1 chapter 4 intravenous infusion. 2 one compartment model with iv infusion this can be obtained by...
TRANSCRIPT
1
CHAPTER 4
INTRAVENOUS INFUSION
2
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
3
PK of Drug Given by IV Infusion
Zero-order Input (infusion rate, R)
First-order Output (elimination)
4
Integrated equationZero-order Input (infusion rate, R)
First-order Output (elimination)
By integration,
pelp CkR
dt
dC
)1( tk
eldp
elekV
RC
5
Stopping the Infusion Stopping the infusion before reaching steady state
Infusion stops
6
Stopping the Infusion Equations
tkpp
eleCC 0
)1( tk
eldp
elekV
RC
7
Steady State ConcentrationIV Infusion until reaching Css
Cl
RCss
8
Steady State Concentration (Css)
Theoretical SS is only reached after an infinite infusion time
Rate of elimination = kel Cp
)1( ekV
RC
eldp
Cl
R
kV
RC
eldss
9
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 .……
10
Steady State Concentration (Css)
In clinical practice, the SS is considered to be reached after five half-lives
11
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.
12
Loading Dose plus IV Infusion DL with IV infusion at the same time
)1( tk
eld
tk
d
Lp
elel ekV
Re
V
DC
tk
d
Ltkp
elel eV
DeCC
1
)1(2tk
eld
elekV
RC
Loading dose
IV infusion
DL + IV infusion
13
Loading Dose plus IV Infusion
DL is used to reach SS rapidly
)1( tk
eld
tk
d
Lp
elel ekV
Re
V
DC
tk
eldeld
tk
d
Lp
elel ekV
R
kV
Re
V
DC
tk
eld
tk
d
L
eldp
elel ekV
Re
V
D
kV
RC
14
Reaching SS Immediately
Let , DL = CssVd But, CssVd = R / kel
Therefore, if a DL = R / kel is given SS will be reached immediately
tk
eld
tk
d
L
eldp
elel ekV
Re
V
D
kV
RC
eldp kV
RC
eldss kV
RC but
15
Reaching SS Immediately IV DL equal to R /kel is given, followed by IV infusion at a rate R
16
DL + IV Infusion