Fig. 3. Free fraction (top ) and unbound concentration (bottom ) versus  age in the biliary atresia group (closed symbols) and the other group (open symbols) before surgery (circles) and 48 h after the operation (triangles). The solid lines are the fitted free fraction (unbound concentration) 30 min after the beginning of infusion and the dashed lines are the fitted free fraction (unbound concentration) 48 h after infusion initiation. The free fraction decreases with time because of the increase in α-1 acid glycoprotein concentration, but the unbound concentration (which is considered as the toxic moiety) increases. Note that two infants had unbound concentrations higher than 0.2 μg/ml.