Clinical Trials

❘❙❚■ Chapter 28 | Repeated MeasurementsFigure 3. Calculation of C max, T max, and AUC for a subject’s plasma concentration profile.8T maxC maxPlasma concentration (ng/mL)642AUC00 24 6 8Time relative to dose (hours)AUC = area under the curve; C max= the peak concentration of the drug in the body; T max= the time to reach the peakconcentration of the drug from dosing.In pharmacokinetic studies, the peak plasma concentration (C max) and the time toachieve it (T max) are used to assess the speed or rate of absorption of a study drug.C maxand T maxcan be derived from a subject’s plasma concentration profile,as shown in Figure 3. The data in Figure 3 suggest that in this subject the studydrug has a very rapid absorption, reaching a peak of about 6.67 ng/mL in less thanan hour after administration.Area under the curveA method that makes use of all available response values, as well as the lengthsof the time intervals, is an AUC approach (see Figure 3). Mathematically,AUC can be calculated for any time serial data in which an outcome variable isobserved at different time points (with equal or unequal intervals) by using thetrapezoidal rule, but it is particularly useful in situations where the total uptakeof a drug concentration is of interest. The unit for AUC is the unit of drugconcentration multiplied by the unit of time, eg, for the AUC calculated from thepharmacokinetic profile in Figure 3, the unit is hour.ng/mL.324