A new low molecular weight heparin derivative. In vitro and in vivo studies

Enhanced Antiviral Function of Magnesium Chloride-Modified Heparin on a Broad Spectrum of Viruses

Previous studies reported on the broad-spectrum antiviral function of heparin. Here we investigated the antiviral function of magnesium-modified heparin and found that modified heparin displayed a significantly enhanced antiviral function against human adenovirus (HAdV) in immortalized and primary cells. Nuclear magnetic resonance analyses revealed a conformational change of heparin when complexed with magnesium. To broadly explore this discovery, we tested the antiviral function of modified heparin against herpes simplex virus type 1 (HSV-1) and found that the replication of HSV-1 was even further decreased compared to aciclovir. Moreover, we investigated the antiviral effect against the new severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) and measured a 55-fold decreased viral load in the supernatant of infected cells associated with a 38-fold decrease in virus growth. The advantage of our modified heparin is an increased antiviral effect compared to regular heparin.

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

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

Pharmacokinetics of Subcutaneous Low Molecular Weight Heparin (Enoxaparin) in Dogs

Unfractionated heparin has been the standard heparin used in human and veterinary medicine for its anticoagulation effect; however, it has a complex pharmacodynamic profile that requires close monitoring. Low molecular weight heparins have a more predictable bioavailability, allowing standardized dosing without individual patient monitoring. This project was designed to a) evaluate the pharmacokinetics of the subcutaneous (SC) administration of the low molecular weight heparin, enoxaparin, in dogs using anti-Xa activity as a marker of plasma enoxaparin concentrations and b) to establish the dose necessary to maintain activity within an established target range. Enoxaparin at 0.8 mg/kg SC q 6 hours consistently maintained target levels of anti-Xa activity in normal dogs without evidence of hemorrhagic complications.

Recent advances in the treatment of thromboembolic diseases: Venous thromboembolism

Venous thromboembolic diseases are the major concern of rising cost of healthcare and are commonest health problem across the globe. Both genetic and acquired risk factors are believed to be strongly linked with these diseases. Commonly encountered problems to the therapy include dose fixing and routine monitoring, yet some serious problems of bleeding also necessitate the immediate need to develop new agents. The review is primarily concerned with the new developments in the treatment of thromboembolic diseases. Therapeutic applications of anticoagulants, antiplatelets, and thrombolytics have been discussed in enough detail.

Antifactor Xa activity in intensive care patients receiving thromboembolic prophylaxis with standard doses of enoxaparin

BACKGROUND

Low-molecular-weight heparins (LMWHs) have become increasingly used to prevent thromboembolic complications in intensive care patients. Unlike in medical and surgical patients, no data on the anticoagulant effectiveness of standard LMWH dosages exist in intensive care patients. Therefore, we prospectively investigated antifactor Xa (aFXa) levels after subcutaneous administration of 40 mg of enoxaparin in 89 intensive care patients over a 24-h period.

METHODS

AFXa levels were measured before, 4, 12 and 24 h after subcutaneous administration of enoxaparin. Laboratory parameters including prothrombin time, activated partial thromboplastin time, antithrombin III, fibrinogen as well as platelet count were collected at same intervals. Demographics included age, sex, height, weight, body mass index, admission diagnosis, a thromboembolic risk score and a modified Goris multiple organ dysfunction score.

RESULTS

At 4, 12 and 24 h, 56.5%, 39.3% and 12.6% of the study patients were within recommended antithrombotic aFXa levels (0.1-0.3 U ml(-1)). Presence of multiple organ dysfunction as well as high body weight were significantly correlated with low aFXa levels.

CONCLUSION

European standard dosages of 40 mg of enoxaparin once daily proved to be ineffective in achieving recommended antithrombotic aFXa levels in intensive care patients. This was most pronounced in patients with high body weight and presence of multiple organ dysfunction.

Treatment of Venous Thromboembolism with Low-Molecular-Weight Heparin

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

Is anticoagulation and central neural blockade a safe combination?

The indiscriminate insertion of epidural or subarachnoidal needles or catheters in patients who are anticoagulated or are about to be anticoagulated carries the inherent risk of the potential development of a compressing vertebral canal haematoma, which may severely jeopardize the patient's (quality of) life. Although the isolated use of aspirin or non-steroidal anti-inflammatory drugs in general is no longer considered a problem, its combination with any form of heparin therapy is. Intraoperative heparinization during cardiac or vascular surgery can be safely performed provided a minimum time interval between the regional anaesthetic block and the subsequent heparinization is respected and indwelling catheters are removed after the disappearance of any remaining heparin effect. Similarly, central neural blockade in combination with the thromboprophylactic use of standard unfractionated heparin or low-molecular-weight heparins is possible if: (1) only thromboprophylactic heparin doses are used; and (2) a specific minimum time interval between the previous or the next dose of the anticoagulant and the initiation of the block or the removal of the indwelling catheter is observed.

Bleeding complications with enoxaparin for deep venous thrombosis prophylaxis

The safest and most efficacious method of deep venous thrombosis prophylaxis remains controversial. With the use of enoxaparin, a low-molecular-weight heparin, becoming ubiquitous in many institutions, we specifically examined bleeding complications related to its use. A case-control study was conducted on consecutive patients receiving enoxaparin prophylaxis after primary or revision total knee or total hip arthroplasty or hip hemiarthroplasty. Matched controls receiving no pharmacologic anticoagulation were identified. Patient and operative characteristics, hematologic values, and timing of enoxaparin dosing were analyzed as related to major and minor bleeding complications. A total of 152 procedures with enoxaparin and an equal number of control cases were included for a total of 304 patients. The enoxaparin group had a 23.7% total complication rate compared to 16.5% for the control group (P = .11). The power of the test was .35 and indicated that approximately 970 patients would need to be reviewed to have at least an 80% chance of finding a statistically significant difference. Major complications occurred in 5 patients (3.3%) in the enoxaparin group and 2 (1.3%) in the control group (P = .25, power = .21). Minor complications in the enoxaparin group were slightly higher but not significant at 20.4% versus 15.1% in the control group (P = .23). There were significantly fewer minor complications in the enoxaparin group after primary single-joint procedures (16.50%) than all other procedures (32.4%). Patients receiving the first dose of enoxaparin 10 hours or more postoperatively had significantly fewer complications (P = .05). The postoperative hematocrit drop was significantly greater for the enoxaparin group for all procedures (P = .003) as well as for primary single procedures (P = .0005). The postoperative transfusion requirement was significantly greater after primary single procedures (P = .02) in the enoxaparin group. One patient with an epidural catheter and receiving enoxaparin postoperatively developed an epidural hematoma. Although there were not significantly more complications with enoxaparin, there was evidence of significantly increased postoperative bleeding. The low-power analysis reveals that a large number of patients (970-1,700) are required to show a statistically significant difference in bleeding complications between the 2 groups. To minimize complications, a short period to allow initial hemiostasis postoperatively is recommended, as is preferential use of enoxaparin for primary single-joint replacements. Enoxaparin used in conjunction with an indwelling epidural catheter is not recommended.

Use of enoxaparin, a low-molecular-weight heparin, and unfractionated heparin for the prevention of deep venous thrombosis after elective hip replacement. A clinical trial comparing efficacy and safety. Enoxaparin Clinical Trial Group

A randomized, parallel-group, open-label clinical trial (the physicians, patients, and staff were not blinded with regard to the regimen that had been used) was conducted, between December 1988 and September 1990, to compare the safety and efficacy of enoxaparin, a low-molecular-weight heparin, with the safety and efficacy of unfractionated heparin for the prevention of deep venous thrombosis after elective hip replacement. Six hundred and ten patients were randomized, and 607 patients received one of the study medications. The evaluations of efficacy included contrast-media venography, non-invasive vascular examination, and clinical examination. Data on efficacy were available for 604 patients, who had been assigned to one of three treatment groups: thirty milligrams of enoxaparin every twelve hours (194 patients), forty milligrams of enoxaparin once daily (203 patients), or 5000 units of unfractionated heparin every eight hours (207 patients). All drugs were administered subcutaneously. Dosages were not adjusted on the basis of the results of coagulation tests or the body weight of the patient. Treatment was initiated within twenty-four hours after the operation and continued for a maximum of seven days. The primary safety outcome was the occurrence of bleeding episodes. An intent-to-treat patient analysis revealed that deep venous thrombosis occurred in nine (5 per cent) of the 194 patients who received thirty milligrams of enoxaparin every twelve hours, thirty (15 per cent) of the 203 patients who received forty milligrams of enoxaparin once daily, and twenty-four (12 per cent) of the 207 patients who received unfractionated heparin. The rate of deep venous thrombosis was significantly lower in the group that received thirty milligrams of enoxaparin every twelve hours than in the group that received unfractionated heparin (p = 0.03) and in the group that received forty milligrams of enoxaparin once daily (p = 0.0002). No clinically symptomatic pulmonary embolism was observed during the treatment or follow-up phase of this study in the group that received thirty milligrams of enoxaparin every twelve hours. Analysis of evaluable patients revealed a marked reduction in the rate of deep venous thrombosis in the group that received thirty milligrams of enoxaparin every twelve hours (eight [6 per cent] of 136 patients) compared with the group that received heparin (twenty-one [15 per cent] of 145 patients) (p = 0.10); however, this difference was not significant because of the small number of patients included in this analysis.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparison of subcutaneous low-molecular-weight heparin with warfarin sodium for prophylaxis against deep-vein thrombosis after hip or knee implantation

BACKGROUND

Deep-vein thrombosis is a potentially life-threatening complication of total hip or knee replacement. There are few data on the effectiveness and safety of warfarin as compared with low-molecular-weight heparin as prophylaxis against this problem.

METHODS

We therefore performed a randomized, double-blind trial in 1436 patients to evaluate the effectiveness and safety of low-molecular-weight heparin (given subcutaneously once daily) as compared with adjusted-dose warfarin to prevent venous thrombosis after hip or knee replacement. Treatment with the drugs was started postoperatively. The primary end point was deep-vein thrombosis as detected by contrast venography (performed a mean of 9.4 days after surgery in each group).

RESULTS

Among the 1207 patients with interpretable venograms, 231 of 617 patients (37.4 percent) in the warfarin group and 185 of 590 patients (31.4 percent) in the low-molecular-weight-heparin group had deep-vein thrombosis (P = 0.03). The reduction in risk with low-molecular-weight heparin as compared with warfarin was 16 percent, and the absolute difference in the incidence of venous thrombosis was 6 percent in favor of low-molecular-weight heparin (95 percent confidence interval, 0.8 to 11.4 percent). The incidence of major bleeding was 1.2 percent (9 of 721 patients) in the warfarin group and 2.8 percent (20 of 715 patients) in the low-molecular-weight-heparin group (P = 0.04), and the absolute difference was 1.5 percent in favor of warfarin (95 percent confidence interval, 0.1 to 3.0 percent).

CONCLUSIONS

Our data demonstrate that the small reduction in the incidence of venous thrombosis with low-molecular-weight heparin, as compared with warfarin, was offset by an increase in bleeding complications. Although the use of low-molecular-weight heparin is simpler, because it is administered subcutaneously without the need for monitoring, it may be more costly than warfarin. Warfarin is inexpensive, but the overall cost of its use is increased by the need to monitor the intensity of anticoagulation. At this time it is unclear which of these approaches is the most cost effective.

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Involvement of heparin cofactor II in chymotrypsin neutralization and in the pancreatic proteinase-antiproteinase interaction during acute pancreatitis in man

Heparin cofactor II is a proteinase inhibitor which inhibits both chymotrypsin and thrombin, and displays great similarities with antithrombin III, the main inhibitor of thrombin in human plasma. Since acute pancreatitis is known to be associated with modification of the proteinase-antiproteinase equilibrium, we studied heparin cofactor II and antithrombin III as well as other biochemical and haematological parameters in 10 patients experiencing attacks of acute pancreatitis. Heparin cofactor II activity decreased during the first week of illness, while its antigen concentration remained subnormal. This discrepancy between antigen concentration and activity which persisted during the first week of illness was due both to complex formation of heparin cofactor II with its target proteinases and to partial proteolysis of the inhibitor. Heparin cofactor II was shown to form a complex with chymotrypsin in the plasma of such patients. Antithrombin III levels remained unchanged throughout the study, with no discrepancy between its activity and antigen concentration. No modification of haemostasis was shown either, except for a rise in the fibrinogen level during the first days of illness. It is concluded that, unlike antithrombin III, heparin cofactor II is involved in the proteinase-inhibitor equilibrium in patients with acute pancreatitis, and that heparin cofactor II might react as an inhibitor of pancreatic proteinases rather than an inhibitor of thrombin.

Structural determinants of the capacity of heparin to inhibit collagen synthesis in 21-day fetal rat calvariae

Earlier work from our laboratory demonstrated that heparin inhibits type I collagen and DNA synthesis in fetal rat calvariae in vitro. In this paper we have analyzed the structural features of heparin that determine its inhibitory effect on collagen synthesis. These experiments were performed using unmodified heparins and low-molecular-weight heparins from different manufacturers, nonheparin glycosaminoglycans, desulfated heparins, anticoagulant and nonanticoagulant heparin, and chemically defined heparin oligosaccharides. Low-molecular-weight heparin (Mr 3700-5100) inhibited collagen synthesis, but oligosaccharides (disaccharides to decasaccharide, Mr 665-3000) did not. The glycosaminoglycans chondroitin sulfate B, heparan sulfate, and hyaluronic acid did not alter collagen synthesis but dextran sulfate was as inhibitory as unmodified heparin. Nonanticoagulant as well as anticoagulant low-molecular-weight heparin fractions inhibited collagen synthesis. Modification of heparin by total desulfation, O-desulfation, or N-desulfation and re-N-acetylation resulted in the loss of inhibitory property, suggesting that the degree of sulfation contributed to heparin's inhibitory effect. Low-molecular-weight heparins from different manufacturers were just as inhibitory as native heparin on collagen synthesis. We therefore conclude that low-molecular-weight heparin compounds offer no protection against heparin-induced osteoporosis. Our findings also suggest that the size and sulfation of a heparin-derived oligosaccharide contribute to its ability to inhibit collagen synthesis in bone.

Clinical potential of low molecular weight heparins

In recent years there has been an explosion of clinical trials evaluating low molecular weight (LMW) heparin both in the prevention of venous thrombosis and in the treatment of established venous thrombosis. Results to date would indicate that LMW heparin is an effective method of prophylaxis and has a negligible risk of bleeding, provided the anti-factor Xa levels 4-6 h after injection do not exceed 0.2 units/ml. There is suggestive evidence that, if LMW heparin is given in doses which produce anti-factor Xa levels of more than 0.4 units/ml, there is an increased risk of perioperative bleeding in surgical patients. Although three studies have reported that LMW heparin is more effective than standard unfractionated low dose heparin in the prevention of venous thrombosis, further studies evaluating risks and benefits are required. The promising experimental findings that LMW heparin produces less bleeding for equivalent antithrombotic efficacy has yet to be established in man. Results of clinical trials in neurosurgical patients, patients undergoing knee surgery and patients undergoing cardiac surgery may establish whether LMW heparin is advantageous in such patients at very high risk for bleeding. Finally, the early results from randomized trials suggest that LMW heparins are effective in the treatment of established venous thrombosis, but further trials are required.

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

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

Pharmacokinetics of heparin and related polysaccharides

The pharmacodynamic profile of standard heparin (SH), a low molecular weight derivative (CY 216) and of dermatan sulfate (DS), a new potential antithrombotic drug, was investigated in the rabbit over a large range of doses. After bolus i.v. injection of low doses, the biological activity of SH disappeared exponentially; however, its half-life was prolonged when the dose injected increased, and over 158 micrograms/kg (100 anti-factor Xa U/kg) the biological activity disappeared as a concave-convex curve. CY 216 disappeared more slowly than SH at low doses but faster than SH at higher doses. More than 90% of the DS biological activity present 1 minute after the i.v. injection disappeared exponentially without dose-dependent effects. Increasing doses of the three drugs were then delivered for 5 h under continuous infusions. Below 500 micrograms/kg/h the DS and CY 216 plateau concentrations were higher than that of SH while above this dose the SH concentration was higher than that of DS and CY 216. These observations may be explained by the results of pharmacokinetics experiments where 125I-labeled compounds were delivered by bolus i.v. injection in association with increasing doses of their unlabeled counterparts. For SH there was a 10-fold difference between the half-life of the lower dose (32 micrograms/kg or 5 anti-factor Xa U/kg) and that of the higher dose (3200 micrograms/kg); it was demonstrated that the half-life of SH continuously shortened as its plasma concentration decreased. In contrast the CY 216 and DS half-lives were very close, independent of the dose delivered, and therefore longer than that of SH at low doses and shorter than that of SH at higher doses. The renal contribution to the clearance of SH, CY 216, and DS was also investigated by injecting a low dose (150-200 micrograms/kg) and a 10 times higher dose to sham-operated or binephrectomized animals: renal function is critical for the elimination of the three compounds from the blood except for SH at low doses. These observations are promising for the development of DS and may have clinical implications.

A prospective randomized trial of low molecular weight heparin-DHE and conventional heparin-DHE (with acenocoumarol) in patients undergoing gynaecological surgery

The antithromboembolic efficacy of once a day low molecular weight heparin in fixed combination with dihydroergotamine (LMWH-DHE) was compared with conventional heparin-DHE in combination with Acenocoumarol (heparin-DHE/A) in 191 patients undergoing gynaecological surgery. LMWH-DHE proved equally effective in preventing thromboembolic complications, with a similar incidence of postoperative bleeding and side effects. Deep vein thrombosis occurred once in each group and one non-fatal pulmonary embolism occurred in the LMWH-DHE group. The main advantage of LMWH-DHE was significantly better patient acceptance of the single daily subcutaneous injection as compared with the two injections of conventional heparin-DHE (P = 0.02). On the other hand, LMWH-DHE was associated with significantly increased incidence of intraoperative bleeding (P less than 0.02). The bleeding did not, however, cause any clinical problems. Discontinuation of therapy due to bleeding or pain at the site of injection occurred three times in each group. We consider the use of LMWH-DHE to be an attractive, economic and safe method of thromboembolic prophylaxis.

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.

The antithrombotic activity and pharmacokinetics of enoxaparine, a low molecular weight heparin, in humans given single subcutaneous doses of 20 to 80 mg

The pharmacokinetics of enoxaparine, a low molecular weight heparin, was randomly studied in 12 healthy male volunteers. Doses of 20, 40, 60, and 80 mg were injected subcutaneously in randomized cross-over fashion. Anti-IIa and anti-Xa activities (using amidolytic methods), and calcium thrombin time, were measured over 36 hours. The maximum Amax of the anti-IIa and anti-Xa activities appeared 3 to 4 hours after administration. The terminal half-lives of anti-IIa and anti-Xa activities were approximately 2 and 4 hours, respectively, with no significant variation between the different doses. For the anti-Xa activity, there was a highly significant positive correlation between the dose injected and individual values of Amax (r = +0.915; P less than .001) and AUC (r = +0.913; P less than .001). Enoxaparine displays a relatively small apparent volume of distribution (about 7.0 L) and its total body clearance is about 1.25 L/hr. The mean residence time ranges from 4.6 to 7.6 hours. Thus, the pharmacokinetic profile of enoxaparine is characterized by a linear relationship between dose and absorption, a relatively low clearance and long elimination half-life, and a high anti-Xa/anti-IIa ratio.

Clinical studies with low-molecular-weight heparin(oid)s: an interim analysis

In this review an interim analysis was made of all clinical studies performed with low-molecular-weight heparin(oid)s (LMWH) up to January 1987. Thus far, many experimental studies on LMWH show these substances to have an increased benefit/risk ratio concerning efficacy and bleeding as compared to standard heparin. In man, this increased ratio was verified in some small open studies. However, until the present day, controversy still exists. Some of the difficulties in assessing the results of different investigations include the existence of various kinds of LMWH and the lack of a consensus as to the unitage in which they are expressed. Furthermore, no international agreement exists as to the test measuring dosage/effect and its standard. In the following review all published clinical studies were analyzed for patient groups. Important issues concerning controversy with regard to efficacy, bleeding risk, diagnosis, and testing are discussed. In general, it may be concluded that LMWH have an antithrombotic potential comparable to that of heparin, and that the benefit/risk ratio i.e., decreased bleeding potential when compared to standard heparin, as found in animal experiments, has not been clearly demonstrated in man.

Low molecular weight heparin compared with unfractionated heparin in prevention of postoperative thrombosis

Three consecutive randomized open studies have been carried out to determine the optimal dosage of low molecular weight heparin (LMWH) in the prevention of postoperative thrombosis in general surgery (892 patients). All patients undergoing abdominal, gynaecological, thoracic or urological surgery were over 40 years old and presented at least one of the following risk factors for thrombosis: previous thromboembolism, obesity, varicose veins, malignancy (30 per cent), pre-operative hospitalization over 5 days, oestrogen therapy, chronic cardiac disease or bronchitis. Isotopic venous thrombosis and bleeding complications were assessed after subcutaneous administration of a LMWH fragment (LMWH, Enoxaparine) or unfractionated heparin (UH). The three studies compared 3 X 5000 units UH daily with 1 X 60 mg, 1 X 40 mg, 1 X 20 mg LMWH daily. Thromboembolic events rates were not significantly different from group to group (UH: 3.8 per cent, 2.7 per cent, 7.6 per cent respectively compared with LMWH: 2.9 per cent, 2.8 per cent, 3.8 per cent). Bleeding episodes including wound haematoma formation, perioperative blood losses and systemic haemorrhage were not significantly different in patients receiving LMWH or UH. Significant decreases in haematocrit and haemoglobin were only observed in patients receiving 60 mg Enoxaparine (as compared to UH). An analysis using the 'intention to treat' approach gave results consistent with those of an analysis of good compliers. An overview of isotopic thromboses in the three studies gave no evidence of differences amongst the effects of the three doses of LMWH (P = 0.20), and pooling the results of the three studies using the Mantel-Haenszel procedure gave no evidence of a global difference between Enoxaparine and UH (P = 0.54). These results suggest that an optimal dosage of 20 mg/day of Enoxaparine is safe and effective in the prevention of postoperative thrombosis in this population.

Selective binding of heparins to human endothelial cells. Implications for pharmacokinetics

Cultured endothelial cells isolated from human umbilical vein bind heparin and heparin fragments. The binding capacity of endothelial cells for 35S-heparin was for 38% composed of high affinity binding sites (Kd = 11 X 10(-8) M) and for 62% of sites with much lower affinity (Kd = 14 X 10(-7) M). The affinity of unlabeled compounds for heparin binding sites was determined by competition with binding of 125I-heparin. I50 found for unlabeled heparin was 16 X 10(-8) M, which is in agreement with the Kd for binding of heparin to high affinity sites. PK 10169, a low molecular weight fragment of heparin, competed only at relatively high concentrations (I50 = 10(-5) M). Competition experiments with subfractions of PK 10169 showed that I50 was inversely correlated with molecular weight. Gelfiltration of 35S-heparin and 35S-PK 10169 before and after binding to endothelial cells demonstrated a selective binding of high molecular weight molecules from polydisperse heparin and PK 10169 preparations. Bound heparin and PK 10169 molecules were detached from the cell-surface by proteolytic treatment and tested for antifactor-Xa and antifactor-IIa activity. Released heparin is slightly more active in antifactor-Xa and antifactor-IIa activity than its parent preparation. Released PK 10169 was 4 fold more active in antifactor-Xa and 8 fold more active in antifactor-IIa assays than heparin.

A randomized controlled trial of a low-molecular-weight heparin (enoxaparin) to prevent deep-vein thrombosis in patients undergoing elective hip surgery

There is experimental evidence that low-molecular-weight fractions of heparin are as effective as the standard form but cause less bleeding. We therefore performed a double-blind, randomized trial comparing PK10169 low-molecular-weight heparin with placebo for the prevention of venous thrombosis in patients undergoing elective hip surgery. Prophylactic treatment with a fixed dose was begun postoperatively and continued for 14 days. Fifty patients in each treatment group underwent surveillance with [125I]fibrinogen leg scanning and impedance plethysmography. In the first 24 patients, venography was performed only if either surveillance test was positive. Because the rate of venous thrombosis detected in those patients was unexpectedly low, venography was requested in the remaining 76 patients, even if the screening tests were negative. In this latter group, venous thrombosis occurred in 4 patients (10.8 percent) given PK10169 heparin and 20 patients (51.3 percent) given placebo (P = 0.0002); the corresponding rates for proximal-vein thrombosis were 5.4 percent and 23.1 percent, respectively (P = 0.029). In the entire group of 100 patients, venous thrombosis occurred in 12 percent of those given PK10169 heparin and 42 percent of those given placebo (P = 0.0007), and the corresponding rates for proximalvein thrombi were 4 percent and 20 percent, respectively (P = 0.014). The observed hemorrhagic rate was 4 percent in each treatment group. We conclude that prophylaxis with fixed-dose PK10169 heparin is effective and safe for patients undergoing elective hip replacement.

Heparin fractions with high and low affinities to antithrombin III are cleared at different rates

The clearance characteristics of standard heparin (SH) and its fractions with high and low affinity to antithrombin III (HAH and LAH respectively) were studied by injecting 125I-labelled SH, HAH and LAH intravenously into the rabbits in increasing doses. Serial blood samples were then collected from an indwelling cannula for measurement of clearance, based both on radioactivity and anticoagulant activity. For equivalent weights injected, the radioactivity of HAH was cleared more slowly from the circulation than that of either SH or LAH. The radioactivity of SH, in turn, was cleared more slowly than that of LAH. The clearance of HAH, measured both by radioactivity and by anticoagulant activity were similar, whereas the clearance of the radioactivity of SH was more rapid than its anticoagulant activity (i.e. anti-factor Xa activity). These observations suggest that the radioactivity clearance curves of SH reflect a "net" estimation of the more complex clearance curves of the different heparin moieties whereas the anticoagulant clearance curves of SH reflects the clearance of the anticoagulant activity of a specific heparin fraction, in this case, the clearance of the anti-factor Xa activity of HAH. These differences suggest that the HAH:LAH ratio is, at any given time, greater in vivo than the same ratio measured in vitro.

Low molecular weight heparin plus dihydroergotamine for prophylaxis of postoperative deep vein thrombosis

In a prospective, double-blind investigation of the prophylaxis of deep vein thrombosis (DVT) in patients undergoing elective major abdominal surgery, 269 patients were randomized into two groups. One hundred and thirty-two patients received a fixed combination of heparin sodium 5000 units plus dihydroergotamine mesylate 0.5 mg (H/DHE) twice a day and 137 patients received a fixed combination of low molecular weight heparin 1500 units plus dihydroergotamine mesylate 0.5 mg (LMWH/DHE) once a day as well as one injection of placebo per day. Treatment was initiated 2 h pre-operatively in both groups and continued for 7-10 days. The frequency of DVT determined by the 125I-labelled fibrinogen uptake test and phlebography was 10.3 per cent in patients receiving H/DHE and 10.4 per cent in those receiving LMWH/DHE. DVT of the femoral vein was detected in four patients of the H/DHE group and in none of the LMWH/DHE group. Intra- and postoperative blood loss did not differ significantly between both groups. Also no difference in the development of wound haematoma and injection site haematoma was found. While intra-operative volume substitution was comparable in both groups, significantly more patients under H/DHE prophylaxis received volume substitution during the postoperative phase. These results show that once-daily prophylaxis with the combination of low molecular weight heparin and dihydroergotamine is equally as effective and as safe as the twice-daily regimen using a combination of unfractionated heparin and dihydroergotamine in patients undergoing elective, major abdominal surgery. The advantages of the once-daily regimen of LMWH/DHE include greater patient acceptance, less nursing time and greater cost effectiveness, provided the new combination can be sold at a cost which maintains this advantage.

Clinical efficacy of heparin fractions: issues and answers

The recent development of heparin fractions and fragments for clinical use has created the prospect of some new agents at our disposal for the treatment of thrombotic disorders. The development of a drug that will block thrombosis but will not impair hemostasis now appears to be a possibility. Due to lack of understanding of all of the mechanisms of the pathology of thrombosis, we are not certain what the properties of the ideal anticoagulant should be. Of the heparins and heparin fractions, fragments, and heparinoids now available to us, we have yet to fully understand the mechanism of their pharmacologic activity. It has been amply demonstrated that decreasing the average molecular weight decreases the antithrombin activity while retaining the anti-Xa activity of heparin derivatives. Studies on animal models have proven the antithrombotic potency of some of these low molecular weight heparins to be equal to that of unfractionated heparin. There has been some evidence that these fractions are less likely than unfractionated heparin to cause hemorrhage in animal models as well as in at least one human clinical trial. A recently published human clinical trial revealed an unexpected incidence of hemorrhage following major surgery when a certain heparin fraction was given as prophylaxis against thrombosis. We are desperately in need of heparin derivatives, heparinoids or other anticoagulants that can be used in place of standard heparin in patients who are allergic to heparin or who have heparin-induced thrombocytopenia. Patients with these problems not infrequently require cardiopulmonary bypass surgery in which the use of heparin has been mandatory. There is now evidence from animal and human studies that such a procedure is possible with a heparin fraction or a heparinoid. This is true for hemodialysis as well. Studies in progress offer hope that a low molecular weight fragment with potent anti-Xa activity will not cause thrombocytopenia in patients with heparin-induced thrombocytopenia. Whether this agent, a pentasaccharide, will have sufficient antithrombotic potency for clinical use remains an important question. An important property of some of the newer heparin fractions is a prolonged duration of action which may permit fewer doses, thus reducing the cost as well as patient discomfort and inconvenience.

Comparative effects of heparin and PK 10169, a low molecular weight fraction, in a canine model of arterial thrombosis

The comparative properties of heparin and PK 10169, a low molecular weight fraction, were studied using an antithrombotic test in anaesthetized dogs. The antithrombotic properties of the two compounds were evaluated by measuring inhibition of thrombus formation following transluminar stimulation of coronary artery with anodal current and by measuring anticoagulant properties, anti Xa and anti IIa activities. The results show that PK 10169 displayed significant antithrombotic activities above 0.625 mg/kg and was equipotent at 2.5 mg/kg s.c. with heparin 10 mg/kg s.c. No correlation could be observed between antithrombotic/anti Xa ratio of both compounds. Moreover it was shown that, unlike heparin, PK 10169 s.c. was devoid of obvious anticoagulant properties and induced a negligible anti IIa activity contrasting with a high anti Xa level. A similar dissociation between anti Xa and anti IIa activities was observed following i.v. administration of 2.5 mg/kg of PK 10169 but not with heparin. This low molecular weight heparin fraction might thus be regarded as a potential arterial antithrombotic agent devoid of appreciable anticoagulant effect.

Assay of unfractionated and LMW heparin with chromogenic substrates: twin methods with factor Xa and thrombin

Utilizing two newly synthesized chromogenic substrates (CS), two different assay methods for heparin in plasma have been developed. The assay with bovine factor Xa and the highly reactive "Substrate FXa-1" (CH3 OCO-D-CHA-Gly-Arg-pNA X AcOH) measures both unfractionated (UF) heparin and low molecular weight (LMW) heparin within a single standard curve in the 0.05-1.5 U/ml plasma range. The very similar (and less expensive) assay with bovine thrombin and "Substrate Th-1" (2AcOH X H-D-CHG-Ala-Arg-pNA), measures UF heparin, but not LMW heparin. The standard curves are highly reproducible (CV 3.5-4.7%). For clinical work, a linear standard curve is obtained with three standards and lin-log plot. The "within run" SD was 0.007-0.026 U/ml. Mean recovery of 0.5 U/ml heparin added to 10 pathological plasma samples ranged 0.46-0.53 U/ml (SD 0.034-0.040). Activities of three UF heparin and three LMW heparin preparations are reported.