Mean trough concentrations of alemtuzumab during intravenous therapy. The mean trough concentrations during treatment (measured 48 hours after a dose, once a week) are plotted, with standard deviations, for 8 patients who ultimately reached less than 0.4% CLL cells in the bone marrow (▵) and compared with 22 patients who still had residual CLL cells at the end of treatment (•).