Kinetics of CH50 and free eculizumab levels in PNH patients following eculizumab injection. Plasma from 6 PNH patients receiving eculizumab were drawn before eculizumab injection, 1 hour, 3 days, 6 days, and 9 days after injection of eculizumab, and immediately prior to the next injection (day 14 in most cases). Dose-response curves are represented using CH50 (left y-axis) and levels of free eculizumab (right y-axis) by timing after injection (days, x-axis). Half-life (T1/2) was 4.3 days for (A) patient 1, (B) 5.7 days for patient 21, (C) 8.6 days for patient 7, (D) 20.3 days for patient 14, (E) 11.2 days for patient 12, and (F) 5 days for patient 19.