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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
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 6.5.1 Linear Plot of Cp versus Time showing Combined and Separate Curves for Both Infusions
Click on the figure to view the interactive graph
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
Calculator 6.5.1 Calculate Cp given fast and slow k0, kel and V at time t

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