Analysis of Time to Complete Response after Defibrotide Initiation in Patients with Hepatic Veno-Occlusive Disease/Sinusoidal Obstruction Syndrome after Hematopoietic Cell Transplantation

Hepatic veno-occlusive disease/sinusoidal obstruction syndrome (VOD/SOS) is a potentially life-threatening complication that occurs after hematopoietic cell transplantation (HCT). The mortality associated with untreated VOD/SOS with multiorgan dysfunction (MOD) has been reported to be >80%. The recommended dose of defibrotide is 6.25 mg/kg every 6 hours, administered as a 2-hour i.v. infusion, for a minimum of 21 days or until resolution of VOD/SOS signs and symptoms. The objective of this analysis was to evaluate the time to complete response (CR) in patients with post-HCT VOD/SOS treated with defibrotide. The time to defibrotide discontinuation due to a CR served as a surrogate for time to CR in an expanded access study (T-IND; ClinicalTrials.gov NCT00628498; n = 1000), and was analyzed separately from the time to CR data pooled from a phase 2 randomized dose-finding study (NCT00003966; n = 74 patients who received 25 mg/kg/day) and a phase 3 historically controlled study (NCT00358501; n = 102). For all studies, a CR was defined as total serum bilirubin <2 mg/dL with resolution of VOD/SOS-related MOD (renal and/or pulmonary dysfunction); the phase 2 study also required resolution of central nervous system dysfunction. In the T-IND, 390 patients discontinued treatment due to a CR and had sufficient data for analysis. The median time to discontinuation was 22 days (range, 2 to 64 days). Discontinuation due to CR occurred beyond 21 days in 235 patients (60%) and beyond 28 days in 57 patients (15%). The pooled phase 2 and 3 studies included 60 patients who achieved a CR, with a median time to CR of 24.5 days (range, 7 to 123 days). A CR was achieved beyond 21 days in 32 patients (53%) and beyond 28 days in 24 patients (40%). The Kaplan-Meier estimate of day +100 survival rate was substantially higher in patients who discontinued due to a CR compared with those who did not (92.5% versus 37.3%). Treatment-emergent adverse events occurred in 185 of 390 patients (47%) who discontinued due to a CR in the T-IND and in 55 of 60 patients (92%) who achieved a CR in the pooled phase 2 and 3 studies, and rates did not differ according to duration of treatment (≤21 days versus >21 days). Taken together, these results highlight the importance of continued defibrotide therapy until resolution of VOD/SOS signs and symptoms, as currently indicated in the approved product labels, which may occur beyond the recommended minimum of 21 days.