Drug conc-time profile

When the drug elimination process follows first-order process, the following equation describes the drug amount-time profile after iv bolus administration.

A = A0e-kt

Plotting the amount of the drug versus time will give a straight line on a semilog scale, with slope equal to -k/2.303

Slope =

log y2 - log y1

x2 - x1
=

-k

2.303

A0

Since, drug conc = drug amount/Vd

Cp = Cp0 e-kt

Plotting the plasma drug concentration versus time will give a straight line on a semilog scale, with slope -k/2.303

Slope =

log y2 - log y1

x2 - x1
=

-k

2.303

Cp0

The two lines that describe the plasma drug concentration vs. time and the drug amount vs. time on semilog scale have similar slopes (slope = -k/2.303).