Cplate = B * e- * t
This equation is similar to the equation for the late plasma concentration values after oral administration with a one compartment model. This line will be linear if plotted on semi-log graph paper.
From the slope of this line a value of can be determined. The t1/2 calculated as 0.693/ is often called the biological half-life or terminal half-life. It is the half-life describing the terminal elimination of the drug from plasma. [For the one compartment model the biological half-life is equal to 0.693/kel].
Figure XIX-4, Semi-Log Plot of Cp Versus Time Showing Cplate Extrapolated Back to B
The difference between the Cplate values at early times and the actual data at early times is again termed the 'residual'
Residual = Cp - Cplate = A * e-*t
Figure XIX-5, Semi-Log Plot of Cp Versus Time Showing Residual Line and Line
From the slope of the residual line the value of can be calculated with the A read off the concentration axis. With A, B, , and calculated we can calculate the microconstants given the formulas.