Fondaparinux differs from unfractionated heparin (UFH) in that it:

• A Is a direct thrombin inhibitor that does not require antithrombin III as a cofactor
• B Covalently binds thrombin in a 1:1 complex, causing irreversible anticoagulation not reversible by protamine
• C Is a synthetic pentasaccharide that selectively activates antithrombin III to inhibit factor Xa only (not thrombin/IIa), and does not cause heparin-induced thrombocytopenia (HIT) ✓
• D Has equal anti-Xa and anti-IIa activity (1:1 ratio) and requires aPTT monitoring

Explanation

Fondaparinux is a synthetic analogue of the antithrombin-binding pentasaccharide sequence of heparin. It selectively activates antithrombin III, which then specifically inhibits factor Xa (anti-Xa:anti-IIa ratio = infinity, no IIa inhibition). Because the fondaparinux-antithrombin complex is too small to simultaneously bridge to thrombin. It does not bind platelet factor 4 and thus does not cause HIT. UFH inhibits both Xa and IIa equally. Argatroban/bivalirudin are direct thrombin inhibitors.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.