Fondaparinux is the preferred anticoagulant in heparin-induced thrombocytopenia (HIT) because:

• A Fondaparinux directly inhibits thrombin without requiring antithrombin, avoiding heparin-PF4 complex formation
• B Fondaparinux is a direct thrombin inhibitor like argatroban, making it the safest choice in HIT
• C Fondaparinux does not cross-react with HIT antibodies because it inhibits factor Xa directly without antithrombin
• D Fondaparinux is a small synthetic pentasaccharide that binds only antithrombin and does not bind platelet factor 4 (PF4), so it does not form the antigen complex that triggers anti-PF4 antibodies ✓

Explanation

HIT is an immune-mediated syndrome where IgG antibodies form against PF4-heparin complexes, causing paradoxical thrombosis. Fondaparinux is a synthetic pentasaccharide analog of the antithrombin-binding region of heparin. It binds antithrombin III and causes selective factor Xa inhibition (AT-mediated). Critically, due to its small size and synthetic structure, fondaparinux does NOT bind platelet factor 4 (PF4), so it cannot form the immunogenic PF4-fondaparinux complex, and does NOT cross-react with anti-PF4/heparin antibodies. No cases of HIT have been causally attributed to fondaparinux. Alternative agents in HIT include argatroban and bivalirudin (direct thrombin inhibitors).

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.