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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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