Venous thromboembolism remains the greatest single threat to life during the extended postoperative period after total hip arthroplasty.1 Several prophylactic measures are currently used, including elastic stockings and intermittent pneumatic compression to reduce stasis, and aspirin or various forms of anticoagulation to counteractact hypercoagulability. Evidence for the effectiveness of these different forms of prophylaxis varies from large multicentre trials in thousands of patients to small single centre studies, and there is no clear consensus on the best form of prophylaxis. Thrombosis is less likely if venous stasis is minimised, and this is the rationale for the use of elastic support stockings and raising the foot of the bed. These passive measures have been used for years, and, though they help prevent venous thromboembolism, they are not sufficiently effective on their own after major joint replacement. Nevertheless, intermittent pneumatic compression of the legs in 500 patients undergoing hip replacement reduced the overall rate of deep vein thrombosis to 5%, with a 1% incidence of pulmonary embolism.2 This compares favourably with a 50% incidence of deep vein thrombosis in patients given no prophylaxis.3 The efficacy …

International standards are used to assess the potency of a variety of biological drugs employed in the field of haemostasis and thrombosis. These include therapeutic concentrates for the treatment of inherited coagulation defects, such as haemophilia, thrombolytic drugs such as streptokinase for the treatment of heart attacks, and anticoagulant drugs such as heparin. Some of these standards have existed for over 25 years, and they continue to play a vital role in ensuring consistent potency, and hence safety, of manufactured drugs. The growing complexity of new products, particularly in the area of recombinant technology, represents a continuing challenge for the field of biological standardization.

The effect of systemic interleukin-1 (IL-1) on venous endothelium in the presence and absence of stasis has been studied by scanning electron microscopy (SEM). Recombinant human IL-1 beta at a concentration of 1 micrograms/kg or saline was injected intravenously into rabbits and allowed to circulate for 0.5 or 4.0 h after which complete stasis was induced for 1 h in an isolated segment of each jugular vein. One vein segment was then excised and the contents examined macroscopically for thrombi, while the other segment was fixed for SEM examination. When examined by SEM the endothelium from rabbits injected with IL-1 beta was perturbed with increased surface microvilli, blebs and gaps at cell junctions when compared with saline controls. Fibrin deposition was also observed after IL-1 beta, as was the adherence of essentially non-activated platelets to intact endothelium. However, macroscopic thrombi were not formed in isolated vein segments. We conclude that although fibrin strands and platelets were deposited on the endothelium, IL-1 is not a sufficiently powerful procoagulant stimulus to lead to an occlusive thrombus in acute experiments.

The in vitro anticoagulant activities of recombinant desulphatohirudin (r-hirudin) were studied in the activated partial thromboplastin time (APTT) and the thrombin generation test systems. In the APTT, at concentrations below 5 micrograms/ml, r-hirudin showed a dose-response curve. At concentrations above 5 micrograms/ml, the plasma became unclottable, but in the thrombin generation test, at least 10 micrograms/ml of r-hirudin was required for full inhibition of thrombin generation. The antithrombotic effect was assessed using a rabbit venous stasis model; 150 micrograms/kg r-hirudin completely prevented thrombus formation at 10 and 20 min stasis. At this full antithrombotic dose, the mean bleeding time ratio measured in a rabbit ear template model, was not prolonged over control values. At higher doses, the bleeding time ratios were higher than those observed for the same dosage of heparin. These data indicate that while r-hirudin is an effective antithrombotic agent, antithrombotic doses have to be carefully titrated to avoid excessive bleeding.

Cette revue resume les difficultes qui s'opposent a l'etablissement d'un standard biologique de reference. Un nouveau standard Heparine de faible poids moleculaire (LMWH) a ete etabli. Ce produit assigne un unitage de 1,68 UI par test anti Xa et 665 par test anti IIa. 3 objections se sont opposees a ce standard. Plusieurs LMWH sont commercialisees et chaque firme definit ses propres unites. Heureusement les caracteristiques communes aux differentes LMWH sont plus sures que leurs differences

SummaryWe have examined the effect in impairing thrombus formation of a preparation of dermatan sulphate (DS) alone and DS plus small amounts of unfractionated heparin (UFH). In rabbits given a dose of 150 μg/kg of DS alone, there was minimal reduction in serum-induced stasis thrombosis (Wessler model), with an overall score of 92.5% (100% = no impairment of thrombus formation). When the same dose of DS containing UFH was given (two different subgroups given DS containing 0.25 and 2.5% heparin by dry weight, respectively), the overall thrombus score was reduced to 60% (P <0.003), with no significant difference between the two subgroups. To achieve a comparable result with DS alone, a dose of 1 mg/kg was required. We conclude that very small amounts of UFH significantly enhance the antithrombotic action of DS, by a mechanism that has yet to be determined.

Annals of the New York Academy of SciencesVolume 556, Issue 1 p. 132-145 Anticoagulant Activities of Heparin and Fragments T. W. BARROWCLIFFE, T. W. BARROWCLIFFE National Institute for Biological Standards and Control Potters Bar, Hertfordshire EN6 3QG, United KingdomSearch for more papers by this authorD. P. THOMAS, D. P. THOMAS National Institute for Biological Standards and Control Potters Bar, Hertfordshire EN6 3QG, United KingdomSearch for more papers by this author T. W. BARROWCLIFFE, T. W. BARROWCLIFFE National Institute for Biological Standards and Control Potters Bar, Hertfordshire EN6 3QG, United KingdomSearch for more papers by this authorD. P. THOMAS, D. P. THOMAS National Institute for Biological Standards and Control Potters Bar, Hertfordshire EN6 3QG, United KingdomSearch for more papers by this author First published: June 1989 https://doi.org/10.1111/j.1749-6632.1989.tb22497.xCitations: 5AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume556, Issue1Heparin and Related Polysaccharides: Structure and ActivitiesJune 1989Pages 132-145 RelatedInformation

The antithrombotic efficacy of unfractionated heparin (UFH), a low molecular weight heparin (LMWH) and a synthetic pentasaccharide (PENTA) has been compared in an animal model for stasis thrombosis. We have also compared the relative ability of these three agents to impair thrombin generation in vitro and in vivo, and measured their effects on anti-Xa activity and thrombin clotting times. UFH, LMWH and PENTA all had the capacity to impair thrombogenesis, although there were marked differences in their relative effectiveness. Reduction of thrombin generation to 20% of control values was closely correlated with the prevention of thrombosis after 20 minutes' stasis, but this was only achieved with UFH. The same dry weight dose of LMWH or PENTA reduced thrombin generation to about half control values, and neither significantly impaired thrombus formation after 20 minutes' stasis. Impaired thrombin generation correlated better than anti-Xa activity with prevention of stasis thrombosis. In this model, UFH was clearly superior to LMWH and PENTA as an antithrombotic agent.

In a standardized animal model, unfractionated heparin (UFH) prevents venous thrombogenesis at a dose of 80 micrograms/kg. Oligosaccharide fragments of heparin, with very high anti-Xa activity both in vitro and in ex vivo plasma samples were less effective than UFH in preventing thrombosis. A decasaccharide fragment was virtually inactive in impairing thrombosis at this dose, although a 20-22 monosaccharide fragment showed some impairment. Dermatan sulfate, which has no anti-factor Xa activity, partially impairs both thrombin generation and stasis thrombosis. However, dermatan sulfate could not suppress thrombin generation below about 35% of control at the doses studied. Neither oligosaccharides nor dermatan sulfate were as effective on a weight basis as UFH in impairing thrombosis, particularly after 20 minutes' stasus. Maximal antithrombotic effects are achieved when both factor Xa and thrombin are inhibited. Drugs which act primarily on factor Xa (oligosaccharides) or thrombin by non-ATIII pathways (dermatan sulfate) are less efficient than UFH as antithrombotic drugs.

For many years the anticoagulant activity of heparin has been estimated by coagulation assays, in which the prolongation of clotting times by heparin is measured under various conditions. More recently, assays have been developed which measure the inhibitory action of heparin on isolated coagulation enzymes, notably Factor Xa and thrombin, using specific amidolytic peptide substrates.

The effects of four sulphated polysaccharides on bleeding time and lipase release in rabbits have been compared. Unfractionated heparin (UFH) and pentosan polysulphate both gave significant prolongation of bleeding times and high lipase release. Low molecular weight heparin had reduced effects on bleeding time and lipase release, while dermatan sulphate had no influence on either parameter. There was a highly significant correlation (r = 0.97) between these two measurements. These results suggest that the same structural features influence both the haemorrhagic and lipase-releasing properties of sulphated polysaccharides.

British Journal of HaematologyVolume 70, Issue 4 p. 393-395 REDUCING THE RISK OF VIRUS TRANSMISSION BY BLOOD PRODUCTS Duncan P. Thomas, Corresponding Author Duncan P. Thomas National Institute for Biological Standards and Control, Potters Bar, Herts.Dr Duncan P. Thomas, National Institute for Biological Standards and Control, Potters Bar, Herts. EN6 3QG.Search for more papers by this author Duncan P. Thomas, Corresponding Author Duncan P. Thomas National Institute for Biological Standards and Control, Potters Bar, Herts.Dr Duncan P. Thomas, National Institute for Biological Standards and Control, Potters Bar, Herts. EN6 3QG.Search for more papers by this author First published: December 1988 https://doi.org/10.1111/j.1365-2141.1988.00393.xCitations: 6AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume70, Issue4December 1988Pages 393-395 RelatedInformation

In the pathogenesis of venous thrombosis, stasis is essentially a permissive factor, allowing the normal defense mechanisms of the body to be circumvented. Although a platelet monolayer is an insufficient stimulus for fibrin formation, even in the presence of stasis, trace amounts of an activated clotting factor are highly thrombogenic in an area of retarded blood flow. The available clinical and experimental data suggest that, if thrombin generation is reduced, the great majority of venous thrombi are prevented.

Measurement of the in vitro anticoagulant activities of low molecular weight (LMW) heparins against an unfractionated heparin (UFH) standard has given problems of non-parallel assays, wide variability between laboratories and differences between methods. These problems have been largely overcome by establishment of a new LMW heparin standard against which other LMW heparin can be compared. The LMW heparin standard is calibrated with two separate potencies, one for anti-Xa and the other for thrombin inhibition assays. Animal studies have shown a correlation between the anti Xa and antithrombotic activities of several LMW heparins but, below a M.Wt. of approximately 4,000, this correlation breaks down. This may be partly due to the method of measurement of anti-Xa activity and partly due to the inability of very LMW fragments to potentiate thrombin inhibition, which has recently been shown to be an important component of antithrombotic action. However, substances with either anti-Xa activity alone or thrombin inhibitory capacity alone are less effective antithrombotic agents than heparin. Several studies in animals have shown that LMW heparins give less enhancement of bleeding than UFH, but this does not seem to be due to their anticoagulant effects and may be related to their relative effects on platelets.

SummaryIn this study, the anticoagulant and antithrombotic properties of unfractionated heparin (UFH) and dermatan sulphate (DS) were compared. The ability of UFH and DS to impair thrombin generation in vitro and in ex vivo plasma samples was also studied. DS has minimal anticoagulant activity by conventional assays but impairs thrombin generation both in vitro and in ex vivo plasma samples. However, thrombin generation could not be suppressed below about 35% of control values at all doses of DS studied. While this was sufficient to impair experimental venous thrombosis during 10 minutes’ stasis, DS was ineffective in preventing thrombosis following 20 minutes’ stasis in doses up to 1.25 mg/kg. In contrast, 1 μg/ml of UFH completely suppressed thrombin generation in vitro, and 150 μg/kg prevented throm- bogenesis over a period of 20 minutes’ stasis. Neither drug prolonged the bleeding time (BT) at effective antithrombotic doses, but 2.5 mg/kg UFH significantly increased the BT, whereas DS did not. While DS has antithrombotic activity, it is less effective than UFH in inhibiting thrombin generation, and as an antithrombotic agent.

Dermatan sulphate (DS) has been shown to accelerate thrcmbin inhibition by its action on heparin cofactor II (HCII) but has no effect on anti thrombin III (Tollefson et al., 1983). In this study, we have examined the in vitro anticoagulant effect of a purified preparation of DS (free from heparin and heparan sulphate), m comparison with that of unfractionated heparin (UEH). We have also studied the effect of DS and UEH in preventing experimental venous thrombosis in rabbits and in inhibiting thrombin generation, both in vitro and in ex vivo plasma samples.Dermatan had low activity in vitro by APTT and anti-Xa assays (< 5 iu/ mg). When thrombin generation was measured in vitro, 1 μg/ml UEH was sufficient to inhibit thrombin formation. Although 1 μg/ml DS reduced thrombin generation to 40% of control values, there was no further reduction when the concentration of DS was increased to 8 μg/ml.When DS was injected into rabbits (n = 10), a dose of 150 μg/kg inpaired thrombogenesis m a Wessler stasis model. The mean thrombus score was reduced to 25% of the control values, although thrombosis could not be completely prevented, even after an eight-fold increase m dose (1250 μg/kg). When the duration of stasis was extended from 10 to 20 minutes, there was no impairment of thrombosis (mean thrombus score 100%) following 1250 μg/kg of DS. Thrombin generation measured in ex vivo plasma after 150 μg/kg of DS was 72% (s.e.m. 63-81) of that measured in pre-injection plasma. In contrast, 150 μg/kg of heparin prevented thrombosis after both 10 and 20 minutes stasis (mean score 0%) and thrombin generation was reduced to 17% (s.e.m. 12-23) of control values m ex vivo plasma samples.Unlike heparin, DS does not completely abolish thrcmbin generation in vitro and is not as potent as UEH in inhibiting thrombin generation m ex vivo plasma. While DS has demonstrable antithrombotic activity under defined conditions, it is less effective than heparin and increasing doses of DS do not improve antithrombotic effectiveness in this model.