›Reduce dose for renal impairment
›CrCl 30 to 60 mL/min: reduce to 0.08 to 0.1 mg/kg/h
›CrCl <30 mL/min: reduce to 0.03 to 0.05 mg/kg/h
›Monitoring target
›aPTT 1.5 to 2.5 times baseline
›First check at 2 hours after initiation
›Titrate by 0.05 mg/kg/h increments
›Clearance 80% enzymatic, 20% renal
›Preferred when combined hepatic and renal dysfunction
›Anaphylaxis reported rarely
›Does not artificially prolong INR as significantly as argatroban
›Fondaparinux subcutaneous
›Weight-based once-daily dosing
›<50 kg: 5 mg SC daily
›50 to 100 kg: 7.5 mg SC daily
›>100 kg: 10 mg SC daily
›Avoid if CrCl <30 mL/min — renal elimination
›Does not cross-react with HIT antibodies
›Useful for patients outside ICU who can tolerate SC injection
›No routine monitoring of anti-Xa levels required in most patients
›Cannot be reversed by protamine
›Direct oral anticoagulants
›Rivaroxaban has most supporting data for HIT
›15 mg PO twice daily with food for 3 weeks then 20 mg PO daily for VTE treatment
›Reasonable for clinically stable patients without hemodynamically significant PE
›Apixaban alternative
›10 mg PO twice daily for 7 days then 5 mg PO twice daily
›DOAC initiation timing
›Start at time of DTI discontinuation when clinically stable
›Not recommended for acute limb-threatening arterial thrombosis or hemodynamically significant PE
›ASH 2018 guidelines conditionally recommend DOACs for non-acute HIT management
Transition to long-term anticoagulation
›Warfarin transition
›Initiate only when platelets >=150 x10^9/L
›Overlap with DTI or fondaparinux for minimum 5 to 7 days
›Target INR 2.0 to 3.0 for most indications
›If using argatroban as bridge, target INR approximately 4.0 on combined therapy
›Chromogenic factor X assay confirms adequate anticoagulation during transition
›Duration of anticoagulation
›Isolated HIT without thrombosis: minimum 4 weeks; some guidelines recommend up to 3 months
›HIT with thrombosis: minimum 3 months
›Anticoagulation duration based on thrombosis extent and recurrence risk
Refractory and autoimmune HIT
›IVIG for refractory or autoimmune HIT
›IVIG 1 g/kg IV daily for 2 days
›Inhibits FcgammaRIIA-mediated platelet activation
›Consider in autoimmune HIT presenting after heparin cessation
›Also consider in HIT with severe thrombocytopenia and ongoing thrombosis on DTI
›Platelet transfusion
›Avoid platelet transfusions in HIT unless active life-threatening bleeding
›Thrombosis risk outweighs benefit in most HIT patients
›If transfusion necessary, threshold platelets <50 x10^9/L with active bleeding
›ACCP Grade 1C recommendation against routine platelet transfusion in HIT
Surgical and interventional management
›Vascular interventions
›Catheter-directed thrombolysis for iliofemoral DVT causing phlegmasia
›Surgical thromboembolectomy for acute limb ischemia
›IVC filter placement generally avoided in HIT — additional thrombogenic risk
›If filter required, use non-heparin anticoagulation perioperatively