Myelofibrosis patients with severe thrombocytopenia were effectively excluded from JAK inhibitor therapy, since dose reductions for low platelets undermined efficacy. Vonjo (pacritinib) was approved specifically for them.
Pacritinib inhibits JAK2 and IRAK1 while largely sparing JAK1, allowing full dosing without the additional myelosuppression that limits other agents in this population. The twice-daily capsule treats adults with intermediate or high-risk primary or secondary myelofibrosis and a platelet count below 50,000.
Vonjo received accelerated approval, leaving a confirmatory trial obligation as its principal regulatory risk, and it holds orphan designation with no generic competition. Its niche is defined by platelet count, making it complementary to rather than directly competitive with ruxolitinib.
