The effect of heparin fragments of different molecular weights on experimental thrombosis and haemostasis

Development of low molecular weight heparin by H2O2/ascorbic acid with ultrasonic power and its anti-metastasis property

Low molecular weight heparins (LMWHs) are currently used as an anticoagulant agent since unfractionated heparin (UFH) can cause serious adverse drug reactions. LMWHs are commercially prepared using different methods such as nitrous acid cleavage and β-elimination under strong reaction conditions or with harsh chemicals, which may cause the saccharide units within the polysaccharide backbone to be decomposed and noticeably modified. This study demonstrates an effective method for depolymerizing heparin via the production of large amounts of free radicals from H₂O₂/ascorbic acid and ultrasonic power; this results in highly pure products because ascorbic acid can decompose during the reaction, which is different from the previously reported H₂O₂/Cu²⁺ method. The reaction conditions-including concentration of ascorbic acid, reaction temperature and intensity of ultrasonic power-were investigated and optimized. We found that the degradation behavior of heparin in this combined physicochemical process conformed to first-order reaction kinetics. The chemical composition and structures of different LMWHs were analyzed. The results showed the primary structure and sulfate esters were well preserved after the depolymerization, the major repeat units are (1-4)-linked glucosamine and iduronic acid. The further in vitro assays indicated that the LMWHs produced by H₂O₂/ascorbic acid with ultrasonic power have an anti-metastatic effect in A549 cells, which suggested the LMWHs rapidly prepared in this physicochemical way have a potential for anti-tumor metastatic function.

Parenteral anticoagulants: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article describes the pharmacology of approved parenteral anticoagulants. These include the indirect anticoagulants, unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs), fondaparinux, and danaparoid, as well as the direct thrombin inhibitors hirudin, bivalirudin, and argatroban. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a unique pentasaccharide sequence and catalyze the inactivation of thrombin, factor Xa, and other clotting enzymes. Heparin also binds to cells and plasma proteins other than antithrombin causing unpredictable pharmacokinetic and pharmacodynamic properties and triggering nonhemorrhagic side effects, such as heparin-induced thrombocytopenia (HIT) and osteoporosis. LMWHs have greater inhibitory activity against factor Xa than thrombin and exhibit less binding to cells and plasma proteins than heparin. Consequently, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties, have a longer half-life than heparin, and are associated with a lower risk of nonhemorrhagic side effects. LMWHs can be administered once daily or bid by subcutaneous injection, without coagulation monitoring. Based on their greater convenience, LMWHs have replaced UFH for many clinical indications. Fondaparinux, a synthetic pentasaccharide, catalyzes the inhibition of factor Xa, but not thrombin, in an antithrombin-dependent fashion. Fondaparinux binds only to antithrombin. Therefore, fondaparinux-associated HIT or osteoporosis is unlikely to occur. Fondaparinux exhibits complete bioavailability when administered subcutaneously, has a longer half-life than LMWHs, and is given once daily by subcutaneous injection in fixed doses, without coagulation monitoring. Three additional parenteral direct thrombin inhibitors and danaparoid are approved as alternatives to heparin in patients with HIT.

Heparin and Low-Molecular-Weight Heparin

This article about unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) is part of the Seventh American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a pentasaccharide, catalyzing the inactivation of thrombin and other clotting factors. UFH also binds endothelial cells, platelet factor 4, and platelets, leading to rather unpredictable pharmacokinetic and pharmacodynamic properties. Variability in activated partial thromboplastin time (aPTT) reagents necessitates site-specific validation of the aPTT therapeutic range in order to properly monitor UFH therapy. Lack of validation has been an oversight in many clinical trials comparing UFH to LMWH. In patients with apparent heparin resistance, anti-factor Xa monitoring may be superior to measurement of aPTT. LMWHs lack the nonspecific binding affinities of UFH, and, as a result, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties. LMWHs have replaced UFH for most clinical indications for the following reasons: (1) these properties allow LMWHs to be administered subcutaneously, once daily without laboratory monitoring; and (2) the evidence from clinical trials that LMWH is as least as effective as and is safer than UFH. Several clinical issues regarding the use of LMWHs remain unanswered. These relate to the need for monitoring with an anti-factor Xa assay in patients with severe obesity or renal insufficiency. The therapeutic range for anti-factor Xa activity depends on the dosing interval. Anti-factor Xa monitoring is prudent when administering weight-based doses of LMWH to patients who weigh > 150 kg. It has been determined that UFH infusion is preferable to LMWH injection in patients with creatinine clearance of < 25 mL/min, until further data on therapeutic dosing of LMWHs in renal failure have been published. However, when administered in low doses prophylactically, LMWH is safe for therapy in patients with renal failure. Protamine may help to reverse bleeding related to LWMH, although anti-factor Xa activity is not fully normalized by protamine. The synthetic pentasaccharide fondaparinux is a promising new antithrombotic agent for the prevention and treatment of venous thromboembolism.

Estudo experimental comparativo da eficácia antitrombótica da heparina convencional e da heparina de baixo peso molecular

Em estudo randomizado e cego comparou-se a eficácia antitrombótica (redução do peso do trombo) de duas heparinas; uma de baixo peso molecular (HBPM) e outra não fracionada - heparina convencional (HC). Foram utilizados dois procedimentos de trombose venosa experimental: no grupo I a trombose venosa foi induzida injetando-se oleato de etanolamina na veia jugular de 30 coelhos e glicose a 50% em mais 30, todos da raça New Zealand. No Grupo II a trombose venosa foi induzida por estase mediante a ligadura da veia cava de 30 ratos da raça Wistar. Não se encontrou diferenças estatisticamente significantes com relação à redução do peso do trombo em ambos os grupos. Também concluiu-se que a eficácia antitrombótica das drogas estudadas não variou conforme o tipo de estímulo indutor da trombose nos modelos testados, e que o oleato de etanolamina induziu de forma mais significante a formação de trombos no grupo I.

Comparative study on the in vitro and in vivo activities of heparinoids derivative investigated on the animal model

In this study we compared the antithrombotic and anticoagulant properties of sodium and calcium derivatives of pentosan polysulfate (Na-PPS, Ca-PPS), unfractionated heparin (UFH), and low-molecular-weight heparin (Fraxiparin). The antithrombotic effects of these agents have been investigated in an experimental thrombosis model in which rat mesenteric venules with a diameter of 20-30 microm were injured by well-defined argon laser lesions. Furthermore, the in vivo and in vitro anticoagulant activities [activated partial thromboplastin time (aPTT), Heptest] of these agents have been studied. Thrombus formation was significantly inhibited after s.c. injection of Na-PPS and Ca-PPS in doses >10 mg/kg. The duration of the antithrombotic effect lasted 8 h for Na-PPS and 12 h for Ca-PPS. After oral administration of Na-PPS, an antithrombotic effect was not observed. Oral application of Ca-PPS in doses >20 mg/kg significantly inhibited thrombus formation. Na-PPS and Ca-PPS markedly prolonged clotting time in aPTT and Heptest in concentrations ranging from 0.01 to 0.2 mg/ml rat PTT. Two h after s.c. administration of these agents in a dose of 10 mg/kg, the aPTT increased threefold and the Heptest 2.5-fold compared with controls. After oral application of 50 mg/kg Na-PPS and Ca-PPS, no effect on the coagulation test could be measured. Intravenous injection of UFH prolonged the Heptest after 1 min and the aPTT after 30 min. In ex vivo studies of aPTT and Heptest performed in rat plasma between 2 and 24 h after s.c. injection of 0.2 mg/kg Fraxiparin, no inhibition of any coagulation test was measured. The antithrombotic effect of 0.2 mg/kg Fraxiparin after s.c. injection was significant. Intravenous injection of 20 U/kg UFH significantly inhibited thrombus formation. The smallest antithrombotic effect was after i.v. injection of UFH.

Low-molecular-weight heparins for acute coronary syndromes

OBJECTIVE

To review published literature regarding the use of low-molecular-weight heparins (LMWHs) for the acute coronary syndromes of unstable angina and acute myocardial infarction (MI).

METHODS

A MEDLINE search (January 1986-August 1997) was performed to identify all pertinent articles. Selected references from these articles and abstracts of recent clinical trials were also included.

DISCUSSION

LMWHs have several distinct advantages over standard unfractionated heparin (UFH). These advantages include convenient once- or twice-daily standardized administration without the need for activated partial thromboplastin time monitoring. While the use of LMWHs as prophylaxis and treatment of venous thromboembolism is fairly well-established, the use of LMWHs for treating acute myocardial ischemia is evolving. Published studies and abstracts have shown LMWHs to be as effective as or more effective than UFH in preventing death, myocardial infarction, and recurrent ischemia in patients with unstable angina or acute MI. The comparative incidence of bleeding between LMWHs and UFH is controversial, with some studies reporting lower or similar rates of bleeding with LMWHs, while one study demonstrated a higher bleeding rate than with UFH. The cost-effectiveness of using LMWHs over UFH for acute coronary syndromes also remains to be established.

CONCLUSIONS

LMWHs appear to be as effective as, and potentially more effective than, UFH in preventing complications of acute coronary syndromes. However, further studies are needed to better define the comparative bleeding risks of LMWHs and UFH. This, plus the lack of published peer-reviewed trial results and pharmaco-economic analyses, preclude the recommendation of routinely using LMWHs for treating unstable angina and acute MI at this time.

Antithrombotic and platelet activating effects of heparin in prevention of microarterial thrombosis

It has been proposed that the limited effectiveness of heparin in preventing arterial thrombosis may be caused by heparin-mediated platelet activation. The effect of heparin on platelets and thrombus formation in vivo was investigated using a microarterial model of thrombosis involving registration of labeled platelets. Three groups of six rabbits each were treated with either saline, standard heparin, or heparin with low affinity for antithrombin III (LA-heparin), which exhibits a low anticoagulant potential but has a molecular weight distribution similar to standard heparin. (Fifty to 70 percent of standard heparin consists of low-affinity material). The heparins were infused intravenously at doses of 1 mg/kg body weight, followed by maintenance injections. Platelet accumulation was significantly increased in the LA-heparin group compared with the saline group, demonstrating heparin-induced platelet activation in vivo. In contrast to a powerful anticoagulant response observed in rabbit plasma, the antithrombotic effect of standard heparin was expressed incompletely. (Only two of three of the treated vessels remained patent). This study demonstrates heparin-induced platelet activation in vivo in conditions of platelet-mediated thrombus formation. The observations are consistent with the concept of heparin-induced platelet activation as one of the mechanisms explaining the limited effects of heparin in preventing arterial thrombosis.

Perioperative morbidity in maxillofacial orthopaedic surgery: a retrospective study

The data of 2049 patients, who underwent maxillofacial orthopaedic surgery, were retrospectively analysed for major intra- and immediate postoperative complications. Immediate life-threatening complications were very rare. They can in most cases be avoided by good anaesthetic and surgical techniques and adequate postoperative care. The most frequently encountered problem in maxillary surgery is excessive blood loss, whilst a compromised airway due to swelling is the most frequent complication in mandibular surgery. Good co-operation between anaesthetist and surgeon is essential to prevent major intraoperative and immediate postoperative problems.

Heparin as adjunctive therapy to coronary thrombolysis in acute myocardial infarction

For many years anticoagulation has played a role in the prevention and management of thromboembolic complications associated with acute myocardial infarction. However, the role of heparin therapy after pharmacologic thrombolysis in myocardial infarction remains controversial. Debate continues regarding the necessity of heparin treatment after thrombolytic therapy as well as the mode by which it is administered. The purpose of this review is to summarize the findings of clinical trials designed to evaluate the effectiveness and safety of heparin as an adjuvant agent to thrombolytic therapy in acute myocardial infarction. Data regarding the clinical effectiveness of heparin are presented. Information and recommendations regarding the optimal dose, route of administration, timing of initiation, and duration of heparin treatment are provided.

Binding and growth-inhibitory effect of heparin and oligo-heparin (2kDa) in Balb/c 3T3 cells: lack of effect on PDGF- or serum-induced inositol lipid turnover

1. The ability of heparins (bovine heparin sm 1026, Av. mol. wt. 36.9 kDa and bovine heparin EP 756, Av. mol. wt. 12.9 kDa) and heparin fractions of different molecular weights (low molecular weight heparin, LMW 2123/OP, Av. mol. wt. 4.5 kDa and oligo-heparin, Av. mol. wt. 2 kDa) to inhibit the proliferation and signalling of Balb/c 3T3 fibroblasts was investigated. 2. Heparin and heparin fractions of 4.5 and 2 kDa significantly inhibited DNA synthesis as monitored by [2H]-thymidine incorporation. 3. 3H-labelled heparin fractions of 4.5 and 2 kDa were prepared by gel-chromatography fractionation on Sephadex G-75 of an 3H-labelled commercial heparin after treatment with heparinase. 4. The binding of unfractionated and oligo-heparin of 2 kDa to Balb/c 3T3 fibroblasts was studied; we determined the specificity of heparin and oligo-heparin binding to the cells by means of displacement of bound 3H-labelled compound in response to increasing concentrations of unlabelled compounds. Scatchard analysis of binding data obtained using [3H]-heparin as ligand revealed the presence of a single class of high affinity binding sites (Kd = 28 nM) for heparin. Scatchard analysis of binding data obtained using [3H]-oligo-heparin as ligand revealed the presence of a single class of low affinity binding sites (Kd = 3.2 microM) for oligo-heparin. 5. In addition heparin displaced [3H]-oligo-heparin at a concentration of approximately 100 fold of the Kd determined in displacement studies. Furthermore, oligo-heparin significantly displaced [3H]-heparin at a concentration of approximately 10 fold of the Kd determined by displacement studies. 6. Both heparin and oligo-heparin exert their inhibitory effects on Balb/c 3T3 DNA synthesis stimulated by PDGF or serum. However these molecules did not affect the inositol lipid turnover triggered by PDGF at a concentration which did not produce maximal response. The increase of inositol phosphate metabolism produced by 20% serum was also unaffected by heparin. This concentration of serum elicited a response comparable to that induced by a submaximal concentration of PDGF.

RD heparin compared with warfarin for prevention of venous thromboembolic disease following total hip or knee arthroplasty. RD Heparin Arthroplasty Group

The efficacy and safety of RD heparin, a low-molecular-weight heparin, for the prevention of venous thromboembolic disease among patients managed with an elective total hip or total knee arthroplasty were compared with the efficacy and safety of warfarin in an open-label prospective, multicenter trial. Patients were randomized to receive either a fixed dose of fifty anti-factor-Xa units of RD heparin per kilogram of body weight, administered subcutaneously twice daily, beginning postoperatively; a fixed dose of ninety anti-factor-Xa units of RD heparin per kilogram of body weight, administered subcutaneously once daily, beginning postoperatively; or five milligrams of warfarin, administered orally preoperatively, followed by a daily adjusted dose of warfarin to prolong the prothrombin time ratio to 1.2 to 1.5. The primary measure of efficacy was contrast venography of the treated limb, performed by local radiologists blinded to the type of treatment that had been assigned. Nine hundred and sixty-nine patients had a complete assessment for the presence of deep-vein thrombosis. The over-all rates of venous thromboembolic disease were 16 percent (95 pecent confidence interval, 13 to 21 percent) (fifty-three) for the 328 patients who received RD heparin twice daily, 21 percent (95 percent confidence interval, 17 to 26 percent) (sixty-eight) for the 320 patients who received RD heparin once daily, and 27 percent (95 percent confidence interval, 22 to 32 percent) (eighty-seven) for the 321 patients who received warfarin (p < 0.001 for RD heparin administered twice daily compared with warfarin; p = 0.13 for RD heparin administered once daily compared with warfarin). Compared with warfarin, RD heparin administered twice daily and RD heparin administered once daily reduced the risk of venous thromboembolic disease by 41 percent (95 percent confidence interval, 20 to 56 percent) and 18 percent (95 percent confidence interval, -6 to 37 percent), respectively. The rates of venous thromboembolic disease after 523 total hip arthroplasties were 8, 14, and 14 percent for the patients who received RD heparin twice daily, those who received it once daily, and those who received warfarin (p = 0.07 for RD heparin administered twice daily compared with warfarin; p = 0.82 for RD heparin administered once daily compared with warfarin).(ABSTRACT TRUNCATED AT 400 WORDS)

Prevention of experimental venous thrombosis in rabbits with low molecular weight heparin, dextran and their combinations, administered before or during induction of venous endothelial trauma

An in vivo experimental venous thrombosis model based on endothelial damage and flow reduction was used to investigate the effect of low molecular weight heparin (LMWH) alone and in combination with dextran and the effect of surgical and endothelial trauma on thrombus formation, formation of occlusive thrombi and thrombus weights. Five groups with 15 rabbits in each were studied. Two groups received dalteparin (50 anti-Xa IU/kg i.v.) before surgical trauma or after, during the endothelial trauma and two groups received dalteparin (50 anti-Xa IU/kg i.v.) with dextran 70 (1 g/kg i.v.) before surgical trauma or after, during the endothelial trauma. Compared to a control group (saline) all treatment regimes reduced significantly the frequency of thrombosis and occlusive thrombi as well as thrombus weights. No significant difference was observed between the identical treatment groups when the substances were introduced before respective after surgical trauma. It is concluded, from the present study that thromboprophylaxis with LMWH in this particular in vivo model, given before or after surgical trauma is equally effective. Dextran has a certain augmenting thromboprophylactic effect when added to LMWH in this model.

Antithrombotic activity of recombinant tick anticoagulant peptide and heparin in a rabbit model of venous thrombosis

An in vivo rabbit model of venous thrombosis which includes physiological blood flow was used to compare the efficacy of the potent and specific factor Xa inhibitor recombinant tick anticoagulant peptide (rTAP) with standard heparin in the prevention of venous thrombus formation. In anesthetized rabbits, an autologous thrombus was induced with thrombin in a jugular vein and the increase in thrombus size was determined by measuring the accretion of intravenously injected [125I]fibrin(ogen) onto the developing thrombus. The effects of rTAP on hemostasis were monitored by changes in APTT values and template bleeding times. Inhibition of thrombus formation by an intravenous bolus followed by infusion of either rTAP or heparin exhibited a dose-response relationship with an IC50 of 0.9 micrograms/kg/min and 0.12 units/kg/min, respectively. At the IC50 doses, both rTAP and heparin inhibited fibrin(ogen) deposition without any significant effect on APTT or bleeding times. Bleeding times were modestly elevated at the fully efficacious doses of rTAP and heparin. Significant changes in APTT (1.9 +/- 0.3 fold over baseline) were only evident at the highest dose of rTAP while heparin caused a significant dose-dependent increase from 1.3 +/- 0.2 to greater than 4.2 +/- 0.6 fold over baseline. Therefore, in this rabbit model of venous thrombosis, specific inhibition of factor Xa by rTAP is an effective antithrombotic mechanism that does not require changes in systemic hemostatic parameters.

Prophylaxis of postoperative thromboembolism with low molecular weight heparins

To evaluate the thromboprophylactic use of low molecular weight heparins (LMWHs), publications from 27 orthopaedic trials and 35 studies of patients undergoing general or gynaecological surgery were scrutinized and subjected to a partial meta-analysis. In orthopaedic surgery, LMWHs were superior to placebo or dextran and at least as efficient as unfractionated heparin in the prevention of deep vein thrombosis (DVT). Compared with unfractionated heparin, one of the LMWH preparations significantly reduced the total incidence of DVT. The rate of non-fatal pulmonary embolism was 0.49 per cent in patients receiving LMWH and 1.22 per cent in controls. Seven orthopaedic patients (0.15 per cent) died from pulmonary embolism, none of whom received LMWH. In general surgery, the LMWHs were at least as efficient as unfractionated heparin, with a trend towards a lower risk of pulmonary embolism with the former. Compared with unfractionated heparin, LMWHs did not reduce the postoperative mortality rate, nor did they cause haemorrhage. LMWHs provide safe and efficient prophylaxis by administration once daily.

Extracorporeal circuit heparinization in selective low density lipoprotein apheresis: changes in patient hemostasis and low molecular weight heparin benefit

Treatment by low density lipoprotein (LDL) apheresis using dextran sulfate columns (DSC) leads to hemostasis alterations with prolonged activated partial thromboplastin time (APTT) of more than 120 seconds. In order to explain this hypocoagulability, we studied hemostasis parameters both in patients and in the extracorporeal circulation (ECC). Hemostasis changes are first related to unfractionated heparin (UFH)--needed to avoid circuit coagulation--which leads to high residual heparinemia in the patient (more than 3 times the recommended level for therapeutic use). Second, the hypocoagulability is induced by a coagulation factor decrease (primarily factors V, VIII, and X) mainly due to an adsorption mechanism on dextran sulfate. Studies on samples from column inflow, outflow, and eluate confirm this mechanism. Low molecular weight heparin (LMWH) can be used in LDL apheresis on DSC without major changes in lipid removal or coagulation factors compared to UFH. The benefit of using LMWH is to reduce residual heparinemia into the therapeutic range.

Deep vein thrombosis prophylaxis: a survey of current practice in Australia and New Zealand

A survey of current practice for deep vein thrombosis (DVT) prophylaxis was undertaken in Australia and New Zealand. The most common indications for prophylaxis were a history of thrombo-embolism, the type and length of surgery and obesity. Prophylaxis was used in 65% of patients having hip surgery and in 39% undergoing knee surgery. In general surgery the corresponding rate was around 67% for colorectal surgery, hepatobiliary, upper gastrointestinal and major abdominal vascular surgery. Apart from open-heart cardiothoracic surgery (66%), use in other specialties was less than 50%. Physical methods (anti-embolism stockings, calf stimulation and calf compression devices) were most commonly used for prophylaxis (46%) with heparin being used by 40%. The main side effect reported with heparin was bleeding (18%). The estimated incidence of DVT and pulmonary embolus (PE) was 2.8 and 0.4% for general surgery, 2.7 and 0.7% for orthopaedic surgery and 6.6 and 1.3% for hip surgery. Intravenous heparin followed by oral anticoagulants was the most commonly used treatment for established DVT and nearly all respondents used intravenous heparin and oral anticoagulants for treatment of PE. Venography was the favoured objective test for diagnosing DVT. The principal reason for considering a change in prophylactic policy was the potential availability of an agent with increased efficacy and a reduced incidence of haemorrhagic complications.

Heparin pharmacokinetics and pharmacodynamics

Heparin was discovered approximately 75 years ago and has been used extensively for the last 50 years to treat thromboembolic disorders. An endogenous glycosaminoglycan, heparin is found largely in the liver, lung and intestine. It is available for exogenous administration both as unfractionated and low molecular weight heparin. Unfractionated heparin is a heterogenous mixture of polysaccharide chains of varying length resulting in a range of molecular weights from 3000 to 30,000D while low molecular weight heparin ranges from 3000 to 6000D. Heparin produces its antithrombotic effect by binding to antithrombin III and this complex then binds to thrombin. In order to accomplish this a total of 18 to 22 monosaccharide units is necessary including a specific pentasaccharide binding site for antithrombin III. After either subcutaneous or intravenous injection heparin is distributed primarily within the intravascular space. A short distribution phase is seen which is thought to correspond to endothelial cell binding and internalisation. The disposition curve for unfractionated heparin has a unique concave-convex shape which is the result of combined saturable and nonsaturable elimination mechanisms. The nonsaturable elimination mechanism is renal and is the primary route of elimination for low molecular weight heparins. For this reason, the concave-convex pattern is not seen with low molecular weight preparations. Both forms of heparin are useful antithrombotic agents; however, the correlation between the antithrombotic effect and an in vitro laboratory test for either type still needs further clarification.

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.

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

Treatment of deep venous thrombosis with low molecular weight heparin (LMWH-Novo, Logiparin) was carried out with two different doses of Logiparin, 75 XaI U/kg b.w. twice daily and 150 XaI U/kg b.w. once daily subcutaneously for 5 days. Simultaneously warfarin was given from the first day of heparin treatment. Mean age of the twenty patients was 65 years and one third was females. No serious side effects, hematomas, pulmonary emboli or signs of recurrent thrombosis occurred during treatment with either dose regime. Venografic assessment with Marder scoring one week after initiation of Logiparin treatment showed a slight not significant improvement apparent in 40% of the patients. The activities of F-IIaI and F-XaI in the blood plasma were found to increase after injection of Logiparin. These two parameters seem to be the most suitable for monitoring the effect during treatment. For future studies on the therapeutic effect of Logiparin in deep venous thrombosis a single dose of 150 to 200 F-XaI activity per 24 hours seems to be most suitable.

Beneficial effect of low molecular weight heparin on the hemodialysis model in dogs

The effect of FR-860, one of low molecular weight heparins, was investigated on the hemodialysis model in dogs for comparison with that of conventional unfractionated heparin (UF-heparin). In a bolus injection model, FR-860 at 12.5-100 U/kg prolonged the dialysis time (the time until the arterial circuit pressure reaching 500 mmHg) in a dose-dependent manner and UF-heparin at 50 U/kg also prolonged it. Additionally, FR-860 (12.5-50 U/kg/hr) and UF-heparin (25 and 50 U/kg/hr) continuously inhibited the rise of the arterial circuit pressure in an infusion model. In both models, the efficacy of FR-860 was more potent than that of UF-heparin. FR-860 and UF-heparin decreased the amount of blood loss remaining in the dialyzer in the infusion model. During hemodialysis, both FR-860 and UF-heparin showed activated plasma anti-F.Xa activity, prolongation of aPTT and such of thrombin time in a dose-dependent manner in those models. However, FR-860 was higher in anti-F.Xa activity and weaker in prolongation of aPTT and thrombin time than UF-heparin. These results suggest that FR-860 is more beneficial in in efficacy and higher in safety against the bleeding risk than UF-heparin hemodialysis.

Comparison of two experimental thrombosis models in rats effects of four glycosaminoglycans

Two experimental thrombosis models in rats have been compared with regard to the composition of the formed thrombi and the effects of various treatments on thrombus formation. In the first model thrombosis is induced in the vena cava by a combination of venous stasis and hypercoagulability; these thrombi consist merely of red cells and fibrin with only a few platelets. In the second model thrombosis is induced in an arterio-venous shunt in which the formed thrombi consist of red cells, fibrin and a large amount of platelet aggregates adhering to the foreign material. Antiplatelet serum and acetylsalicylic acid, which reduce blood platelet activity, inhibited thrombus formation only in the arteriovenous shunt model. Dicumoxane, an oral anticoagulant, was active in both models. The glycosaminoglycans heparin, Org 10172, Fragmin and the pentasaccharide, representing the AT-III binding sequence of heparin, were active in both models. However, there were qualitative and quantitative differences between the effects of the glycosaminoglycans suggesting differences in their modes of action.

Pharmacology and special clinical applications of low-molecular-weight heparins

In this overview, the rationale of the development of low-molecular-weight (LMW) heparins and their toxicological, anticoagulant, fibrinolytic, lipolytic, and protamine interactions are summarized. Clinical experiences are reviewed on the benefit of LMW heparin for anticoagulation in patients with bleeding and other complications on conventional anticoagulants and during pregnancy. It is concluded that animal experiments have demonstrated the safety of LMW heparins, that the pharmacologic profile is improved compared with normal heparin, and that the simple and safe applicability of LMW heparins gives rise to new indications for the long-term prophylaxis of thromboembolism.

Characterization of platelet binding of heparins and other glycosaminoglycans

The binding of glycosaminoglycans to intact washed human platelets was studied. The platelet binding of a 3H-labeled unfractionated heparin was saturable and reached equilibrium in 10-15 minutes. Heparin binding was specific: a 50-fold molar excess of an equivalent unlabeled heparin displaced up to 90% of labeled heparin, while chondroitin sulfate A and hyaluronic acid minimally displaced the binding of labeled heparin. Low molecular weight heparin fragments showed intermediate efficacy in displacing the binding of unfractionated [3H]heparin. Dextran sulfate (Mr 8,000, sulfation 17%) was as potent as unfractionated heparin in displacing binding, while neutral dextrans were ineffective. We observed that platelet activation by the calcium ionophore A23187 increased heparin binding by 2 to 3-fold, principally by enhancement of binding capacity not binding affinity. This process of heparin binding to the platelet surface may mediate some of the reported effects of heparin on platelet behavior.

Antithrombotic activity of a synthetic heparin pentasaccharide in a rabbit stasis thrombosis model using different thrombogenic challenges

A synthetic pentasaccharide, representing the critical sequence required in heparin for binding to antithrombin III (AT III), produces strong anti-factor Xa activity in vitro in the presence of AT III and is devoid of any activity directed towards thrombin. This pentasaccharide provides a unique tool to study the question of whether an agent capable of inhibiting factor Xa but devoid of anti-factor IIa activity in vitro, has the capacity to produce an antithrombotic effect in vivo. We have previously demonstrated in a rabbit stasis thrombosis model using a human serum challenge, a significant antithrombotic effect of the pentasaccharide. This finding and discrepancies with some earlier reports on the antithrombotic actions of other oligosaccharide fragments, led us to extend these studies. Four modifications of the stasis thrombosis model were developed using the following thrombogenic challenges selected for their specified induction sites of thrombosis, thromboplastin, an activated prothrombin complex concentrate, a non-activated prothrombin complex concentrate administered simultaneously with Russell's viper venom, and factor Xa. Dose-dependent antithrombotic responses were obtained in all four systems with ED50 values between 25-43 ug/kg for pentasaccharide as compared to 16-47 ug/kg for heparin. Complete inhibition of induced thrombosis was obtained in all four systems for pentasaccharide. Ex vivo analysis revealed expected anti-factor Xa levels but no anti-factor IIa activity. It is concluded that an oligosaccharide with high anti-factor Xa activity and devoid of anti-factor IIa activity is capable of inhibiting thrombosis induced in rabbit stasis models, but that higher dosages than heparin are required for this effect.

The effect of low molecular weight heparin on experimental thrombosis and haemostasis--the influence of production method

Three low molecular weight heparins prepared by enzymatic depolymerization, chemical degradation, and fractionation, respectively were studied in experimental thrombosis and haemostasis models in vivo and in biological assays in vitro. The three low molecular weight heparins, which had comparable molecular weight distributions, showed very similar activities both in vitro and in vivo. All three showed dose dependent thromboprophylactic effect. The antithrombotic effects of the low molecular weight heparins and conventional heparin administered in the same dose (30 XaI u/kg b.w.) did not differ. Neither LMW heparin nor conventional heparin (60 or 90 XaI u/kg b.w.) showed significant effects on the haemostatic plug formation time in the rabbit mesenteric microcirculation. These experiments confirm that low molecular weight heparins are potential antithrombotic drugs, which by intravenous administration have effects similar to those of standard heparin. The method of preparation seems to be of no or minor importance, at least if the molecular weight distributions of the products are similar.