PK of IV Infusion Flashcards
1 mg/hr to mg/min
0.0167 mg/min
1 mg/hr to mcg/min
16.7 mcg/min
1 mg/L to mcg/ml
1 mcg/ml
1 L/hr to ml/min
16.7 ml/min
steady-state
rate in = rate out
Rate in
R
Rate out
Cl * C
when infusion starts
R > Cl * C
What happens to elimination rate when you increase concentration?
Increases
When you increase the infusion rate, what happens to Css?
Increases
If you increase the R, what happens to tss?
it doesn’t change because tss is only impacted by half-life
when is Css achieved?
3.3 t1/2
Which formula do you use when choosing the bigger R method for reaching the targeted Css?
R=Cl* C / (1-e^-kt)
Continuous infusion before s-s
Two concepts/formulas
1) rate in > rate out
2) C = Css (1-e^-kt)
At s-s, which formula do we use?
1) rate in = rate out
2) R=Cl*Css
Stopped infusion
concept/formulas
1) rate in = 0
2) C = Css * e^-kt
3) DL=Css * V
1t1/2
50% Css
2 t1/2
75% Css
3 t1/2
87.5% Css
3.3 t1/2
90% Css
What does being at steady-state mean?
rate of drug infused is equal to rate of drug eliminated
what are the units of R?
mg/hr
Why do we say that drug input is independent?
the concentration of the drug in the body does not affect the rate of administration
formula for the time required to reach fraction x
tx = -1.44 * t1/2 * ln(1-x)
time to steady-state is only determined by
t1/2 which is 3.3 t1/2
t1/2 is only determined by
clearance and volume
clearance is only determined by
clearance hepatic and clearance renal
Vd is only determined
- body weight for most drugs
- fraction unbound for drugs with a high Vd
if t > 3.3 t1/2
which formula do we apply?
Apply the C after stopping formula and use Css instead of C when stopped
For IV bolus, we can say that C0 is equal to
Css
When it takes too long to reach Css on the R we have chosen, what are the two options we can use?
- Choose a bigger R
- Give a bolus dose
