Mean hydroxyurea (HU) concentration (μg/mL) per time (hour) profiles in children on chronic HU therapy (HU_chronic) and children who are receiving the first dose of drug (HU_first). Error bars represent standard deviation of the mean.Figure 1A. The coefficient of determination (R²) of the linear correlation between plasma concentration (DV) and observed AUC_inf at 4.0 hours in all children (HU_treated and HU_first) to therapy.