Population Pharmacokinetics of Ruxolitinib in Patients with aGVHD Who Had an Inadequate Response to Corticosteroids

Background: Jakafi® (ruxolitinib) is currently approved for the treatment of adult patients with intermediate- and high-risk myelofibrosis (MF) and for the treatment of adult patients with polycythemia vera (PV) who have had an inadequate response to or are intolerant to hydroxyurea. A prospective, open-label, single-cohort, Phase 2 study (REACH1) was conducted to evaluate the safety and efficacy of Jakafi® (ruxolitinib) in patients with acute graft versus host disease (aGVHD) who have had an inadequate response to corticosteroids. A population PK analysis was employed to characterize the PK of ruxolitinib in this patient population.

Patients and Methods: REACH1, Study INCB 18424-251, and COMFORT-I are the 3 studies supporting the population PK of ruxolitinib; the first study is in participants with aGVHD who have had an inadequate response to corticosteroids, and the other 2 studies are in participants with MF. First, the final PK model for ruxolitinib in patients with MF was applied to the data in patients with MF and aGVHD. When significant biases were observed in this validation process, new population PK models were developed based on the pooled data. The accuracy and robustness of the final population PK model were assessed using a predictive check method.

Results: An under-prediction bias was observed at the population level when existing PK model in MF was applied to pooled data in patients with MF and aGVHD. A new model was developed to account for the under prediction bias at the population level. The final population PK model for ruxolitinib was a 2 compartment disposition model with first order absorption, absorption lag time, and linear elimination. Body weight and gender were significant predictors of the volume of distribution of the central compartment and oral clearance, respectively. Patients with aGVHD showed lower oral clearance (66.7%) and slower rate of absorption (~28%) than that in patients with MF. The stage of liver involvement in GVHD and use of moderate or potent CYP3A4 inhibitors were identified as covariates for ruxolitinib CL.

Conclusion: The population PK analysis supports the proposed dose regimen in patients with aGVHD who had an inadequate response to corticosteroids as well as dose recommendations for DDI and subjects with organ dysfunction.