In acute deep-vein thrombosis, reviparin regimens are more effective than unfractionated heparin in reducing the size of the thrombus. Reviparin is also more effective than unfractionated heparin for the prevention of recurrent thromboembolism and equally safe.

Platelet aggregometry is an important technique which is frequently used by hemostaseologists and researchers. Gustav Born introduced the principle more than 40 years ago. Many different ways to perform aggregometry have been published. The results of aggregometry may become more comparable if some rules would be generally accepted. (1) The pre-analytical procedures are probably the most important factors which influence aggregometry results. Besides correct blood sampling important factors are the preparation of platelet-rich plasma (PRP), incubation of the PRP at room temperature and awareness of time-dependent changes of aggregometry results. (2) A major point concerns the agonists. Agonists of different sources have to be compared to verify that they lead to the expected results. Even different salts of ADP lead to different results and different collagen preparations lead to a large variation of aggregation response (3). The frequently used procedure of adjusting the platelet number in the PRP is cumbersome, affects platelet activation and is not necessary. (4) Aggregometers should comply with some simple rules. The changes in optical density should be linearized so that--if this is required--percentages can be given. The recorder speed should be standardized and all recorders should provide 1?cm/min. Calibration of the aggregometer sensitivity should be possible. (5) If aggregometry is used to define the response to antiaggregating agents agreement on the inducer concentrations is essential. If some rules are applied aggregometry is a relatively simple and reliable method, and well suited for clinical studies and for experimental research.

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A method to induce microthrombi in small mesenteric arteries (ø 15–25 μm) has been developed to study platelet reactions and to investigate antithrombotic drugs. A high power water immersion interference contrast system, based on a Leitz Orthoplan microscope, was used. In Nembutal-anesthetized male Wistar rats and in fawn hooded bleeder rats, vascular lesions were produced with a Hadron-512-Ruby-bio-laser or with a Coherent CR-2 supergraphite ion laser (Argon laser). The ruby laser produced intravascular precipitates consisting of proteins and erythrocytes which usually stuck to the vessel wall and on which platelets immediately adhered, transformed with pseudopode formation and formed loose aggregates. The Argon laser induced vascular damage, usually without intravascular heat precipitates which also led to platelet adhesion, transformation and aggregation. Fibrin threads rarely formed in the early platelet thrombi. Thrombus formation was significantly reduced in this model by dipyridamole (10 mg/kg orally), by Ditazole (50 mg/kg orally), heparin (100 IU/kg i.v.), Molsidomine (50 mg/kg orally), Nafazatrom (Bay G 6575, 10 mg/kg i.v. and orally), Ticlopidine (100 and 200 mg/kg orally) and Tioxaprofen (EMD 26644, 10 mg/kg orally). Thrombus formation was also significantly reduced in fawn hooded bleeder rats.

The augmentation of the antiaggregatory effects of GPIIb/IIIa inhibitors by aspirin and clopidogrel and the lack of antisecretory effects of GPIIb/IIIa inhibitors may favor their combination with clopidogrel.

Low-molecular-weight and unfractionated heparins are frequently used to treat venous thromboembolism, but it is not known whether they are equally effective in inhibiting in vivo generation of thrombin. In this multicenter trial, 1048 patients were randomized to intravenous unfractionated heparin (group A), twice daily low-molecular-weight heparin (reviparin) for 1 week (group B), or once daily reviparin for 4 weeks (group C). All patients received vitamin K antagonists. Blood samples withdrawn at the baseline and at weeks 1 and 3 were analyzed using markers of in vivo thrombin generation and other coagulation parameters. During the first 3 weeks symptomatic recurrent deep vein thrombosis-pulmonary embolism (DVT/PE) occurred in 17 (4.5%) of 375 patients in group A compared with 4 (1.0%) of 388 patients in group B, and 9 (2.4%) of 374 patients in group C. Forty percent of patients in group A, 53.4% in group B, and 53.5% in group C showed 30% or greater reduction in thrombus size assessed by venography. Patients in group B had significantly greater reduction in D-dimer, prothrombin fragments 1 and 2 (F1 ؉ 2), endogenous thrombin potential (ETP), and thrombin-antithrombin (TAT) complexes compared to groups A and C. Greater release of tissue factor pathway inhibitor (TFPI) and reduction in levels of thrombin activatable fibrinolysis inhibitor (TAFI) and fibrinogen were significantly more pronounced in group C patients. Reviparin administered twice daily plus vitamin K antagonist is more effective in inhibiting in vivo thrombin generation compared to intravenous unfractionated heparin plus vitamin K antagonist, and reviparin once daily produced significantly higher TFPI release and greater reduction in TAFI and fibrinogen levels. (Blood. 2002;99:1965-1970

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