SummaryDermatan sulphate (MF 701) is a natural glycosaminoglycan that catalyses thrombin inhibition by heparin cofactor II. The aim of the study was to evaluate the efficacy and safety of MF 701 for prevention of deep vein thrombosis (DVT) in patients with hip fracture. A randomised, double-blind, placebo-controlled design was used to assess two dose regimens of MF 701 in two consecutive study phases. Treatment was started within 48 h from the trauma and continued for 14 days for non-operated patients or until the 10th postoperative day. Bilateral mandatory venography was used to assess the end-point. Eighty patients were included in the first phase (40 MF 701, 40 placebo). MF 701, 100 mg IM b. i. d., did not reduce incidence of DVT from that on placebo and did not induce any bleeding. In the second phase 126 patients were included, with a randomisation ratio of 2:1 (84 MF 701, 300 mg IM b.i.d., 42 placebo). Bilateral venography was obtained for 110 patients. The incidence of DVT was 64% (23/36) in the placebo group and 38% (28/74) in the MF 701 group (p = 0.01; odds ratio [OR] = 0.34, 95% confidence limits [CL] = 0.15-0.80); proximal DVTs were 42% (15/36) and 20% (15/74), respectively (p = 0.02; OR = 0.36, CL = 0.15-0.89). No significant differences were found in haemorrhagic complications (2.4% in each group), blood loss from drains, blood transfusions, haemoglobin and haematocrit values. This study is the first demonstration that dermatan sulphate is a clinically effective antithrombotic agent without bleeding effects. It also provides evidence of the biological role of heparin cofactor II.

Thrombus extension in patients with venous thromboembolism is due to the accretion of fibrin onto existing thrombi. Extension is promoted by both circulating and thrombus-bound thrombin, which convert fibrinogen to fibrin. Heparin is an effective antithrombotic agent, but it requires continuous administration to achieve persistent inhibition of thrombus extension. Heparin is highly effective in inhibiting fluid phase thrombin, but is a relatively ineffective inhibitor of thrombus- bound thrombin. Hirudin, unlike heparin, inactivates both circulating and fibrin-bound thrombin and, therefore, has the potential to prevent thrombus extension even after a short course of treatment. The aim of this study was to evaluate the time course of the accretion of new fibrin onto preexisting rabbit jugular vein thrombi after a 3-hour infusion of saline, heparin, and hirudin. Heparin and recombinant (r)- hirudin (CGP 39399) were infused at doses that doubled the activated partial thromboplastin time (aPTT). At the end of the 3-hour infusions in rabbits treated with saline, heparin (0.75 mg/kg), or r-hirudin (1.25 mg/kg), accretion of 125I-fibrinogen was 59 +/- 5 micrograms, 34 +/- 4 micrograms, and 21 +/- 2 micrograms, respectively (heparin and r- hirudin v saline, P less than .01; r-hirudin v heparin, P less than .01). Three hours after the end of the infusions, the accreted 125I- fibrinogen in the saline-, heparin-, and hirudin-treated animals was 89 +/- 6 micrograms, 51 +/- 7 micrograms, and 23 +/- 3 micrograms, respectively; 9 hours after the end of the infusions, the accreted 125I- fibrinogen was 112 +/- 9 micrograms, 82 +/- 7 micrograms, and 25 +/- 3 micrograms, respectively. aPTT and thrombin clotting time (TCT) returned to the baseline value 90 minutes after the end of heparin or r- hirudin infusion. During in vitro experiments, human fibrin clots previously incubated in human plasma containing r-hirudin did not promote fibrinopeptide A (FPA) generation when washed and then incubated in human plasma in the absence of thrombin inhibitors. This persistent inhibition of FPA production was not observed after incubation in human plasma of human plasma clots preincubated with heparin. We conclude that heparin is effective in inhibiting thrombus extension while it is present in the circulation, but that this effect is rapidly lost after its plasma clearance. In contrast, the antithrombotic activity of r-hirudin is sustained beyond its plasma clearance, presumably because of its ability to inactivate thrombus- bound thrombin. Our findings indicate that r-hirudin might be an effective antithrombotic agent even when used for short periods.

Our results provide an explanation for the effectiveness of LMWHs administered either once or twice daily. High and sustained plasma antithrombin activity is achieved when LMWHs are administered in therapeutic doses used in contemporary trials with only a moderate prolongation of the aPTT.

SummaryThe pharmacokinetics and haemostatic effects of MF 701 dermatan sulfate (DS) administered by i. v. infusion were studied in 11 healthy volunteers. Each subject received 0.6 mg kg-1 h-1 MF 701 for 10 h. DS plasma concentrations were measured by a chromogenic assay based on the catalysis of thrombin inhibition by HCII. DS plasma levels followed a single compartment pharmacokinetic model, with a half-life of 1.28 ± 0.46 h, a plasma clearance of 2.75 ± 0.46 1/h and a volume of distribution of 4.92 ± 1.36 1 (means ± SD). Steady-state was reached 3 to 6 h after infusion started. The maximal DS plasma concentration was 16.4 ± 5.7 μg/ml. Maximal APTT prolongation over pre-infusion values was 42 ± 7%; TCT performed with bovine and human thrombin was prolonged by 16 ± 7% and 83 ± 35% respectively. No anti-IIa or anti-Xa activities were detected by chromogenic tests. The treatment was well tolerated. The pharmacokinetics of MF 701 infusion are consistent with those previously described after i. v. bolus administration. The infusion of MF 701 allows fast achievement and steady maintenance of elevated DS plasma concentrations.

Thrombus extension in patients with venous thromboembolism is due to the accretion of fibrin onto existing thrombi. Extension is promoted by both circulating and thrombus-bound thrombin, which convert fibrinogen to fibrin. Heparin is an effective antithrombotic agent, but it requires continuous administration to achieve persistent inhibition of thrombus extension. Heparin is highly effective in inhibiting fluid phase thrombin, but is a relatively ineffective inhibitor of thrombus- bound thrombin. Hirudin, unlike heparin, inactivates both circulating and fibrin-bound thrombin and, therefore, has the potential to prevent thrombus extension even after a short course of treatment. The aim of this study was to evaluate the time course of the accretion of new fibrin onto preexisting rabbit jugular vein thrombi after a 3-hour infusion of saline, heparin, and hirudin. Heparin and recombinant (r)- hirudin (CGP 39399) were infused at doses that doubled the activated partial thromboplastin time (aPTT). At the end of the 3-hour infusions in rabbits treated with saline, heparin (0.75 mg/kg), or r-hirudin (1.25 mg/kg), accretion of 125I-fibrinogen was 59 +/- 5 micrograms, 34 +/- 4 micrograms, and 21 +/- 2 micrograms, respectively (heparin and r- hirudin v saline, P less than .01; r-hirudin v heparin, P less than .01). Three hours after the end of the infusions, the accreted 125I- fibrinogen in the saline-, heparin-, and hirudin-treated animals was 89 +/- 6 micrograms, 51 +/- 7 micrograms, and 23 +/- 3 micrograms, respectively; 9 hours after the end of the infusions, the accreted 125I- fibrinogen was 112 +/- 9 micrograms, 82 +/- 7 micrograms, and 25 +/- 3 micrograms, respectively. aPTT and thrombin clotting time (TCT) returned to the baseline value 90 minutes after the end of heparin or r- hirudin infusion. During in vitro experiments, human fibrin clots previously incubated in human plasma containing r-hirudin did not promote fibrinopeptide A (FPA) generation when washed and then incubated in human plasma in the absence of thrombin inhibitors. This persistent inhibition of FPA production was not observed after incubation in human plasma of human plasma clots preincubated with heparin. We conclude that heparin is effective in inhibiting thrombus extension while it is present in the circulation, but that this effect is rapidly lost after its plasma clearance. In contrast, the antithrombotic activity of r-hirudin is sustained beyond its plasma clearance, presumably because of its ability to inactivate thrombus- bound thrombin. Our findings indicate that r-hirudin might be an effective antithrombotic agent even when used for short periods.