CHAPTER 4 INTRAVENOUS INFUSION

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

PK of Drug Given by IV Infusion Zero-order Input (infusion rate, R) First-order Output (elimination)

Integrated equation Zero-order Input (infusion rate, R) First-order Output (elimination) By integration,

Stopping the infusion before reaching steady state Infusion stops

Stopping the Infusion Equations

Steady State Concentration IV Infusion until reaching Css

Steady State Concentration (Css) Theoretical SS is only reached after an infinite infusion time Rate of elimination = kel Cp

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 …….

Steady State Concentration (Css) In clinical practice, the SS is considered to be reached after five half-lives

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.

Loading Dose plus IV Infusion DL with IV infusion at the same time Loading dose IV infusion DL + IV infusion

Loading Dose plus IV Infusion DL is used to reach SS rapidly

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

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

DL + IV Infusion