Updated Results from a Large, Ongoing, Treatment IND Study Using Defibrotide for Patients with Hepatic Veno-Occlusive Disease

Background: Severe hepatic veno-occlusive disease (VOD, also referred to as sinusoidal obstruction syndrome) with associated multi-organ failure (MOF) is a life-threatening complication of hematopoietic stem cell transplant (HSCT) and has an associated mortality rate >80%. Defibrotide has been shown to have a protective effect on injured endothelium and to restore the thrombo-fibrinolytic balance. In severe VOD, defibrotide has improved complete response (CR) rates and survival at Day +100 post HSCT compared with historical controls, and has also been shown to have a favorable safety profile. In the EU, defibrotide is now approved for the treatment of severe hepatic VOD in HSCT therapy. It is indicated in adults, adolescents, children, and infants >1 month of age. In the USA, there are currently no approved therapies for this complication; however, defibrotide has been made available since 2007 through an expanded access protocol directed treatment IND (T-IND). The aim of the T-IND is to gather additional data on safety and efficacy of defibrotide in a broader patient population, including those with severe VOD/MOF post HSCT, non-severe VOD post HSCT, and VOD following chemotherapy in the non-HSCT setting. This is the largest prospective evaluation of defibrotide for the treatment of VOD. Here we provide an update on the safety of defibrotide from this ongoing study.

Methods: The original T-IND protocol required patients to have a diagnosis of VOD by Baltimore criteria (total bilirubin ≥2.0 mg/dL with ≥2 of the following: hepatomegaly, ascites, or 5% weight gain) with MOF (either renal and/or pulmonary failure) following HSCT; the study was amended to allow inclusion of patients with non-severe VOD (defined as no MOF) occurring either post-HSCT or post-chemotherapy. Key exclusion criteria include clinically significant bleeding or the need for >1 vasopressor. Defibrotide was given as a 2-hour infusion at 6.25 mg/kg IV every 6 hours (25 mg/kg/d) with a recommended minimum treatment duration of 21 days.

Results: The current interim safety analysis is based on 612 patients enrolled between December 2007 and December 2013 (including 99 in 2013) for whom safety data is available and who received ≥1 dose of defibrotide. Across the USA, over the course of the study approximately 86 centers were active to enroll patients. Median patient age was 12 years (range <0.1–69), with 24.2% aged <1 month to 2 years, 39.4% aged >2 to 18 years, 34.9% aged >18 to 65 years, and 1.2% aged >65 years. Patients were primarily male (55.8%) and predominantly white (65.6%).

Overall, 454 patients (74.2%) reported ≥1 treatment emergent adverse events (AEs). Of these, 138 patients (22.5%) had AEs that investigators assessed as related (possibly, probably, or definitely) to study medication. Related AEs in >2.0% were pulmonary hemorrhage (4.7%), gastrointestinal hemorrhage (3.6%), epistaxis (3.1%), and hypotension (2.8%). Serious AEs (SAEs) were reported by 368 patients (60.1%). The majority of SAEs were assessed as not related to study treatment; 82 patients (13.4%) had an SAE at least possibly related to study treatment, most commonly pulmonary hemorrhage (3.9%) and gastrointestinal hemorrhage (2.9%). AEs leading to death occurred in 254 patients (41.5%); these AEs were deemed by the investigators to be possibly related to study medication in only 17 patients (2.8%).

Previously reported efficacy data at D +100 in 425 patients evaluable for outcome have shown survival of 55% (by Kaplan-Meier estimate) for patients following HSCT, and survival of 62% (by Kaplan-Meier estimate) in 45 patients following chemotherapy (without HSCT), respectively.

Conclusions: Defibrotide therapy in patients with VOD was generally well tolerated in this population, with manageable toxicity, and promising results seen in terms of response and survival. Safety results from prior studies, which have also been associated with a low incidence of defibrotide-associated toxicities, have proven very consistent with the favorable tolerability profile seen in this largest experience to date. Enrollment to the T-IND study continues; updated results will be presented at the meeting.

Support:Jazz Pharmaceuticals

Off-Label Use

Defibrotide is an investigational treatment for hepatic veno-occlusive disease in the United States.