INTRAVENOUS INFUSION

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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

• 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