Ibrutinib protocol design and PK and PD at 3 doses of ibrutinib. (A) Clinical protocol design for the systematic reduction of ibrutinib dosing in patients with CLL over the course of three 28-day cycles, from 420 to 280 mg/d and then to 140 mg/d. Peripheral blood samples were collected from each patient at the indicated times (arrows). (B-G) Plasma and cellular pharmacology of ibrutinib over the course of 3 cycles of treatment with ibrutinib at 420 mg/d (green), 280 mg/d (light green) and 140 mg/d (gray). (B) Ibrutinib plasma levels in a representative patient with CLL (patient 2) over the course of 3 cycles of treatment. (C-D) Mean plasma ibrutinib levels (n = 8) on (C) D1 24 hours and (D) D28 24 hours. (E) Intracellular ibrutinib levels in a representative patient with CLL (patient 2) over the course of 3 cycles of treatment. Mean intracellular ibrutinib level (n = 6) on (F) D1 24 hours, (G) D28 24 hours, as measured by high-performance liquid chromatography-MS. Error bars represent standard errors of the mean (SEMs). Paired comparisons were performed using 2-sided Wilcoxon signed rank test. ns, not significant.