Population Pharmacokinetic and Exposure-Safety Analyses of Ibrutinib for the Treatment of Chronic Graft-Versus-Host Disease.

The population pharmacokinetic (PK) and exposure-response (E-R) analyses for the safety of ibrutinib for the treatment of chronic graft-versus-host disease (cGVHD) is presented. This work aims to develop a population PK model for ibrutinib based on data from clinical studies in subjects with cGVHD, to evaluate the impact of intrinsic and extrinsic factors on PK parameters as well as systemic exposure levels, and to assess an E-R relationship for selected safety end points. Pooled data from 162 subjects with cGVHD enrolled in 4 clinical studies were included in the population PK analysis. In the studies, an ibrutinib dose of 420 mg once daily was administered orally. With the exception of 1 study, the study protocols instructed for a reduction of the ibrutinib dose to 140 or 280 mg once daily, depending on concomitant CYP3A inhibitor use. Concomitant CYP3A inhibitor use was found to be a primary covariate for relative bioavailability (F1): the F1 value increased 2.22-fold with concomitant moderate CYP3A inhibitors and 3.09-fold with concomitant strong CYP3A inhibitors, compared with the F1 value in the absence of CYP3A inhibitors. In addition, Japanese ethnicity led to an F1 value that was 1.70-fold higher than that in the non-Japanese population. Simulations using the final PK model suggest that ibrutinib exposure was appropriately controlled within the therapeutic range in the entire cGVHD population by applying dose reductions depending on the use of CYP3A inhibitors, and that additional dose modification for the Japanese population would not be required. The subsequent E-R analysis suggests no apparent association between the systemic exposure to ibrutinib and the selected safety end points.