Wagner

The fraction of the dose remaining to be absorbed can be calculated from the plasma concentration-time data as described previously.

The W-N method can be used to calculate the absorption rate constant when the absorption process follows zero-order or first-order.

A - When drug absorption is first-order: A plot of the fraction of the bioavailable dose remaining to be absorbed versus time on the semilog scale is a straight line. The slope of the line is equal to -ka/2.303.

B - When drug absorption is zero order: A plot of the fraction of the bioavailable dose remaining to be absorbed versus time on the linear scale is a straight line. The slope is equal to - the fraction of the bioavailable dose absorbed per unit time.