Vonjo (pacritinib)

One of 4 JAK inhibitors approved for myelofibrosis, alongside ruxolitinib (Jakafi), fedratinib (Inrebic) and momelotinib (Ojjaara), and the only one whose approval is specifically for people with platelets below 50,000. It was approved on spleen shrinkage under accelerated approval, and its confirmatory PACIFICA trial is ongoing.

Myelofibrosis is often driven by overactive JAK2 signaling, which pushes the bone marrow to make abnormal cells and inflammatory signals. Pacritinib blocks JAK2, including the common mutant form JAK2 V617F, along with FLT3 and IRAK1, 2 other enzymes involved in signaling for blood cell production and immune function. At the doses used it does not block JAK1. It also blocks a receptor called ACVR1 (also known as ALK2)^[1]. Its approval is based on shrinking the enlarged spleen^[1].

Vonjo has no boxed warning. In the PERSIST-2 trial, the most common side effects on Vonjo 200 mg twice daily vs best available therapy were diarrhea (48% vs 15%), low platelets (34% vs 23%), nausea (32% vs 11%), anemia (24% vs 15%), swelling in the legs (20% vs 15%), vomiting (19% vs 5%), dizziness (15% vs 5%) and fever (15% vs 3%). Diarrhea usually started early and became less common over time (41% in the first 8 weeks, 8% in weeks 16 to 24), and the label calls for an anti-diarrhea medicine such as loperamide to be prescribed at the start. Serious bleeding occurred in 13% and fatal bleeding in 2% of patients with platelets below 50,000, so Vonjo is avoided with active bleeding and stopped 7 days before surgery. Other warnings cover QT prolongation (a change in heart rhythm) and, based on another JAK inhibitor, heart attack and stroke, blood clots, lymphoma and other cancers, and serious infections. Symptoms of myelofibrosis can flare if Vonjo is stopped suddenly^[1].

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Approved for adults with intermediate or high-risk primary myelofibrosis, or myelofibrosis after polycythemia vera or essential thrombocythemia, whose platelet count is below 50,000 per microliter. Safety and effectiveness in children have not been established. It cannot be used with strong CYP3A4 inhibitors or inducers. Avoid if the baseline QTc is over 480 msec or eGFR is below 30 mL/min. Breastfeeding is not recommended during treatment and for 2 weeks after the last dose.

Source: VONJO Connect

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PERSIST-2 (NCT02055781) randomized 311 adults with myelofibrosis and platelets at or below 100,000 to Vonjo 400 mg once daily, Vonjo 200 mg twice daily, or best available therapy, which could include ruxolitinib, hydroxyurea or watchful waiting; about half had taken ruxolitinib before. Among the 63 patients with platelets below 50,000 who formed the approval population, 29% on 200 mg twice daily had at least a 35% reduction in spleen volume at week 24, against 3.1% on best available therapy, and the median spleen volume reduction was 27.3% vs 0.9%. The 400 mg once-daily dose was not shown to be safe and is not approved^[1][7]. The confirmatory Phase 3 PACIFICA trial (NCT03165734) compares Vonjo with physician's choice therapy in people with platelets below 50,000; it has enrolled 407 patients, and Sobi lists its data readout for 2027^[8][6].

Pacritinib was first studied under the code SB1518^[9] and was developed through Phase 3 by CTI BioPharma. The FDA placed pacritinib on a full clinical hold in February 2016, and CTI announced the hold's removal on January 5, 2017^[10][11]. The FDA granted Vonjo accelerated approval on February 28, 2022, requiring a randomized trial to confirm its benefit in people with platelets below 50,000^[2][3]. Sobi agreed to acquire CTI BioPharma on May 10, 2023 and completed the acquisition on June 26, 2023^[4][5].

The FDA has approved 4 JAK inhibitors for myelofibrosis: ruxolitinib (Jakafi, November 2011), fedratinib (Inrebic, August 2019), pacritinib (Vonjo, February 2022) and momelotinib (Ojjaara, September 2023). Vonjo's approval is for people with platelets below 50,000 per microliter, and Ojjaara's is for people with anemia.