients with a history of previous venous thromboembolism with or without thrombophilia. Dalteparin sodium has been compared with heparin for the prevention of thrombotic complications during haemodyalisis and haemofiltration. These studies have shown promising results but further work is required before dalteparin sodium can be recommended for these indications.

Anticoagulant pharmacodynamics of tinzaparin following 175 iu/kg subcutaneous administration to healthy volunteers

Tinzaparin, a sodium salt of a low-molecular-weight heparin (LMWH) produced via heparinase digestion, is used for the treatment of deep vein thrombosis (DVT) and pulmonary embolism in conjunction with warfarin for the prevention of DVT in patients undergoing hip or knee replacement surgery, and as an anticoagulant in hemodialysis circuits. Its average molecular weight ranges between 5500 and 7500 daltons (Da); the percentage of chains with molecular weight lower than 2000 Da is not more than 10% in the marketed tinzaparin formulation. While this fraction is generally considered pharmacologically inactive, this has never been evaluated in vivo. The importance of the < 2000 Da fraction on the anticoagulant pharmacodynamics of tinzaparin assessed by anti-Xa and anti-IIa activity was studied in a two-way crossover trial. In this trial, 30 healthy volunteers received a single 175 IU/kg subcutaneous administration of tinzaparin containing approximately 3.5% of the < 2000 Da fraction and a tinzaparin-like LMWH containing 18.3% of the < 2000 Da fraction. The anti-Xa/anti-IIa ratios of the drug substances were comparable at 1.5 and 1.7 for tinzaparin and the tinzaparin-like LMWH, respectively. Both formulations were safe and well tolerated. Mean maximum plasma anti-Xa activity (A(max)) was approximately 0.818 IU/ml at 4 h following tinzaparin injection. Mean maximum plasma anti-IIa activity was 0.308 IU/ml at 5 h postdose. Intersubject variation was lower (< 18% for both anti-Xa and anti-IIa metrics) than in previous fixed-dose administration studies. There was no correlation between anti-Xa or anti-IIa AUC or A(max) and bodyweight in the present study supporting the weight-adjusted dosing regimen. Individual anti-Xa and anti-IIa profiles following the single 175 IU/kg subcutaneous administration of the tinzaparin-like LMWH were similar to that obtained with tinzaparin. Based on average equivalence criteria, the two LMWH preparations were determined to be bioequivalent using either anti-Xa or anti-IIa activity as biomarkers. The calculated intrasubject variabilities were low (< 14% for anti-Xa activity and < 18% for anti-IIa activity) yielding little evidence for a significant Subject x Formulation interaction. In summary, anti-Xa and anti-IIa activity following a single subcutaneous administration of tinzaparin 175 IU/kg to healthy volunteers yielded activity consistent with targeted therapeutic levels derived from previous trials in adult DVT patients. Weight-based dosing for the treatment of DVT appears rational based on the reduction in anti-Xa and anti-IIa variability consistent with the recommendation derived from earlier fixed-dose pharmacokinetic studies. Furthermore, differences in the percentage of molecules in the < 2000 Da molecular weight fraction of tinzaparin do not translate into differences in anti-Xa and anti-IIa activity in vivo.

Dalteparin: an update of its pharmacological properties and clinical efficacy in the prophylaxis and treatment of thromboembolic disease

Dalteparin is a low molecular weight heparin (LMWH) with a mean molecular weight of 5000. Compared with unfractionated heparin (UFH), the drug has markedly improved bioavailability and increased plasma elimination half-life, and exerts a greater inhibitory effect on plasma activity of coagulation factor Xa relative to its effects on other coagulation parameters. Dalteparin also has less lipolytic activity than UFH. Dalteparin 2500U once daily subcutaneously is of similar antithrombotic efficacy to UFH 5000IU twice daily, and 2 studies have shown superiority over UFH 2 or 3 times daily of dalteparin 5000U once daily in patients requiring surgical thromboprophylaxis. After total hip arthroplasty, dalteparin was superior to adjusted-dosage warfarin and was of greater thromboprophylactic efficacy when given for 35 than for 7 days. Intravenous or subcutaneous dalteparin is as effective as intravenous UFH when given once or twice daily in the initial management of established deep vein thrombosis (DVT). The drug is also effective in long term home treatment. Dalteparin has been shown to be effective in combination with aspirin in the management of unstable coronary artery disease (CAD), with composite end-point data from 1 study suggesting benefit for up to 3 months. Current data indicate potential of the drug in the management of acute myocardial infarction (MI). Dalteparin is also of similar efficacy to UFH, with a single bolus dose being sufficient in some patients, in the prevention of clotting in haemodialysis and haemofiltration circuits. Pharmacoeconomic data indicate that overall costs relative to UFH from a hospital perspective can be reduced through the use of dalteparin in patients receiving treatment for venous thromboembolism. Dalteparin has also been shown to be cost effective when used for surgical thromboprophylaxis. Overall, rates of haemorrhagic complications in patients receiving dalteparin are low and are similar to those seen with UFH.

CONCLUSIONS

Dalteparin is effective and well tolerated when given subcutaneously once daily in the prophylaxis and treatment of thromboembolic disease. The simplicity of the administration regimens used and the lack of necessity for laboratory monitoring facilitate home or outpatient treatment and appear to translate into cost advantages from a hospital perspective over UFH or warfarin. Dalteparin also maintains the patency of haemodialysis and haemofiltration circuits, with beneficial effects on blood lipid profiles and the potential for prophylaxis with a single bolus injection in some patients. Data are also accumulating to show dalteparin to be an effective and easily administered alternative to UFH in patients with CAD.

Heparin and low-molecular-weight heparin in the treatment of venous thromboembolism

Venous thromboembolism (deep vein thrombosis and pulmonary embolism) continues to constitute a major clinical challenge. Effective and safe prophylactic measures against venous thromboembolism are now available for most high risk patients. In spite of this, pulmonary embolism is responsible for approximately 150,000 to 200,000 deaths per year in the United States alone. Over the past 20 years, based on a number of high quality (Level I) clinical trials, patterns of practice with respect to the treatment of venous thromboembolism have changed dramatically. The standard treatment of venous thromboembolism has been the use of unfractionated heparin by continuous intravenous infusion, with laboratory monitoring using the activated partial thromboplastin time (APTT), with warfarin starting on day 1 or 2 and continued for 3 months. Unfractionated heparin has withstood the test of time and has been shown to be safe and effective in preventing recurrent venous thromboembolism and death in numerous clinical trials. The response of individual patients to heparin is highly variable, requiring frequent laboratory monitoring. Heparin has a number of other troublesome side effects including bleeding, heparin-induced thrombocytopenia and osteoporosis. The low-molecular-weight heparins have a number of advantages over unfractionated heparin. In particular, their increased bio-availability and prolonged half-life permit once daily subcutaneous injections and their predictable antithrombotic response based on body weight permits treatment without laboratory monitoring. Low-molecular-weight heparin in therapeutic doses causes less bleeding than unfractionated heparin and evidence is accumulating that the incidence of heparin-induced thrombocytopenia and osteoporosis are decreased as well. In individual clinical trials and meta-analyses, low-molecular-weight heparin treatment results in decreased recurrent thromboembolism, major bleeding and death when compared with unfractionated heparin in the treatment of deep vein thrombosis and pulmonary embolism. These agents have also been shown to be both effective and safe for the out-of-hospital treatment of venous thrombosis. Therefore, in many countries, low-molecular-weight heparin has replaced unfractionated heparin for the treatment of venous thromboembolism.

Unfractionated and low-molecular-weight heparin. Comparisons and current recommendations

Intravenous heparin followed by warfarin has been the classical anticoagulant therapy of acute venous thromboembolism for the past 30 years. In recent years a number of low-molecular-weight heparins have become available for clinical trials. These agents have a number of advantages over unfractionated heparin and are now being used internationally for the prevention and treatment of venous thromboembolism. 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.

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.

Determination of the anti-factor Xa activity of the synthetic pentasaccharide SR 90107A/ORG 31540 and of two structural analogues

The anti-factor Xa activity of the synthetic pentasaccharide SR 90107A/ORG 31540 was assayed by a chromogenic method at pH 8.4 and pH 7.35, comparatively to the 4th International Heparin Standard (IHS) or to the Ist International Low Molecular Weight Heparin Standard (LMWHS). At pH 8.4, SR 90107A/ORG 31540 was found to have a specific anti-factor Xa activity of 639 +/- 14 and 659 +/- 19 IU/mg (mean +/- sem, n = 6) when assayed in comparison with the 4th ISH and the Ist LMWHS respectively. At pH 7.35, the corresponding figures were 864 +/- 6 and 1160 +/- 51 IU/mg (mean +/- sem, n = 6) respectively. The dissociation constants of the ATIII-pentasaccharide complex formed by SR 90107A/ORG 31540 and by two close analogues: SR 80327A and SR 80027A in the presence of purified human ATIII were found to be 41 +/- 8, 96 +/- 1 and 3 +/- 1.4 nM (mean +/- sem, n = 3) respectively. For the three compounds, the pseudo-first order molar catalytic constants for factor Xa inactivation by the ATIII-pentasaccharide complex were shown to be statistically comparable, in the range of 7-8 x 10(7) min-1 per mole. It is concluded that the differences in specific anti-factor Xa activities between SR 90107A/ORG 31540 and its synthetic chemical analogues can be attributed to variations of the dissociation constants whereas the catalytic constants for factor Xa inactivation remain unchanged.

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.

A cross-over study of a new low molecular weight heparin (Logiparin) in hemodialysis

The safety and effectiveness of a low molecular weight heparin (LMWH) of 4500 +/- 1500 Daltons were evaluated in eight hemodialysis (HD) patients, in comparison with unfractionated heparin (UFH). In phase A of the study 3000 +/- 500 anti-factor Xa (AFXa) IU of LMWH were administered in bolus for the three consecutive HD sessions of a week. In phase B, 10000 +/- 2500 IU of UFH were administered to the same patients for the same time. Were observed no significant differences in hematocrit (Ht), platelets (Pt), fibronogen (FG) and prothrombin time (PT). Whole blood activated coagulation time (WBACT) was more prolonged with LMWH, 24 and 48 hours (start of next session) after administration (p < 0.05), and less prolonged at 5, 60, 120, 180, 240 min compared to UFH (p < 0.001). The activated partial thromboplastin time (APTT) and AFXa activity were more prolonged with UFH at 60 and 240 min (p < 0.001). The clinical effectiveness of the two preparations was similar as judged by thrombus formation and compression time. In conclusion, the present study found no real differences between LMWH and UFH, except for prolongation of WBACT 24 and 48 hours after the administration of LWMH. This probably indicates a cumulative effect of the LMWH and needs further investigation.

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.

N' alkylamine low molecular mass heparins (LMM-heparin-tyramine and LMM-heparin-tyramine-fitc) exhibit long lasting anticoagulant effects

The pharmacodynamic and pharmacokinetic properties of endpoint-attached N'alkylamine derivatives of low molecular mass heparin (LMMH), low molecular mass heparin (LMMH), low molecular mass heparin-tyramine (LMMH-tyr) and low molecular mass heparin-tyramine-fluorescein-5-isothiocyanate (LMMH-tyr-fitc) were investigated ex vivo. After intravenous bolus injection of LMMH, LMMH-tyr and LMMH-tyr-fitc (150 aXa U/kg) to Sprague-Dawley rats (n = 8), LMMH-tyr and LMMH-tyr-fitc displayed decreased clearances. The beta-half-life time of the antifactor Xa (aXa) of "endpoint-attached heparins" was significantly prolonged: LMMH-tyr (125 min), LMMH-tyr-fitc (141 min) compared to LMMH (69 min). The pharmacokinetics of LMMH-tyr-fitc were measured with reversed phase high performance liquid chromatography (RP-HPLC). It showed a decreased clearance and a prolonged half-life time (132 min). The selectively tagged LMMH-tyramine and LMMH-tyramine-fitc may be used to investigate the pharmacokinetics, plasma protein and cellular binding of low molecular mass heparins.

Inhibition of thrombin generation by heparin and low molecular weight (LMW) heparins in the absence and presence of platelet factor 4 (PF4)

The ability of several low molecular weight (LMW) heparins and unfractionated heparin (UFH) to inhibit thrombin generation, and their anti-Xa and anti-IIa activities, were measured in the absence and presence of platelet factor 4 (PF4). The LMW heparins studied were 2-5 times less potent, on a weight basis, than UFH as inhibitors of thrombin generation in platelet-poor plasma; the inhibition of thrombin generation by LMW heparins correlated better with their anti-IIa activity (r = 0.98) than with their anti-Xa activity (r = 0.69). At low concentrations of PF4, the activity of LMW heparins in the thrombin generation test was neutralized less than that of UFH, but at higher PF4 concentrations all their activities could be neutralized except in anti-Xa assays. These observations support the hypothesis that anti-IIa activity is important for inhibition of thrombin generation by LMW heparins in vitro. However, when all the anti-IIa activity of LMW heparins was neutralized by PF4, considerable inhibitory activity remained in thrombin generation and anti-Xa assays, indicating that a portion of the anti-Xa activity of LMW heparins also contributes towards inhibition of thrombin generation.

Ratios of anti-factor Xa to antithrombin activities of heparins as determined in recalcified human plasma

Anti-factor Xa and anti-thrombin activities of unfractionated (UF) and low molecular weight (LMW) heparins have been measured in human plasma and with purified human antithrombin III (ATIII) in the absence and presence of 1.5 mM calcium. The anti-factor Xa and anti-thrombin activities were measured directly, by assessing the heparin-dependent pseudo-first order rate constants of inactivation of human factor Xa or thrombin. These activities were studied with the 4th International Standard for UF heparin, the 1st International Standard for LMW heparin, CY216, enoxaparin, CY222, and the synthetic pentasaccharide. In plasma, calcium equally well increased the specific anti-factor Xa catalytic activities as compared to purified ATIII. That is, 1.5 mM calcium stimulated the UF standard heparin-catalysed inactivation of factor Xa 2.1-2.4 times. In the presence of the LMW heparins the effect of calcium was smaller (1.3-1.7 times), and in plasma there was no effect of calcium on the pentasaccharide-catalysed inactivation of factor Xa. Thus, the largest effects of calcium in the inactivation reaction of factor Xa is seen with UF standard heparin. Calcium reduced the anti-thrombin activities of all the heparin preparations studied about 1.5 times when purified ATIII was used, although in plasma this effect was less clear. Consequently, in the presence of 1.5 mM calcium the ratio of the anti-factor Xa to the anti-thrombin activities of UF standard heparin approximated those of the LMW heparins. The only exception was CY222, which under all conditions retained anti-factor Xa/anti-thrombin ratios significantly higher than those of UF standard heparin.

Prevention of venous thromboembolism after surgery: a review of enoxaparin

This review discusses the problem of deep vein thrombosis (DVT) after operation and identifies three levels of risk of DVT: low (less than 10 per cent), moderate (10-40 per cent) and high (40-80 per cent). Special emphasis is placed on the most recent prophylactic treatment, low molecular weight heparins (LMWHs), particularly enoxaparin. Several LMWHs are now available, but they differ slightly and each must be evaluated on its own merits. In general, however, LMWHs are both effective and safe in those patients at moderate or high risk of DVT. Thromboprophylaxis is cost effective when analysed using health-economic methodology.

Effects of two dosages of subcutaneous low molecular weight heparin (Parnaparin) and of unfractionated heparin on fibrin formation and lipolysis in acute myocardial infarction

Although low molecular weight heparins (LMWH) have been extensively investigated for the prophylaxis and treatment of venous thromboembolism in surgical environments, few data in acute myocardial infarction are available in the literature. In this study two dosages of a new LMWH, Parnaparin, and unfractionated heparin (UF) were investigated in 50 pts with acute myocardial infarction. 20 pts received UF (15.000 units, three subcutaneous injections, Group 1), 20 pts received Parnaparin (6.400 units, single injection, Group 2) and 10 pts received a higher dose of Parnaparin (12.800 units, single injection, Group 3). Similar fibrinopeptide A (FpA) levels were observed in Group 1 and Group 2. In Group 3 the dosage of Parnaparin resulted in a significant prolongation of the APTT and in lower FpA levels. Fibrin formation was decreased by Parnaparin in a concentration-dependent way, according to both the anti-Xa activity and the APTT ratio. Parnaparin did not result in a significant increase in free fatty acid concentration, in comparison with UF. Thus, Parnaparin may offer the advantage of a single subcutaneous injection in patients with acute myocardial infarction.

Evaluation of an amidolytic test for comparative calibration of HMW- and LMW-heparins

Amidolytic chromogenic substrate assays are frequently used to determine the anticoagulant activities of various commercial heparins. With the help of a combined assay method heparin characterization is made possible using the TAT/XAT quotient under consideration of the simultaneous inhibition of the two serine proteases thrombin and factor Xa by antithrombin III. The test is primarily designed for qualitative characterization where a numerical value can be assigned to every heparin. However, quantitative aspects may also be evaluated.

Prevention of deep vein thrombosis after hip replacement: randomised comparison between unfractionated heparin and low molecular weight heparin

OBJECTIVE

To evaluate the efficacy and safety of two subcutaneous prophylactic regimens for postoperative deep vein thrombosis after total hip replacement.

DESIGN

Prospective open randomised multicentre trial.

SETTING

28 European departments of orthopaedic surgery.

INTERVENTION

All patients had bilateral phlebography 10 days after surgery. 31 patients receiving low molecular weight heparin and 29 receiving unfractionated heparin were excluded from the efficacy analysis for various reasons.

PATIENTS

349 patients undergoing total hip replacement between September 1988 and May 1989. 174 patients received subcutaneously a low molecular weight heparin (Fraxiparine) with anti-factor Xa activity of 41 IU/kg/day for three days, then 62 IU/kg/day from day 4 to day 10. 175 patients received subcutaneous unfractionated heparin at intervals of eight hours; doses were adjusted to maintain the activated thromboplastin time at two to five seconds above control values.

MAIN OUTCOME MEASURE

Total incidence of deep vein thrombosis and incidence of proximal deep vein thrombosis on bilateral phlebography.

RESULTS

The total incidence of deep vein thrombosis was 16% in patients receiving unfractionated heparin and 12.6% in patients receiving low molecular weight heparin (p = 0.45), and the incidence of thrombosis of the proximal veins was 13.1% and 2.9% respectively (p less than 0.001). Four patients receiving unfractionated heparin and one receiving low molecular weight heparin developed pulmonary embolism. The incidence of bleeding complications was low and comparable in the two groups.

CONCLUSION

Low molecular weight heparin is at least as effective as unfractionated heparin in preventing deep vein thrombosis and is more effective at preventing thrombosis of the proximal veins in patients undergoing hip replacement. Low molecular weight heparin is not more likely to cause bleeding complications and is simpler to give than unfractionated heparin.

The use of a low molecular weight heparinoid (Org 10172) for extracorporeal procedures in patients with heparin dependent thrombocytopenia and thrombosis

We report two cases of heparin induced thrombocytopenia (HIT), in patients who required anticoagulation for extracorporeal procedures (haemodialysis and cardiopulmonary bypass) one associated with recurrent thrombosis of the artificial circuits. Resolution of thrombocytopenia and successful anticoagulation were achieved using a low molecular weight heparinoid (LMWH) Org 10172. Anticoagulation was monitored using estimations of plasma anti-factor Xa activity. These cases demonstrate that LMWH provides safe and effective anticoagulation in patients in whom unfractionated heparin has caused HIT.

Pharmacodynamics of CY 216 in healthy volunteers: inter-individual variations

The pharmacodynamic parameters of a low molecular weight heparin (LMWH, CY 216) and their inter-individual variations were investigated. In a cross over study 100 anti-factor Xa IC U/kg were injected, one week apart, to 12 healthy volunteers by intravenous (IV) or subcutaneous (SC) route. The pharmacological effects were followed by performing activated partial thromboplastin time (APTT), thrombin clotting time (TCT) and a chromogenic anti-factor Xa assay. The main pharmacodynamic parameters were calculated from the anti-factor Xa activity disappearance curves. Five to ten min after IV injection, the APTT ranged between 56 and 98 sec (baseline 40 sec), the TCT between 28 and 99 sec (baseline 19 sec) and the anti-factor Xa activity between 1.58 and 2.28 IC U/ml. The anti-factor Xa activity half-life ranged between 1.5 and 2.9 h. After SC injection, there were no detectable APTT and TCT prolongations; the maximum anti-factor Xa activity ranged between 0.36 and 0.88 IC U/ml and the half life between 1.5 and 6.4 h. These results indicate that, as for standard heparin, there are large inter-individual variations in the anticoagulant responses to a given dose of CY 216 an observation which may have clinical implications.

Treatment of acute venous thromboembolism with low molecular weight heparin (Fragmin). Results of a double-blind randomized study

We performed a prospective, randomized, double-blind trial in 194 unselected patients to determine the safety and efficacy of low molecular weight heparin (Fragmin) compared with standard heparin as the initial treatment of acute venous thromboembolism. Ninety-eight patients received continuous intravenous heparin, and 96 patients received Fragmin for 5-10 days. Doses were adjusted to maintain anti-Xa levels between 0.3 and 0.6 unit/ml for patients with a high risk for a bleeding complication and between 0.4 and 0.9 unit/ml for patients with a low risk for bleeding. Treatment was stopped when a therapeutic level of anticoagulation (International Normalized Ratio greater than 3.5) was reached with coumarins. Thirteen patients in the heparin group and 10 patients in the Fragmin group had a major bleeding complication. The incidence of major and minor bleeding complications combined decreased from 48.9% to 38.5% (95% confidence interval for the difference, -3.5% to +24.2%), corresponding with a relative bleeding risk reduction of 21.2%. There were no significant differences in efficacy as defined by new high-probability defects on repeat ventilation-perfusion scintigraphy of the lung in 80 patients: six of 46 patients in the heparin group and 3 of 34 patients in the Fragmin group had new defects (95% confidence interval for the difference, -9.4% to +17.8%). We conclude that low molecular weight heparin (Fragmin) given in adjusted, continuous, and intravenous doses is safe and effective as initial treatment of acute venous thromboembolism compared with heparin. There is a trend in risk reduction for bleeding in favor of low molecular weight heparin, a trend, however, that is smaller than expected compared with animal studies.

Current status of the clinical use of heparin fractions

In recent years, numerous low molecular weight heparin (LMWH) fractions have become available for clinical use, and the widespread registration of some of these products is expected soon also in Italy. An increased benefit/risk ratio concerning efficacy and safety has been shown in animal models as compared to standard heparin. In order to assess whether there is sufficient evidence supporting their use in replacement of unfractionated heparin, a review of the results of the main clinical studies is performed, discussing LMWH effectiveness and bleeding risk separately in the different clinical applications.