Chapter 6

Intravenous Infusion

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Combined Infusion and bolus administration

One reason we give a drug by IV is because we need a quick therapeutic response. One way to achieve a therapeutic concentration more quickly is to give a loading dose by rapid intravenous injection and then start the slower maintenance infusion.

For Drugs which can be given as a bolus

For example, using theophylline again.

To achieve Cpss = 14.1 mg/L; k0 = 60 mg/hr; V = 25 L; kel = 0.17 hr- 1.

A loading dose can be calculated from

thus

DOSE = V • Cp0 = 25 x 14.1 = 353 mg

Combined IV Bolus and Infusion
Dose (Bolus) 353 mg, k0 = 60 mg/hr, V = 25 L, kel = 0.17 hr-1

Linear Plot of Cp versus Time Showing Bolus, Infusion, and Combined Curves

Figure 6.4.1 Linear Plot of Cp versus Time Showing Bolus, Infusion, and Combined Curves

Click on the figure to view the interactive graph

The plasma concentration from the combined bolus and infusion regimen is shown as the black horizontal line in Figure 6.4.1

Javascript Calculators using Equation 6.2.3 and 4.5.2

Calculator 6.4.1 Calculate Cp given k0, Bolus Dose, kel and V at time t

Enter your own values into each field
k0 (zero order mass/time)
Dose (bolus dose - mass)
kel (first order reciprocal time)
V (volume)
t (time)
 
Cp from the bolus dose (mass/volume) is:
Cp from the maintenance infusion (mass/volume) is:
The total Cp (mass/volume) is:

An IV bolus and maintenance infusion is one way to achieve a steady state plasma concentration rapidly and maintain it. However, we may not be able to give a bolus dose intravenously so another approach may be necessary.

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