Based on results from the phase 3, placebo-controlled JAKARTA trial in JAK inhibitor-naive MF and the phase 2, single-arm JAKARTA2 trial in patients previously treated with ruxolitinib, fedratinib, an oral Janus kinase-2 (JAK2) inhibitor, has been approved for patients with myelofibrosis (MF) and platelet counts ≥50×109/l.

In patients with baseline platelet counts of 50 to <100×109/l (“Low-Platelets” cohorts), comprising 14/96 patients (15%) in JAKARTA and 33/97 (34%) in JAKARTA2, researchers assessed the effectiveness and safety of fedratinib 400 mg/day. The Low-Platelets group and patients with baseline platelet counts ≥100×109/l  (the “High-Platelets” cohort) did not have substantially different spleen response rates at 24 weeks in JAKARTA (36% vs. 49%, respectively; P=0.37) or JAKARTA2 (36% vs. 28%; P=0.41).

Additionally, there was no significant difference in symptom response rates between the groups with low and high platelets. In both platelet-count cohorts, fedratinib was generally well tolerated. There were no significant thrombocytopenia occurrences, although new or worsening thrombocytopaenia was more common in the Low-Platelets (44%) group than in the High-Platelets (9%) cohort. Only 3/48 Low-Platelets patients terminated fedratinib because of thrombocytopenia, which was frequently treated with dosage adjustments.

According to the results, fedratinib 400 mg/day is safe and effective for patients with MF and low pretreatment platelet counts, and there is no need to change the drug’s starting dose for them.