BTK occupancy. The level of drug binding to BTK over time in PBMCs. BTK target occupancy ELISA was performed on PBMC lysates using biotin-tagged probes. The figure shows data from the assessment at day 8 prior to the subsequent dose (steady-state trough) and day 28. “Pre” refers to time point preceding the morning dose. “Post” refers to 4 hours after the dose. The horizontal lines indicate the median value. Statistical significance was determined using an unpaired, parametric, 2-tailed Student t test (descriptive P values were reported). BID, twice daily; ELISA, enzyme-linked immunoassay; QD, once daily.