For example. Using the previous data
For theophylline, kel = 0.17 hr^{1}; V = 25 L; with a required Cp = 14.1 mg/L
If we wish to give a loading infusion over 30 minutes we need to give the infusion at a rate which will produce Cp = 14.1 mg/L at 30 minutes. Therefore:
Cp^{30 min} = 14.1 mg/L
(Equation VI2 above)
thus
k0 = 735 mg/hr
Therefore we need to give a dose of 367 mg over 30 minutes to achieve a plasma concentration of 14.1 mg/L at 30 minutes.
It is important to realize what the steady state plasma concentration would be if we didn't turn this fast infusion off.
which would be quite toxic.
Figure VI4. Linear Plot of Cp versus Time showing Combined and Separate Curves for Both Infusions
Plasma Concentration versus Time Plots
The dosing regimen (or controlled sequence of drug administration) to achieve the desired plasma concentration is:
a) a loading dose by IV infusion of 367 mg/30 minutes followed by
b) a maintenance IV infusion of 60 mg/hr
Calculate Cp given fast and slow k0, kel and V at time t

Copyright 2001 David W.A. Bourne