Effect of Hepatic Impairment on the Pharmacokinetics of Itacitinib

Itacitinib is a potent, selective JAK-1 inhibitor currently in development for the treatment of chronic graft-vs-host-disease in combination with corticosteroids. Itacitinib is primarily eliminated via cytochrome P450 3A metabolism with minimal renal elimination. The purpose of this open-label study was to investigate the effect of hepatic impairment, as determined by Child-Pugh grade, on itacitinib pharmacokinetics. All participants received a single 300-mg dose of itacitinib orally in the fasted state. Blood samples were collected serially through 96 hours after dosing; 4 hours after dosing, an additional sample was collected for protein binding determination. Participants with moderate hepatic impairment (N = 8) had an approximate 2.5-fold increase in total exposure (area under the plasma concentration-time curve from time 0 to infinity [AUC_0-∞ ]) and an approximate 2-fold increase in maximal exposure (C_max ) compared to those with normal hepatic function (N = 8) (geometric mean ratio, 2.51 [90% confidence interval (CI), 1.54-4.08] for AUC_0-∞ and 1.95 [90%CI, 1.14-3.35] for C_max ). Participants with severe hepatic impairment (N = 6) had an approximate 4-fold increase in total exposure (AUC_0-∞ ) and an approximate 3.5-fold increase in maximal exposure compared to participants with normal hepatic function (geometric mean ratio, 4.08 [90%CI, 2.41-6.89] for AUC_0-∞ and 3.48 [90%CI, 1.94-6.23] for C_max ). Protein binding was similar between participants with moderate or severe hepatic impairment and participants with normal hepatic function, with average unbound fractions (percent free) of 25.7%, 31.5%, and 25.6%, respectively. There were no serious or fatal treatment-related adverse events. The results of this study combined with exposure, efficacy, and safety data from the pivotal study in the relevant patient population will inform final dosing recommendations.