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Time (Hours)

Figure 11 Plot of plasma concentrations (circles) versus time with the curve divided into vertical segments (data shown in Table 7).

Time (Hours)

Figure 11 Plot of plasma concentrations (circles) versus time with the curve divided into vertical segments (data shown in Table 7).

Example. The AUC for Figure 11 can be calculated from the data given in Table 7.

Assuming that the AUC for a 100-mg IV dose given to the same group of volunteers was 86.7 hr.mg/mL, the absolute bioavailability of the extravascular dosage form is

AUCm 67.2

Absolute bioavailability = -1 x 100 = -— x 100 = 77.5%

It is not necessary to apply the trapezoidal rule to the entire plasma concentration versus time curve to calculate the total AUC. After the semilogarithmic plot becomes a straight line, the remaining area out to t =1 can be calculated using the following equation:

Once a semilogarithmic plasma concentration versus time plot begins to follow simple first-order elimination kinetics, the remaining AUC can be calculated in one step using equation (45).

Example. In the previous problem, the AUC from 24 hours to infinity is given by

It follows that if the entire semilogarithmic plot were straight, as would be the case for a one-compartment drug following IV administration, the total AUC would be given by c

Table 7 Calculation of AUC using the Trapezoidal Rule

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