The purpose of this study is to evaluate whether low-molecular-weight heparin could be equally or more effective than oral anticoagulation in the long-term treatment of deep venous thrombosis.

The open-label prospective randomized clinical trial compares subcutaneous LMWH (tinzaparin)administered for 6 months versus initial treatment using subcutaneous LMWH followed by oral anticoagulants given for a similar period of time in patients with proximal venous thrombosis.

Inclusion Criteria:

• Consecutive, symptomatic patients with a first or recurrent episode of acute proximal-vein thrombosis of the lower limbs.
• either sex and over 18 years of age
• referred to the Vascular Surgery Department of the hospital
• onset of symptoms less than 2 weeks
• documented by compression ultrasonography,

Exclusion Criteria:

• received heparin, low-molecular-weight heparin or oral anticoagulant therapy for more than 2 days for the present disease
• pulmonary embolism requiring thrombolytic therapy
• Need of surgical thrombectomy or vena cava interruption
• receiving oral anticoagulant treatment or antiplatelet agents for other conditions
• contraindication to anticoagulant treatment (active bleeding, severe blood pressure or allergy to the study drugs)
• platelet count lower than 100x103 /μl or hemoglobin concentration lower than 7 g/dl or history of heparin-associated thrombocytopenia
• severe renal failure necessitating dialysis
• pregnancy
• lumbar puncture within the previous 24 hours