Life-threatening thromboembolism (TE) is the most feared complication in patients with paroxysmal nocturnal hemoglobinuria (PNH). Thrombophilia in PNH likely involves a hypercoagulable state, possibly due to intravascular hemolysis with scavenging of the coagulation regulator nitric oxide, and platelet activation. Approximately 45% of PNH deaths result from TE. Thrombosis is more frequent in patients with larger PNH clones, but can occur in patients with smaller clones. Primary prophylactic anti-coagulation may reduce the thrombotic risk in PNH patients, although controlled studies have not been performed and there is a known serious hemorrhage risk. A randomized, placebo-controlled, 26-week phase 3 study of the terminal complement inhibitor eculizumab in 87 PNH patients (TRIUMPH) recently demonstrated dramatic reductions in intravascular hemolysis and RBC transfusions; 1 TE was reported with placebo and 0 with eculizumab. This single study was not powered to examine the effect of eculizumab on TE, and we prospectively examined the aggregate TE event rate in eculizumab-treated patients from TRIUMPH, the two other PNH trials, and the subsequent phase 3 extension study as compared to each patient’s pre-treatment event rate. Before receiving eculizumab, examination of patient records identified 126 TE events in 195 patients, and 103 were on anticoagulants. While pre-treatment TE event rates were variable in the 3 individual PNH studies, eculizumab reduced TE in each study. The TE event rate with eculizumab treatment was 1.22 per 100 patient years, compared to 7.49 (p<0.001) in the same patients before eculizumab treatment, corresponding to a reduction of 84% (2 events with eculizumab vs. 12.3 events expected). Sensitivity analyses showed the effect to be robust. With restriction of the pre-treatment observation period to the 12-months immediately before initiation of the trials, the TE event rate with eculizumab was reduced 93% from 17.21 to 1.22, respectively (p=0.013). The TE event rate was reduced from 21.95 pre-treatment in patients with TE prior to the trials (n=63) to 3.42 during eculizumab treatment (p<0.001). Most TE events prior to eculizumab treatment occurred in patients receiving anti-coagulants, indicating that this therapy may be insufficient to prevent thrombosis. Of 103 patients on anticoagulants, there were 54 TE events in 30 patients over 385.73 patient years (14.00/100 patient years) pre-eculizumab compared to no TE events with eculizumab in 101 patient years (0.0/100 patient years; p<0.001), demonstrating that eculizumab reduces the risk of thrombosis in anticoagulated, highly thrombophilic PNH patients. These data show that long-term eculizumab treatment results in a clinically and statistically significant reduction in thrombosis in patients with PNH.

Topics:
complement inhibitor, eculizumab, paroxysmal nocturnal hemoglobinuria, thrombosis, anticoagulants, thrombophilia, coagulants, erythrocyte transfusion, nitric oxide, thromboembolism

Disclosures: There is no label for eculizumab as it is an investigational drug.; Drs Rollins, Rother and Bell are employees of Alexion Pharmaceuticals, Inc.; Drs Hillmen and Schubert have served as consultants for Alexion Pharmaceuticals, Inc.; Drs. Rollins, Rother and Bell have equity ownership in Alexion Pharmaceuticals, Inc.; Dr Hillmen has received grant support from Alexion Pharmaceuticals, Inc. Dr Young reports that Alexion made an unrestricted donation to the NHLBI in support of this research.; Drs Hillmen, Schubert, Brodsky, Socie, Luzzatto and Hill have received lecture fees from Alexion Pharmaceuticals, Inc.; Drs Muus, Hill, Schubert, Brodsky and Luzzatto have served on Advisory Committees for Alexion Pharmaceuticals, Inc.

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2006, The American Society of Hematology
2006
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