*3.1.1. Mechanism of action*

Both UFH and LMWHs exert their anticoagulant activity by inhibiting thrombin-activated conversion of fibrinogen to fibrin [46]: binding of a unique pentasaccharide to antithrombin causes a conformational change in antithrombin that accelerates its interaction with thrombin and factor Xa by about 1000 times. Binding of the pentasaccharide to antithrombin results directly in inhibition of factor Xa, and the pentasaccharide also blocks the activation of factor IX and neutralizes factor Xa by activating factor X inhibitor.

#### *3.1.2. Indications*

Heparins, and in particular LMWHs, indications comprehend: DVT prophylaxis during perioperative or postoperative period of general/orthopedic surgery or in bedridden patients; DVT treatment in patients affected by pulmonary embolism; instable angina and non-ST-elevation myocardial infarction (NSTEMI) prophylaxis with concomitant use of acetylsalicylic acid; coagulation prevention in patients undergoing dialysis; and symptomatic VTE (proximal DVT and/ or pulmonary embolism) to reduce the recurrence of VTE in patients with solid tumor cancers.
