Comparison between commercial heparin, low molecular weight heparin and pentosan polysulfate on hemostasis and platelets in vivo

Sodium pentosan polysulfate efficacy as thromboprophylaxis agent in high-risk women following gynecological surgery

AIM

Sodium pentosan polysulfate (Na-PPS) is a plant-based agent that has similar action with low-molecular-weight heparin. It inhibits factor Xa, preventing blood clot formation. To date, its use in clinical practice as thromboprophylaxis agent is still limited. In addition, the efficacy and safety profile of this agent was not robustly reported globally, especially for countries with major Muslim population. We hypothesized that Na-PPS was equally effective as the standard thromboprophylaxis. We aim to compare the efficacy and safety of Na-PPS against standard agent (fondaparinux or enoxaparin).

METHODS

This was a randomized control, open-label trial. Women underwent major gynecological surgery were randomized to receive either subcutaneous 50 mg of Na-PPS twice daily or subcutaneous enoxaparin 40 mg once daily. Fondaparinux 2.5 mg once daily was given to Muslim women as an alternative to enoxaparin. The treatment was started 6 h postoperatively, for at least 3 days. All the patients received thromboembolic deterrent stockings. The primary efficacy outcome was venous thromboembolism up to 3 days postsurgery. The main safety outcomes were minor and major bleeding.

RESULTS

Among 109 participants, there was no incidence of venous thromboembolism. None of the women developed major bleeding. Minor bleeding was observed in 28.3% (15/53) and 5.4% (3/56) of Na-PPS and standard thromboprophylaxis group, respectively (P = 0.001).

CONCLUSION

Na-PPS was associated with increased risk of minor bleeding. There was insufficient data to conclude its efficacy as thromboprophylaxis. Further research is needed to evaluate Na-PPS safety as a standard thromboprophylactic agent.

Thromboprophylaxis in non-surgical cancer patients

Acutely ill medical patients with cancer and cancer patients requiring non-surgical therapy are considered as non-surgical cancer patients and are at moderate to high risk of venous thromboembolism (VTE): approximately 10-30% of these patients may develop asymptomatic or symptomatic deep-vein thrombosis (DVT) or pulmonary embolism (PE), and the latter is a leading contributor to deaths in hospital. Other medical conditions associated with a high risk of VTE include cardiac disease, respiratory disease, inflammatory bowel disease, rheumatological and infectious diseases. Pre-disposing risk factors in non-surgical cancer patients include a history of VTE, immobilisation, history of metastatic malignancy, complicating infections, increasing age, obesity hormonal or antiangiogenic therapies, thalidomide and lenalidomide therapy. Heparins, both unfractionated (UFH) and low molecular weight heparin (LMWH) and fondaparinux have been shown to be effective agents in prevention of VTE in the medical setting with patients having a history of cancer. UFH and LMWH along with semuloparin also have a role in outpatients with cancer receiving chemotherapy. However, it has not yet been possible to demonstrate a significant effect on mortality rates in this population. UFH has a higher rate of bleeding complications than LMWH. Thromboprophylaxis has been shown to be effective in medical patients with cancer and may have an effect on cancer outcomes. Thromboprophylaxis in patients receiving chemotherapy remains controversial and requires further investigation. There is no evidence for the use of aspirin, warfarin or mechanical methods. We recommend either LMWH, or fondaparinux for the prevention of VTE in cancer patients with acute medical illnesses and UFH for those with significant severe renal impairment. For ambulatory cancer patients undergoing chemotherapy we recommend LMWH or semuloparin. These are safe and effective agents in the thromboprophylaxis of non-surgical cancer patients.

VTE prophylaxis for the medical patient: where do we stand? - a focus on cancer patients

Acutely ill medical patients are at moderate to high risk of venous thromboembolism (VTE): approximately 10-30% of general medical patients may develop deep-vein thrombosis or pulmonary embolism, and the latter is a leading contributor to deaths in hospital. Medical conditions associated with a high risk of VTE include cardiac disease, cancer, respiratory disease, inflammatory bowel disease, rheumatological and infectious diseases. Pre-disposing risk factors in medical patients include a history of VTE, history of malignancy, complicating infections, increasing age, thrombophilia, prolonged immobility and obesity. Hence active cancer and a history of cancer are both strongly related to VTE in medical (non-surgical) patients. Heparins, both unfractionated (UFH) and low molecular weight (LMWH) and fondaparinux have been shown to be effective agents in prevention of VTE in this setting. However, it has not yet been possible to demonstrate a significant effect on mortality rates in this population. In medical patients, unfractionated heparin has a higher rate of bleeding complications than low molecular weight heparin. Thromboprophylaxis has been shown to be effective in medical patients with cancer and may have an effect on cancer outcomes. Thromboprophylaxis in patients receiving chemotherapy remains controversial and requires further investigation. There is no evidence for the use of aspirin, warfarin or mechanical methods. We recommend either low molecular weight heparin or fondaparinux as safe and effective agents in the thromboprophylaxis of medical patients.

Low-molecular-weight heparin and unfractionated heparin in prophylaxis against deep vein thrombosis in critically ill patients undergoing major surgery

The objective of the present study was to compare the efficacy and safety of low-dose unfractionated heparin (UFH) and a low-molecular-weight heparin (LMWH) as prophylaxis against venous thromboembolism in critically ill surgical patients undergoing major surgery. This was a randomized prospective study in which critically ill patients scheduled to undergo major elective surgery were allocated to receive subcutaneously either LMWH once daily and a placebo injection containing sterile 0.9% normal saline or 5000 IU UFH twice daily subcutaneously. Each patient was evaluated postoperatively clinically and confirmed by Doppler study for development of deep vein thrombosis (DVT). One hundred and fifty-six patients completed the protocol. There was similar efficacy of UFH as compared with LMWH in the prophylaxis of DVT. There was also no statistically significant difference in the incidence of major complications in the heparin group as compared with the LMWH group. However, minor hemorrhagic complications such as wound hematoma and surgical site bleeding were significantly more in the heparin group as compared with the LMWH group. Both UFH 5000 units subcutaneously twice daily and LMWH 40 mg once daily provide highly effective and well tolerated prophylaxis for critically ill surgical patients. Considering the advantage of once-daily dosing, a wider adoption of prophylaxis with LMWH may be justified on the basis of patient acceptability and saving of nursing time.

Pharmacological prevention of venous thromboembolism in medical patients at risk

Acutely ill general medical patients are at moderate-to-high risk of venous thromboembolism (VTE); approximately 10-30% may develop deep vein thrombosis or pulmonary embolism, the latter being a leading contributor to deaths in hospital. Medical conditions associated with a high risk of VTE include cardiac disease, cancer, respiratory disease, inflammatory bowel disease, and infectious disease. Predisposing risk factors for VTE in medical patients include history of VTE, history of malignancy, complicating infections, increasing age, thrombophilia, prolonged immobility, and obesity. Unfractionated heparin (UFH), low-molecular weight heparin (LMWH), and fondaparinux sodium have been shown to be effective agents in the prevention of VTE in medical patients. In this setting, UFH has a higher rate of bleeding complications than LMWH. There is no evidence supporting the use of aspirin, warfarin, or mechanical methods to prevent VTE in medical patients. We recommend either LMWH or fondaparinux sodium as well tolerated and effective thromboprophylactic agents in medical patients.

Formulary management of low molecular weight heparins

Low molecular weight heparins (LMWHs) are increasingly being utilised as anticoagulants in healthcare settings. These agents offer several advantages over standard unfractionated heparin. Indications for LMWHs include deep vein thrombosis and pulmonary embolism prophylaxis, deep vein thrombosis treatment, use in coronary procedures associated with a high risk for bleeding, and in acute coronary syndromes. Prior to being added to formularies, LMWHs should be evaluated for efficacy, safety and economic benefits over other anticoagulants. Institutions should be prepared to conduct their own economic assessments in the absence of readily available studies. There is clear evidence that LMWHs are cost saving or are at least cost effective as thromboprophylactic agents in major orthopaedic surgery. The economic benefits of LMWHs in other surgical situations is less clear. Consistent evidence from several countries indicate that LMWHs are cost saving as anticoagulants for the initial treatment of DVT. Further studies are needed to evaluate the efficacy, safety and economics of LMWHs in other conditions besides hip and knee arthroplasty and general surgery.

Thromboprophylaxis, coagulation disorders, and regional anaesthesia

The surgery and trauma-induced modulation of the coagulation system includes a considerable risk of perioperative thromboembolic complications unless effective thromboprophylactic treatment is given. In the present survey the patient at risk of deep vein thrombosis (DVT) and pulmonary embolism (PE) is characterized and the documented efficacy of different currently used thromboprophylactic regimens is summarized. Systemic thromboprophylactic treatment may include a risk of an increased bleeding tendency which may lead to haemorrhagic complications. In patients with a coagulation abnormality or in patients receiving anticoagulants for perioperative thromboprophylaxis there is a fear among anaesthesiologists that the use of regional anaesthesia (spinal or epidural) may be associated with spinal haemorrhagic complications, i.e. with spinal haematoma formation leading to compression of the spinal cord and severe neurologic sequelae. Present aspects on the risk of spinal haematoma formation at the combined use of pharmacological thromboprophylactic regimens and spinal or epidural anaesthesia/ analgesia are therefore summarized. Pregnancy is associated with changes in the haemostatic system, which in the preeclamptic or eclamptic patient may be rather pronounced and constitute a clinical problem since regional anaesthetic techniques are often preferred for obstetric anaesthesia/analgesia. The specific problems to be considered prior to the choice of regional anaesthesia/analgesia for a parturient with a suspected coagulation disorder are therefore commented on in more detail. Finally, recommendations are given for safe spinal and epidural analgesic and anaesthetic routines in patients with potential haemostatic disturbances due to thromboprophylactic treatment with anticoagulants or bleeding disorders.

Patients at risk of venous thromboembolism--clinical results with reviparin

Perioperative thromboembolism can be effectively prevented by low-dose heparin. However, its clinical benefit is limited, due to the risk of bleeding, the need for multiple daily doses, infrequent disorders of platelet function and other potential side effects. Low molecular weight heparin (LMWH) was developed with the aim that the antithrombotic efficacy of heparin could be maintained, while the risk of bleeding and other side effects would be reduced. Prior to recent studies, the anticipated clinical benefit of LMWH remained a controversial issue. We have reviewed the clinical pharmacology and the results of several prospective trials using reviparin a LMWH which has been compared with unfractionated heparin (UFH) and another LMWH. The efficacy and safety of reviparin was examined in the prevention of venous thromboembolism in high risk patients undergoing elective major abdominal and hip surgery. The results of these clinical trials show that reviparin is as effective as UFH in preventing venous thromboembolism whilst having a lower incidence of bleeding complications. Of major significance was the finding that a very low dose of reviparin, namely 1750 anti-Xa IU once daily, was found to be as effective as UFH in preventing deep vein thrombosis whilst having a significantly lower incidence of bleeding complications in patients undergoing major abdominal surgery. Reviparin has also been shown to be effective and safe as enoxaprin in patients undergoing elective hip surgery. Further clinical trials are required to test different dosage regimens as a thromboprophylactic agent in high risk patients. It is possible that reviparin and other LMWHs with similar pharmacological properties may have an important clinical benefit over earlier compounds. However, this needs to be assessed in large scale, double-blind, randomised clinical trials.

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.

Thromboembolic disease and thromboprophylaxis in oral and maxillofacial surgery: experience and practice

OBJECTIVE

(i) To determine the incidence of thromboembolic disease (TED) in major maxillofacial surgery and in particular deep vein thrombosis (DVT) and pulmonary embolism (PE). (ii) To determine current thromboprophylactic practice in the specialty.

DESIGN

Retrospective survey by questionnaire of five year experience and current practice in UK maxillofacial surgical units.

SUBJECTS

The patients of 130 consultants carrying out major maxillofacial surgery.

MAIN OUTCOME MEASURES

(i) The number of cases of fatal and non-fatal PE and the number of diagnosed cases of DVT not progressing to PE. (ii) The frequency of use of mechanical and pharmacological thromboprophylactic measures.

RESULTS

(i) There was a 79% return of questionnaires and from these were reported 60 cases of PE of which 14 were fatal with 64 cases of DVT not progressing to PE. Of the PE group almost 60% followed operations for orocervical malignancy while 25% were related to maxillofacial trauma. 64% of respondents had encountered no episodes of perioperative DVT and 68% no cases of PE. (ii) Mechanical thromboprophylactic measures included the use by 76% of respondents of a graduated compression garment, ripple mattress by 47% and intermittent inter-operative calf pressure by 38.5%. Of pharmacological agents 45% used low dose heparin, 14.5% a dextran infusion and 6% an antiplatelet agent. 58.3% gave advice about smoking and 37.5% recommended temporary discontinuation of the contraceptive pill.

CONCLUSIONS

The incidence of DVT and PE in major maxillofacial surgery is low. Nevertheless it is recommended that there is rigid compliance with the recommendations for surgery in general from the thromboembolic risk factors consensus group (THRIFT) and from similar groups in Europe and the USA.

Low molecular weight versus standard heparin for prevention of venous thromboembolism after major abdominal surgery. The Thromboprophylaxis Collaborative Group

Low-molecular-weight heparin (LMWH) is effective in the prevention of postoperative venous thromboembolism but does it have the safety advantages over standard heparin (SH) that have been claimed? In a multicentre randomised trial in 3809 patients undergoing major abdominal surgery (1894 LMWH, 1915 SH) heparin was given preoperatively and continued for at least 5 postoperative days. Patients were assessed in the postoperative period and were followed up for at least 4 weeks, the emphasis being on safety. Major bleeding events occurred in 69 (3.6%) patients in the LMWH group and 91 (4.8%) patients in the SH group (relative risk 0.77, 95% confidence interval 0.56-1.04; p = 0.10). 93 indices of major bleeding were observed in the 69 LMWH patients and 141 in the SH patients. (p = 0.058). Severe bleeding was less frequent in the LMWH group (1.0% vs 1.9%; p = 0.02), as was wound haematoma (1.4% vs 2.7%; p = 0.007). Bleeding episodes with LMWH were less likely to lead to further surgery to evacuate a haematoma or to control bleeding, and injection site bruising was also less common in the LMWH group. No significant differences were found in the efficacy of the two agents. Perioperative death rates were 3.3% in the LMWH group and 2.5% in the SH group; pulmonary emboli were detected in 0.7% and 0.7%; and deep-vein thrombosis was diagnosed in 0.6% of patients in each group. Follow-up was done on 91% of 3699 evaluable patients. There were 19 further deaths (10 LMWH, 9 SH group) and 25 patients with thromboembolic complications (15 and 10). Of the 3 patients with fatal pulmonary emboli during follow-up 2 had received LMWH and 1 SH. The two drugs were of similar efficacy. The primary end point, the frequency of major bleeding, showed a 23% reduction in the LMWH group, but this difference was not significant. The secondary safety end points revealed that LMWH was significantly better than SH. Fatal pulmonary embolism occurs rarely (0.09%) following discharge from hospital so the cost benefit ratio would not justify prolonged prophylaxis in this setting.

Low molecular weight heparin in prevention of perioperative thrombosis

OBJECTIVE

To determine whether prophylactic treatment with low molecular weight heparin reduces the incidence of thrombosis in patients who have had general or orthopaedic surgery.

DESIGN

Meta-analysis of results from 52 randomised, controlled clinical studies (29 in general surgery and 23 in orthopaedic surgery) in which low molecular weight heparin was compared with placebo, dextran, or unfractionated heparin.

SUBJECTS

Patients who had had general or orthopaedic surgery.

INTERVENTION

Once daily injection of a low molecular weight heparin compared with placebo, dextran, or unfractionated heparin.

MAIN OUTCOME MEASURES

Incidence of deep venous thrombosis, pulmonary embolism, major haemorrhages, and death.

RESULTS

The results confirm that low molecular weight heparins are more efficacious for the prophylactic treatment of deep venous thrombosis than placebo (common odds ratio 0.31, 95% confidence interval 0.22 to 0.43; p < 0.001) and dextran (0.44, 0.30 to 0.65; p < 0.001). The results suggest that low molecular weight heparins are also more efficacious than unfractionated heparin (0.85, 0.74 to 0.97; p = 0.02), with no significant difference in the incidence of major haemorrhages (1.06, 0.93 to 1.20; p = 0.62).

CONCLUSIONS

Low molecular weight heparins seem to have a higher benefit to risk ratio than unfractionated heparin in preventing perioperative thrombosis. However, it remains to be shown in a suitably powered clinical trial whether low molecular weight heparin reduces the risk of fatal pulmonary embolism compared with heparin.

Effect on primary haemostasis of prophylactic regimens of low molecular weight heparin, unfractionated heparin, dextran and their combinations. An animal experimental study

The aim of the study was to determine whether an impairment of the haemostasis could be observed experimentally when thromboprophylactic substances, which act differently on the haemostatic mechanism, were given single or in combination in prophylactic doses. In 36 rabbits we measured the primary haemostatic plug formation time (PHT), rebleedings and total haemostatic plug formation time (THT) after transection of venules and arterioles using an intravital microscope. We combined unfractionated heparin (UH) and low molecular weight heparin (LMWH) in low dose with either dextran 70 or polygeline (placebo volume expander) in a randomized double-dummy set up. In the placebo group (NaCl and polygeline) the median PHT was 55 and 101 seconds for arterioles and venules respectively, which are well-comparable to earlier results from our group. Most prolonged PHT and THT for arterioles were seen for dextran+NaCl, actually less prolongation was seen for UH+dextran. We did not observe any differences, except for a prolongation of THT for venules in rabbits given dextran+NaCl (p less than 0.05). Thus, in thromboprophylactic doses used, there does not seem to be an impaired or additive effect between heparins and dextran 70 in primary haemostasis in rabbits.

Rationale for development of low-molecular-weight heparins and their clinical potential in the prevention of postoperative venous thrombosis

Interest in low-molecular-weight heparins (LMWHs) as potential antithrombotic agents was stimulated by two observations in the mid-1970s and early 1980s. The first was finding that LMWH fractions prepared from unfractionated heparin (UFH) progressively lost their ability to prolong the activated partial thromboplastin time (APTT) while retaining their ability to inhibit Factor Xa. The second was the observation that LMWHs prepared by chemical depolarization of UFH are antithrombotic in experimental animal models but produce less microvascular bleeding in experimental models for an equivalent antithrombotic effect than the UFH from which they are derived. Subsequently, it was shown that LMWHs inhibit platelet function and impair vascular permeability less than standard heparin and that LMWHs have a longer biological half-life than standard heparin. A number of LMWHs have been evaluated in clinical trials in general and orthopedic surgery and in the treatment of venous thrombosis. LMWHs are highly effective in orthopedic surgery, where they appear to be more effective than standard heparin. LMWHs have also been shown to be either as effective or more effective than UFH in preventing postoperative thrombosis following general surgery. In preliminary studies, LMWHs appear to be as effective as standard heparin in the treatment of venous thrombosis, but larger studies are required using clinically relevant outcome measures.

Comparative effects of heparin and LMW heparin on hemostasis

We performed studies to investigate the effect of protamine sulfate neutralization on both the anticoagulant and hemostatic effects of enoxaparin and heparin. Although the anti-Factor Xa effect of enoxaparin was incompletely neutralized by protamine sulfate in an experimental animal model, protamine sulfate reversed bleeding induced by hemorrhagic doses of enoxaparin.

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.

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.

Does protamine chloride neutralize low molecular weight heparin sufficiently?

The heparin neutralizing properties of protamine chloride on conventional heparin (porcine mucosa) and on low molecular weight heparin (Kabi 2165) were studied in vitro. Protamine chloride neutralized 99% of the delaying effect of conventional heparin on the activated partial thromboplastin time, whereas only 70% of the effect of low molecular weight heparin was neutralized. The neutralizing effect of protamine chloride on the inhibition of factor Xa (clot test) was 95% for conventional heparin and 55% for low molecular weight heparin, whereas the effect of both heparin preparations on the thrombin inhibition could be completely neutralized. We conclude that conventional heparin is neutralized more effectively in vitro by protamine chloride than is the low molecular weight heparin. The findings do not exclude that protamine chloride is able to suppress in vivo bleedings caused by low molecular weight heparin.

Heparin/dihydroergotamine for venous thrombosis prophylaxis: comparison of low-dose heparin and low molecular weight heparin in hip surgery

In a prospective, double-blind controlled study we have compared the prophylactic efficacy against deep vein thrombosis of low-dose heparin + dihydroergotamine (A), low molecular weight heparin + dihydroergotamine (B) and placebo (C). A total of three hundred and fifty-six patients undergoing total hip replacement were randomized into three groups and 316 patients were analysed. All thrombi were verified by ascending phlebography. One-third of the patients developed deep vein thrombosis in group A and B, differing significantly from group C. The operative blood loss in group B was higher than that in groups A and C. However, the number of patients transfused and their transfusion requirements did not differ. Severe bleeding occurred in one patient in each group. No deaths were registered during the study. Our study indicates that prophylactic treatment against postoperative deep vein thrombosis with low molecular weight heparin + dihydroergotamine once daily is as effective and safe as conventional low-dose heparin + dihydroergotamine twice daily in patients undergoing total hip replacement. The once-daily regimen has the advantage of better patient acceptance and less nursing time.

Haemodynamic and haematologic alterations with protamine reversal of anticoagulation: comparison of standard heparin and a low molecular weight heparin fragment

Reversal of anticoagulation with protamine sulfate causes many adverse haemodynamic and haematologic effects which could be due to differences in the mechanism of action of standard and low molecular weight heparin. Three groups of dogs were investigated: one group received normal saline pretreatment followed by heparinisation with standard heparin 150 IU/kg followed by protamine sulfate reversal 1.5 mg/kg after aortic interposition grafting: the second group were given normal saline pretreatment followed by heparinisation with low molecular weight heparin 150 U antiXa/kg and after grafting protamine sulfate reversal 1.5 mg/kg. The third group were given protamine sulfate pretreatment 2.25 mg/kg followed by low molecular weight heparin 150 U antiXa/kg and later protamine sulfate reversal 1.5 mg/kg after grafting. The same haemodynamic changes were seen regardless of the type of heparin or pretreatment with protamine given along with low molecular weight heparin. There was a suggestion that regular heparin cause a more pronounced increase in pulmonary artery pressure and a decrease in heart rate. On the other hand the systemic hypotension and reduction of cardiac output seemed more pronounced in the low molecular weight heparin group. Platelet count decreased less in the low molecular weight heparin group, but white blood cell count was equally reduced. Pretreatment with protamine did not abolish the adverse effects of protamine when reversing anticoagulation achieved with low molecular weight heparin, a finding not shared with standard heparin-protamine interactions.

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.

Low molecular weight heparin (KABI 2165, Fragmin): pharmacokinetics after intravenous and subcutaneous administration in human volunteers

The pharmacokinetics of a low molecular weight heparin (LMWH) with a mean mw of 4000-6000 D (KABI 2165, Fragmin) was studied in 6 healthy volunteers after intravenous (iv) and subcutaneous (sc) administration of 120 U (anti FXa)/kg. The half-life in plasma of the anti FXa activity after iv injection was 119 +/- 17 min, the volume of distribution (Vd) 3.4 +/- 0.5 1 and the total clearence 20.5 +/- 2.5 ml/min. The maximal anti FXa activity determined 3 min after iv bolus injection amounted to 2.2 +/- 0.3 U (anti FXa)/ml with a corresponding increase of the APTT from 31 +/- 7 sec to 113 +/- 35 sec. The elimination of the anti FXa activity was a monoexponential first order process. After sc administration the plasma half-life of the anti FXa activity was longer than after iv injection, 228 +/- 40 min, corresponding to the absorption rate thus found to be the rate limiting step. After sc administration the peak was reached after 4 hours (0.6 +/- 0.1 U (anti FXa)/ml; APTT increase 5 sec). The bioavailability after sc injection was calculated to be 87 +/- 6%. As a consequence of the high bioavailability and long T1/2 of the anti FXa activity, Fragmin administered sc seems to induce adequate levels of heparin-like activity making this regimen worth further investigation as an alternative for the treatment of deep venous thrombosis.

Low molecular weight heparin once daily compared with conventional low-dose heparin twice daily. A prospective double-blind multicentre trial on prevention of postoperative thrombosis

In a randomized, prospective, double-blind multicentre trial, the effect of conventional low-dose heparin 5000 units twice daily, was compared with that of a low molecular weight heparin fragment (4000-5000) 5000 anti-factor Xa units once daily. Four hundred and thirty-two patients fulfilled the inclusion criteria and were analysed for development of deep vein thrombosis (125I-labelled fibrinogen test) and haemorrhagic complications. Thrombosis occurred in a 4.3 per cent of patients in the low-dose heparin group and in 6.4 per cent of patients in the heparin fragment group, a difference which is not significant. There was a significant delay in the onset of thrombosis in the heparin fragment group. Mortality did not differ between the groups, nor did peroperative blood loss or transfusion requirements or infectious complications. Haemorrhagic complications occurred significantly more often in the fragment group (11.6 per cent) than in the conventional heparin group (4.6 per cent). Patients in the heparin fragment group experienced local pain following the subcutaneous injection significantly less often.

[Severe thrombopenia associated with treatment with pentosan polysulfate]

Two cases of severe thrombocytopaenia associated with acute thrombo-embolic manifestations during treatment by pentosan polysulphate, a low molecular weight heparinoid, are reported. Plasma samples from both patients caused in vitro aggregation in the presence of pentosan polysulphate. Interruption of the drug led to the recovery of the platelet count. The hypothesis of an immunoallergic mechanism similar to heparin associated thrombocytopaenia is supported. Furthermore, it seemed likely to be found with all the polysulphated X glycosaminoglycans. During treatment by pentosan polysulphate, platelet count should be monitored to avoid this potentially life-threatening syndrome.

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.

Quantitative analysis of a polysulfated xylan (SP54) in urine using gas-liquid chromatography

A sensitive analytical method for the quantitation of a polysulfated xylan (SP54) in urine has been developed. SP54 and urinary glycosaminoglycans have been isolated from urine using cetylpyridinium chloride. This method removes all glycosaminoglycans with molecular weights less than 3000 Da. Following isolation, SP54 and urinary glycosaminoglycans have been selectively hydrolyzed under conditions (0.5 M HCl/105 degrees C/30 min) which produce an efficient yield of xylose from SP54 but not from the glycosaminoglycans. Xylose derived from SP54 has subsequently been determined using gas-liquid chromatography. Levels of SP54 down to 10 micrograms/ml have been determined using this technique.

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

The effect of heparin fragments of different molecular weights has been compared with that of conventional sodium heparin on experimental thrombosis in vivo and ex vivo and experimental haemostasis in vivo. In the first part of the study fragments of different molecular weights were given (4,900, 6,500, 9,500 and 22,200 dalton). All preparations including the control gave a significant prolongation of the haemostatic plug formation time in the rabbit mesenteric microcirculation, and all except the fragment with the lowest molecular weight reduced the frequency of jugular vein thrombosis (induced by a combination of endothelial denudation and stasis). There was a correlation between the XaI activity of the different heparin fragments and frequency of thrombosis. Using an ex vivo method (modification of Chandler's model) a dose dependent lag phase until start of thrombus formation was found. In the second part of the study a dose response investigation was made comparing different doses of a fragment (6,500 dalton) with conventional heparin in the same XaI doses (10, 30 and 60 units/kg). Sodium heparin in the highest dose prolonged the haemostatic plug formation time whereas none of the fragment doses did. The lowest dose both of the fragment and conventional heparin did not reduce the frequency of thrombosis, whereas the two higher doses did. Thus it may be possible to obtain preventive effect on thrombus formation with a heparin fragment.

The influence of a new low molecular weight sulphated polysaccharide from mussel broth (Org 30016) on haemostasis

The effect on haemostasis of a new low molecular weight sulphated polysaccharide (4300 dalton) from mussel broth (Org 30016) was investigated. In an APT time test system it had an anticoagulant effect corresponding to 30-40% of that of heparin. It had no antithrombin effect. It exerted its effect only in test systems containing phospholipids. It did not prolong haemostatic plug formation time in the rabbit mesenteric microcirculation as did heparin. Formation of ex vivo Chandler thrombi was significantly inhibited. The practical interest of the substance comes from the combination of an antithrombotic effect and little influence on primary haemostasis.

In vitro evaluation of a biologic graft surface. Effect of treatment with conventional and low molecular weight (LMW) heparin

Human umbilical vein grafts were treated with either conventional or LMW heparin, followed by exposure to alcohol. The grafts were investigated for their ability to adsorb and inactivate thrombin, and comparison was made with non-heparinized and saline-alcohol treated grafts and grafts supplied with a covalently bonded layer of conventional heparin. In addition, the effect of protamine exposure to heparin-alcohol and LMW heparin-alcohol treated grafts as well as native human umbilical veins (HUV) was studied. Native HUV and heparin treated graft surfaces adsorbed and inactivated thrombin, whereas non-heparinized and saline-alcohol treated grafts inactivated surface-bound thrombin to only a small degree. Surface-bound LMW heparin exhibited a significantly lower ability to inactivate thrombin as compared with conventional heparin, but LMW heparin-alcohol surfaces were better than non-heparinized ones. Protamine treatment of "heparinized" surfaces impaired the thrombin inhibiting ability of the heparin-alcohol surface, whereas this property was totally abolished for the LMW heparin-alcohol surface. The findings indicate that LMW heparin, despite its weaker thrombin inhibiting capacity, may be an alternative to conventional heparin, for "heparinizing" the human umbilical vein graft. Protamine exposure may be potentially harmful for a heparin treated surface, although protamine concentrations used in the present in vitro study may not be reached in vivo. The native HUV was not at all affected by protamine exposure regarding its ability to inactivate thrombin.

The effect of sodium hyaluronate and sodium chondroitin sulfate on the coagulation system in vitro

Healon (sodium hyaluronate) and sodium chondroitin sulfate (CDS) are injected in the ocular cavities in a variety of operations, mainly intraocular lens (IOL) implantation. Both Healon and CDS are structurally similar to heparin. We found that like heparin CDS has an inhibiting action on blood coagulation in vitro. The inhibiting activity is of the antithrombin type. Healon does not possess anticoagulant activity. Since the anticoagulant effect of sodium chondroitin sulfate is observable at concentrations likely to occur in vivo the substance may impair ocular hemostasis.

Anticoagulant effects of two types of low molecular weight heparin administered subcutaneously

Two types of LMW heparin were prepared by gel filtration of standard heparin (LMW fraction) and by degradation of heparin by nitrous acid (LMW fragment), respectively. The effects on factor Xa inhibition (XaI), APTT, platelet aggregation and AT III level of these preparations were studied after subcutaneous administration to humans and compared with those of standard heparin. At a dose of 5000 IU (XaI) the LMW fraction and LMW fragment induced peak plasma XaI activity of 0.32 IU/ml and 0.41 IU/ml respectively, compared to 0.07 IU/ml for heparin. Still 11.5 h after administration both LMW preparations gave higher activities than heparin ever induced. Following administration of 10,000 IU (XaI) of the LMW fragment the plasma peak XaI activity was 0.81 IU/ml. This prolonged the APTT from 36 sec to 46 sec only. The half-lives of the XaI activity in plasma were between 3 and 4 hours. No effect on platelet aggregation or AT-III level was demonstrated.