FDA Grants Fast Track Designation to Sobi’s VEXAS Therapy

Rare Daily Staff

The U.S. Food and Drug Administration has granted Fast Track designation to Sobi’s pacritinib for VEXAS syndrome, a rare and potentially life-threatening inflammatory disorder with no approved treatments.

The designation is intended to facilitate the development and expedite the regulatory review of medicines for serious conditions with unmet medical needs; it does not constitute FDA approval of pacritinib for VEXAS.

VEXAS is a systemic condition driven by acquired mutations in the UBA1 gene. First described in 2020, it combines inflammatory manifestations—such as recurrent fevers, skin disease, chondritis, vasculitis and pulmonary involvement—with hematologic abnormalities. The disorder can progressively affect multiple organ systems and cause severe, sometimes life-threatening complications.

Treatment has been difficult. Patients often require moderate to high doses of corticosteroids because existing immunomodulatory therapies may not adequately control disease activity. Sobi said there are no approved treatment options specifically for VEXAS.

Pacritinib, a dual IRAK1/JAK2 inhibitor marketed in the United States as Vonjo for certain patients with myelofibrosis, is being studied in a phase 2 trial as a possible treatment for VEXAS, short for vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic syndrome.

Pacritinib is already approved in the United States under accelerated approval for adults with intermediate- or high-risk primary or secondary myelofibrosis and platelet counts below a specified threshold.

The Fast Track designation comes as Sobi advances PAXIS, a randomized phase 2 study assessing whether pacritinib can prevent VEXAS disease flares as patients taper glucocorticoids. The trial, which began in 2024, is enrolling adults with inflammatory VEXAS who are receiving ongoing corticosteroid treatment.

In the double-blind portion of the study, participants are assigned in a 1:1:1 ratio to one of two pacritinib dose groups or placebo for up to 24 weeks. Those who complete the blinded phase, as well as certain participants who meet early-failure criteria, can move into an open-label treatment period lasting up to 48 weeks. The principal efficacy measure is the proportion of patients who achieve an overall clinical response during the 24-week blinded phase.

Beyond disease activity, the study is evaluating flare-free days at corticosteroid doses below 10 mg, hematologic responses, inflammatory biomarkers including C-reactive protein, fatigue, physical function, sleep disturbance and other quality-of-life measures. The trial is being conducted at sites in the United States, Canada, Europe and Japan.

Sobi expects topline PAXIS data in 2027. If the findings are positive, pacritinib could offer a steroid-sparing option for patients who frequently face chronic disease activity and limited therapeutic choices.

“Achieving FDA’s Fast Track designation for pacritinib is an important milestone and recognizes its potential as an investigational treatment for people living with VEXAS syndrome,” said Lydia Abad-Franch, Sobi’s chief medical officer and head of research and development and medical affairs.