Safety of warfarin anticoagulation in patients with heparin-induced thrombocytopenia

Objectives: Venous limb gangrene has been reported to occur after high warf arin doses in heparin-induced thrombocytopenia (HIT), and this observation has been used to exclude warfarin management in this condition. The outcome of patients receiving modest doses of warfarin was studied. Design: Retrospective study of 114 consecutive HIT patients who received di agnoses by platelet aggregometry; 51 of the 114 patients received warfarin. Setting: Tertiary-care medical center. Results: Thirty-five patients received warfarin for non-HIT indications, an d 16 received warfarin for heparin-associated thrombosis. Warfarin was give n to 23 patients (47%) 2.4 +/- 0.4 days prior to the onset of HIT, in 19 wh ile receiving IV heparin for an overlap of 2.7 +/- 0.4 days. Twenty-eight p atients (53%) received warfarin 2.8 +/- 1.0 days after the diagnosis of HIT . Patients received 11 +/- 1 doses of warfarin over 16 +/- 2 days, with a m ean daily dose of 3.5 +/- 0.5 and a maximum dose of 9 +/- 0.5 mg. Prothromb in time at discharge was 17.3 +/- 0.4 s with a maximum of 22.8 +/- 0.8. The final international normalized ratio was 2.9 +/- 0.3, and the maximum was 7.5 +/- 1.4. The minimum therapeutic range was reached in 59% of determinat ions. When compared to the 63 patients who did not receive warfarin, warfar in patients received more IV heparin (86% vs 41%; p < 0.001), open heart su rgery (78% vs 43%; p < 0.001), and had a lower mortality (8% vs 43%; p < 0. 001), but had no differences in thrombosis. Conclusions: Modest doses of warfarin were not associated with a worse outc ome in patients with HIT.