Prophylaxis of venous thromboembolism in general surgery in Spain. Analysis of a national survey

INTRODUCTION

Venous thromboembolism (VTE) represents a serious postoperative complication that can be prevented by adequate thromboprophylaxis. Surveys provide relevant information about clinician's attitudes and preferences regarding VTE prophylaxis.

METHODS

Transversal, descriptive study based on a survey sent to general surgeons members of the Spanish Association of Surgeons (AEC), that included 31 questions regarding postoperative VTE and its prevention, as well as three clinical scenarios.

RESULTS

530 surgeons, 21.8% of the 2,429 invited by electronic mail to participate, completed the survey. Most of the answering clinicians work on in big teaching hospitals, and 28.5% are residents. VTE represents a serious problem for 28% of participants. Although 81% consider that their knowledge on the prevention of postoperative VTE is adequate, a similar percentage recognizes the need for further education. The vast majority (98.7%) use low molecular weight heparins, which are considered the most effective and safe modality, followed by mechanical methods. The Caprini risk assessment score is used by 81% of surgeons, who usually start pharmacological prophylaxis preoperatively. However, there are remarkable differences in the dosing of heparins, timing of initiation, and duration, especially in non-oncologic surgical patients.

CONCLUSIONS

Most Spanish surgeons are interested in the prevention of postoperative VTE. Overall, the level of knowledge on thromboprophylaxis is adequate. However, our results indicate that there is a need for better education on relevant practical aspects of prophylaxis that could be achieved by incorporating recommendations from recent guidelines to local hospital-based protocols.

Product Individuality of Commercially Available Low-Molecular-Weight Heparins and Their Generic Versions: Therapeutic Implications

The currently available brand-name low-molecular-weight heparins (LMWHs) in the United States include dalteparin (Pfizer), enoxaparin (Aventis), and tinzaparin (Pharmion). Other products available, in Europe, include certoparin (Novartis), reviparin (Abbott), nadroparin (GlaxoSmithkline), and parnaparin (Alpha-Wasserman). Each of these LMWHs has a characteristic molecular weight profile and biological activity in terms of an anti-FXa and anti-FIIa potency. The mean molecular weight of these drugs ranges from 4.0 kDa to 7.0 kDa and the anti-FXa:anti-FIIa ratio ranges from 1.5 to 3.5. These agents may also be characterized by the presence of specific chemical end groups such as 2-O-sulfo-4-enepyranosuronic acid at the nonreducing terminus (enoxaparin) or 2,5-anhydro-D-mannose at the reducing terminus (dalteparin). Further, the component oligosaccharide chains exhibit product-specific distribution profiles. It is now widely accepted that individual LMWHs are chemically unique agents and cannot be interchanged therapeutically. Each commercial LMWH has been individually developed for specific clinical indications, which are dose and product dependent. Recently, several generic LMWHs have become available in India (Cutenox and Markaparin) and South America (dilutol, clenox, dripanina), and three companies have filed for regulatory approval of a generic version of enoxaparin in the United States. As the primary aim of a generic drug is to reduce cost without compromising patient care, a generic drug is required to be chemically and biologically equivalent to the pioneer drug. Because LMWHs represent complex natural mucopolysaccharide drugs that have undergone chemical and enzymatic modifications, physicochemical and biological information in addition to molecular weight and anti-FXa:anti-FIIa ratio should be used to determine generic equivalency to the branded drug. We have utilized a previously reported approach to systematically compare three generic versions of enoxaparin obtained from India and Brazil with the branded enoxaparin (Lovenox) available in the United States. Testing included molecular and structural profiling, evaluation in clot-based and amidolytic anti-FXa and anti-FIIa assays, and heparinase-I digestion profiles. While the molecular profiles (4.8 ± 1.8kD) and anticoagulant potencies as determined by activated partial thromboplastin time (APTT) were comparable for all four agents, the generic products showed variations in the thrombin time (TT) and Heptest assays. Two generic and the branded enoxaparin were readily digested by heparinase-I, losing most of their anticoagulant activity, but one generic product resisted digestion. This may have been due to a unique structural feature in this product. These studies show that, while generic LMWHs may exhibit acceptable molecular weight and anti-FXa profiles, they can exhibit assay-based differences and digestion profiles. Testing in animal models to determine safety, efficacy, and pharmacodynamic parameters may be important to verify equivalence. In order to assure that the generic LMWHs are equivalent to branded LMWHs such that equivalent clinical results are obtained, there is a need to develop clear stepwise guidelines that will establish equivalency in terms of physical, chemical, biochemical, pharmacokinetic, and pharmacodynamic properties for these anticoagulant drugs.

Generic Forms of Low-Molecular-Weight Heparins: Some Practical Considerations

This commentary briefly reviews the controversies of therapeutic and generic interchangeability, as they apply to the antithrombotic drug class called low-molecular-weight heparin (LMWH). Recommendations are prepared for the generic LMWH approval process by various regulatory bodies.

Collaborative study for the establishment of replacement batches of heparin low- molecular-mass for assay biological reference preparations

A collaborative study was run by the European Directorate for the Quality of Medicines & HealthCare (EDQM) in the context of the Biological Standardisation Programme (BSP), under the aegis of the Council of Europe and the European Commission, to establish replacement batches for the dwindling stocks of the Heparin low-molecular-mass for assay European Pharmacopoeia Biological Reference Preparation (BRP). The replacement batches of BRP are intended to be used in the assays for anti-Xa and anti-IIa activities, as described in the European Pharmacopoeia (Ph. Eur.) monograph Heparins, low-molecular-mass (0828). Three freeze-dried candidate batches were calibrated against the current International Standard (IS) for Heparin, lowmolecular- weight (2nd IS, 01/608). For the purpose of the continuity check between subsequent BRP batches, the current Heparin low-molecular-mass for assay BRP (batch 5) was also included in the test panel. Thirteen official medicines control and manufacturers laboratories from European and non-European countries contributed data. A central statistical analysis of the datasets was performed at the EDQM. On the basis of the results, the 3 candidate materials were assigned a potency of 104 IU/vial for the anti-Xa activity and 31 IU/vial for the anti-IIa activity. Taken into account the preliminary stability data and the results of this collaborative study, the 3 batches of candidate BRP were adopted in June 2010 by the Commission of the Ph. Eur. as Heparin low-molecular-mass for assay BRP batches 6, 7 and 8.

Variability of heparins and heterogeneity of low molecular weight heparins

Chemical and physical characteristics, building blocks, constitutive disaccharides, sulfation degree, and biological activities of heparins (UFHs) and of low molecular weight heparins (LMWHs) obtained by different depolymerization processes are examined comparatively in terms of structure characteristics, content of 1,6-anhydro rings, and other fingerprints. The heterogeneity of different LMWHs depends on different manufacturing processes and on particular specifications of pharmacopoeias. The reported examples prove that the variability among samples of LMWHs manufactured by the same process is quite limited. Most of the variability is derived from the parent UFH. In contrast, fingerprint groups and residues are specific to the depolymerization process and their extent can be roughly controlled through the process parameters.

Collaborative study to establish the Low-molecular-mass heparin for assay--European Pharmacopoeia Biological Reference Preparation

Thirty laboratories participated in a collaborative study to calibrate replacements for the 1st International Standard for Low Molecular Weight Heparin and the European Pharmacopoeia Low-molecular-mass heparin for assay Biological Reference Preparation. Two freeze-dried materials and one liquid preparation were included in the study. All three samples gave excellent intra- and inter-laboratory variations (majority of mean % geometric coefficient of variation < 10 %) when assayed against the 1st International Standard by both anti-Xa and anti-IIa assays. There were no major differences found between potency estimates using all methods and that obtained using European Pharmacopoeia method only. Overall, this study showed that the differences between the candidates are marginal. Based on the results of the study Sample B, 01/608 was established as the 2nd International Standard for Low Molecular Weight Heparin. Sample A, 01/592 and sample C, the liquid preparation, were established as replacements for the European Pharmacopoeia 'Low-molecular-mass heparin for assay' Biological Reference Preparation.

Low-molecular-weight heparin as bridging anticoagulation during interruption of warfarin: assessment of a standardized periprocedural anticoagulation regimen

BACKGROUND

The treatment of patients at increased risk for arterial thromboembolism who require temporary interruption of warfarin sodium therapy is a common clinical problem. We investigated the efficacy and safety of a standardized periprocedural anticoagulation regimen with low-molecular-weight heparin.

METHODS

We studied 650 consecutive patients with a mechanical heart valve, chronic atrial fibrillation, or embolic stroke who required interruption of warfarin therapy because of an invasive procedure. Warfarin was stopped 5 or 6 days before the procedure, and patients received subcutaneous dalteparin sodium, 100 IU/kg twice daily, starting 3 days before the procedure. The risk of postprocedural bleeding determined postprocedural anticoagulant management. In patients undergoing a non-high-bleeding-risk procedure who had adequate postprocedural hemostasis, warfarin was resumed on the evening of the procedure, and dalteparin sodium, 100 IU/kg twice daily, was resumed on the next day and continued until the international normalized ratio was 2.0 or more. If postprocedural hemostasis was not secured, the resumption of dalteparin was delayed. In patients undergoing a high-bleeding-risk procedure, warfarin was resumed on the evening of the procedure, but dalteparin was not given after the procedure.

RESULTS

Patients were followed up during the preprocedural and postprocedural period for a mean of 13.8 days (range, 10-18 days). In 542 patients who underwent a non-high-bleeding-risk procedure, there were 2 thromboembolic events (0.4%), 4 major bleeding episodes (0.7%), and 32 episodes of increased wound-related blood loss that precluded postprocedural dalteparin administration (5.9%). In 108 patients who underwent a high-bleeding-risk procedure, there were 2 deaths (1.8%) possibly due to thromboembolism and 2 major bleeding episodes (1.8%).

CONCLUSIONS

In patients at increased risk for arterial thromboembolism who require temporary interruption of warfarin therapy, a standardized periprocedural anticoagulant regimen with low-molecular-weight heparin is associated with a low risk of thromboembolic and major bleeding complications.

Anticoagulation therapy

Despite refinements and standardization in the use of anticoagulants, many problems remain for clinicians. Dr. Crowther describes appropriate starting and maintenance doses of warfarin, factors accounting for inter- and intra-observer variability and importantly, the management of the over-anticoagulated patients and bleeding patients. Dr. White compares unfractionated heparin (UFH) and low molecular weight heparin (LMWH) and addresses whether there truly are differences in the efficacy and safety of different LMWH's for both arterial and venous indications. Dr. Ortel discusses the management of the problem patient who requires anticoagulants, the management of heparin-induced thrombocytopenia, the pregnant patient, the obese patient, patients who have renal insufficiency and/or liver disease, patients with malignant disease, and other challenging patient populations.

Randomized trial of different regimens of heparins and in vivo thrombin generation in acute deep vein thrombosis

Low-molecular-weight and unfractionated heparins are frequently used to treat venous thromboembolism, but it is not known whether they are equally effective in inhibiting in vivo generation of thrombin. In this multicenter trial, 1048 patients were randomized to intravenous unfractionated heparin (group A), twice daily low-molecular-weight heparin (reviparin) for 1 week (group B), or once daily reviparin for 4 weeks (group C). All patients received vitamin K antagonists. Blood samples withdrawn at the baseline and at weeks 1 and 3 were analyzed using markers of in vivo thrombin generation and other coagulation parameters. During the first 3 weeks symptomatic recurrent deep vein thrombosis-pulmonary embolism (DVT/PE) occurred in 17 (4.5%) of 375 patients in group A compared with 4 (1.0%) of 388 patients in group B, and 9 (2.4%) of 374 patients in group C. Forty percent of patients in group A, 53.4% in group B, and 53.5% in group C showed 30% or greater reduction in thrombus size assessed by venography. Patients in group B had significantly greater reduction in D-dimer, prothrombin fragments 1 and 2 (F1 + 2), endogenous thrombin potential (ETP), and thrombin-antithrombin (TAT) complexes compared to groups A and C. Greater release of tissue factor pathway inhibitor (TFPI) and reduction in levels of thrombin activatable fibrinolysis inhibitor (TAFI) and fibrinogen were significantly more pronounced in group C patients. Reviparin administered twice daily plus vitamin K antagonist is more effective in inhibiting in vivo thrombin generation compared to intravenous unfractionated heparin plus vitamin K antagonist, and reviparin once daily produced significantly higher TFPI release and greater reduction in TAFI and fibrinogen levels.

Anticoagulation management of valve replacement patients

Anticoagulation regimens vary according to surgeon, nature of the valve (mechanical or biological), its position and other risk factors for stroke. The American College of Chest Physicians (2001) have made the following recommendations to protect patients with prosthetic heart valves from developing a stroke: (i) For mechanical heart valves: Anticoagulation with Warfarin at an INR range 2-3 for patients with a bileaflet mechanical valve in the aortic position; (ii) in the mitral position, an INR of 2.5-3.5 is recommended; an alternative recommendation is an INR of 2-3 in combination with aspirin (80 mg/day); and (iii) in patients with a mechanical valve and a history of systemic embolization, an INR of 2.5-3.5 combined with low-dose aspirin (80-100 mg) is recommended; when Warfarin therapy is initiated, the doses for patients aged <70 years is 4 mg, and for patients aged >70 years it is 3 mg. While it is important to recognize that the therapeutic range for Warfarin is narrow, recommendations have also been established to manage patients with high INRs and for the temporary discontinuation of anticoagulant therapy when they undergo surgical procedures. Rapid anticoagulation can be achieved either with unfractionated heparin or with low-molecular weight heparin (LMWH). Heparin is initiated with an intravenous bolus of 80 U/kg bodyweight, and an infusion of 18 U/kg/h. The activated thromboplastin time should be 60-80 s. An alternative to intravenous heparin is subcutaneous LMWH, which is prescribed in a mg/kg dose. In the event of valve thrombosis in patients who are hemodynamically unstable, surgical exploration with thrombectomy is indicated, with or without valve replacement. In patients who are hemodynamically stable, thrombolytic therapy is recommended initially.

Cost comparison of tinzaparin versus enoxaparin as deep venous thrombosis prophylaxis in spinal cord injury: preliminary data

Thromboembolic events are major causes of morbidity and mortality in patients with spinal cord injuries. Low molecular weight heparins are recommended as prophylaxis against such events. The purpose of the current study was to perform a cost analysis of tinzaparin versus enoxaparin using published efficacy and safety data as deep vein thrombosis and pulmonary embolism prophylaxis in this population. All published English language articles evaluating either tinzaparin or enoxaparin as pharmacoprophylaxis in spinal cord-injured patients were identified. Data from these studies were subjected to cost-effectiveness analyses followed by sensitivity analyses to determine which agent is the most cost-effective in these patients. Results demonstrated that tinzaparin 3500 U daily and enoxaparin 30 mg every 12 h are both cost-effective agents for thromboembolism prophylaxis in patients with spinal cord injuries.

The outcome of ambulatory DVT management using a multidisciplinary approach

Low molecular weight heparins (LMWHs) have been demonstrated to be at least as safe and effective as unfractionated heparin (UFH) in the initial management of deep vein thrombosis (DVT). However, the effectiveness of using LMWH in the ambulatory management of DVT in a 'real-life' setting has yet to be evaluated. This multicentre retrospective study involving 697 patients considers the outcome data of patients under- going ambulatory DVT treatment with tinzaparin (Innohep(R), Leo Pharmaceuticals, Risborough, Buckinghamshire, UK). During the 6 months following presentation, 17 (2.5%) patients had confirmed thromboembolic complications, of which 14 occurred subsequent to the initial LMWH treatment phase ('late'). There were no deaths in this group. Bleeding complications were reported in 23 (3.4%) patients, with 13 of these being classified as 'late'. Of these, two events were considered major resulting in hospitalization and death. Hospitalization for all causes was 6.8% (45 patients) with 32 patients being admitted for thromboembolic or bleeding complications. Overall mortality was 6.7%. These results compare favourably with published clinical trial data. This study demonstrates that ambulatory treatment of proven DVT with LMWH is both safe and effective.

Heparins and venous thromboembolism: current practice and future directions

Unfractionated heparin (UFH) in adjusted doses and low-molecular-weight heparins (LMWH) in fixed doses are the chosen therapy for the initial treatment of venous thromboembolism. The use of UFH protocols ensures that virtually all patients will promptly achieve the therapeutic range for the activated partial thromboplastin time. However, proper use of UFH requires considerable expertise, can cause inconvenience and has limitations. Unmonitored therapy with subcutaneous LMWH is at least as effective and safe as adjusted-dose UFH, is associated with a considerable reduction of mortality in cancer patients, and permits the treatment of suitable patients in an outpatient setting. LMWH in high prophylactic doses is more effective than UFH and oral anticoagulants for prevention of postoperative venous thrombosis in major orthopedic surgery. Whether thromboprophylaxis should be continued for a few additional weeks after hospital discharge is controversial. LMWH and UFH are equally effective for prevention of postoperative deep-vein thrombosis in cancer patients. In a recent controlled randomized trial, enoxaparin in high prophylactic doses was an effective and safe measure of thromboprophylaxis in ordinary bedridden patients. The efficacy and safety of pentasaccharide (the smallest antithrombin binding sequence of heparin) in the treatment and prevention of venous thromboembolic disorders is currently under investigation.

Low molecular weight heparin therapy for percutaneous coronary intervention: a practice in evolution

Unfractionated heparin (UFH) remains the principal antithrombotic agent during percutaneous coronary intervention (PCI) but is associated with significant limitations including an unpredictable anticoagulation dose response, the requirement for frequent monitoring, and transient rebound hypercoagulability. Low molecular weight heparin (LMWH) represents an attractive alternative due to its predictable dose response relationship, superior antithrombotic efficacy and potential for improved clinical safety, and has been used increasingly in patients with acute coronary syndromes prior to coronary angiography. The rationale and existing data regarding the use of LMWH in PCI is summarized and reviewed. Preliminary clinical guidelines for the use of LMWH in the transition from medical stabilization of patients with acute coronary syndromes to invasive management in the catheterization laboratory are presented.

Home treatment of deep venous thrombosis with low molecular weight heparin: Long-term incidence of recurrent venous thromboembolism

Outpatient treatment of deep venous thrombosis (DVT) with low molecular weight heparin (LMWH) seems as safe and effective as inpatient treatment with unfractionated heparin (UFH). However, most of the randomized trials comparing a LMWH with UFH described clinical outcomes within 3-6 months. The long-term incidence of recurrent VTE after treatment of DVT with LMWH remains to be established. The primary objective of this retrospective study was to document the long-term incidence of recurrent venous thromboembolism (VTE) in patients with DVT treated with a LMWH, nadroparin in an outpatient basis. The patients were evaluated 46 months after inclusion in two cohorts comparing home treatment with nadroparin (n = 130) with in-hospital treatment with intravenous UFH (n = 149). More than 60% of the patients in the nadroparin group could be treated at home, either entirely or after a short stay in hospital. The age-adjusted thrombosis-free survival was not statistically significant between nadroparin and UFH-treated patients (P = 0.084). There was a nonsignificant trend favoring nadroparin as compared with UFH. The hazard ratio (HR) for recurrent VTE in the nadroparin group with respect to the UFH group was 0.44 (95% confidence interval, 0.17-1.12). No significant differences were observed in overall mortality or major hemorrhage between the two treatment groups. Our study suggests that home treatment of DVT with LMWH is at least as effective and safe as in-hospital UFH after a long-term follow-up period.

Prophylaxis and treatment of deep-vein thrombosis

In 1980, unfractionated heparin (UFH) was the established agent for the prophylaxis of venous thromboembolic (VTE) disease in patients undergoing general surgery. VTE prophylaxis was the first indication in which low-molecular-weight heparins (LMWHs) were tested. Approximately 40 trials have demonstrated that LMWHs are at least as effective and safe as UFH. LMWHs exhibit a number of advantages over UFH, including ease of administration, convenient once-daily dosing, and facilitation of outpatient management. The ideal time of administration and the dose of the initial one or two injections of LMWH remain unresolved issues. LMWHs are used with increasing frequency in the treatment of acute deep vein thrombosis (DVT), having been studied in comparison to UFH in 16 major clinical trials. LMWHs are at least as effective as UFH in the prevention of VTE, but higher doses than those used for prophylaxis are required. There is still an ongoing debate about whether the daily dose should be administered in one or two subcutaneous injections. In some recent studies, symptomatic new DVTs or pulmonary emboli (PE) were the primary end points, which had to be verified by objective methods, but such end points may be not be sensitive enough to detect major differences in the efficacy of different LMWHs.

Comparative efficacy of low-molecular-weight heparins in orthopedic surgery

The low-molecular-weight heparins (LMWHs) have been evaluated in the prevention of postoperative thromboembolic disease and have been found to be clinically efficacious and safe. Studies conducted in similar surgery settings have resulted in significantly different reductions in the incidence of deep-vein thrombosis, making an analysis of grouped studies complex. Only two studies have reported head-to-head comparisons of two different LMWHs and showed no difference in clinical end points between enoxaparin and either reviparin or tinzaparin. Our study at the Aalborg hospital in Denmark, comparing two different dosage regimens of LMWH tinzaparin, supported the conclusions of the head-to-head comparative studies. LMWHs are distinct drug entities that cannot be interchanged at equivalent anti-Xa dosages, and the interpretation of their relative efficacy and safety may be biased by the degree of clinical experience of the individual investigators.

Antithrombotics and anticoagulants in coronary syndromes and stroke

The low-molecular-weight heparins (LMWHs) have been proven superior to placebo in reducing the incidence of acute coronary ischemic syndromes. Comparative studies vs. unfractionated heparin have not demonstrated superiority in favor of the LMWH dalteparin. In the Efficacy and Safety of Subcutaneous Enoxaparin in Non-Q-wave Coronary Events (ESSENCE) trial, enoxaparin was demonstrated to have a benefit over heparin. The results have contributed to a better understanding of the relative efficacy of LMWHs in acute coronary syndromes. A second trial with enoxaparin supported the conclusions of the ESSENCE trial. The antithrombotic effects of LMWHs have also been evaluated for the management of ischemic stroke with varied results. A trial assessing tinzaparin in acute ischemic stroke has completed enrollment, and its results may shed new light on the use of an LMWH for the management of stroke.

An update on heparins at the beginning of the new millennium

Unfractionated heparin has enjoyed the sole anticoagulant status for almost half a century. Besides an effective anticoagulant, this drug has been used in several additional indications. Despite the development of newer anticoagulant drugs, unfractionated heparin has remained the drug of choice for surgical anticoagulation and interventional cardiology. In the area of hematology and transfusion medicine, unfractionated heparin has continued to play a major role as an anticoagulant drug. The development of low-molecular-weight heparins (LMWHs) represents a refinement for the use of heparin. These drugs represent a class of depolymerized heparin derivatives with a distinct pharmacologic profile that is largely determined by their composition. These drugs produce their major effects by combining with antithrombin and exerting antithrombin and anti-Xa inhibition. In addition, the LMWHs also increase non-antithrombin-dependent effects such as TFPI release, modulation of adhesion molecules, and release of profibrinolytic and antithrombotic mediators from the blood vessels. The cumulative effects of each of the different LMWHs differ and each product exhibits a distinct profile. Initially these agents were developed for the prophylaxis of postsurgical deep-vein thrombosis. However, at this time these drugs are used not only for prophylaxis, but also for the treatment of thrombotic disorders of both the venous and arterial type. To a large extent, the LMWHs have replaced unfractionated heparin in most subcutaneous indications. With the use of these refined heparins, outpatient anticoagulant management has gone through a dramatic evolution. For the first time, patients with thrombotic disorders can be treated in an outpatient setting. Thus, the introduction of LMWHs represents a major advance in improving the use of heparin. The development of the oral formulation of heparin and LMWHs also provides an important area that may impact on the use of heparin and LMWHs. The increased awareness of heparin-induced thrombocytopenia has necessitated the development of newer methods to identify patients at risk of developing this catastrophic syndrome. Furthermore, a strong interest has developed in alternate drugs or the management of patients with this syndrome. Despite the development of alternate anticoagulants that are mostly antithrombin derived (hirudins, hirulog), these agents have failed to provide similar clinical outcome as heparin in many indications. However, antithrombin drugs are useful in the anticoagulant management of heparin-compromised patients. The FDA has approved a recombinant hirudin (Refludan) and a synthetic antithrombin agent, argatroban (Novastan), for this indication. The development of synthetic heparin pentasaccharide and anti-Xa agents may have an impact on the prophylaxis of thrombotic disorders. However, these monotherapeutic agents do not mimic the polytherapeutic actions of heparin. Furthermore, these agents do not inhibit thrombin. Heparin and LMWHs are capable of inhibiting not only factor Xa and thrombin, but other serine proteases in the coagulation network. The only way the newer drugs can mimic the actions of heparin is in combination modalities (polytherapeutic approaches). It has been suggested that newer antiplatelet drugs also exhibit anticoagulant actions. While these drugs may exhibit weak effects on thrombin generation, none of the currently available antiplatelet drugs exhibit any degree of antithrombin actions. It is likely that heparins synergize or augment the effects of the new antiplatelet drugs. Currently, combination approaches are used to anticoagulate patients in these studies. The dosage of heparins has been arbitrarily reduced. This may not be an optimal procedure. Additional clinical studies are needed to study these combinations where the alterations of these drugs are compared. Such combinations will require newer monitoring approaches. The development of oral thrombin agents, GP IIb

Development of tinzaparin: a heparinase-digested low-molecular-weight heparin

Although heparin and its properties had been discovered in the early 1920s, the different characteristics associated with different molecular-weight fractions of heparin were only recognized in the late 1970s. Tinzaparin is a low-molecular-weight heparin (LMWH) produced by heparinase digestion of heparin. Preclinical research on tinzaparin established that there were no differences in the antithrombotic activity compared with heparin. Clinical studies evaluating tinzaparin vs. standard heparin for thromboprophylaxis of deep-vein thrombosis in general and orthopedic surgery found that tinzaparin was as effective as standard heparin. Tinzaparin was also evaluated vs. standard heparin in the treatment of acute proximal vein thrombosis; time-to-event curves suggested that this LMWH could be more effective than standard heparin.

An equivalence study of two low-molecular-weight heparins in the prevention and treatment of deep-vein thrombosis after total hip replacement

Low-molecular-weight heparins have been evaluated against unfractionated heparin and have been shown to have clinical benefits in the perioperative setting during orthopedic surgery. Two low-molecular-weight heparins, tinzaparin and enoxaparin, were assessed for equivalency in efficacy and safety in 499 patients undergoing elective hip replacement. The two anticoagulants were found to be effective and safe in this setting in the specified patient type. No statistical difference was observed in the incidence of bleeding. Clinical side effects tended to be greater in patients with a higher body mass index, which could serve as a possible indicator for the risk of deep vein thrombosis.

Low-molecular-weight heparin during pregnancy

Thromboembolism is an infrequent, yet serious cause of both maternal and fetal morbidity and death during pregnancy and the puerperium. Pregnancy itself increases the risk of thromboembolic complications probably owing to a combination of hypercoagulability and venous stasis due to venous dilation. Recent studies have indicated that some serious obstetric complications are correlated with inherited or acquired thrombophilia. The prevalence of venous thromboembolism (VTE) has been extimated to be 1 per 1000-2000 pregnancies in retrospective studies. Anticoagulant treatment and prophylaxis both before and during pregnancy are based on unfractionated heparin (UH), low-molecular-weight heparin (LMWH) and warfarin. Warfarin is teratogenous if administered between the 6th and the 12th week. LMWH is replacing UH in the prevention and treatment of VTE both outside and more recently during pregnancy with the same indications, and also for obstetric complications. This paper assesses the safety and efficacy of heparin therapy during pregnancy and the puerperium. Its cardiovascular and obstetric indications and regimens and maternal and fetal side-effects are also discussed.

Anti-thrombotic efficacies of enoxaparin, dalteparin, and unfractionated heparin in venous thrombo-embolism

BACKGROUND

Few data exist by which the anti-thrombotic efficacy of different anticoagulants may be compared. We used a radiolabeled antibody specific for polymerizing fibrin to compare the in vivo anti-thrombotic potencies of different systemic anticoagulants (enoxaparin, dalteparin, and unfractionated heparin).

METHODS AND RESULTS

Deep venous thrombi (DVTs) were induced in dogs' femoral veins. The dogs were then treated with one of the following subcutaneous regimens: enoxaparin 100 units/kg (1.0 mg/kg) every 12 hours (n=4), dalteparin 200 units/kg every 24 hours (n=4), or unfractionated heparin 240 units/kg every 8 hours with dose adjustment via aPTT (n=3). 111Indium-labeled anti-fibrin antibodies, specific for propagating thrombi, were given intravenously and nuclear scans of the legs were taken over the following 24 hours. Thrombus propagation was estimated by the ratio of gamma emissions from the legs containing DVTs divided by the emissions from the contralateral "control" legs. DVTs accumulated labeled anti-fibrin antibodies at the same rates in both the enoxaparin group and the dalteparin group (gamma emissions 171+/-6% and 168+/-36% of control by 24 hours, respectively). DVTs in the adjusted dose unfractionated heparin group tended to accumulate antibodies at a slower rate (129+/-19% of control by 24 hours).

CONCLUSIONS

Enoxaparin and dalteparin inhibited propagation of pre-formed thrombi to the same degree. Subcutaneous unfractionated heparin, adjusted every 8 hours by aPTT, tended to suppress ongoing thrombosis more than either LMWH.

The role of low-molecular-weight heparins in arterial diseases: optimizing antithrombotic therapy

On the basis of current evidence, all patients with acute coronary syndromes should receive optimized medical therapy, whether or not they ultimately undergo an invasive revascularization procedure, to improve both clinical outcomes and cost effectiveness. While standard aspirin and unfractionated heparin (UFH) have improved short-term outcomes, they do not eliminate the risk of recurrent ischemic episodes. The recent introduction of platelet fibrinogen receptor antagonists and low-molecular-weight heparins (LMWHs) has offered an opportunity to develop more aggressive antithrombotic regimens. The LMWHs have been thoroughly evaluated in unstable angina and non-Q wave myocardial infarction (UA/NQMI), and have demonstrated improved efficacy compared to standard UFH, without an increase in major complications caused by bleeding. Experience has also been gathered using LMWHs in other arterial diseases (such as pregnant patients with prosthetic heart valves) and as an adjunctive therapy with thrombolytics for acute myocardial infarction. Lastly, studies are currently underway evaluating LMWHs in patients with atrial fibrillation.

For the initial treatment of venous thromboembolism: are all low-molecular-weight heparin compounds the same?

Low-molecular-weight heparin compounds have been used in the treatment of patients with venous thromboembolism for approximately 15 years. Ever since their introduction, there has been discussion about whether low-molecular-weight heparin compounds differ in their efficacy and safety. The best answer would be provided by direct comparison of different low-molecular-weight heparin preparations; however, these trials have not been conducted. Classical meta-analysis has its limitations for such a comparison since only a very small number of trials with the respective low-molecular-weight heparin compounds are available. The objective of the present analysis has been the use of meta-regression to compare the efficacy and safety of different low-molecular-weight heparin compounds in the initial treatment of patients with venous thromboembolism. We used computerized literature searches to identify studies that compared dose-adjusted unfractionated heparin treatment with fixed dose subcutaneous low-molecular-weight heparin treatment in patients with established venous thromboembolism. The individual odds ratios of the studies were plotted against the absolute percentage of the major outcomes in the unfractionated heparin control group. Linear regression was used to find differences between different low-molecular-weight heparin compounds. There appears to be some variation in efficacy and safety among the currently available low-molecular-weight heparin preparations.

Do the low molecular weight heparins improve efficacy and safety of the treatment of deep venous thrombosis? A meta-analysis

BACKGROUND AND OBJECTIVES

We compared the efficacy and safety of low molecular weight heparins (LMWH) and unfractionated heparin (UFH) in the treatement of deep venous thrombosis (DVT). A comparison between two daily subcutaneous injections of LMWH against a single injection was also performed.

DESIGN AND METHODS

The study was performed by a meta-analysis. Clot improvement in venography, recurrency, total mortality and major hemorrhages were assessed in 4,472 patients with DVT from 21 studies treated with subcutaneous LMWH or UFH.

RESULTS

An improvement in clot reduction (odds ratio 0.73, 95% confidence interval 0.59 to 0.90, p = 0.004), a decrease in total mortality (0. 68, 0.50 to 0.91, p = 0.012) and a lower incidence of hemorrhage (0. 65, 0.43 to 0.98, p = 0.047) were observed in LMWH treated patients. There were no differences in recurrences (0.78, 0.59 to 1.04, p = 0. 10). A single dose of LMWH was better than two in reducing major bleeding (c2 = 4.99, p = 0.025); however, the two dose regimen was more effective in clot reduction (c2 = 8.56, p = 0.004).

INTERPRETATION AND CONCLUSIONS

LMWH is superior to UFH in terms of safety and efficacy. A single daily dose of LMWH dose is a suitable therapeutic regimen and could facilitate the outpatient treatment of venous thromboembolism.

Production and chemical processing of low molecular weight heparins

Heparin is an animal tissue extract that is widely used as an anticoagulant drug. A number of low molecular weight heparins (LMWHs), introduced in the past decade, are beginning to displace pharmaceutical (or compendial) grade heparins as clinical antithrombotic agents. This article describes the chemical properties of the glycosaminoglycan (GAG) heparin and how it is prepared and processed into pharmaceutical grade heparin. There are several commercially produced LMWHs that are prepared through the controlled depolymerization of pharmaceutical grade heparin. The chemistry of the commercial processes used for manufacturing LMWHs is discussed. Structural differences are found in the LMWHs prepared using different commercial processes. Careful control of process variables has generally resulted in the reproducible preparation of LMWHs that are structurally uniform and of high quality. The specifications, however, remain different for each LMWH. Thus, LMWHs are a group of similar but different drug agents. As the structural properties of LMWHs vary significantly, the bio-equivalence or inequivalence of these agents must ultimately be established by the pharmacologists and the clinicians.

Deep-vein thrombosis prophylaxis in orthopedic surgery: hip surgery

Hip replacement surgery carries a high risk of thromboembolic complications, and pharmacological prophylaxis is routinely adopted in clinical practice. Meta-analyses have indicated that low molecular weight heparins (LMWHs) are clinically superior to conventional prophylaxis with unfractionated heparin. These analyses have regarded LMWHs as one chemical entity, despite differences in their physicochemical, biological, and pharmacodynamic properties. Comparing data from trials of different LMWHs is difficult despite standardization in trial design, patient selection criteria, and efficacy assessments, as the influences of concurrent disease and variation in venogram interpretation are difficult to interpret. Furthermore, variations in bleeding assessment limit conclusions on the safety profile of different LMWHs. Two clinical trials have compared enoxaparin with tinzaparin and reviparin respectively. Efficacy equivalence was demonstrated despite differences in the anti-Xa activities of the doses given. These trials support the position of the United States Food and Drug Administration and the World Health Organization that LMWHs are distinct, noninterchangeable compounds and cannot be therapeutically substituted based upon anti-factor Xa levels. The extent of clinical experience with each LMWH is an important factor influencing clinical use.

In vitro studies on the biochemistry and pharmacology of low molecular weight heparins

Low molecular weight heparins (LMWHs) are obtained from unfractionated heparin by diverse chemical and enzymatic processes and findings with one LMWH cannot be extrapolated to another. Functional assays performed in vitro, evaluating antiprotease activity mediated via antithrombin III, heparin cofactor II interactions, antithrombin III binding, and plasma protein binding, showed wide variations between LMWHs, indicating that compositional differences among the LMWHs have a major impact on function. Evaluation in vitro showed varying potency in United States Pharmacopeia (USP) and anti-Xa assays. LMWHs tested at anti-Xa-adjusted concentrations exhibited varying potencies with anti-IIa, Heptest, and activated partial thromboplastin time (APTT) assays. Evaluation of these assays showed differences between LMWHs and a link with molecular weight. Each LMWH also varied in the in vitro neutralization by platelet factor 4, thrombin, and heparinase. LMWHs also varied in platelet interactions as assessed by whole blood clotting, thromboelastography and P-selectin expression, and in tissue factor pathway inhibitor release in cell culture. It was concluded that compositional variations in LMWHs give each product a unique biochemical profile. This profile, plus varying endogenous interactions and pharmacokinetic profiles may give rise to the clinical differences observed with LMWHs in specific indications.

Differentiation of low molecular weight heparins in treatment of acute deep vein thrombosis

The safety and efficacy of several low molecular weight heparins (LMWHs) in the treatment of deep vein thrombosis have recently been established. The available LMWHs differ in physicochemical properties, in vitro activity and pharmacodynamics, but it is not yet known what if any effect these differences exert on clinical efficacy. Clinical trials have compared individual LMWHs with unfractionated heparin or different dose regimens of the same LMWH, but no comparisons between individual LMWHs have been performed. Variations in dosing regimens and patient populations among the trials make meaningful comparisons between individual LMWH efficacy and safety profiles problematic. Thus, while it is likely there are clinical safety and efficacy differences between the LMWH treatment regimens, it will not be possible to characterize one agent as superior to another until head-to-head trials are reported.

Past, present and future considerations on low molecular weight heparin differentiation: an epilogue

This epilogue represents a final summary of the issues discussed and highlighted at the International Summit on Differentiation of Low Molecular Weight Heparins (LMWHs). International scientists and physicians presented and discussed the physicochemical differences between LMWHs, and concluded that different production processes result in the formation of distinct drugs with unique preclinical and clinical profiles. Important data was presented showing that different LMWHs continue to show marked differences in antithrombotic action, and pharmacokinetic and pharmacodynamic profiles measured in animal models. Human data also demonstrate that LMWHs are not bioequivalent. Moving to the clinical arena, it is clear that there are issues to be resolved regarding drug inequivalence. No apparent clinical efficacy differences have been observed in deep-vein thrombosis prophylaxis using a number of relatively low doses of LMWH. However, two studies have demonstrated clinical equivalence using different anti-Xa doses of LMWHs, strongly suggesting product inequivalence. This also suggests that anti-Xa doses are not reflective of the entire pharmacologic effects of LMWHs. It is unknown whether the higher dosages employed in the treatment of DVT will help provide evidence of clinical inequivalence. In the management of acute coronary syndromes, higher drug dosages than those used in prophylaxis have revealed an efficacy advantage; while two LMWHs have shown short-term improvement in acute coronary syndromes, only one provided a long-term treatment benefit, suggesting a drug-specific therapeutic advantage. This is in keeping with the position of the United States Food and Drug Administration and the World Health Organization, who regard each individual LMWH as a distinct drug requiring individual clinical trials for use in a specific clinical indication. In this epilogue, the chairpersons, Professors Jawed Fareed, Sylvia Haas and Arthur Sasahara, offer some final thoughts on this intriguing scientific and clinical issues of LMWH differentiation.

Low molecular weight heparins: differences and similarities in approved preparations in the United States

There is adequate preclinical data to support the differential biochemical and pharmacological behavior of the currently approved low molecular weight heparins (LMWHs) in the United States. Initial studies on the anti-Xa, anti-IIa, and U.S. Pharmacopoeial (USP) potencies have clearly demonstrated differences among these products. Furthermore, the ratios between the anti-X and anti-IIa activities vary from one product to another. This is primarily due to the composition of each product manufactured by using different patented methods. Studies in pharmacologic animal models, using gravimetric dosages or adjusted anti-Xa dosages of the LMWHs, produce product-specific results. The pharmacokinetics and pharmacodynamics of each product also vary markedly and are not predictable on the basis of any pharmacopoeial potency designation. These agents are capable of releasing tissue factor pathway inhibitor (TFPI), an inhibitor of the coagulation process. Its release is also dependent on the type of LMWH. In the United States enoxaprin, dalteparin, and ardeparin have been approved for DVT prophylaxis. Only enoxaparin and dalteparin have been approved for the acute coronary syndrome. Recently the clinical differentiation among these LMWHs has been demonstrated in the treatment of acute coronary syndrome. Similarly, when these drugs are used at high dosages, they are expected to produce product-specific pharmacodynamic effects. It must be noted that while these drugs may be interchangeable at clinically optimized/approved dosages, these drugs are not interchangeable at equivalent anti-Xa dosages. Even at optimized dosages, the clinical provile of each drug may be different. Thus, each of the LMWHs should be considered a distinct entity and their use in a given clinical situation should be validated in proper clinical trials.

Long-term anticoagulation of outpatients with adverse events to oral anticoagulants using low-molecular-weight heparin

Bleeding complications are one of the major risks during oral anticoagulation. If further anticoagulation is indicated, low-molecular-weight heparin (LMWH) may offer an alternative treatment in those patients. In a prospective, nonrandomized study, 120 patients have been switched from oral anticoagulants to LMWH because of bleeding complications or other severe side effects during treatment with vitamin K antagonists. Indication for further anticoagulation was prophylaxis of recurrent thromboembolism, artificial heart valve replacement, atrial fibrillation with embolism and cardiomyopathy. The treatment period ranged from 2 months to 10.8 years. No fatal embolism occurred. One major but not severe episode of gastrointestinal bleeding occurred in a patient with an as yet unknown colon carcinoma. The cumulative treatment period amounts to 250 years. No drop in platelet count occurred in any patient. No other side effects were observed. LMWH was injected subcutaneously at doses ranging from 2500 to 15,000 anti-factor Xa units per day by the patient himself. The dose was adjusted on the basis of body weight, bleeding risk and thromboembolic risk. The results indicate that LMWH may be effectively and safely used as alternative anticoagulant regimen in patients with side effects or other complications on oral anticoagulants.

A collaborative study of proposed European Pharmacopoeia reference preparations of low molecular mass heparin

A European collaborative study, in which 16 laboratories participated, was carried out to assess the performance of the European Pharmacopoeia (EP) monograph methods for anticoagulant activities (anti-Xa and anti-IIa assays) of low molecular mass (LMM) heparin and to assess the suitability of six candidate materials as the EP working standard for LMM heparin. There was good interlaboratory agreement for both types of assays as indicated by most gcy's being less than 10%, indicating acceptable performance of the EP assay methods. All the candidate preparations gave dose-response curves parallel to the 1st International Standard for Low Molecular Weight heparin and to each other. All preparations, possibly with the exception of E and F, gave similar performance as measured by interlaboratory agreement and would be suitable as working standards. Based on these data, preparations A, B, C and D have been established by the EP as official EP Biological Reference Preparations and they will be issued as successive batches.

Low molecular weight heparin (CY-216) versus unfractionated heparin in chronic hemodialysis

In 14 patients undergoing chronic hemodialysis, we investigated the safety and efficacy of the low molecular fragment (CY-216) in comparison to unfractionated heparin (UFH) in the prevention of clotting in the extracorporeal circuit (ECC). In this study, 168 hemodialysis sessions were undertaken with UFH in 2 bolus doses (5,437 +/- 1,477 SD IU) and 231 with CY-216 in a single bolus dose [initial dose 150 anti-Xa U Institut Choay (IC)/kg]. There were no clots in the bubble trap in any UFH sessions, and 14.8% had coagulated fibers in the dialyzer. Clotting in the bubble trap was observed in 2 CY-216 sessions (0.8%) and coagulated fibers in 22.6% of the sessions. At the end of the study, the mean dose of CY-216 was 250 anti-Xa UIC/kg but a dose of 350 anti-Xa UIC/kg was needed in the 2 patients treated by recombinant human erythropoietin. Anti-Xa levels at the end of the runs were higher (0.47 +/- 0.1 U/ml) in the CY-216 group than in the UFH group (0.28 +/- 0.1 U/ml). There was a correlation between anti-Xa levels and efficacy in the CY-216 group. An anti-Xa activity above 0.4 U/ml was needed in order to minimize thrombus formation. Antithrombin III-protease complexes (ATM) and D dimer fibrin derivatives (D dimer) were used as thrombotic markers but they were of little value for the detection of fibrin formation in the ECC. Our findings suggest that CY-216 administered as a single bolus dose seems to be of similar effectiveness to UFH.