Selective inhibition by a synthetic hirudin peptide of fibrin-dependent thrombosis in baboons.

To determine the importance of the thrombin substrate recognition exosite for fibrinogen binding in the formation of both arterial and venous thrombi, we evaluated the antithrombotic effects of the tyrosine-sulfated dodecapeptide from residues 53-64 of hirudin (H peptide) in a nonhuman primate model. This peptide was studied because it inhibits thrombin cleavages of fibrinogen by simple competition without blocking enzyme catalytic-site function. When an exteriorized arteriovenous access shunt model was used in baboons (Papio anubis), thrombus formation was induced by placing a thrombogenic device made of (i) a segment of tubing coated covalently with type I collagen, which generated platelet-rich thrombi under arterial flow conditions, and (ii) two subsequent annular regions of flow expansion that produced fibrin-rich thrombi typically associated with venous valves and veins. Thrombus formation was quantified by measurements of 111In-labeled platelet and 125I-labeled fibrinogen deposition in both arterial-flow and venous-flow portions of the device. Continuous infusion of H peptide (0.5, 15, and 75 mg/kg) proximal to the device for 40 min interrupted, in a dose-response fashion, formation of fibrin-rich thrombus in the regions of disturbed flow and generation of fibrinopeptide A. In contrast, H peptide did not inhibit the capacity of platelets to deposit on the collagen surface (P greater than 0.2 at all doses) or to form hemostatic plugs (as assessed by measurements of bleeding time; P greater than 0.1 at all doses). These findings suggest that, by competitive inhibition of fibrinogen binding to thrombin, fibrin-rich venous-type thrombus formation may be selectively prevented. This strategy may be therapeutically attractive for preserving normal platelet function when conventional anticoagulant therapy is contraindicated.     

Pharmacology of recombinant hirudin

Hirudin is the anticoagulative product of the salivary glands of the medical leech Hirudo medicinalis. It is characterized by a direct, bifunctional inhibition mechanism and a high, exclusive specificity and a strong ability to bind to thrombin (tight binding). Further characteristics are the organic-chemical structure of hirudin (peptide), which allows only parenteral administration; the missing metabolism in the organism; and the exclusive glomerular filtration of hirudin in kidneys as the effective elimination mechanism. Recombinant hirudin (r-hirudin) is a product of genetic engineering that is identical to the hirudin found in nature and has the same biochemical and pharmacological characteristics as natural hirudin.     

Immunologic response to recombinant hirudin in HIT type II patients during long-term treatment

We prospectively investigated 27 patients with heparin-induced thrombocytopenia (HIT) type II who were subsequently treated with r-hirudin. Patients with venous or arterial thromboembolism were treated with activated partial thromboplastin time (aPTT)-controlled intravenous r-hirudin (n = 19; mean 19.3 d) followed by subcutaneous r-hirudin (n = 6; mean 22.5 d) and oral anticoagulation. Patients without thromboembolism were treated with subcutaneous r-hirudin (n = 8; mean 25.9 d). Four patients were readmitted to subcutaneous r-hirudin for a mean duration of 32 d. The incidence of r-hirudin antibodies was 84% for intravenously treated patients and 50% in subcutaneously treated patients. The patients (n = 27) showed a 74% overall incidence of r-hirudin antibodies, mainly of the IgG-subclass, without seroconversion before day 6 and after day 32 of r-hirudin treatment or during r-hirudin treatment. None of the patients showed onset or recurrence of venous or arterial thromboembolism, systemic allergic reactions or IgE-antibody development. During intravenous and subcutaneous administration of r-hirudin the aPTT and the ecarin clotting time was increased in the antibody-positive patients compared to antibody-negative patients. Therefore we assume that r-hirudin antibodies may reduce r-hirudin metabolism.     

Production and evaluation of recombinant hirudin

Hirudin, a 65 amino acid polypeptide form the medicinal leech, is an extremely efficient and specific thrombin inhibitor whose therapeutic potential has been demonstrated in a number of animal models. We have developed protocols for the production of recombinant hirudin by secretion from S. cerevisiae and carried out a full biologic evaluation of the purified product. These studies showed that natural and recombinant hirudin was similar in structure and in biologic function in vitro. Moreover, the recombinant protein displayed strong antithrombotic activity in several experimental thrombosis models in vivo, confirming the molecule's promise in the therapy of thrombotic disorders.     

Use of recombinant hirudin in heparin-induced thrombocytopenia and thrombosis (HITT) and renal failure--a case report

Treatment of critically ill patients who have heparin-induced thrombocytopenia and thrombosis (HITT) and also renal failure is a challenge. Recombinant hirudin (Refludan, Hoechst Marion Roussel) is a direct thrombin inhibitor indicated for anticoagulation in HITT and approved by the United States Food and Drug Administration. Because this drug is renally cleared, a single dose of hirudin may induce prolonged (up to one week) unpredictable anticoagulation in patients with renal insufficiency. There are a few case reports of patients with renal failure and suspected heparin-induced thrombocytopenia (HIT) in which patients were anticoagulated with Refludan for catheter thrombosis. There is no literature on the therapeutic use of Refludan to treat HITT in patients with diffuse thrombosis and renal failure. The authors report the case of a 44-year-old female dialysis patient with HITT and extensive life-threatening thrombosis. The patient developed common iliac vein occlusion extending to the right atrium with progressive right internal jugular vein thrombus developing while on heparin. Her platelet count dropped to 60,000/microL. She was lethargic and hemodynamically unstable. Refludan was initially given as a bolus of 0.2 mg/kg (total, 12 mg) at a 50% dose reduction based on the patient's ideal body weight. This dose was based on the published pharmacokinetics of Refludan in patients with renal failure. Only 2 additional boluses of 6 mg and 3 mg were needed to extend the duration of therapeutic anticoagulation (measured by PTT) to 140 hours. The patient improved both clinically and radiographically after the treatment with Refludan. There were no additional thromboembolic events or bleeding complications. The platelets returned to normal within a few days. The patient was transitioned to coumadin and discharged from the hospital. She remains stable at 1-year follow-up.     

The use of intravenous recombinant hirudin in the treatment of deep vein thrombosis in a patient with an acute heparin allergy

We report a case in which intravenous heparin, given for the treatment of acute deep vein thrombosis, precipitated an acute allergic reaction, and an alternative anticoagulant, recombinant hirudin, provided rapid and successful therapeutic intervention.     

Short- and long-term results after thrombolytic treatment of deep venous thrombosis

OBJECTIVES: The goal of this study was to assess the short- and long-term efficacy of different thrombolytic therapy regimens in patients with leg or pelvic deep venous thrombosis (DVT). BACKGROUND: It is unclear whether locoregional or systemic thrombolysis is superior in treating acute leg DVT or even whether lysis is more effective than anticoagulation therapy in preventing postthrombotic syndrome. METHODS: A total of 250 patients averaging 40 years of age with acute DVT were randomized into five groups to receive full heparinization (1,000 IU/h) and compression treatment, with four groups also administered locoregional tissue plasminogen activator (20 mg/day) or urokinase (100,000 IU/day) or systemic streptokinase (3,000,000 IU daily) or urokinase (5,000,000 IU daily). All groups then received anticoagulation and compression treatment for one year. Primary efficacy criteria included the change after one year in the number of closed vein segments and the occurrence of postthrombotic syndrome. RESULTS: Systemic thrombolytic therapy significantly reduced the number of closed vein segments after 12 months in patients with acute DVT compared with conventional treatment (p < 0.05). Postthrombotic syndrome also occurred with less frequency in systemically treated patients versus controls (p < 0.001). High-dose thrombolysis led to better rates of complete recanalization after seven days (p < 0.01) than locoregional lysis. However, 12 patients receiving thrombolysis (9 systemic, 3 local) suffered major bleeding complications; 9 patients on systemic treatment developed pulmonary emboli. CONCLUSIONS: Systemic thrombolytic treatment for acute DVT achieved a significantly better short- and long-term clinical outcome than conventional heparin/anticoagulation therapy but at the expense of a serious increase in major bleeding and pulmonary emboli. Given the inherent risks for such serious complications, systemic thrombolysis, although effective, should be used selectively in limb-threatening thrombotic situations.     

Thrombolytic therapy for prosthetic valve thrombosis: short- and long-term results

BACKGROUND: Thrombolytic therapy (TT) has evolved as an alternative to surgery for prosthetic valve thrombosis (PVT), but its utility in patient management is still debated and the long-term results are not available. METHODS: From 1990 through 1999, we treated 110 consecutive patients (52 men, mean age 35.4 +/- 10.8 years) of left-sided obstructive PVT (96 mitral, 14 aortic) with TT (streptokinase in 108, urokinase in 2) according to a specified protocol of prolonged infusion. Serial echo Doppler parameters were monitored in all patients to guide the duration of TT and to quantify its efficacy. Ninety of the 102 survivors of the index episode were followed up for a mean period of 31.3 +/- 27.8 months (range 1-112 months). RESULTS: Complete hemodynamic response (on cinefluoroscopy and echo Doppler criteria) was seen in 90 (81.8%) episodes, partial response in 11 (10%), and failure in 9 (8.2%). The mean duration of TT was 42.8 +/- 20.4 hours. Five of the 7 patients who were initially seen in cardiogenic shock/overt pulmonary edema died during therapy. After these patients were excluded, the rate of complete response did not differ among patients with New York Heart Association class I/II (80%), class III (86.3%), or class IV (81.5%). The response rate also did not vary with the type, position of prosthesis, duration of symptoms, or time lag since surgery. There were 21 (19.1%) embolic episodes during therapy, including 6 strokes. These were significantly more frequent in patients with atrial fibrillation (AF) (odds ratio on multivariate analysis 2.3, 95% confidence interval 1.3-3.9, P =.01). On follow-up, there were 25 recurrences of PVT, of which 20 again received TT with a complete response in 14 (70%). At 5 years the actuarial survival was 85.2% and the event-free survival was 61.5%. The presence of chronic AF was a significant predictor of recurrence of PVT (odds ratio 2.2, 95% confidence interval 1.2-3.9, P =.008). CONCLUSIONS: TT is effective in the majority of patients with PVT but is associated with a high rate of embolism, especially in patients with AF. Excluding patients with cardiogenic shock/overt pulmonary edema (in whom TT is largely ineffective), the success of TT does not vary with the New York Heart Association class, duration of symptoms, or other patient variables. The recurrence rates of PVT are high after even successful TT, especially in patients with AF.     

In vivo thrombin generation and activity during and after intravenous infusion of heparin or recombinant hirudin in patients with unstable angina pectoris

In patients with unstable angina, intravenous heparin reduces thrombin activity but does not influence thrombin generation. Recombinant hirudin, a direct thrombin inhibitor, may be more effective in inhibiting both thrombin generation and activity. We measured the plasma levels of prothrombin fragment 1+2 (a marker of thrombin generation) and fibrinopeptide A (a marker of thrombin activity) in 67 patients with unstable angina enrolled in the GUSTO (Global Use of Strategies to Open Occluded Coronary Arteries) IIb trial who were receiving either recombinant hirudin (31 patients) or heparin (36 patients). Blood samples were obtained at baseline (before any treatment), after 3 to 5 days of study drug infusion (immediately before discontinuation), and 1 month later. In the patients receiving recombinant hirudin, the prothrombin fragment 1+2 levels measured immediately before drug discontinuation were significantly lower than at baseline (P:=0.0014), whereas they had not changed in the patients receiving heparin; at this time point, the difference between patients receiving hirudin and those receiving heparin was statistically significant (P:=0.032). One month later, the prothrombin fragment 1+2 levels in both groups were similarly persistently high and did not differ from baseline. Fibrinopeptide A plasma levels at the end of infusion were significantly lower than at baseline in both treatment groups (P:=0. 0005 for hirudin and P:=0.042 for heparin) and remained lower after 1 month (P:=0.0001 for both hirudin and heparin). The fibrinopeptide A plasma levels were not different between patients treated with hirudin versus heparin at baseline, at the end of infusion, and after 1 month. Thus, in patients with unstable angina, in vivo thrombin generation and activity are reduced during intravenous infusion of recombinant hirudin. However, the inhibition of thrombin generation is not sustained, and after 1 month, the majority of patients have biochemical signs of increased thrombin generation.     

Anticoagulation with recombinant hirudin and danaparoid sodium in pediatric patients

Patients receiving heparin are at risk of developing heparin-induced thrombocytopenia (HIT). Whereas in HIT I only reversible mild thrombocytopenia occurs within the first days of heparin treatment, HIT II may lead to potentially life-threatening thromboembolic events. Pediatric patients suffering from HIT II have been reported in a study on newborns and in a few reports on children and adolescents. However, thrombotic complications can be as severe in children as they are in adults. In the case of HIT II, the withdrawal of heparin is required and alternative anticoagulation should be started. In contrast to numerous investigations in adult patients, including prospective studies, experience with alternative anticoagulants in pediatric patients is limited. The available data were analyzed according to HIT II complications, alternative anticoagulation, and clinical outcome. In conclusion, HIT II represents a potentially dangerous complication of heparin therapy in pediatric patients also. Alternative anticoagulation applied in pediatric patients mainly included danaparoid sodium and recombinant hirudin. In most patients treated with these anticoagulants, effective anticoagulation and clinical improvement were observed. Because of limited experience, more data are required for optimal management of HIT II in young patients.     

Surgical treatment of left-sided prosthetic valve thrombosis: short and long-term results

We report a single center experience of surgical treatment of 30 cases of left-sided prosthetic valve thrombosis (PVT). In our series, a diagnosis of PVT was established based on clinical and echocardiographic examinations. Thrombosis was the major etiologic factor in 25 patients (83.3%), while 22 of 25 patients (88%) had a subtherapeutic anticoagulation level. The early hospital mortality rate was 7.1% in patients with New York Heart Association (NYHA) functional classes II - III, and 31.3% in NYHA functional class IV. The median interval from the surgical procedure to follow-up for these patients was 29.2 months. No recurrence or deaths were observed during 3 to 73 months following the surgical procedure.     

Fibrinolytic therapy of deep vein thrombosis with continuous intravenous infusion of a recombinant tissue plasminogen activator

Recombinant human rt-PA was administered to 22 patients with deep vein thrombosis at a dosage of 30 to 120 mg/day (0.5 to 1.76 mg/kg body weight/24 hr) over 2 to 10 days. rt-PA induced phlebographically documented substantial recanalization in 18 of 21 patients. The lowest dose of 0.5 mg/kg/24 hr tested here was thrombolytically effective, whereas a dose of 0.95 mg/kg/24 hours and more led to hemorrhagic complications and premature discontinuation of therapy in four of six patients. Blood clotting analysis did not reveal any substantial decrease in fibrinogen concentrations, whereas the euglobulin clot lysis time and thromboelastography demonstrated a systemic fibrinolytic effect. Therapy with rt-PA can thus be considered as an alternative and effective method of therapy in treatment of deep vein thrombosis. The results of this study show that even a dosage of lower than 0.5 mg/kg/24 hr might prove to be effective. Further studies would be required to show whether the fibrin specificity of rt-PA leads to a superiority of this fibrinolytic substance over the conventional thrombolytic agents, streptokinase and urokinase.