Lepirudin. As described previously, 2 prospective observational studies by Greinacher et al15,16 report the results of patients with HIT or HITTS who were treated with lepirudin. A 2-part analysis was performed in each study. The first analysis reported the frequency of the outcomes for the entire prospective cohort of patients treated with lepirudin. The second analysis in each of the studies compared outcomes in a subgroup of the lepirudin-treated patients with those documented in a group of historical controls. The proportions of the patients with HIT and HITTS in the 2 studies were not provided. The same controls were used for both studies. In the first prospective study, the composite outcome (death, amputation, and new TECs) occurred in 18.3% of lepirudin-treated patients, including death in 7.3%, amputation in 3.7%, and new TECs in 9.8%.15 In the second prospective study, 29.5% of lepirudin-treated patients had the combined outcomes of death in 9.8%, amputation in 8.9%, and new TECs in 17.9%.16 In the second analysis, when a subgroup of the lepirudin-treated patients was compared with a historical control group, the combined outcome was present in 25.4% of the lepirudin-treated patients in the first study and 30.5% of lepirudin-treated patients in the second study. The combined outcome was present in 52.5% of controls, giving an RRR of 0.52 for the first study and 0.42 for the second study. Death occurred in 8.5% of lepirudin-treated patients in the first study, 10.5% of lepirudin-treated patients in the second study, and 24.2% of controls (RRRs, 0.65 and 0.56, respectively). In the first study, 5.6% patients treated with lepirudin ultimately underwent a limb amputation, compared with 8.3% of the controls (RRR, 0.32). For the second study, the percentages with amputation were 9.5% (lepirudin-treated patients) and 8.3% (controls), for an RRR of −0.14.15,16 New TECs occurred in 18.3% and 17.9% of lepirudin-treated patients (first and second studies, respectively) and in 31.7% of controls (RRRs, 0.42 and 0.43 respectively).