NONMEM posthoc model of serum asparaginase enzymatic activity. The data are from 23 adult patients who had 2 or more serum specimens after a single intravenous dose (2000 IU/m²) of pegaspargase. Each color indicates an individual patient, showing the variability between patients. Several patients had enzymatic activity of 0.2 IU/mL or greater on day 28. The NONMEM posthoc (best fit) model is shown in yellow circles demonstrating T_1/2 = 7 days (95% CI, 6.04-7.90) and volume of distribution = 2.43 L/m², which is equal to plasma volume in adults.