Efficacy of Fondaparinux in the Treatment of Heparin-Induced Thrombocytopenia with Venous Thromboembolism: Reduction of Thromboembolic Burden, Normalization of Platelet Count and Disappearance of Anti-Platelet Factor 4/Heparin Antibodies.
Authors: Piovella Franco , Barone Marisa , Beltrametti Chiara , Piovella Chiara , D’Armini Andrea M. , Marzani Federico Capra , Arici Vittorio , De Amici Mara , Barco Stefano L. , Castellani Gianluca , Langer Martin 
Published: October 2019

Abstract
Heparin-induced thrombocytopenia (HIT) and heparin-induced thrombocytopenia with thrombosis (HITT) may develop during anticoagulant treatment in patients submitted to various regimens of unfractionated or low-molecular weight heparins. Several molecules have been studied as alternative anticoagulants in patients with HIT or HITT, including danaparoid, argatroban, lepirudin. Lepirudin requires dosage adjustments in patients with renal insufficiency and has potential for antibody formation. Argatroban requires dosage adjustments in patients with hepatic insufficiency. Argatroban increases the International Normalized Ratio (INR) when co-administered with warfarin, leading to dosage difficulties when transitioning to warfarin therapy. Anticoagulation of patients with HIT or HITT may be limited by antibodies cross-reactivity with danaparoid and by new generation of antibodies with lepirudin.
Fondaparinux is the first of a new class of synthetic antithrombotics: the selective inhibitors of coagulation factor Xa. It is the most advanced competitor of low molecular weight heparins, which are the reference drugs in prophylaxis and treatment of venous thromboembolism. Fondaparinux does not bind to platelet factor 4 (PF4) and does not react with anti-PF4/heparin antibodies in in vitro testing.
We treated 20 patients who develop HIT (3 patients) or HITT (17 patients, of whom 4 had both DVT and PE). Nine patients were previously submitted to extracorporeal circulation with unfractionated heparin (UFH) followed by low-molecular weight heparin (LMWH) for major cardiac surgery. The remaining patients had been previously treated with either UHF or LMWH at therapeutic or prophylactic dosage in internal medicine or surgery wards. In the 17 patients who developed HITT, we applied therapeutic dosages of fondaparinux, i.e. 7.5 mg QD or lower, accordingly with their bleeding risk. To the remaining patients with HIT we gave prophylactic dosages of fondaparinux, i.e. 2.5 mg QD. Patients with HITT were treated for 4 to 25 days before starting warfarin. Fondaparinux was stopped when INR of 2.0 or more was reached.
All patients showed a significant reduction of their thromboembolic burden. One episode of major bleeding was recorded in a post-surgical patient. All patients but one showed sustained normalization of the platelet number. In the remaining patient platelet count remained unchanged. Treatment was switched from fondaparinux to lepirudin and after few days her platelets reverted to close-to-normal levels.
In seven patients, submitted to therapeutic dosages of fondaparinux, anti-PF4/heparin antibody titers were determined using a PF4/heparin enzyme-linked immunosorbent assay (ELISA): in all cases antibody levels progressively decreased close to disappearance by 30–45 days.
This series of cases provides further evidence for the safety and efficacy of fondaparinux in the treatment of both HIT or HITT.