Study Objective. To evaluate the safety, efficacy, and dosing requirements of bivalirudin in patients with heparin-induced thrombocytopenia (HIT). Design. Retrospective cohort study Setting. University-affiliated hospital. Patients. Thirty-seven adults with a diagnosis or history of HIT who were treated with bivalirudin between january 1, 2004, and March 31, 2007. Measurements and Main Results. Patients had a mean SD age of 50 16 years and weighed 80 20 kg; 62% were male, 73% were Caucasian, and 95% were treated in the intensive care unit. Patients were divided into three renal function groups for assessment of bivalirudin dosing requirements.creatinine clearance (Cl-cr) greater than 60 ml/minute (12 patients, group 1); Cl-cr, 30-60 ml/minute (1]. patients, group 2); and Clcr lower than 30 ml/minute or receiving continuous renal replacement therapy ([RRT]1.4 patients, group 3). Except for renal function, baseline demographic characteristics were similar among groups. A total of 19 (51%) of the 37 patients achieved goal activated partial thromboplastin time (aPTT) with initial mean SD bivalirudin doses of 0.14 +/- 0.04 (median 0.15), 0.1 +/- 0.07 (median 0.08), and 0.05 +/- 0.05 (median 0.05) mg/kg/hour in groups 1, 2, and 3, respectively Doses remained similar over the study period and were 0.13 0.04 (median 0.15), 0.1 0.06 (median 0.1), and 0.04 0.02 (median 0.03) mg/kg/hour for groups 1, 2, and 3, respectively The mean SD aPTT value after achieving goal range was 64 9 seconds (all patients). Bivalirudin dosing requirements correlated with Cl-cr (1-2 = 0.37, p<0.000.1). Therapy duration was a mean SD of 11 +/- 13 days (median 7 days). Systerriic thrombosis and bleeding while receiving bivalirudin were also evaluated. Thrombosis occurred in one patient;, clinically significant bleeding occurred in two patients. Conclusion. Bivalirudin dosing requirements correlated with renal function; therefore, dosage reduction is required in patients with moderate or severe renal dysfunction. Starting bivalirudin at 0.15 mg/kg/hour in patients with Cl, greater than 60 ml/minute, 0.08-0.1 mg/kg/hour in patients with Cl, 30-60 ml/minute, and 0.03-0.05 mg/kg/hour in patients with Cl-cr,. below 30 ml/minute or receiving continuous RRT is effective at achieving goal aPTT values in most patients.