Sustained‐release ruxolitinib: Findings from a phase 1 study in healthy subjects and a phase 2 study in patients with myelofibrosis

Ruxolitinib is the first Janus kinase (JAK) inhibitor approved for the treatment of myelofibrosis, where its efficacy is often associated with cytopenia. It is possible that the severity of cytopenia is in part driven by C (max). A once‐daily sustained‐release (SR) formulation of ruxolitinib was therefore developed to decrease the C (max)/C (min) ratio relative to twice‐daily immediate‐release (IR) ruxolitinib. An SR formulation was identified based on pharmacokinetic evaluation in a phase 1 study in healthy adults (N = 9). This was followed by an open‐label phase 2 study in patients with myelofibrosis (N = 41). Ruxolitinib SR treatment was well tolerated with blood cell counts relatively unchanged through week 16. In terms of efficacy, 7 patients (17.1%) had clinical improvement and 33 (80.5%) had stable disease. While this study has raised the possibility of an increased therapeutic index for ruxolitinib via an SR formulation, further studies are required to validate the hypothesis.