Preliminary safety evaluation of a taurocholate-conjugated low-molecular-weight heparin derivative (LHT7): a potent angiogenesis inhibitor.

In our previous studies, taurocholic acid (TA)-conjugated low-molecular-weight heparin derivative (LHT7) has been proven to be a potent anti-angiogenic agent by demonstrated successful blockage capability of vascular endothelial growth factors (VEGF). Preliminary safety evaluations were conducted based on its mechanism of action and chemical behavior. For this purpose, acute toxicity study, and hematological and serological evaluations were carried out. Additionally, in order to evaluate mechanism-related side effects, both blood pressure and the occurrence of proteinuria were measured using a treatment regime of multiple high doses of LHT7 in a biodistribution study. LD50 values for LHT7 in female and male mice were 56.9 and 64.7 mg kg(-1) doses, respectively. There were no vital fluctuations in the serological and hematological parameters, except for the elevated levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) at 100 and 200 mg kg(-1) doses of LHT7, representing vital changes in the liver function. Moreover, the results of mechanism-related studies showed that blood pressure at 50 mg kg(-1) did not change but showed elevated levels of protein in urine. In the biodistribution study, a slight accumulation of LHT7 in the kidney and the liver were observed at the 50 mg kg(-1) repeated dose owing to the presence of bile acid. No fatal damage was observed in this study; most observations were related to the chemical composition or the mechanism of action of the material.

Prevention effect of orally active heparin conjugate on cancer-associated thrombosis.

Thrombogenesis is a major cause of morbidity and mortality in cancer patients. Prophylaxis with low-molecular-weight heparin (LMWH) is recommended for cancer patients, but requires non-parenteral delivery methods for long-term treatments. In this study, we sought to generate a new oligomeric-bile acid conjugate of LMWH that can be used for oral delivery. We first synthesized a tetramer of deoxycholic acid (tetraDOCA), which was site-specifically conjugated at the end saccharide of LMWH. When LMWH-tetraDOCA conjugate (LHe-tetraD) was orally administered at a dose of 5 mg/kg in ICR mice, the maximum anti-factor Xa level was increased up to 0.62±0.05 IU/mL without any evidence of liver toxicity, gastrointestinal damage, or thrombocytopenia. The cancer-associated thrombosis was induced in tumor-bearing mice by local heat application, and the fibrin deposition in tumors was evaluated. The oral administration of LHe-tetraD (either a single dose or multiple daily doses for up to 10 days) in mice substantially abolished the coagulation-dependent tropism of fibrinogen in the heated tumors and significantly decreased hemorrhage, compared to the mice treated with saline or subcutaneous injection of LMWH. Thus, the anticoagulation effect of oral LHe-tetraD invokes the benefits of oral delivery and promises to provide an effective and convenient treatment for cancer patients at risk of thrombosis.

Orally active desulfated low molecular weight heparin and deoxycholic acid conjugate, 6ODS-LHbD, suppresses neovascularization and bone destruction in arthritis.

The regulation of angiogenesis is an interesting area to consider for novel therapeutic approaches to rheumatoid arthritis (RA). Chemically modified heparins have been developed as possible candidates for angiogenesis inhibitor; however, they have a major clinical drawback in exhibiting poor oral bioavailability. Here, orally absorbable O-desulfated low molecular weight heparin (ODS-LMWH) derivatives were newly synthesized by conjugating 2-O- or 6-O-desulfated LMWH with deoxycholic acid (DOCA) or bisDOCA (a dimer of DOCA), and their physicochemical properties, antiangiogenic potency and pharmacokinetic profiles were assessed. After selecting the best candidate among those derivatives, its therapeutic efficacy on arthritis was investigated in a murine collagen antibody-induced arthritis (CAIA) model. ODS-LMWH derivatives significantly inhibited the capillary-like tube formation of human umbilical vein endothelial cells (HUVECs) and basic fibroblast growth factor (bFGF)-induced angiogenesis in the Matrigel plug assay. Among all the compounds, 6ODS-LHbD showed the highest oral bioavailability in rats (19.3%). In the CAIA mouse model, 6ODS-LHbD (10 mg/kg, p.o., S.I.D.) significantly inhibited neovascularization in the joint, the increase of hind-paw thickness, and the structural damage in the bone. Therefore, 6ODS-LHbD would be a promising candidate for an orally active drug for the treatment of RA.

Prevention of VTE in nonsurgical patients: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines.

BACKGROUND: This guideline addressed VTE prevention in hospitalized medical patients, outpatients with cancer, the chronically immobilized, long-distance travelers, and those with asymptomatic thrombophilia. METHODS: This guideline follows methods described in Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement. RESULTS: For acutely ill hospitalized medical patients at increased risk of thrombosis, we recommend anticoagulant thromboprophylaxis with low-molecular-weight heparin (LMWH), low-dose unfractionated heparin (LDUH) bid, LDUH tid, or fondaparinux (Grade 1B) and suggest against extending the duration of thromboprophylaxis beyond the period of patient immobilization or acute hospital stay (Grade 2B). For acutely ill hospitalized medical patients at low risk of thrombosis, we recommend against the use of pharmacologic prophylaxis or mechanical prophylaxis (Grade 1B). For acutely ill hospitalized medical patients at increased risk of thrombosis who are bleeding or are at high risk for major bleeding, we suggest mechanical thromboprophylaxis with graduated compression stockings (GCS) (Grade 2C) or intermittent pneumatic compression (IPC) (Grade 2C). For critically ill patients, we suggest using LMWH or LDUH thromboprophylaxis (Grade 2C). For critically ill patients who are bleeding or are at high risk for major bleeding, we suggest mechanical thromboprophylaxis with GCS and/or IPC at least until the bleeding risk decreases (Grade 2C). In outpatients with cancer who have no additional risk factors for VTE we suggest against routine prophylaxis with LMWH or LDUH (Grade 2B) and recommend against the prophylactic use of vitamin K antagonists (Grade 1B). CONCLUSIONS: Decisions regarding prophylaxis in nonsurgical patients should be made after consideration of risk factors for both thrombosis and bleeding, clinical context, and patients' values and preferences.

Pharmacokinetic evaluation of an oral tablet form of low-molecular-weight heparin and deoxycholic acid conjugate as a novel oral anticoagulant.

This study was designed to develop a solid oral dosage form of deoxycholic acid (DOCA)-conjugated low-molecular-weight heparin (LMWH) and to evaluate its oral absorption, distribution, and metabolic stability for the prospect of providing an orally bioavailable LMWH. The LMWH derivative (LHD) was synthesised and then formulated with solubilisers and other pharmaceutical excipients to form a solid tablet. Its absorption and distribution after oral administration were evaluated in mice, rats, and monkeys. The in vitro metabolic stability of LHD was examined by liver microsome assays. More than 80% of LHD was released from the tablet within 60 minutes, guaranteeing rapid tablet disintegration after oral administration. Oral bioavailability of LHD in mice, rats and monkeys were 16.1 ± 3.0, 15.6 ± 6.1, and 15.8 ± 2.5%, respectively. After the oral administration of 131I-tyramine-LHD, most of the absorbed drug remained in the blood circulation and was eliminated mainly through the kidneys. LHD was hardly metabolised by the liver microsomes and showed a stable metabolic pattern similar to that of LMWH. In a rat thrombosis model, 10 mg/kg of orally administered LHD reduced thrombus formation by 60.8%, which was comparable to the anti-thrombotic effect of the subcutaneously injected LMWH (100 IU/kg). Solid tablets of LHD exhibited high oral absorption and statistically significant therapeutic effects in preventing venous thromboembolism. Accordingly, LHD tablets are expected to satisfy the unmet medical need for an oral heparin-based anticoagulant as an alternative to injectable heparin and oral warfarin.

M-118, a novel, low-molecular-weight heparin for the potential treatment of cardiovascular disorders.

Safe inhibition of thrombosis is a key therapeutic strategy in modern cardiovascular medicine, and both unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) are commonly used in clinical practice. However, both have several drawbacks, such as the unpredictable pharmacokinetics of UFH and the non-reversibility of LMWH. M-118, being developed by Momenta Pharmaceuticals Inc, is a novel LMWH that has been engineered to overcome the drawbacks of UFH and currently available LMWHs, while maintaining their beneficial attributes. In preclinical studies and phase I clinical trials, M-118 demonstrated potent activity against thrombin and Factor Xa, which could be reversed with protamine; M-118 also demonstrated a high and predictable bioavailability, and a short half-life. Promising results were observed in a phase II clinical trial in patients undergoing coronary interventions, although phase III clinical trials are required to establish the role for M-118 in contemporary medicine.

CB-01-05-MMX, a novel oral controlled-release low molecular weight heparin for the potential treatment of ulcerative colitis.

CB-01-05-MMX (LMW Heparin MMX), being developed by Cosmo Pharmaceuticals SpA, is a novel oral parnaparin sodium formulation for the potential treatment of ulcerative colitis. At the time of publication, clinical trial data were limited and the mechanism of action had not been elucidated. However, in one phase I and one phase IIb trial in patients with left-sided ulcerative colitis, CB-01-05-MMX had an acceptable safety profile and was not associated with bleeding complications, which is a known side effect of unfractionated heparin and low molecular weight heparin compounds previously evaluated for the treatment of ulcerative colitis. Evaluable efficacy data from the phase IIb trial revealed significant improvements in the clinical activity index values in the CB-01-05-MMX group, but this was not accompanied by mucosal healing. More research, including placebo-controlled trials in patients with left-sided ulcerative colitis and trials in patients with pancolitis, would determine the role of CB-01-05-MMX in the current spectrum of available medications for this condition.

Old versus new anticoagulants: focus on pharmacology.

Heparin, low molecular weight heparin (LMWH) and warfarin are well-established anticoagulants still in widespread use despite their well known drawbacks. Heparin requires continuous monitoring, has serious side-effects such as haemorrhage, thrombosis and osteoporosis, and lacks an oral route of administration. LMWH is a safer, more convenient anticoagulant to use but it cannot be given orally, does not have an antidote and may be difficult to administer in patients with renal failure. Warfarin has a narrow therapeutic window, interacts with other drugs and foods and requires monitoring like heparin. The limitations of all three of these established anticoagulants have prompted the search for better more convenient agents. The major examples of these newer anticoagulants are the direct and indirect factor Xa inhibitors and the direct thrombin inhibitors. These new agents tend to have more predictable pharmacokinetic properties, superior efficacy and safety and some can be administered orally. In this review, we summarise the advantages and disadvantages of three established anticoagulants (heparin, LMWH and warfarin) and the most promising new anticoagulants (fondaparinux, idraparinux, rivaroxaban, apixaban, dabigatran and ximelagatran) by discussing their pharmacodynamics and pharmacokinetics. We also discuss recent patents in the field of anticoagulation, which aim to improve the safety and effectiveness of antithrombotic agents currently in use or offer alternative ways for anticoagulation.

Relative antithrombotic and antihemostatic effects of protein C activator versus low-molecular-weight heparin in primates.

The anticoagulant and anti-inflammatory enzyme, activated protein C (APC), naturally controls thrombosis without affecting hemostasis. We therefore evaluated whether the integrity of primary hemostasis was preserved during limited pharmacological antithrombotic protein C activator (PCA) treatment in baboons. The double-mutant thrombin (Trp215Ala/Glu217Ala) with less than 1% procoagulant activity was used as a relatively selective PCA and compared with systemic anticoagulation by APC and low-molecular-weight heparin (LMWH) at doses that inhibited fibrin deposition on thrombogenic segments of arteriovenous shunts. As expected, both systemic anticoagulants, APC (0.028 or 0.222 mg/kg for 70 minutes) and LMWH (0.325 to 2.6 mg/kg for 70 minutes), were antithrombotic and prolonged the template bleeding time. In contrast, PCA at doses (0.0021 to 0.0083 mg/kg for 70 minutes) that had antithrombotic effects comparable with LMWH did not demonstrably impair primary hemostasis. PCA bound to platelets and leukocytes, and accumulated in thrombi. APC infusion at higher circulating APC levels was less antithrombotic than PCA infusion at lower circulating APC levels. The observed dissociation of antithrombotic and antihemostatic effects during PCA infusion thus appeared to emulate the physiological regulation of intravascular blood coagulation (thrombosis) by the endogenous protein C system. Our data suggest that limited pharmacological protein C activation might exhibit considerable thrombosis specificity.

Tetradecylmaltoside (TDM) enhances in vitro and in vivo intestinal absorption of enoxaparin, a low molecular weight heparin.

Tetradecylmaltoside (TDM) was evaluated as a potential gastrointestinal absorption enhancer for low molecular weight heparin (LMWH), enoxaparin. The in vitro efficacy of TDM (0.0625, 0.125 and 0.25% w/v) in enhancing transport of 3H-enoxaparin or 14C-mannitol was investigated in human colonic epithelial cells (C2BBel). Metabolic stability of the drug was determined in C2BBel cell extracts. Transepithelial electrical resistance (TEER) was measured before and after exposure of the cells to TDM. Enoxaparin was further administered to anesthetized Sprague-Dawley rats in oral formulations in the absence or presence of increasing concentrations of TDM and drug absorption was monitored by measuring anti-factor Xa activity in rat blood. In vitro permeability study shows that apparent permeability (Papp) of 3H-enoxaparin across C2BBe1 cells was increased by 8-fold in the presence of 0.0625% TDM compared to untreated cells. The movement of 14C-mannitol across the cell monolayer followed a similar pattern in the presence of increasing concentrations of TDM. No degradation or depolymerization of enoxaparin was observed when the drug was incubated in C2BBel cell extract. TEER was reversible after 60 min exposure of the cells to 0.0625% (w/v) TDM. Oral formulations of enoxaparin containing TDM administered to anesthetized rats significantly and rapidly increased gastrointestinal absorption as compared to those animals which received enoxaparin plus saline (p < 0.05). In the presence of 0.125% TDM in the formulation, enoxaparin oral bioavailability was increased by 2.5-fold compared to the saline control group. Overall, the data on the effect of TDM on the in vitro and in vivo intestinal permeation of enoxaparin suggest that TDM may represent a promising excipient for use in oral LMWH formulations.

Orally administered heparins prevent arterial thrombosis in a rat model.

Our previous studies demonstrated that orally administered heparins prevent thrombosis in a rat jugular vein thrombosis model, where bovine unfractionated heparin (UFH) and the low molecular weight heparin tinzaparin reduced thrombotic incidence by 50% at 7.5 and 0.1 mg/kg, respectively. Our objectives were to determine if similar antithrombotic effects of oral heparin could be observed in an arterial thrombosis model. In this model, filter paper soaked in 30% ferric chloride was applied to the exposed rat carotid artery. A flowmeter recorded blood flow over a 60 min period determining time when the thrombus began forming (TTB) and time till occlusion (TTO). Immediately following, the thrombus was removed, dried and weighed 24 h later. Bovine UFH (7.5 mg/kg), tinzaparin (0.1 mg/kg) or saline was administered by stomach tube at 2, 5 and 25 h prior to thrombus initiation. TTB was significantly increased when UFH was given at 5 and 25 h but not 2 h prior, and when tinzaparin was given at 5 but not 2 or 25 h prior compared to rats given oral saline. TTO was significantly increased for both UFH and tinzaparin when given 5 and 25 h but not 2 h prior (one-way ANOVA). There was no difference in TTO and TTB between UFH and tinzaparin treated groups. A trend in reduction in thrombus weight was observed for UFH at 5 and 25 h prior and tinzaparin at 5 h prior to thrombus initiation (one-way ANOVA). Although no significant changes were observed in activated partial thromboplastin times, Heptest or anti-Xa activity from plasma of heparin treated rats, endothelial heparin concentrations were significantly greater than controls for UFH at 5 h and for tinzaparin at 2, 5, and 24 h. Thus, heparins administered by the oral route are effective antithrombotic agents in arterial as well as venous models.

Localization of heparin and low-molecular-weight heparin in the rat kidney.

Unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) are cleared, at least in part, by the kidneys through a poorly understood process. This study was undertaken to explore the mechanism of renal clearance of these drugs. Rats were given fluorescein-5-isothiocyanate (FITC)-labeled UFH or LMWH intravenously. At intervals after injection, rats were euthanized and the kidneys were harvested and subjected to immunohistochemical analysis and fluorescence microscopy. Both UFH and LMWH were localized to renal tubular cells and no immunoperoxidase staining or fluorescence was detected in glomeruli. Autoradiography demonstrated similar intracellular distribution of radio-labeled UFH suggesting that this phenomenon is independent of the method used to label heparin. Fluorescence in the tubules increased as a function of time after UFH injection, but reached a plateau after LMWH injection suggesting that the rate of renal tubular uptake depends on the molecular size of the heparin. When administered prior to FITC-labeled UFH or LMWH, probenecid, a renal organic anion inhibitor, decreased the renal tubular uptake of the heparins, whereas cimetidine, a renal organic cation inhibitor, had no effect. These findings suggest that renal excretion of UFH and LMWH primarily reflects tubular uptake via an organic anion transport mechanism.

Studies on the intestinal absorption of low molecular weight heparin using saturated fatty acids and their derivatives as an absorption enhancer in rats.

Intestinal absorption of low molecular weight heparin (LMWH) as well as unfractionated heparin (UFH) is limited due to its large molecular size and extensive negative charge. Development of its oral formulations would allow outpatient treatment with LMWH and UFH, and contribute a reduction in hospital expenses. The present study was aimed at evaluating the absorption enhancers Labrasol and Gelucire 44/14, which mainly consist of glycerides and fatty acids esters, to improve the intestinal absorption of LMWH. The absorption effects of saturated fatty acids with several carbon chain lengths (C6-C14) were also investigated. LMWH formulated with or without absorption enhancer was administered to the duodenum of fasted rats. The doses of LMWH and absorption enhancer were 20 mg/kg and 30 mg/kg, respectively. Plasma anti-Xa activity was measured as a marker of the LMWH absorption. By administration of the LMWH formulation with Labrasol but not with Gelucire 44/14, the plasma anti-Xa activity was increased to a level above 0.2 IU/ml which is the critical level for elucidation of its anticoagulant activity. Saturated fatty acids also enhanced the intestinal absorption of LMWH, and the order of absorption-enhancing effect was C10=C12>C14>C16>C8> or =C6. These results suggest that the intestinal absorption of LMWH varies with carbon chain lengths of the saturated fatty acids.

Pharmacokinetics and pharmacodynamics of low-molecular-weight heparins and glycoprotein IIb/IIIa receptor antagonists in renal failure.

Data regarding the use of low-molecular-weight heparins (LMWHs) and glycoprotein (GP) IIb/IIIa receptor antagonists in patients with renal failure are limited. Renal failure has the potential to increase the risk of adverse drug events associated with LMWHs and GP IIb/IIIa receptor antagonists. This is due to changes in the pharmacokinetic and pharmacodynamic profiles of these agents in patients with renal failure. Until more data are available, clinicians should consider alternative therapies in this patient population.

A chronopharmacodynamic study on standard heparin, a low molecular weight heparin (nadroparin) and danaproid: establishing and comparing the daily variations of these drugs in rats.

The effects of dosing time on the anticoagulant activity of unfractionated heparin, low molecular weight heparin (nadroparin) and danaproid were investigated. The chronopharmacological comparisons of the drugs were done on the anti-Xa, anti-IIa activities and activated partial thromboplastin time assays. Several dosing times were considered and an analysis based on a population approach was adopted. Under unfractionated heparin, the pharmacological activities did not exhibit significant daily variations. In contrast, significant daily profiles were observed in all the biological assays performed with low molecular weight heparin. Anti-Xa and anti-IIa activities showed some fluctuations over a 24-hour period with a peak at noon. As for the variations of the activated partial thromboplastin time, two peaks were noted early in the morning and at the beginning of nightfall. As for danaproid, only a daytime maximum of anti-Xa activity could be found.

A simulated post-angioplasty low molecular weight heparin schedule in a non-human primate model.

Due to a variety of pathophysiologic processes the long-term success rate of percutaneous transluminal angioplasty (PTCA) is only 50-70%. Acute restenosis also occurs in 30-40% of patients. Currently, studies are in progress to investigate the influence of low molecular weight heparin (LMWH) prophylaxis on the patency rate after PTCA. Our aim was to determine an optimal schedule to start the LMWH prophylaxis after the routinely performed heparinization. The alterations of the hemostatic parameters during the drug regimen change-over were evaluated. Non-human primates (Macaca mulatta) were divided into 6 treatment groups (n = 3/group). Three groups received heparin i.v. at 15 U/kg to mimic the end phase of therapeutic treatment infusion given 12-24 hrs. after PTCA. Three groups received full heparinization (250 U/kg i.v.) to mimic patients without the above interim phase therapy. Following both regimens, LMWH (Mono-Embolex) (1 mg/kg s.c.) was started at various intervals. The group initially treated with 15 U/kg heparin exhibited a continued anticoagulant effect when LMWH was started 30 min. after the heparin injection. Whereas, when LMWH was started after 2 hrs. the measurable anticoagulant effect was lost during 1 and 3 hrs. after the heparin injection. When LMWH was started 2 or 4 hrs. after the 250 U/kg dose, the anticoagulant response was sustained. Aside from the anti-IIa and the anti-Xa activity, there was no significant difference in other coagulation parameters between these two regimens. The fibrinolytic system was not altered in the therapeutic heparinization group. However, after the initial bolus of 250 mg/kg heparin, the monkeys treated with LMWH exhibited higher t-PA and D-dimer levels. Although our data shows definite differences between the two drug treatment schedules, further studies are warranted before an optimal drug regimen can be suggested for clinical use.

Pharmacokinetic considerations on Orgaran (Org 10172) therapy.

Pharmacokinetic investigations on Orgaran (Org 10172) have been conducted by monitoring the following biological effects: plasma anti-Xa, anti-IIa and IIa-generation-inhibiting (IIaGI) activities. In addition, a limited number of studies were conducted on the basis of concentrations of the No-affinity glycosaminoglyc(uron)an (NoA-GAG) fraction as determined by a competitive binding assay. In humans, widely different pharmacokinetic profiles for various biological effects were observed, with relatively short elimination half-lives for the anti-IIa and IIaGI activities of 4.3 +/- 3.5 and 6.7 +/- 3.2 h, respectively, but a relatively long elimination half-life of anti-Xa activity of 24.5 +/- 9.6 h. These differences in half-life mainly reflect differences in the rate of elimination of individual components of Orgaran. Rapid elimination of some of these components may explain why twice daily dosing is required for optimal thrombosis prophylaxis with Orgaran. In a comparative study in healthy male volunteers, the pharmacokinetics of the following low molecular weight heparin(oid)s were determined after intravenous administration: Orgaran (3,750 anti-Xa units), Fragmin (5,000 anti-Xa units), Fraxiparine (7,500 IC units) and Clexane (40 mg). Between these products, wide differences in pharmacokinetics were observed. Particularly, the half-lives of anti-Xa activity and IIaGI activity were much longer for Orgaran than for the other products. At the same time, a relatively low area under the curve of anti-IIa activity was observed. The absolute bioavailability of Orgaran following subcutaneous administration was determined on the basis of plasma anti-Xa and IIaGI activities and the NoA-GAG fraction concentrations. Absorption from subcutaneous tissues was found to be close to 100%, which is significantly higher than of heparin; a finding which indicates that the subcutaneous route is reliable for the administration of Orgaran. The elimination of Orgaran components occurs by renal and possibly non-renal routes. With respect to anti-Xa activity, about 50% of the total clearance can be accounted for by urinary excretion. Therefore, in severe renal failure, a reduction of the maintenance dose of Orgaran would seem to be indicated. Studies on the influence of enzyme induction as a result of treatment with pentobarbital suggest that the pharmacokinetics of Lomoparan are relatively insensitive to changes in hepatic function. In a number of studies, the influence of conditions such as age, body weight and drug interactions were studied. Generally, only minor changes in the pharmacokinetic parameters of Orgaran were observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Strategy for the development of the low molecular weight heparin fraction CY 216 in the prevention of postoperative deep vein thromboses in general surgery.

The polymorphism in the composition and actions of heparin and the parallel complexity of the thrombotic process have led to the design of a cautious, methodical, and pragmatic program of development of the first low molecular heparin fraction presently available in France (CY 216). The main idea was always to present the objective observation of facts and to reject any theoretical construction. After many stages, the value of this fraction in this indication, which appears as safe as possible but more effective than unfractionated heparin, has become obvious.