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CHAPTER 4 INTRAVENOUS INFUSION

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**ONE COMPARTMENT MODEL WITH IV INFUSION**

This can be obtained by high degree of precision by infusing drugs i.v. via a drip or pump in hospitals

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**PK of Drug Given by IV Infusion**

Zero-order Input (infusion rate, R) First-order Output (elimination)

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**Integrated equation Zero-order Input (infusion rate, R)**

First-order Output (elimination) By integration,

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**Stopping the infusion before reaching steady state**

Infusion stops

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Stopping the Infusion Equations

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**Steady State Concentration**

IV Infusion until reaching Css

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**Steady State Concentration (Css)**

Theoretical SS is only reached after an infinite infusion time Rate of elimination = kel Cp

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**Steady State Concentration (Css)**

Rate of Infusion = Rate of Elimination The infusion rate (R) is fixed while the rate of elimination steadily increases The time to reach SS is directly proportional to the half-life After one half-life, the Cp is 50% of the CSS, after 2 half-lives, Cp is 75% of the Css …….

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**Steady State Concentration (Css)**

In clinical practice, the SS is considered to be reached after five half-lives

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**Increasing the Infusion Rate**

If a drug is given at a more rapid infusion rate, a higher SS drug concentration is obtained but the time to reach SS is the same.

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**Loading Dose plus IV Infusion**

DL with IV infusion at the same time Loading dose IV infusion DL + IV infusion

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**Loading Dose plus IV Infusion**

DL is used to reach SS rapidly

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**Reaching SS Immediately**

Let , DL = CssVd But, CssVd = R / kel Therefore, if a DL = R / kel is given SS will be reached immediately but

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**Reaching SS Immediately**

IV DL equal to R /kel is given, followed by IV infusion at a rate R

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DL + IV Infusion

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